Schizophrenia Research Forum - A Catalyst for Creative Thinking

Live Discussion: DISC1 Roundtable 2009


Akira Sawa

Nick Brandon

Ty Cannon

Chat leaders Akira Sawa of Johns Hopkins University, Nick Brandon of Wyeth Research, and Ty Cannon of UCLA led us in a wide-ranging discussion of all things DISC1 on January 13, 2009, including the following:

  • The molecular biology of DISC1 and its various isoforms.
  • Approaches to studying disruptions of the gene in rodents and other organisms.
  • The value of DISC1 in efforts to categorize and treat neuropsychiatric disease.
As we await the posting of the transcript, we invite you to read the background text and to offer your comments.

View Transcript of Live Discussion — Posted 24 March 2009

View Comments By:
Barbara Lipska, Joel Kleinman — Posted 11 January 2009
Carsten Korth — Posted 11 January 2009
Anil Malhotra — Posted 12 January 2009
David J. Porteous — Posted 12 January 2009
David St Clair — Posted 12 January 2009
Steven Clapcote — Posted 12 January 2009
Mikhail Pletnikov — Posted 13 January 2009
Tatiana Lipina — Posted 16 January 2009
Jesus Requena — Posted 16 January 2009
Peter Penzes — Posted 19 January 2009
David J. Porteous — Posted 4 March 2009
Alexander Arguello — Posted 27 March 2009


Background Text
by Akira Sawa and Nick Brandon

It has been a very productive two years in the DISC1 area since the previous Schizophrenia Research Forum roundtable (see Porteous’s background text and Sawa’s post-meeting summary), and as the field is poised for its next batch of publications, especially in generation of model animals for DISC1 (Wang et al., 2008) and identification of molecular pathways involving DISC1 and other genetic risk factors (e.g., Kamiya et al., 2008; see SRF news story). Therefore, we believe that it is again a good time to get a group together to look at the progress that has been made and to make suggestions on areas in which we need to work harder.

Genetically, DISC1 is a major risk factor for a wide range of psychiatric disorders, including schizophrenia (Chubb et al., 2008). A rare variant with strong biological impact associated with the disorders in the DISC1 locus was identified from a large Scottish Pedigree (St. Clair et al., 1990). Some, but not all, association studies have supported that DISC1 is a risk factor for schizophrenia; nonetheless, such association becomes more promising when specific disease-related endophenotypes are considered (Cannon et al., 2005). It is still an excellent question as to what are the nature and effects of DISC1 variants in psychiatric genetics. This question is crucially associated with an issue of how we can utilize DISC1 genetically engineered organisms/animals in a translational sense.

From a biology viewpoint, DISC1 is a multifunctional protein localized to several distinct subcellular compartments (Ishizuka et al., 2006). DISC1 interacts with many proteins of importance (Camargo et al., 2007) and seems to function as an anchoring protein to regulate distinct cascades either at certain developmental time-points or in response to various stimuli. Thus, important questions in DISC1 biology are: what is the nature of disease-relevant DISC1 cascades or molecular pathways, and how are these cascades distinctly regulated in a context-dependent manner (e.g. temporally and spatially)? The complexity of DISC1 isoforms is still unsolved and could be critical for this last question. For example, when we consider the recently appreciated centrosomal and synaptic roles of DISC1, where does the underlying versatility derive from? Is it due to different DISC1 isoforms or due to the same species playing different roles at different developmental stages (or both)?

Based on this platform, the following points should be considered for this discussion.

1) The complexity of the DISC1 molecule (isoforms, potential role for antisense transcripts and fusion transcripts)

2) Understanding the cellular roles of DISC1 in partnership with other risk factors for schizophrenia (disease-associated molecular pathways/cascades) in context-dependent situations (cellular compartment, cell types, brain regions, developmental timing)

3) The role for model organisms (mice, flies, zebrafish, etc.) in DISC1 research, especially their translational utilities. With the burgeoning number of DISC1 mice, can we rationalize a path forward? Are all these models in all cases simply interfering with a key neurodevelopmental protein or are they really telling us something about the human disease? In terms of non-mouse models, what are we learning and does it have any relevance to humans?

4) Nature and effects of DISC1 variants on phenotypes/endophenotypes beyond DSM diagnostic criteria

5) Should we expect any therapeutic breakthroughs for schizophrenia and other neuropsychiatric disorders via DISC1 research?

Key papers to be read

1. St Clair DM, Blackwood DHR, Muir WJ, et al. Association within a family of a balanced autosomal translocation with major mental illness. Lancet (1990) 13-16. Abstract

2. Cannon TD, Hennah W, van Erp TG, Thompson PM, Lonnqvist J, Huttunen M, Gasperoni T, Tuulio-Henriksson A, Pirkola T, Toga AW, Kaprio J, Mazziotta J, Peltonen L. Association of DISC1/TRAX haplotypes with schizophrenia, reduced prefrontal gray matter, and impaired short- and long-term memory. Arch Gen Psychiatry . 2005 Nov 1 ; 62(11):1205-13. Abstract

3. Ishizuka K, Paek M, Kamiya A, Sawa A. A review of Disrupted-In-Schizophrenia-1 (DISC1): neurodevelopment, cognition, and mental conditions. Biol Psychiatry . 2006 Jun 15 ; 59(12):1189-97. Abstract

4. Chubb JE, Bradshaw NJ, Soares DC, Porteous DJ, Millar JK. The DISC locus in psychiatric illness. Mol Psychiatry . 2008 Jan 1 ; 13(1):36-64. Abstract

5. Camargo LM, Collura V, Rain JC, Mizuguchi K, Hermjakob H, Kerrien S, Bonnert TP, Whiting PJ, Brandon NJ. Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia. Mol Psychiatry . 2007 Jan 1 ; 12(1):74-86. Abstract

6. Kamiya A, Tan PL, Kubo K, Engelhard C, Ishizuka K, Kubo A, Tsukita S, Pulver AE, Nakajima K, Cascella NG, Katsanis N, Sawa A. Recruitment of PCM1 to the centrosome by the cooperative action of DISC1 and BBS4: a candidate for psychiatric illnesses. Arch Gen Psychiatry . 2008 Sep 1 ; 65(9):996-1006. Abstract

7. Wang Q, Jaaro-Peled H, Sawa A, Brandon NJ. How has DISC1 enabled drug discovery? Mol Cell Neurosci . 2008 Feb ; 37(2):187-95. Abstract


Transcript

Attendees/Participants

Amy Arnsten, Yale University
Verain Bader, University of Duesseldorf
Nick Brandon, Wyeth
Sarah Brown, Edinburgh University
Kate Burdick, The Zucker Hillside Hospital-NSLIJHS
Michael Cahill, Northwestern University in Chicago
Ty Cannon, UCLA
Ross Cardarelli, University of Maryland, Baltimore
Becky Carlyle, Edinburgh University
Tom Comery, Wyeth
Angela Epshtein, Schizophrenia Research Forum
Nao Gamo, Yale University
Hugo Geerts, In Silico Biosciences
Christoph Gruenewald, Edinburgh University
Ellen Gruenewald, Edinburgh University
Hakon Heimer Schizophrenia Research Forum
Michy Kelly, Wyeth
Carsten Korth, University of Duesseldorf
Tatiana Lipina, Samuel Lunenfeld Institute at Mount Sinai Hospital, Toronto
Anil Malhotra, The Zucker Hillside Hospital
Karen Marquis, Wyeth
Pat McCaffrey, Schizophrenia Research Forum
Patricio O'Donnell, University of Maryland
Constantinos Paspalas, Yale University
Peter Penzes, Northwestern University, Chicago
Misha Pletnikov, JHU
Amy Ramsey, Duke University
Akira Sawa, Johns Hopkins University
Dani Smith, Johns Hopkins University
David St. Clair, University of Aberdeen
Marquis Vawter, UCI
Min Wang, Yale University
Tracy Young-Pearse, Harvard Medical School, Brigham & Women’s Hospital

Note: Transcript has been edited for clarity and accuracy.


Hakon Heimer
Let's start off by having all the participants in the "room" introduce themselves. Please type your name and affiliation or institution. I'm Hakon Heimer, editor at Schizophrenia Research Forum.

Tyrone Cannon
I'm Ty Cannon, professor of Psychology and Psychiatry at UCLA.

Amy Arnsten
Amy Arnsten and Nao Gamo are sitting in at Yale.

Angela Epshtein
I'm Angela Epshtein, managing editor at Schizophrenia Research Forum.

Becky Carlyle
Hi Everyone, Becky Carlyle, Edinburgh University.

Nick Brandon
Nick Brandon, Head of Schizophrenia Biology, Wyeth.

Karen Marquis
Karen Marquis, Wyeth.

Dani Smith
Hi, Dani Smith at Johns Hopkins.

Becky Carlyle
Hey, Nao!

David St. Clair
I am David St. Clair, University of Aberdeen.

Patricia McCaffrey
Pat McCaffrey, writer for Schizophrenia Research Forum.

Amy Ramsey
I'm from Duke University, but I'll be starting my lab at University of Toronto this summer.

Michael Cahill
Hi, Michael Cahill, Northwestern University in Chicago.

Tracy Young-Pearse
Tracy Young-Pearse, Harvard Medical School, Brigham & Women’s Hospital.

Thomas Comery
Tom Comery, Wyeth.

Hugo Geerts
I am Hugo Geerts, Scientific Liaison Officer at In Silico Biosciences.

Ross A. Cardarelli
I'm Ross Cardarelli, graduate student at the University of Maryland, Baltimore.

Christoph Gruenewald
Christoph Gruenewald (Kirsty Millar's group in Edinburgh).

Amy Arnsten
Hi, Becky!

Peter Penzes
Peter Penzes, assistant professor of Physiology, Northwestern University, Chicago.

Ellen Gruenewald
Hi all; I'm Ellen Gruenewald from Edinburgh University.

Michy Kelly
Michy Kelly, scientist in Nick Brandon's group, Wyeth.

Mikhail Pletnikov
Hi, Misha Pletnikov, JHU.

Hakon Heimer
All, great turnout!

Sarah Brown
Hi, I’m Sarah Brown, third-year Ph.D., Edinburgh University in David Porteous's lab.

Tatiana Lipina
Hi, Sarah!

Sarah Brown
Hi, Tatiana.

Anil Malhotra
Hello, all. Kate Burdick and I are logged on.

Hakon Heimer
Hi, Anil and Kate!

Tatiana Lipina
Hi, I am Tatiana Lipina from Samuel Lunenfeld Institute at Mount Sinai Hospital, Toronto.

Amy Arnsten
Constantinos Paspalas and Min Wang have also joined from Yale (all at my terminal).

Carsten Korth
Hi, I am Carsten Korth from the University of Duesseldorf. Verain Bader, my postdoc, has also joined.

Patricio O’Donnell
Hi, Hakon!! I'm Patricio O'Donnell, at the University of Maryland.

Hakon Heimer
In the informal spirit of this event, I will only mention that Akira is at Johns Hopkins University, Nick is at Wyeth Research in New Jersey, and Ty is at UCLA, and I thank them for bringing us this idea and for their work to prepare the discussion. I'll now turn to Akira, who I believe will orient us on the plans for the discussion.

Akira Sawa
Welcome. Thank you very much for joining this roundtable discussion on DISC1 and schizophrenia today. We will have five agendas: 1) molecular diversity of DISC1; 2) protein interactions around DISC1 and their biological significance; 3) animal models; 4) clinical phenotypes; and 5) therapeutic strategies. The first two topics will be led by Nick Brandon, the third topic by me, fourth by Ty, and the fifth by me. Why don't we start? Nick, can you initiate?

Nick Brandon
Thank you everyone for your comments; there are some very nice, insightful commentaries. The question of isoforms has been an issue in the field and was flagged at the 2006 roundtable, and seemingly we have not made a lot of progress. But, I have been gradually getting more excited about Barbara Lipska’s work, which ended up in a great talk at the ACNP meeting in December 2008. Finally seeing cloned and expressed versions on a gel of human variants of DISC1 was wonderful and clearly could open up this area. In addition, Barbara has shown enrichment of certain short variants in patient brain—amazingly they are not too distinct from the original putative Scottish truncation. This may mean that all the work performed with the truncation could have additional validity. I think we are going to see great advances in this area. Barbara and Joel, if you’re online, could you please comment? Others, please join in.... Okay, we can come back to this when Joel joins. Could others discuss ways to look at this in terms of generalization (e.g., Carsten, you mentioned the oligomers in your comments).

Carsten Korth
Nick, I was emphasizing the significance of post-translational modifications that are not well characterized so far.

Nick Brandon
Carsten, okay, we'll return to this point in a moment.

Amy Ramsey
I agree with Nick that some of the most exciting work has been to show how aberrant DISC1 biology can extend to patients beyond the familial cases.

Nick Brandon
Amy R., I think the generalizability of DISC1 effects is very important. Akira, what are your thoughts here? You saw the same talk at ACNP.

Akira Sawa
As for isoforms, we still need a lot of sincere efforts to find unknown isoforms. Barbara Lipska is doing a good job in this area.

Tatiana Lipina
Nick, here’s a thought about origin of different isoforms: Maybe comparison of different species could be helpful in the evolutionary perspective? What do you think?

Nick Brandon
To the Edinburgh group, regarding Tatiana’s point, what do you think (as you have worked in this area)? Also, who can comment on any new information from work regarding the analysis of the original family? In particular, who can comment on the progress on fusion transcripts or the role of DISC2? These are areas that I think are critically important but have been overlooked.

Becky Carlyle
Nick, the Edinburgh group is working on fusion transcripts right now. The person responsible is unfortunately not in the chat!

Nick Brandon
To all, on to another point regarding isoforms: But what does this mean for rodents? Clearly we need to ascribe actual amino acid identity to the bands we all recognize on our Westerns. What are all those bands? Are they all DISC1? What are the best antibodies to use? There has been some discussion on the use of peptide antibodies vs. fusion proteins. I have been happy with the polyclonals we’ve made, but agree that we need to take a more systematic approach to this analysis. What do others think of their own reagents and the identity of DISC1 forms? How would people like to see DISC1 antisera characterized? Perhaps we can take this offline and work out a plan that we could all share, ensuring that all our reagents have gone through a systematic quality control process.

Akira Sawa
We have studied two major post-translational modifications: SUMOylations and phosphorylations. The former are required for nuclear targeting of some isoforms. Phosphorylation is developmental dependent.

Michy Kelly
Akira, how are you able to determine “some isoforms” are affected by SUMOylations, and which are they?

Akira Sawa
Michy, mass spectrometry.

Marquis Vawter
Nick and Akira, thanks for hosting this discussion. Here’s my question: Are there drugs that alter DISC1 gene and protein expression in brain or cell lines?

Akira Sawa
Mark's point is very important, and can also be addressed in the fifth topic (therapeutic translation).

Nick Brandon
Mark, Barbara Lispka looked at the effects of antipsychotics on DISC1 expression a few years back. I’d need to refresh my understanding of the findings, but I believe she saw changes in rodents.

Amy Ramsey
Nick, I think so, too. I think that APS increased DISC1. When working in mice, I am mainly detecting two isoforms of DISC1: 100 and 70. Are there other meaningful isoforms in mice?

Christoph Gruenewald
Amy R., possible transcripts predict at least five different isoforms (expected protein sizes are 41, 85, 90, 92, and 93 kDa). To my knowledge, these transcripts have not been linked to proteins on WBs.

Nick Brandon
Christoph and Becky, it will be important to make that connection. Are you referring to human or mouse?

Christoph Gruenewald
Nick, I am talking about mouse at the moment.

Akira Sawa
Amy R., even if we see a 100 kDA immunoreactivity in Western blotting, it may represent more than one isoform.

Nick Brandon
Amy R., 100kD and 70kD are likely the most prominent bands on a straight Western. I think we can start to uncover less abundant but likely critical forms when enriching DISC1 using various antisera. What do others see?

Amy Ramsey
Thanks, Nick; that's an interesting observation.

Akira Sawa
Nick's words "various antisera" are important. If we can systematically test all the antibodies among folks and compare, the field will move more systematically forward.

Marquis Vawter
Nick, Akira, and Amy R., you’re right; here’s the quote from Lipska et al.: “We found that atypical antipsychotics, olanzapine and risperidone, in a clinically relevant dose, increased DISC1 expression levels in frontal cortex, while a typical antipsychotic, haloperidol, did not.”

Nick Brandon
One last point from me on this topic: Other forms of DISC1 from a post-translationally modified version to different oligomerized forms of the protein and associated complexes. We heard from Carsten Korth in the pre-meeting discussions regarding oligomers. What do people think are the most fruitful areas to look into here? Phospho-forms, etc., or SUMOylation as Akira has introduced? Carsten, please add your thoughts.

Carsten Korth
Nick, regarding the oligomers, please keep in mind that ultimately the function of DISC1 is executed at the protein level with native proteins. Our studies (and I think your studies as well) with recombinantly expressed DISC1 indicate that DISC1 forms a homomeric complex. It’s clear that anything that interferes with an orderly assembly of this complex disturbs molecular interactions.

David St. Clair
Has anyone looked for glycosylation?

Nick Brandon
David, not recently. I may have done some crazy experiments into this about a decade ago, but the data are probably lost, and I don’t think the data were striking.

Amy Arnsten
Are there differences in isoforms, phosphorylation state (or protein partners), etc., based on developmental state (i.e., perinatal, adolescence, adult)?

Carsten Korth
Amy A., if we take all splice variants, phosphorylation, and possible degradation of DISC1, the electrophoretic migration pattern gets very complex. I see only immunopurification with single-epitope antibodies and then mass spec as a way of determining the exact identity.

Akira Sawa
Carsten, wonderful approach!

Amy Ramsey
Nick, I like your idea of a biochemical assay to address this question of phosphorylation/SUMO. How does DISC1 affect activity of PDE4B? Is phosphorylation involved?

Sarah Brown
Nick, Akira, and Amy R., I’ve looked at clozapine, bupropion, and rolipram, and have seen no change in DISC1 expression in mouse hippocampus. Could it be that only the atypicals alter DISC1?

Amy Ramsey
I haven't tried these experiments myself but would be willing to try!

Akira Sawa
Regarding DISC1 expression by drugs, how about lithium?

Nick Brandon
Sarah, Akira, and Amy R., this is really interesting. It would be worth expanding this out. Are they acute treatments or chronic? On cells or on animals?

Amy Ramsey
Nick, I would try acute treatment first in wild-type animals, and then see if chronic has an effect.

Sarah Brown
Nick, mine was done with one dose (Tatiana is the dosage expert; I can’t remember off the top of my head!) in mouse. I looked at wild-type and the two DISC1 mutants from Steve Clapcote, none of which showed changes in DISC1.

Amy Ramsey
I noticed that cerebellum is quite high in DISC1. And also has D2 receptors. Has anyone else thought about this?

Tatiana Lipina
Akira, in which brain area do you think it’s more relevant to find DISC1 expression changes after drug treatments, e.g., APDs?

Akira Sawa
Tatiana, interesting question. Maybe frontal cortex, especially OFC as well as the hippocampus and thalamus.

Michy Kelly
Akira, is there some reason to expect a limited effect region-wise beyond the regional limitation of where DISC1 is expressed in the first place?

Akira Sawa
Michy, the reason that I limited the regions is because of the expression pattern or role of DISC1 interactors of interest, such as PCM1.

Tatiana Lipina
Akira, those are very interesting findings about PCM1 and BBS4.

Nick Brandon
Okay, I'm going to bring in the next section: We were at the heart of developing the DISC1 interactome—a solid partnership between the bioinformatician (Camargo) and the wet-lab (Brandon). This piece of work highlighted the diversity of possible pathways in which DISC1 could play a critical role. Clearly a systems approach is required to tackle this beast appropriately. On top of the interactions, we have to layer on the context (it’s been said before but I’ll reiterate). By this I mean developmental time periods, subcellular compartments, regional specificity, post-translational modifications, etc. What do people think are the best approaches to slicing up DISC1 biology for maximal efficiency and progress? What are the principal systems we should be working on in the next four to five years?

Amy Ramsey
Nick, I don't think regional specificity holds the best clues to DISC1 function. My hunch is that it’s doing basically the same thing in different brain regions. I am more interested in which of its interactions lead to mental illness.

Nick Brandon
Amy R., are you sure? Data suggest that DISC1 may do different things in the hippocampus vs. PFC in development. Akira, can you add to this?

Amy Ramsey
Nick, no, I’m not sure at all! I’m a novice in this field, and it’s just my hunch that DISC1 has general roles in neuron physiology.

Tatiana Lipina
Nick, I agree with you.

Michy Kelly
Amy R. and Akira, given the evidence implicating cerebellum dysfunction in schizophrenia, I think the cerebellum is likely to be of interest within the context of DISC1.

Hakon Heimer
Michy, could you remind us of what is (are) the major findings in cerebellum vis-à-vis schizophrenia?

Michy Kelly
Hakon, there's been a bit of structural work showing smaller volumes, or correlating volume with symptom severity. There’s also some evidence to suggest cerebellum dysfunction may contribute to aspects of the cognitive dysfunction observed in patients.

Michael Cahill
Is DISC1 highly expressed in inhibitory neurons within the hippocampus and/or frontal cortex?

Akira Sawa
Michael, DISC1 expression is highly expressed more in pyramidal neurons and granule neurons (DG), but there is some expression in interneurons.

Nick Brandon
Michael, we published old data in 2004 in which we identified DISC1 with our D27 antisera in all cell types in the mouse brain (see Schurov et al., 2004).

Akira Sawa
Nick, Tatiana, and Amy R., it’s true that DISC1 behaves differently in the context (regions).

Amy Arnsten
cAMP does different things in the prefrontal cortex than it does in hippocampus; therefore, DISC1 may be having an overall different function by region. And remember that the cerebellum has an extensive noradrenergic input that likely acts via β receptors.

Michy Kelly
Amy A., very good point regarding cAMP's regionally specific effects.

Nick Brandon
Amy A., I have one last comment on the differential effect of cAMP. It’s critical that we incorporate cAMP into our thinking of DISC1. I think we are starting to see that DISC1 and cAMP signaling are inextricably linked with the work of Miles H. and Edinburgh. Miles, any comments here?

Amy Arnsten
I just received a message from Constantinos Paspalas (who is doing EM of monkey prefrontal cortex). He agrees. He sees DISC1 in dendrites and in spines, the latter of which are of pyramidal cells.

Akira Sawa
Regarding the cerebellum, the network of PFC-thalamus-cerebellum is functionally very important, and may be involved in schizophrenia.

Amy Ramsey
Akira, I agree. Aren't smooth eye tracking movements controlled by the cerebellum and disrupted in schizophrenia?

Nick Brandon
One final question for this section: Can anyone online discuss efforts regarding the deep sequencing of DISC1? What’s it starting to look like?

Marquis Vawter
Nick, I think David Porteous is collaborating with CSHL on the question of deep sequencing of DISC1.

Nick Brandon
Amy A., how does the NHP EM compare to the human data published by Kirkpatrick and Akira?

Amy Arnsten
Nick, the human and NHP look very similar. Constantinos has done both. We also have labeling of centrosomes in the monkey PFC tissue.

Michael Cahill
As for DISC1 animal models, most studies have examined adult mice (12 weeks or older) that show several behavioral deficits. Are younger mice (e.g., three weeks) free of behavioral dysfunctions?

Mikhail Pletnikov
Michael, we’re testing developing mice now, and we’re not yet sure what the results could be.

Tyrone Cannon
Michael, we have not tested younger mice behaviorally. They tend to be difficult to test in standard behavioral assays.

Akira Sawa
Taking the information of isoform, protein interactome, and regional specificity into account, how about moving on to the topic of animal models and clinical phenotypes? The former will be led by me, and the latter by Ty. Ty, thanks! Patricio, you have worked in the area of development of the prefrontal cortex. Let us know your thoughts.

Patricio O’Donnell
Akira, you asked about developmental issues in the prefrontal cortex. We should all keep in mind that pyramidal neurons and more notably interneurons continue maturing through adolescence, so it should not be unexpected to see expression changes or modulation differences in adult vs. adolescent or pre-adolescent mice.

Amy Arnsten
cAMP impairs prefrontal working memory function, so loss of DISC1 may worsen prefrontal functions. We are trying to test this now.

Mikhail Pletnikov
Ty, I meant test batteries for developing rodents.

Tyrone Cannon
Mikhail, yes, I think I understood correctly, and I would be interested in knowing what paradigms can be run on developing mice.

Sarah Brown
Mikhail, can I ask how young you are going? Just out of interest, as I would have thought testing young mice would prove to be rather difficult.

Mikhail Pletnikov
Sarah, again one can start with three- to four-day-old mice.

Sarah Brown
Mikhail, sounds interesting. I look forward to the results.

Amy Ramsey
Me, too.

Michy Kelly
Mikhail, Tyrone, Amy R., I've worked with three-week-old mice in behavioral apparati with no issues: open field, PPI/startle, in particular.

Tatiana Lipina
Michy, what were the results in PPI in three-week-old mice? I think the startle reflex is not ready in three-week-old mice.

Michy Kelly
Tatiana, I was able to measure reliable startle and PPI in C57Bl6 mice and CF-1 mice.

Tatiana Lipina
Michy, good. I tested eight-week-old mice in PPI and found no defect in PPI, but startle was already lower in one of our mutants.

Hakon Heimer
Misha and Ty, would olfactory learning paradigms be useful? That's something you can do at that age.

Mikhail Pletnikov
I think so, Hakon.

Tatiana Lipina
Tyrone, Mikhail, and Amy, you can just observe young mice.

Michy Kelly
Mikhail, Tyrone, and Amy, you can also do in-cage observations of social behavior: huddling, nest building, etc.

Tyrone Cannon
Michy and Hakon, yes, those paradigms would be of interest. We've established the clearest links of transgenic DISC1 disruption on spatial working memory and social preference, but I’m not sure about those paradigms in three-week-old mice. But we have studied whether induction of the transgene early vs. later plays a role. Also, for disruption of DISC1-NUDEL binding, clearly early induction is critical for the effects, whereas adult induction is not.

Michy Kelly
Tatiana, I was not referring to results with DISC1 models in particular, but rather generally speaking of the ability to test developing mice.

Hakon Heimer
Misha, if I remember correctly, there's a big body of literature (WG Hall, Blass) on olfactory learning in neonates, but maybe mostly rats.

Patricio O’Donnell
To all, why would one expect behavioral changes in very young mice? If we think DISC1 genetics is important for schizophrenia, a dysfunction in this system would be expected to provide behavioral anomalies after adolescence. And PFC excitation-inhibition balance does mature during that age. So, one can have a dysfunctional circuit due to DISC1-dependent anomalies, but the deficits won’t be expressed until the circuits mature.

Amy Arnsten
Exactly, Patricio! That was why I was asking about changes in DISC1 at adolescence.

Mikhail Pletnikov
Patricio, I think similar to human data, one might be able to find "prodromal" subtle alterations. Our mice with prenatal expression only might indicate this.

Tatiana Lipina
Patricio, yes, you are right about expectations for schizophrenia development.

Michy Kelly
Patricio, would you necessarily expect cognitive/social dysfunction to appear post-adolescence? I thought those features of disease are observed in patients pre-/during adolescence in comparison to the positive symptoms that classically emerge in early adulthood.

Patricio O’Donnell
Michy, sure, one should perhaps expect "positive" symptom-related alterations after adolescence, and perhaps some cognitive prodromal deficits. But if the definition of prodromal status is quite difficult in patients, can we reliably assess it in mice? Perhaps some cognitive tests may reveal alterations as Misha indicated. It would certainly be worth pursuing, but my point is that even if pre-adolescent deficits are found, the full-fledged set of anomalies should be seen after adolescence.

Mikhail Pletnikov
Patricio, yes, you’re right. I was talking more about subtle preceding abnormalities that may be detectable earlier, but this is still at a very preliminary stage of research.

Marquis Vawter
Patricio, premorbid adjustment difficulties occur prior to onset, so it would be consistent to have DISC1 effects in pre-adolescence.

Amy Ramsey
Wouldn't it be lovely to show relatively normal adolescence and abnormal adult behavior in any mouse model?

Akira Sawa
The developmental changes of mouse model behavior are very important when we consider that the study of subjects with prodromal stages is now a hot topic. What do you think, Ty?

Tyrone Cannon
Akira, yes, I agree. Adolescent synaptic pruning is currently seen as a likely mechanism in the onset of psychosis. Are there any good rodent models of this?

Amy Arnsten
Tyrone, we’re looking at stress-induced pruning of spines, and whether these involve cAMP mechanisms.

Tyrone Cannon
Amy A., very interesting. It may be of interest to try out the stress paradigm in mice with and without TG disruption of the cAMP binding domain.

Amy Arnsten
Tyrone, that’s a great idea.

Tatiana Lipina
It would be interesting to estimate step-by-step appearance of schizophrenia and bipolar symptoms by age.

Anil Malhotra
Tatiana, brain structure and functional changes emerge long before psychosis in schizophrenia—less is known about bipolar disorder, but it appears intact until after or close to illness onset.

Mikhail Pletnikov
Tatiana, I agree; we do need a systematic developmental analysis of our mouse models, if that’s what you meant?

Tatiana Lipina
Mikhail, yes.

Hakon Heimer
Ty, I can see that it would be productive to have a live discussion on the prodrome, and what we really know about putative behavioral abnormalities of the prodrome!

Tyrone Cannon
Hakon, Michy et al., yes, while positive symptoms emerge during adolescence, the working memory and LTM deficits are there earlier and are predictive of future psychosis in those at risk. Gray matter decreases more steeply in those prodromal patients who convert compared with those who do not, particularly in dorsal prefrontal.

Nicola Cascella
Ty, please keep in mind the heterogeneity of schizophrenia. There are patients who do not have long prodromal symptoms.

Tyrone Cannon
Nicola, true. I’m referring to data from those who have a clear prodrome, as these are the ones who have been studied systematically with imaging, etc., through the period of risk for onset.

Nick Brandon
Patricio and Ty, how much effort should we put into the younger animals? Perhaps we can discuss offline?

Akira Sawa
In terms of association of DISC1 with environmental stresses, how about the role of the immune system? Associated with intracellular signaling? Synaptic pruning, etc.? This might be a very important topic.

Becky Carlyle
To all, as a reverse question, do we know if stress paradigms applied to animals affect the quantities of the various known DISC1 isoforms?

Amy Arnsten
Great question, Becky. As far as I know, this has not been studied. Akira, Arthur Simen in our group is looking at cytokines, etc., interactions.

Mikhail Pletnikov
Akira, as you know, we have been looking at DISC1-ploy in interactions and have found that immune activation can change the original phenotype in mice.

Akira Sawa
Yes, you have presented several times, which I found many audiences appreciated.

Nick Brandon
Becky and Amy R., we could look at this easily here.

Becky Carlyle
Nick, I'd be very interested to see that.

Amy Ramsey
I like the stress experiment idea; I hope someone does it.

Tyrone Cannon
Amy R., we could discuss collaboration on that experiment with our DISC1-N line.

Tatiana Lipina
Amy R., we do stress experiments as well as Poly I:C, as Mikhail does.

Peter Penzes
Akira, what would be some good environmental stressors/risk factors that are known in humans to increase schizophrenia risk and can also be applied in rodents?

Michy Kelly
Peter, great question!

Tyrone Cannon
Peter, fetal hypoxia is one of the best.

Akira Sawa
Peter, toxoplasma, some viral infection during development.

Amy Arnsten
There are many stress paradigms in rodents; chronic restraint stress is the classic for gray matter changes.

Akira Sawa
Hi, friends, we only have 12 minutes left. Taking everything together, how about starting a discussion about how DISC1 research can contribute to novel discovery of therapeutic strategies? For example, expression change by drugs?

Amy Ramsey
While looking at current APS effects is a good first step, I would love to see someone take on the challenge of developing in vitro assays for DISC1 function, and ultimately look for drugs that affect DISC1 activity. I understand that first we need to nail down which activities are relevant to disease.

Mikhail Pletnikov
Later on, we might consider "ground-breaking" papers that look at the same factors with different mouse models.

Patricio O’Donnell
I feel a bit uneasy about testing effect of drugs on "normal" animals. If we wanted to learn about antipsychotic properties of an agent, a normal subject may not give us much.

Mikhail Pletnikov
Patricio, quite rightly so; that's why new models may give more interesting clues.

Tyrone Cannon
Patricio, I agree. It’s probably more fruitful to target specific DISC1-interacting partner complexes in mutant mice.

Amy Ramsey
Patricio, absolutely. We have several good mutant lines for modeling schizophrenia; we just need some new drugs to test them.

Nick Brandon
All, for drug discovery, everyone looks to PDE4, but it’s been a well-trodden and so far unsuccessful path. We need to look at the pathway, be brave, and look to be innovative.

Akira Sawa
Nick, how about compounds targeting synaptic protein interactions?

Nick Brandon
Akira, it’s a very attractive proposition. We need to know the interactions we want to modulate and develop the appropriate assays. Many companies get nervous at the thought of modulating interactions, but I believe this is changing.

Nick Brandon
During the pre-discussion comments, David Porteous mentioned the point of collaboration with industry and academia. As David has been central in past efforts to work with a company on DISC1, it’s a shame he cannot suggest alternative, perhaps more successful paths forward in which we can work together with the ultimate aim of bringing forward new innovative medicines based on the biology of DISC1 to improve the lives and outcomes of patients.

Amy Arnsten
Nick, most drug studies have tried to develop PDE4 inhibitors, not activators, which is what would "replace" DISC1. We could think of other agents that inhibit cAMP.

Michy Kelly
To all, given the current hypotheses of how DISC1 is dysfunctional in patients, do we think that DISC1 itself would even be a druggable target?

Akira Sawa
Michy, even if DISC1, as an anchoring protein, is not a direct druggable target, there are many interesting DISC1 interactors for the purpose.

Tyrone Cannon
Akira and Michy, yes, and even if not a direct target, the downstream effect (e.g., cytoskeletal development) could be “patched up” via another signaling pathway.

Patricio O’Donnell
Ty and Michy, exactly! This is where mutant mice may provide a fantastic opportunity!!

Sarah Brown
Patricio, agreed, but this is where the mouse models could be very handy.

Nicola Cascella
cAMP is a very interesting point of "attack."

Sarah Brown
As for pathways, some interesting work is going on in Edinburgh just now throwing up possible pathways and interactions that may be viable future targets.

Tatiana Lipina
Sarah, what pathways? cAMP-dependent?

Sarah Brown
Tatiana, as yet I’m still looking into them to work out, namely, which ones are “real.” Validation is ongoing! But I do think cAMP is looking important at the moment from my data.

Akira Sawa
I am slightly negative to target cAMP for schizophrenia, which impairs both HP and PFC. cAMP-targeted drugs for many other brain disorders can be developed, but not for schizophrenia. What do you think, Amy, Nicola, and other friends?

Tatiana Lipina
Akira, exactly; it is not very specific.

Nicola Cascella
There are interesting cancer meds that can be leaders for cytoskeleton.

Amy Ramsey
I don't know, Akira. I would actually be hopeful about cAMP.

Carsten Korth
Nick, why did Wyeth chose DISC1 as a druggable target?

Nick Brandon
Carsten, DISC1 provides an excellent entry point into trying to understand the disease(s). From this we hope that new drug targets and pathways will emerge. The normal comparison is to compare this historically to AD and the APP/presenilin. What AD teaches us is that it takes time to convert biology into commercialized drugs. Ten-plus years of research into the γ-secretase complex has just seen compounds enter Phase 3.

Michy Kelly
Akira et al., I think we have to be careful when considering targeting the cAMP cascade given regional-specificity and negative feedback loops; however, I think if you target the right component with the right regional/subcellular localization, it could work (we'll see).

Peter Penzes
Regarding new drug development, it seems that of the many interactions of DISC1, we should characterize the functions of the ones that are potentially druggable.

Tyrone Cannon
All, on the issue of targeting pathways, can human data on gene-gene or protein interactions be of guidance? I notice that Anil's group and Leena's group have some interesting data on gene-gene interactions in human samples.

Anil Malhotra
Ty, we have published on NDEL-DISC1 interactions, but our current work is focused on PDE4B (notable interaction at the level of genotype but very low MAF)—and FEZ1—I’m not sure NDEL or FEZ will emerge as targets.

Nick Brandon
Akira, the preclinical data with Rolipram is pretty good with both antipsychotic and procognitive effects. It’s just all the unwanted side effects that go with it. Innovation approaches around PDE4 are still possible.

Akira Sawa
Nick, I think DISC1-PDE4 shows great hope, but we need to be much more cautious in data interpretation, especially focusing on regional-specific effects.

Amy Arnsten
Akira, cAMP improves memory consolidation in the hippocampus, so you’re right; it’s not a simple target. It would be best to find molecules that modulate the pathway that are preferentially localized in the prefrontal cortex or hippocampus. We find working memory impairment with Rolipram in our aged monkeys

Michy Kelly
Amy A., that's via PKA?

Amy Arnsten
Michy, we think it is via HCN channel opening.

Amy Arnsten
Tyrone, I would like to e-mail with you about mice after this is finished.

Tyrone Cannon
Amy A., that sounds great.

Akira Sawa
Amy A., please also send e-mails to the JHU folks. The comparison among various animal models of DISC1 should be very important.

Amy Arnsten
Yes indeed, Akira.

Mikhail Pletnikov
Sure thing. We are sending mice to JAX but would be happy to share with anyone interested.

Nick Brandon
We'd like to be involved, too, in these discussions (if we can)!! Michy Kelly in particular from Wyeth.

Hakon Heimer
All, this may be a bit pie in the sky, but as an example of what might be "druggable" in the future with greater knowledge of DISC1 role in development. A paper in Nature Medicine last month showed rescue of an epilepsy phenotype in a developmental migration disorder model—DcX—by postnatal expression of the protein: Manent et al., 2009.

Amy Arnsten
The question of how to rescue DISC1 function in utero and thus spare developmental defects will be the golden challenge.

Carsten Korth
I think what is not so easy with DISC1 is that its lack of expression is associated with disease. That could mean that you may want to substitute its effect on insufficient molecular interactions.

Michy Kelly
Absolutely.

Amy Arnsten
Human cortex migration is completed in utero, so this will be harder in people.

Nick Brandon
Hakon, I know the paper well, and I got very excited by this reversal. There are clearly developmental issues around this piece of work, as you have to treat in utero, but still a giant stride forward!

Nick Brandon
Amy A., hopefully approaches will come to light that do not require such intervention?

Tyrone Cannon
Amy A., we see differences in the developmental relevance of DISC1 disruption based on whether the C-terminal or N-terminal fragment is impaired, the former clearly requiring early induction to see behavioral/histological effects and the latter not requiring this. But I agree the Holy Grail is prenatal/prevention!

Amy Arnsten
Tyrone, that is an important clue.

Tatiana Lipina
Nick, what do you think about DPSYL2 as a drug target?

Nick Brandon
Tatiana, I’m interested; we flagged in our review in 2008 (Wang et al.). We can talk more offline.

Tatiana Lipina
Nick, thank you. Yes, Wang et al. is a very interesting article.

Akira Sawa
This has been a wonderful hour. Hakon and Nico, thanks for coordinating this roundtable discussion for all of our DISC1 folks. This field is a wonderful one shared by many outstanding investigators. I would also like to say thank you very much to Dr. St. Clair, the real pioneer of this field, together with Drs. Blackwood and Muir in Scotland!

Nick Brandon
All, lots of other points were dropped, so it would be great to have follow-up comments added.

Tatiana Lipina
Bye!

David St. Clair
Thanks for inviting me.

Hakon Heimer
Akira, perhaps we should not wait two years for the next roundtable!

Nick Brandon
Hakon, I agree. I think that in 12 months we may see big strides here in a number of avenues: models, cell biology, clinical, so an annual update might not be a bad idea.

Tyrone Cannon
Many thanks to all and especially Hakon and Nico for coordinating, and Akira and Nick for initiating.

David St. Clair
It’s 20 years next year since the original description of family. Maybe should have a meeting in Scotland?

Hakon Heimer
David, I'll come! Never been to Scotland.

Nick Brandon
David, wonderful idea!

David St. Clair
I’ll discuss with the others.

Nick Brandon
Please wait until my green card has arrived as I cannot leave the U.S. until then!

Hakon Heimer
Nick, Akira, Ty, thanks so much for bringing this large group together for the meeting!

Amy Ramsey
Congratulations to all of you who have contributed to making this such an exciting field of research. I enjoyed the discussion.

Amy Arnsten
Thanks for including us!

Comments on Online Discussion
Comment by:  Barbara LipskaJoel Kleinman
Submitted 11 January 2009
Posted 11 January 2009

If indeed genetic variation in the DISC1 gene confers risk for mental illness, the effects of risk-associated polymorphisms should be detectable at the level of pre-mRNA processing, transcription, post-translational modification of proteins or their subcellular distribution, as these are the most proximal intermediate phenotypes to risk-associated alleles. So far, however, the results of studies searching for molecular correlates of genetic associations have been inconclusive and the mechanisms remain unknown. Although reduced expression of DISC1 mRNA was found in the lymphoblastoid cell lines of family members with the translocation (Millar et al., 2005) and in bipolar disorder patients with a putative risk haplotype (Maeda et al., 2006), no changes were detected in the brain tissue of unrelated patients with schizophrenia or in individuals carrying risk genotypes (Lipska et al., 2006; Dean et al., 2007). Furthermore, in an allele-specific expression assay, two coding SNPs in DISC1 did not show an effect on DISC1 mRNA in the brain tissue (Hayesmoore et al., 2008).

On the other hand, Sawamura et al. (2005) reported enrichment of certain shorter, though uncharacterized, isoform(s) of DISC1 in the nuclear fraction of brain tissue extracts in patients with schizophrenia and major depression. This finding raised an interesting possibility that DISC1 mRNA and/or protein processing and distribution might be altered in patients with major mental illness. Indeed, further evidence for this premise comes from our own data showing that immunoreactivity of the same short, and as yet unidentified, DISC1 isoform(s) is higher in the hippocampus of patients with schizophrenia and predicted by risk-associated SNPs (Lipska et al., 2006). Furthermore, studies probing cells, mouse and human brain protein extracts with a number of well-characterized antibodies have provided ample evidence for the existence of a large variety of unknown DISC1 protein forms, suggesting that DISC1 processing mechanisms are complex and might be altered in mental illness and affected by risk related genetic variation (summarized in Ishizuka et al., 2007). Studies using well characterized, high quality postmortem brain tissues are critical for elucidating how risk-associated alleles in the DISC1 gene affect mRNA processing. Given that schizophrenia is a neurodevelopmental disorder, it might be essential to extend these studies to an early developmental period. Such findings may potentially be crucial for understanding apparent inconsistencies in results of association studies for DISC1, which may involve true genetic heterogeneity (as different SNPs in the same gene may result in the same molecular phenotype).

References:

Dean B, Keriakous D, Scarr E, Thomas EA. Gene expression profiling in Brodmann’s area 46 from subjects with schizophrenia. Aust N Z J Psychiatry. 2007 Apr;41(4):308-20.

Hayesmoore JB, Bray NJ, Owen MJ, O’Donovan MC. DISC1 mRNA expression is not influenced by common Cis-acting regulatory polymorphisms or imprinting. Am J Med Genet B Neuropsychiatr Genet. 2008 Feb 12. Abstract

Ishizuka K, Chen J, Taya S, Li W, Millar JK, Xu Y, Clapcote SJ, Hookway C, Morita M, Kamiya A, Tomoda T, Lipska BK, Roder JC, Pletnikov M, Porteous D, Silva AJ, Cannon TD, Kaibuchi K, Brandon NJ, Weinberger DR, Sawa A. Evidence that many of the DISC1 isoforms in C57BL/6J mice are also expressed in 129S6/SvEv mice Mol Psychiatry. 2007 Oct;12(10):897-9.

Lipska, B.K., Peters, T., Hyde, T.M., Halim, N., Horowitz, C., Mitkus, S., Weickert, C.S., Matsumoto, M., Sawa, A., Straub, R.E., et al. (2006). Expression of DISC1 binding partners is reduced in schizophrenia and associated with DISC1 SNPs. Hum. Mol. Genet. 15, 1245-1258.

Maeda K, Nwulia E, Chang J, Balkissoon R, Ishizuka K, Chen H, Zandi P, McInnis MG, Sawa A. Differential expression of disrupted-in-schizophrenia (DISC1) in bipolar disorder. Biol Psychiatry. 2006 Nov 1;60(9):929-35. Abstract

Millar, J.K., Pickard, B.S., Mackie, S., James, R., Christie, S., Buchanan, S.R., Malloy, M.P., Chubb, J.E., Huston, E., Baillie, G.S., et al. (2005). DISC1 and PDE4B are interacting genetic factors in schizophrenia that regulate cAMP signaling. Science 310, 1187-1191. Abstract

Sawamura N, Sawamura-Yamamoto T, Ozeki Y, Ross CA, Sawa A. A form of DISC1 enriched in nucleus: altered subcellular distribution in orbitofrontal cortex in psychosis and substance/alcohol abuse. Proc Natl Acad Sci U S A. 2005 Jan 25;102(4):1187-92. A HREF=http://www.schizophreniaforum.org/pap/annotation.asp?powID=61745>Abstract

View all comments by Barbara Lipska
View all comments by Joel KleinmanComment by:  Carsten Korth
Submitted 11 January 2009
Posted 11 January 2009

This is my current view of DISC1-related research:

What is the current situation in linking DISC1 to psychiatric disease?
1. There is the Scottish pedigree where DISC1 disruption could be genetically linked to clinical phenotypes of chronic mental diseases

2. Genetic association studies have associated polymorphisms within DISC1 to different psychiatric diseases but these results are sometimes weak and seem inconsistent

3. Animal models modeling the familial DISC1 mutation or other DISC1-related constructs consistently demonstrated behavioral changes, and in some models also subtle neuropathological ones (enlarged third ventricles, etc.).

What are the problems?
1. Does DISC1 have anything to do with sporadic cases of chronic mental disorder (CMD)?

2. If yes, what is the molecular mechanism of action?

3. Given the multitude of molecular interactions of DISC1, is there a smallest common molecular denominator of DISC1 dysfunction with regard to behavioral (or other) phenotypes?

General comments:
I agree that it is of paramount importance to have a valid DISC1-related animal model showing any kind of phenotype, preferably one with a clear and unequivocal behavioral phenotype, and, even better, a clear and unequivocal neuropathological phenotype.

However, I consider it equally important to link DISC1 to sporadic cases of chronic mental diseases because otherwise the animal models would not directly address an important clinical issue. It is unlikely that a role of DISC1 can be established in the majority of sporadic CMD cases given the heterogeneity of human psychiatric diseases. A role of DISC1 in a subset of sporadic cases is exciting enough! How could DISC1 play a role in causing sporadic CMD? Any posttranscriptional and posttranslational modifications in DISC1 could account for this. Starting from the role of differential DISC1 splice variants, to posttranslational DISC1 modifications like phosphorylation, degradation or others.

We have shown that recombinantly expressed full length DISC1 in eukaryotic cells assembles into multimeric complexes. In a cell-free in vitro system, a relevant recombinant DISC1 fragment expressed in E. coli interacted with NDEL1 only as an octameric complex in solution, but not as dimers or high molecular weight multimers (Leliveld et al., 2008). In the same paper, we demonstrated that DISC1 is an aggregation-prone protein that in its insoluble state would loose binding to NDEL1. In fact, we were able to identify a subset of patients with variable clinical phenotypes in the Stanley Foundation Consortium Collection with insoluble DISC1. In my view, this indicates that misassembly of DISC1 could account for its dysfunction in sporadic cases with CMD.

I do not think that this is the end of the story but just demonstrating one mechanism of how posttranslational modifications of DISC1 can affect its function and thereby lead to disease. Remember Alzheimer's disease, where >95 percent of cases are sporadic, i.e., no mutations can be identified, but still amyloid-β and tau are post-translationally modified and considered causative for the clinical phenotype.

View all comments by Carsten KorthComment by:  Anil Malhotra, SRF Advisor
Submitted 12 January 2009
Posted 12 January 2009

DISC1 appears to be related to a number of psychiatric phenotypes, bridging across traditional diagnostic boundaries and influencing key clinical manifestations of illness including neurocognitive function, symptom domains, and neuroimaging parameters. In addition, we (Burdick et al., 2008) and others have recently noted that the DISC1 interactome is also critically related to this broad array of phenotypes, and the specific genetic relationship may be predicated on different DISC1 genetic backgrounds. Therefore, the examination of single genes, and proteins, may not be sufficient to fully assess the biological effects of this system on behavioral phenotypes.

This complexity further complicates the search for relevant animal models, as most genetic models are based upon single gene perturbations. Animal models that incorporate perturbations across multiple genes and that can take into account developmental timing and produce relevant behavioral phenotypes would be a great step forward. In particular, the relationship of DISC1 and its binding partners to treatment response has not been investigated at either the preclinical or clinical level. For a protein with such diverse effects on psychosis not to have an effect on treatment response would be unexpected, but this remains an empirical question to be addressed. The challenges of conducting pharmacogenetics research mirror some of the challenges surrounding the development of animal models. The need for consistent treatment approaches, for careful and reliable assessment of treatment outcomes, yet with increasingly large sample sizes, are currently limiting factors for the field. However, at the end of the day, the key issue surrounding any of this work will be whether or not we can significantly influence the treatment outcome of our patients, and much work remains to be completed before appropriate consideration of this element of the DISC1 research portfolio.

References:

Burdick KE, Kamiya A, Hodgkinson CA, Lencz T, Derosse P, Ishizuka K, Elashvili S, Arai H, Goldman D, Sawa A, Malhotra AK. Elucidating the relationship between DISC1, NDEL1, and NDE1 and the risk for schizophrenia: Evidence of epistasis and competitive binding. Human Molecular Genetics 2008; 17:2462-73. Abstract

View all comments by Anil MalhotraComment by:  David J. Porteous, SRF Advisor
Submitted 12 January 2009
Posted 12 January 2009

I am unfortunately unable to attend the live discussion, but I am pleased to note this topic being revisited. All of the evidence gathered since the last SRF discussion supports my view that the study of DISC1 genetics and biology has much to offer the field. I have followed each of the topic questions with a short comment. I hope you find these helpful and that the discussion is productive. Also, if you haven’t already done so, check out the SRF meetings calendar or go straight to the Keystone Meetings website and register for the following meeting. There is a great lineup of speakers, loads of discussion, plus fantastic snow sports.

Conference: The Molecular Basis of Schizophrenia and Bipolar Disorder
Date: 6-10 March 2009
Location: Keystone Resort, Keystone, CO, U.S.A.
Website: http://www.keystonesymposia.org/Meetings/ViewMeetings.cfm?MeetingID=1008

1) The complexity of the DISC1 molecule (isoforms, potential role for antisense transcripts and fusion transcripts). This is clearly an important issue. DISC1 is a large multi-exon gene with evidence for multiple splice forms. I note Barbara Lipska’s comments regarding the lack of evidence for reduced DISC1 expression in schizophrenia brains, but believe that more detailed characterization during development and in relation to pathology is still warranted. The effect of normal genetic variation and of putative pathogenic variants is likewise relevant. We lack biopsy material from any of the t(1;11) subjects through which DISC1 was identified to test for reduced levels in the brain, but if we extrapolate from cell culture studies and half normal levels of DISC1 are highly penetrant for major mental illness, then our assays need to be very sensitive to detect modest, but still potentially relevant reductions in DISC1 levels in the generality of schizophrenia and other related brain disorders.

2) Understanding the cellular roles of DISC1 in partnership with other risk factors for schizophrenia (disease-associated molecular pathways/cascades) in context-dependent situations (cellular compartment, cell types, brain regions, developmental timing).

The complexity of neuronal types alone and the recognition of the multi-functional nature of the DISC1 complex make these self-evidently key considerations. In this regard, cell and animal model systems must be combined as the scope for human studies is obviously limited. Past limitations may, however, be partially circumvented in the future by application of iPS technology and related pluripotent stem cell approaches. In the meantime, animal models have much to offer that is otherwise obscured from view by the limited access to appropriate and relevant human tissue.

3) The role for model organisms (mice, flies, zebrafish, etc.) in DISC1 research, especially their translational utilities. With the burgeoning number of DISC1 mice, can we rationalize a path forward? Are all these models in all cases simply interfering with a key neurodevelopmental protein or are they really telling us something about the human disease? In terms of non-mouse models, what are we learning and does it have any relevance to humans?

A model is just that. The key issue is to define the hypothesis and the experimental approach to test it. We are at an early stage with all these models. Some consistent themes are emerging from the mouse studies—brain developmental abnormalities and working memory defects—but different studies report on different phenotypes so cross-comparisons are only partial. Each of the several mouse models already available have their value. I believe we still lack a true null. This would be valuable as a test bed on which to test the known and emerging human mutations. I can see some useful insights coming also from Danio and Drosophila which each offer specific experimental advantages.

4) Nature and effects of DISC1 variants on phenotypes/endophenotypes beyond DSM diagnostic criteria. Only the most stubborn skeptic would deny that mutation of DISC1 can be causally related to major mental illness, but as the current state of genetic linkage, candidate gene association, GWAS, CNV, and molecular cytogenetics studies tell us, the full picture of genetic architecture underlying schizophrenia and related brain disorders is barely started. Nor can we estimate the net contribution of DISC1 and DISC1 complex genetic variants to risk, at the individual or population level, but that is true for all current candidates. I would argue, however, that even at this early stage, it is highly likely that a wide range of mutation classes (regulatory, deletion, insertion, missense, nonsense) have already or will soon be found for DISC1. Large-scale resequencing on well-characterized samples (normal and disease) is warranted and likely to be highly informative with regard to structure-function insights.

5) Should we expect any therapeutic breakthroughs for schizophrenia and other neuropsychiatric disorders via DISC1 research?

The gap between expectation and delivery is great, but as a platform from which to develop a program of rational drug development, the DISC1 complex presents as good an opportunity as any currently available. The big question is how and when academia and industry will partner each other successfully in the pursuit. We are not helped in this regard by the current global economic climate and the associated risk-averse nature of research investment. But we have to try.

View all comments by David J. PorteousComment by:  David St Clair
Submitted 12 January 2009
Posted 12 January 2009

I think that it has been a very productive couple of years since your last forum, and DISC1 has established itself as one of the most interesting genes in psychiatric genetics.

The recent work examining CNVs in schizophrenia over the last 12 months indicates 1) that there are likely to be very many other rare high penetrant mutations which, like DISC1 mutations, predispose individuals and families to high risk of schizophrenia and other neuropsychiatric disorders, and 2) that as with DISC1 there is unexpected clinical phenotypic diversity. Most of these CNVs, whether deletions or duplications, disrupt some or many aspects of CNS function at all stages of brain development. In some cases these mutations are so rare that it will be difficult to show statistical association with schizophrenia and evidence of involvement will need to be circumstantial. The great advantage of theDISC1 mutation is that so many members of the family with the mutation are affected that the association is highly unlikely to be due to chance.

Detailed study of all aspects of DISC1 is likely to continue to not only be rewarding in its own right but to help set the framework and ground rules as to how best to study the many other rare mutations that predispose to schizophrenia and related disorders that are now being identified.

Also very interesting is the accumulating genetic evidence implicating a number of direct DISC1 interactors in schizophrenia; the most convincing and interesting are PDE4B, Nde1, and PCM1.

I fully agree with aims 1 and 2 of Sawa and Brandon's discussion text, although they are not my area of expertise. Modeling poses special challenges since the range of phenotypes associated with neuron expressed gene disruptions is so extensive. Key issues will be to try to determine the genetic and environmental factors that influence penetrance and expressivity. These could be studied in rodent and non-rodent models e.g., zebra fish. One of the most interesting findings to emerge in DISC1 mice is a GABAergic deficit. This could be a key translational target, since GABAergic deficits are consistently found in schizophrenia; it is possible that a whole range of upstream genetic lesions can cause downstream GABAergic deficits, and these are responsible for some of the cognitive and perceptual problems that are widespread in schizophrenia. In my opinion, detailed study of these downstream anomalies in DISC1 is as important as the upstream biochemistry.

It is impossible to predict whether therapeutic breakthroughs can be expected. Three potential interesting leads give hope: 1) cAMP appears to affect PDE4B, NUDEL, and DISC1 interaction, so drugs like Rolipram could be of importance for the DISC1 cascade as a whole; 2) GABAergic drugs should be examined; 3) it is possible that prenatal nutritional status could affect penetrance and expressivity of many mutations causing schizophrenia. This can be examined in DISC1 models and if demonstrated could lead to potential preventative interventions, e.g., micronutrient supplementation.

View all comments by David St ClairComment by:  Steven Clapcote
Submitted 12 January 2009
Posted 12 January 2009

After much anticipation, a variety of mutant and transgenic DISC1 mouse lines from several research groups has been published over the last two years. Most of these attempt to mimic the original t(1:11) DISC1 mutation by transgenic expression of truncated DISC1 proteins. The Gogos group introduced a targeted premature stop codon into exon 8 of the endogenous DISC1 of the 129 mouse strain (Koike et al., 2006; Kvajo et al., 2008), which itself was found to carry a spontaneous premature stop codon in DISC1 exon 7 (Koike et al., 2006). The Pletnikov, Sawa and Silva groups generated transgenic lines that have constitutive (Hikida et al., 2007) or inducible (Li et al., 2007; Pletnikov et al., 2008) CaMKIIa promoter-driven expression of truncated human DISC1. The St Clair group generated a BAC transgenic line expressing truncated mouse DISC1 under the influence of the (still not formally identified) DISC1 promoter (Shen et al., 2008). Taking a different tack, the Roder group screened an archive of ENU-mutagenized mice for mutations in DISC1, and found two missense mutations within PDE4B binding sites (Clapcote et al., 2008).

In most cases, the mouse lines have had a predominantly C57BL/6 genetic background (Koike et al., 2006; Kvajo et al., 2008; Hikida et al., 2007; Li et al., 2007; Clapcote et al., 2008), which is an important consideration when comparing the phenotypes of each line. Although the mutations may have different mechanisms, their effects on brain morphology and behavior appear similar; with fairly consistent effects on working memory, brain morphology and prepulse inhibition (see Table 1, Shen et al., 2008). There are still no DISC1 knockout mice available, but we await these with bated breath. It would be interesting to cross DISC1 truncation transgenics with the DISC1 knockouts when they come along, to test whether having a part of DISC1 is better than none at all.

View all comments by Steven ClapcoteComment by:  Mikhail Pletnikov
Submitted 12 January 2009
Posted 13 January 2009

I have tried to answer some of the questions asked by the discussants.

With the burgeoning number of DISC1 mice can we rationalize a path forward?

Combining available animal DISC1 models with other genetic mouse models and/or environmental factors appears as an obvious next thing to try to answer some fundamental questions about psychiatric disorders. Again, we will be using DISC1 as a great discovery tool.

Are all these models in all cases simply interfering with a key neurodevelopmental protein or are they really telling us something about the human disease?

I would suggest both. In other words, by interfering with a key developmental protein, we are beginning to understand better the biology and functions of DISC1 and potential pathogenic process of psychiatric disorders when the functions are perturbed.

In terms of non-mouse models what are we learning and does it have any relevance to man?

I often feel that many investigators are either overly optimistic or too negative towards animal models. Models are just what they are—models. Perhaps we should stop worrying about how well our models reflect/mimic a disease or a symptom. If they are helpful to answer specific BIOLOGICAL questions related to genes, environmental factors or the pathways, we can and should use these models. Fruit fly-based models have helped to uncover several key fundamental biological functions and principles. Are they are relevant to human diseases? Yes, they are as long as the disease has the molecular underpinning. Since we seem to agree that psychiatric diseases have biological roots, we will need to use animal models to experiment. Will animal models be sufficient for describing the psychiatric disease in its entirety? No, they won’t, but what they may show to us is, for example, that there may be several common biological processes that underlie different psychiatric disorders, supporting what is emerging from psychiatric genetics that many genes are equally associated with different clinical diagnoses.

View all comments by Mikhail PletnikovComment by:  Tatiana Lipina
Submitted 16 January 2009
Posted 16 January 2009

The study of Disc1's biological role gives us hope to comprehend much deeper neurobiological processes of such complex psychopathologies as schizophrenia or bipolar disorder. Analysis of Disc1 interactions with many other proteins (Camargo et al., 2007) will help us to dissect the function(s) of each molecular player. Excellent recent reviews by Chubb et al., 2008, and Wang et al., 2008, are very helpful in fully comprehending the biology of Disc1. I will give you some of my comments regarding the preliminary questions for the DISC1 roundtable discussion:

1. The complexity of the DISC1 molecule (isoforms, potential role for antisense transcripts and fusion transcripts). What is the role of multiple isoforms of Disc1? I think the comparison of Disc1 structure, functions between biological species from an evolutionary point of view, might be helpful at least to understand the origins of multiple Disc1 isoforms.

2. Understanding the cellular roles of DISC1 in partnership with other risk factors for schizophrenia (disease-associated molecular pathways/cascades) in context-dependent situations (cellular compartment, cell types, brain regions, developmental timing).

A very exciting area of investigation is to find the biological meaning of Disc1 environment interactions, whereby psychopathological cascades could be triggered by different manipulations of prenatal (like immune activator Poly I:C) or postnatal stress (e.g., chronic social stress). Exposure of different Disc1 mouse mutants with genetic predisposition to the development of schizophrenia or bipolar disorder to the different types of stressful environment is a very productive approach.

3. The role for model organisms (mice, flies, zebrafish, etc.) in DISC1 research, especially in their translational utilities. With the burgeoning number of DISC1 mice, can we rationalize a path forward? Are all these models in all cases simply interfering with a key neurodevelopmental protein or are they really telling us something about the human disease? In terms of non-mouse models, what are we learning and does it have any relevance to humans?

I think that analysis of many animal models will provide better understanding of Disc1’s biological role. Having multiple Disc1 mutants with different alterations of Disc1 protein will help us to identify multiple functions of Disc1 and define its role(s) within the whole psychopathological process underlying schizophrenia or bipolar disorder. Moreover, analysis of Disc1 interactor(s) mouse mutant models will discover new functions of known proteins or possibly reveal new proteins involved in the same psychopathological pathways. It will be interesting to find how conserved the role of Disc1 is among different biological species, and non-mouse models could be very helpful.

4. Nature and effects of DISC1 variants on phenotypes/endophenotypes beyond DSM diagnostic criteria.

Even though we mostly focus on psychopathologies, expanded behavioral procedures could reveal new phenotypes/endophenotypes of Disc1 variants beyond DSM diagnostic criteria. For instance, Disc1 could play an important role in navigation processes, and decoding their role in place cells would be an exciting finding.

5. Should we expect any therapeutic breakthroughs for schizophrenia and other neuropsychiatric disorders via DISC1 research?

Yes, our combined efforts of Disc1 investigations will bring us a lot of new discoveries in the near future.

References:

Camargo LM, Collura V, Rain JC, Mizuguchi K, Hermjakob H, Kerrien S, Bonnert TP, Whiting PJ, Brandon NJ. Disrupted in Schizophrenia 1 Interactome: evidence for the close connectivity of risk genes and a potential synaptic basis for schizophrenia. Mol Psychiatry. 2007 Jan 1;12(1):74-86. Abstract

Chubb JE, Bradshaw NJ, Soares DC, Porteous DJ, Millar JK. The DISC locus in psychiatric illness. Mol Psychiatry. 2008 Jan 1;13(1):36-64. Abstract

Wang Q, Jaaro-Peled H, Sawa A, Brandon NJ. How has DISC1 enabled drug discovery? Mol Cell Neurosci. 2008 Feb 1;37(2):187-95. Abstract

View all comments by Tatiana LipinaComment by:  Jesus Requena
Submitted 15 January 2009
Posted 16 January 2009

I think that there is little doubt that DISC1 is a fantastic tool to probe the mechanism(s) underlying schizophrenia and mental disease in general, and I am convinced that many exciting breakthroughs lie ahead. However, I would like to share some cautioning thought, following up on comments from my colleague Carsten Korth: What if DISC1 has absolutely nothing to do with sporadic cases of mental disease (SMD), because it is upstream of the damage/alterations that occur in these diseases? For example, let´s suppose that DISC1, through its interaction with PDE4B, plays an essential regulatory role in the flow of cAMP to some specific cell location in a given set of neurons, in turn, that cAMP flow regulates the activity of a given effector, "X." Now let´s imagine that 99.9 percent of SMD is caused by a malfunction in X that is caused by an environmental stress (this is just for the sake of argument). DISC1 malfunction, by disrupting the "X route" upstream, would end up in mental disease, but studying the role of DISC1 in neurogenesis, or its interaction with NUDEL (again for the sake of argument) would not be relevant at all. So I think that an important research avenue should be to explore all the routes in which DISC1 is involved.

View all comments by Jesus RequenaComment by:  Peter Penzes
Submitted 13 January 2009
Posted 19 January 2009

The number of publications on DISC1 has been rising steadily and rapidly, from below 15 in 2004 to over 60 in 2008. This pace of discovery will certainly accelerate in the coming years. Light has been shed on many aspects of DISC1 molecular properties, expression, and functions. Mutant mice have been generated with different types of alterations in DISC1 function, and these mice have been analyzed for anatomical alterations, synaptic properties, cognitive functions, and other behaviors. New genetic studies further associated DISC1 with psychiatric disorders.

An important role in brain development for DISC1 acting at the centrosome has been established. Several of its protein interactors, also supported by recent studies, suggest other potential functions for DISC1, in other neuronal compartments. Of these, synaptic functions of DISC1 are particularly interesting, as synaptic dysfunction is thought to play an important role in psychiatric disorders. One good reason why it is worth examining plasticity related functions of DISC1 is because plasticity is ongoing throughout life, and can be therapeutically modulated.

DISC1 knockdown in adult-born dentate granule cells in vivo accelerates dendritic development. Specifically, DISC1 knockdown has been shown to accelerate the formation of dendritic spines in newborn dentate granule cells in adulthood (Duan et al., 2007). This suggests that in dentate gyrus granule cells, wild-type DISC1 normally delays the formation of dendritic spines. These findings seem at odds with findings of reduced dendritic spine density in the hippocampal formation of schizophrenia patients. Furthermore, in cell culture models, DISC1 has been shown to increase, rather than decrease, neurite outgrowth (Kamiya et al., 2005; 2006). Is it possible that the role of DISC1 in dentate granule cells is thus different than its role in other cell types?

Recent evidence supports a role of DISC1 in the activation of ERK and Akt. Specifically, in primary neuronal cultures, the knockdown of DISC1 drastically reduces the phospho-activation of ERK and Akt (about an 80 percent reduction) without affecting the total expression of either molecule (Hashimoto et al., 2006). This is interesting as much evidence suggests that similar to DISC1, ERK, and Akt activation are critical mediators of cortical neuronal migration (Chen et al., 2008; Jossin and Goffinet, 2007; Segarra et al., 2006). As a future direction, it would be interesting to determine if the role of DISC1 mutants in perturbing cortical development (e.g., Kamiya et al., 2005) is mediated by a reduction in ERK and Akt activation. Furthermore, what are the possible signaling pathways that connect DISC1 to ERK and Akt? This is particularly interesting as Akt has been involved in schizophrenia risk.

Some of the morphological abnormalities of DISC1 mutant mice are present in adulthood, but not in juvenile mice (e.g., enlarged lateral ventricles are present in mutant mice at three months but not at six weeks; Hikida et al., 2007). However, most of the behavioral characterization of DISC1 mutants has focused on adulthood. Based upon the delayed emergence of schizophrenia symptoms in humans, one would expect that mutant mice should similarly show behavioral deficits that do not emerge until adolescence/young adulthood. Is there evidence from animal models supporting this?

References:

Duan X, Chang JH, Ge S, Faulkner RL, Kim JY, Kitabatake Y, Liu XB, Yang CH, Jordan JD, Ma DK, Liu CY, Ganesan S, Cheng HJ, Ming GL, Lu B, Song H. Disrupted-In-Schizophrenia 1 regulates integration of newly generated neurons in the adult brain. Cell. 2007 Sep 21;130(6):1146-58. Abstract

Kamiya A, Kubo K, Tomoda T, Takaki M, Youn R, Ozeki Y, Sawamura N, Park U, Kudo C, Okawa M, Ross CA, Hatten ME, Nakajima K, Sawa A. A schizophrenia-associated mutation of DISC1 perturbs cerebral cortex development. Nat Cell Biol. 2005 Dec 1;7(12):1167-78.Abstract

Kamiya A, Tomoda T, Chang J, Takaki M, Zhan C, Morita M, Cascio MB, Elashvili S, Koizumi H, Takanezawa Y, Dickerson F, Yolken R, Arai H, Sawa A. DISC1-NDEL1/NUDEL protein interaction, an essential component for neurite outgrowth, is modulated by genetic variations of DISC1. Hum Mol Genet. 2006 Nov 15;15(22):3313-23. Abstract

Hashimoto R, Numakawa T, Ohnishi T, Kumamaru E, Yagasaki Y, Ishimoto T, Mori T, Nemoto K, Adachi N, Izumi A, Chiba S, Noguchi H, Suzuki T, Iwata N, Ozaki N, Taguchi T, Kamiya A, Kosuga A, Tatsumi M, Kamijima K, Weinberger DR, Sawa A, Kunugi H. Impact of the DISC1 Ser704Cys polymorphism on risk for major depression, brain morphology and ERK signaling. Hum Mol Genet. 2006 Oct 15;15(20):3024-33. Abstract

Chen ZL, Haegeli V, Yu H, Strickland S. Cortical deficiency of laminin gamma1 impairs the AKT/GSK-3beta signaling pathway and leads to defects in neurite outgrowth and neuronal migration. Dev Biol. 2008 Dec 16;Abstract

Jossin Y, Goffinet AM. Reelin signals through phosphatidylinositol 3-kinase and Akt to control cortical development and through mTor to regulate dendritic growth. Mol Cell Biol. 2007 Oct 1;27(20):7113-24. Abstract

Segarra J, Balenci L, Drenth T, Maina F, Lamballe F. Combined signaling through ERK, PI3K/AKT, and RAC1/p38 is required for met-triggered cortical neuron migration. J Biol Chem. 2006 Feb 24;281(8):4771-8. Abstract

Kamiya A, Kubo K, Tomoda T, Takaki M, Youn R, Ozeki Y, Sawamura N, Park U, Kudo C, Okawa M, Ross CA, Hatten ME, Nakajima K, Sawa A. A schizophrenia-associated mutation of DISC1 perturbs cerebral cortex development. Nat Cell Biol. 2005 Dec 1;7(12):1167-78. Abstract

Hikida T, Jaaro-Peled H, Seshadri S, Oishi K, Hookway C, Kong S, Wu D, Xue R, Andradé M, Tankou S, Mori S, Gallagher M, Ishizuka K, Pletnikov M, Kida S, Sawa A. Dominant-negative DISC1 transgenic mice display schizophrenia-associated phenotypes detected by measures translatable to humans. Proc Natl Acad Sci U S A. 2007 Sep 4;104(36):14501-6. Abstract

View all comments by Peter PenzesComment by:  David J. Porteous, SRF Advisor
Submitted 4 March 2009
Posted 4 March 2009

The online DISC1 discussion organized by Akira Sawa, Nick Brandon, and Ty Cannon and hosted by SRF on January 13, 2009, was certainly lively and nicely demonstrated how much the field has moved on since the first such discussion just two years earlier. Most gratifyingly, many new researchers have entered the fray with probing questions and fresh ideas.

If two years ago there was some lingering debate as to whether or not DISC1 was a bona fide genetic risk factor in schizophrenia, that is now well and truly settled in the positive. But the more interesting questions only partially addressed and answered in the discussion are what are the genetic mechanisms (haploinsufficiency, dominant negative), the genetic classes of variation (regulatory, copy number, missense) and their relative abundances, and what are their respective phenotypic effects at the molecular, cellular, neurological, and clinical levels? This to me is one of the main opportunities for the DISC1 field and the challenges to the rest of the field of biological psychiatry. Evidence is growing for both direct and indirect (epistatic) effects of DISC1 variation, covering the full spectrum from polymorphic variant to clear-cut mutation. But it is also clear that we should think more in terms of a DISC1 complex of proteins and therefore also the consequences of genetic variation in the constituent components of the complex to get the full picture. In order to tease out genotype-phenotype correlations, clinical studies, not just of schizophrenia, but also the affective disorders, autisms, and perhaps dementias, too, and not just clinical end phenotypes, but more importantly intermediate phenotypes, need to be integrated with genetically engineered model organism studies (mouse, zebrafish, fruit fly, etc.). This is starting to happen, but more is needed.

Whether DISC1, or rather the DISC1 pathway, is “druggable” came in late to the discussion and met with mixed opinions. My own is that the question is not whether, but how. In the search for novel antipsychotics, antidepressants, mood stabilizers, or cognitive enhancers, there seems little point ploughing the same old furrows in search of a new D2 antagonist or conventional “druggable” targets (receptors, kinases, and the like) whilst proven genetic targets are ignored. The model needs to be reworked if we are, as we surely must be, striving to transform etiological insights from DISC1 into better diagnosis and management. Encouragingly, this discussion provided hints from several directions that these questions are very much live in the minds of participants.

As for next DISC1 online discussion, the question is not whether, but when. With the pace of current progress, we won’t want to wait another two years. The year 2010 marks the 20th anniversary of the Lancet study by David St. Clair and colleagues which first described the Scottish family with a high loading of schizophrenia and related major mental illness co-segregating with a balanced t(1;11) translocation. Coincidently, it is also the 10th anniversary of the Human Molecular Genetics study in which Kirsty Millar and colleagues described the cloning of that translocation breakpoint and the discovery of DISC1. So take this as advance notice of a DISC1-focused meeting, planned for Edinburgh 2010.

View all comments by David J. PorteousComment by:  Alexander Arguello
Submitted 25 March 2009
Posted 27 March 2009

In reading the online DISC1 discussion, which I unfortunately missed, I saw there were many good points concerning DISC1 biology, but there are others that need to be emphasized. The discussion rightly pointed out that DISC1 is a complex gene with potentially many post-transcriptional and post-translational modifications. The group seemed to agree that the tools used to interrogate DISC1 function therefore need to be well calibrated and validated to insure reliability and replicability of any findings. This will be important for identifying which of the many DISC1 biological pathways are relevant to its role in disease risk. This in and of itself is not an easy task, but suggestions are offered below.

The recent past in human genetics and animal models have taught us that translating common genetic variation (e.g., SNPs) into valid animal models is highly difficult. Even if unequivocal risk SNPs are identified for a given locus (to date, this seems not to be the case), the functional effects of those SNPs may be difficult to determine. It is therefore not possible to create an accurate animal model from those genetic data. Rare genetic variants, such as missense or structural mutations, are often more penetrant, the functional effects more transparent, and the creation of genetic animal models more feasible. Thus, any changes observed in animal models of these specific risk alleles are likely to be relevant to the pathogenesis of the human condition.

In the case of DISC1, there is now a long list of potential biological functions from cellular proliferation, neuronal migration, neuritic outgrowth, and intracellular signaling. Unfortunately, there is no easy method for verifying which, if any, of these functions are the critical link between the DISC1 mutation and disease risk in the Scottish family. Studies that manipulate DISC1 function (e.g., by shRNA, overexpression or otherwise) and find a certain neuronal effect often claim that this is evidence of a link between that effect and schizophrenia or depression (e.g., Abbott, 2007; Marx, 2007). It is likely, however, that these methods will identify effects that might be irrelevant to the disease process no matter how appealing the finding may be, based on current, albeit incomplete, hypotheses of pathophysiology. Unfortunately, given the efficacy of current antipsychotic and mood-stabilizing drugs and their failure to aid in the discovery of new therapeutics, responses to current medications are not likely to provide much novel insight and alone cannot be used as tools of validation.

It is thus necessary to gather much better clinical data, such as deep sequencing of DISC1, that are likely to uncover other rare mutations associated with psychiatric disorders, although this itself will not be a trivial matter, as many thousands of patients could be required to show an unequivocal statistical association. It will also be important to carefully characterize carriers of any mutations because these genetic variants may associate with symptom domains across diagnostic categories. These rare mutations can then guide the development of etiologically valid animal models of specific DISC1 risk alleles (i.e., manipulation of the endogenous mouse allele to mimic the human risk variant). Comparison of these various models along with models of other well-defined risk alleles, of which currently there are very few (see, e.g., Stark et al., 2008; Mukai et al., 2008), will likely identify common pathogenetic mechanisms. It is in this context that much of the basic work in DISC1 biology discussed by the group will be of great service.

References:

Abbott A. Model behaviour. Nature. 2007 Nov 1;450(7166):6-7. Abstract

Marx J. Behavioral genetics. Evidence linking DISC1 gene to mental illness builds. Science. 2007 Nov 16;318(5853):1062-3. Abstract

Stark KL, Xu B, Bagchi A, Lai WS, Liu H, Hsu R, Wan X, Pavlidis P, Mills AA, Karayiorgou M, Gogos JA. Altered brain microRNA biogenesis contributes to phenotypic deficits in a 22q11-deletion mouse model. Nat Genet . 2008 Jun 1 ; 40(6):751-60. Abstract

Mukai J, Dhilla A, Drew LJ, Stark KL, Cao L, Macdermott AB, Karayiorgou M, Gogos JA. Palmitoylation-dependent neurodevelopmental deficits in a mouse model of 22q11 microdeletion. Nat Neurosci . 2008 Nov 1 ; 11(11):1302-10. Abstract

View all comments by Alexander Arguello