Working Memory, Cortical Circuitry Disrupted in 22q11DS Mouse Model

31 March 2010. A genomic deletion associated with increased risk for schizophrenia disrupts communication between regions of the brain involved in working memory in mice, according to a study published in Nature on March 31. Mice engineered to mimic the human chromosome 22q11.2 deletion showed impaired signaling between the hippocampus, crucial for memory, and the prefrontal cortex, which is involved in complex mental processes such as decision-making and planning.

Although only 30 percent of people with the 22q11.2 deletion also have schizophrenia, the deletion provides a toehold for researchers trying to understand how this specific genetic defect translates into abnormal behaviors. In 2008, Joseph Gogos and Maria Karayiorgou at Columbia University, New York, introduced a mouse model of the 22q11.2 deletion that lacked a 1.5 Mb region of mouse chromosome 16 that contains the same genes lost in the human deletion. These mice display impaired learning and prepulse inhibition—features that, though not diagnostic of schizophrenia, are commonly found in the disorder. Their neurons also have altered production of certain microRNAs (see SRF related news story) and lack post-translational add-ons called palmitates that anchor proteins to their proper location (see SRF related news story).

In the new study, Gogos and Karayiorgou team up with Joshua Gordon, also of Columbia University, to examine the electrical signals of the brain while the mice learn and perform a working memory task. Although disruptions in how parts of the brain talk to each other have previously turned up in schizophrenia, pinpointing the precise neural circuits involved has been limited by the resolution of human brain imaging. The new study steps into this void by recording activity from single neurons and groups of neurons in a mouse model that carries a clear genetic risk factor for schizophrenia.

Out of synch
Using electrodes implanted in the hippocampus and the prefrontal cortex, first author Torfi Sigurdsson and colleagues simultaneously monitored electrical activity in both regions to measure how synchronized they were—an indicator of how well connected they are—while the mice learned a simple T-maze task. In the sample phase of the task, mice ran down the track to a T-intersection, where they were directed to go into one of the two arms. In the following choice phase, the mice had to remember where they had been and go to the arm that they hadn't visited during the previous sample phase. The researchers focused on the neural activity preceding the mouse's entrance into one of the arms.

The electrodes picked up the action potentials of single neurons as well as field potentials stemming from the summed activity of large populations of neurons. Field potentials oscillate at various frequencies, and one of particular interest is the theta rhythm, which clocks in at 4-12 Hz and is associated with learning and memory. The theta rhythm drives spiking in cells elsewhere in the brain, including the prefrontal cortex, and the synchronous activity that normally results between the two regions indicates a robust connection between them.

The researchers found that, although signals from the hippocampus and prefrontal cortex appeared normal in the 22q11.2DS mice, their timing was off. Compared to wild-type littermates, the theta rhythms in the hippocampus and the prefrontal cortex did not oscillate together as much, and single neurons in the prefrontal cortex did not fire as consistently at the same phase of the hippocampal theta rhythm. This reduced synchrony was apparent during both the sample and choice phases of the task, though like the wild-type mice, synchrony was slightly higher during the choice phase, which requires memory retrieval.

The researchers next explored whether out-of-synch signaling between the hippocampus and prefrontal cortex could explain the longer time it took for the 22q11DS mice to learn the T-maze task. When they measured the theta rhythm synchrony between these two regions that occurred before the mice even began training on the task, they found that mice with weaker synchrony ended up taking longer to learn the task than mice with stronger synchrony. Theta rhythm synchrony grew as the mice—both wild-type and mutants—learned the task. These correlations suggest that reduced synchrony between the hippocampus and prefrontal cortex contributes to a working memory impairment.

The study shows how subtle changes in timing can disrupt information flow in the brain, which in turn can profoundly influence behavior. The authors note that future studies will have to examine the detailed anatomy of the axons and synapses that connect, both directly and indirectly, the prefrontal cortex to the hippocampus in these mice. It will also be important to identify which individual genes or combination of genes within the 22q11.2 deletion contribute to neural synchrony. In the meantime, this study's focus on neural activity and its timing elucidates another important step along the winding route that leads from a specific genetic defect to behavior.—Michele Solis.

Reference:
Sigurdsson T, Stark KL, Karayiorgou M, Gogos JA, Gordon JA. Impaired hippocampal-prefrontal synchrony in a genetic mouse model of schizophrenia. Nature 2010 April 1.

In a recent report, Sigurdsson et al. provide data that synchrony between hippocampal and cortical activity is subtly altered during a specific spatial motor memory task in a mouse model of the 22q11 Deletion syndrome (also known as DiGeorge syndrome). There have been several studies of other mouse models of 22q11 Deletion syndrome, the first of which were published in the late 1990s and early 2000s (Lindsey et al., 1999; Merscher et al., 2001). All of the data indicate that the development and function of the cerebral cortex is compromised by diminished dosage of the approximately 30 genes whose deletion is obligate in the disease. The reason for the intense interest in 22q11 Deletion syndrome is the high (but not invariant) incidence of schizophrenia in patients with this genetic disorder.

The likely disruption of hippocampal/cortical circuitry, based on subtly altered synchrony (but not, apparently, synaptic connectivity) makes sense if one assumes that diminished dosage of 22q11 genes compromises local circuit organization without wholesale changes in basic mechanisms of synaptic communication. Such results can be compared—cautiously—to hypotheses of regional/circuit malfunction in schizophrenic patients. The synchrony argument is intriguing, especially given the currency of models of cognition that invoke oscillatory behavior of forebrain circuits to explain coherence between diverse, related representations that are thought necessary for cognition and complex behaviors. Nevertheless, it is not clear that current experimental methods in humans can identify the subtle task-dependent dysregulation of synchrony that goes awry in the mouse. Thus, the report by Sigurdsson et al., while intriguing, provides a novel starting point for further investigation. Several questions arise in the mouse model: is cortical or hippocampal circuitry compromised in some way that goes beyond detectable changes in synaptic transmission? If so, how? Is some additional neuronal population that receives information from or provides input to both regions compromised by 22q11 deletion? Finally, how do such abnormalities arise? Are they the result of altered development, or disruptions in mature neuronal function?

While these observations raise exciting possibilities for further research in the relationship between 22q11 Deletion syndrome and schizophrenia pathology, some issues should be considered when comparing the mouse work and human disease. It remains difficult to confirm whether the sort of spatial memory tasks used by Sigurdsson et al. are really examples of mouse “executive function,” “working memory,” or the sorts of cognitive domains thought to be selectively compromised in schizophrenic patients. Moreover, it is generally agreed by comparative neuro-anatomists that the mouse does not have "prefrontal cortex" that is comparable to that seen in non-human and human primates—especially the dorsolateral prefrontal cortex. In humans, the performance of working memory tasks relies upon the integrity of this region, and its connections with a number of other cortical and subcortical areas. These circuits remain the focus of investigation in human schizophrenia pathology. Thus, while dysregulation of hippocampal activity and motor association cortical activity in the frontal aspect of the mouse brain (which is not actually prefrontal cortex) is likely occurring in 22q11 Deletion syndrome model mice, additional work must be done to determine how this relates to human behavioral disruptions in schizophrenia.

References:

Lindsay EA, Botta A, Jurecic V, Carattini-Rivera S, Cheah YC, Rosenblatt HM, Bradley A, Baldini A. Congenital heart disease in mice deficient for the DiGeorge syndrome region. Nature . 1999 Sep 23 ; 401(6751):379-83. Abstract

Merscher S, Funke B, Epstein JA, Heyer J, Puech A, Lu MM, Xavier RJ, Demay MB, Russell RG, Factor S, Tokooya K, Jore BS, Lopez M, Pandita RK, Lia M, Carrion D, Xu H, Schorle H, Kobler JB, Scambler P, Wynshaw-Boris A, Skoultchi AI, Morrow BE, Kucherlapati R. TBX1 is responsible for cardiovascular defects in velo-cardio-facial/DiGeorge syndrome. Cell . 2001 Feb 23 ; 104(4):619-29. Abstract

View all comments by Anthony-Samuel LaMantiaComment by:  Wendy Kates
Submitted 7 April 2010
Posted 8 April 2010

The links between genetic variants, neural circuitry, and cognitive dysfunction in schizophrenia are not well understood, due in part to the diagnostic and etiological heterogeneity of schizophrenia, which creates enormous challenges to understanding its pathophysiology. Several research groups are responding to this challenge by investigating the etiologically homogeneous microdeletion disorder, 22q11.2 deletion syndrome (22q11.2 DS), which poses the highest known genetic risk for schizophrenia, second only to having two parents with the disorder. Accordingly, 22q11.2 DS is a compelling model for understanding the pathophysiology of cognitive dysfunction in schizophrenia. Gogos, Karayiorgou, Sigurdsson, and colleagues are investigating this issue with a mouse model of 22q11.2 DS, and their latest, high-impact study of functional connectivity in the context of a working memory paradigm has brought us palpably closer to understanding these elusive links. They elegantly demonstrate that the 22q11.2 microdeletion disrupts prefrontal-hippocampal synchrony, which, in turn, likely contributes to impairments in working memory performance.

Although the specific genes within the microdeletion that are linked to neurocognitive deficits still need to be identified, this study begins to disentangle the complex associations among genetic variants, neural connectivity, and cognition in 22q11.2 DS. The elegance of a mouse model is that it can utilize methods that provide exquisite temporal and spatial resolution that is very difficult to obtain in human studies. Thus, this study identifies, at the neuronal level, disruptions in timing and connectivity that may underlie the white matter deficits that have been observed in neuroimaging studies (Barnea-Goraly et al., 2003; Kates et al., 2001; Simon et al., 2005) of patients with this genetic syndrome, and that putatively account for some of the syndrome’s prominent neurocognitive deficits. These findings provide support for future, more focused studies of neural connectivity, using EEG and diffusion tensor imaging, in patients with this mutation as well as the larger population of patients with schizophrenia.

References:

Barnea-Goraly N, Menon V, Krasnow B, Ko A, Reiss A, Eliez S. (2003) Investigation of white matter structure in velocardiofacial syndrome: a diffusion tensor imaging study. Am J Psychiatry, 160 (10): 1863-9. Abstract

Kates WR, Burnette CP, Jabs EW, Rutberg J, Murphy AM, Grados M, Geraghty M, Kaufmann WE, Pearlson GD. (2001) Regional cortical white matter reductions in velocardiofacial syndrome: a volumetric MRI analysis. Biol Psychiatry, 49 (8): 677-84. Abstract

Simon TJ, Ding L, Bish JP, McDonald-McGinn DM, Zackai EH, Gee J. (2005) Volumetric, connective, and morphologic changes in the brains of children with chromosome 22q11.2 deletion syndrome: an integrative study.Neuroimage. 25 (1): 169-80. Abstract

View all comments by Wendy Kates

While some have expressed frustration over the lack of clear reproducibility of linkage and association findings in schizophrenia, the importance of the chromosome 22q11 deletion syndrome (22q11DS) as a real and significant genetic risk factor for schizophrenia has often been overlooked. While the deletion syndrome is present in a minority of individuals with schizophrenia (estimates of approximately 1 percent), presence of the deletion increases risk of developing schizophrenia some 30-fold, making this one of the clearest known genetic risk factors for a psychiatric illness. As multiple genes are deleted in 22q11DS, it can be a challenge to determine which gene or genes are involved in specific phenotypic elements of this syndrome.

The May 11, 2008, paper by Stark et al. highlights the utility of engineered animals for dissecting the individual effects of multiple genes within a deletion region and provides an important clue into the mechanism likely responsible for at least some of the behavioral aspects of the phenotype. While some may argue about the full validity of animal models of complex human behavior disorders, these systems do have an advantage in manipulability that cannot be achieved in work with human subjects. A key feature of this paper is the comparison of the phenotype of mice engineered to contain a 1.3 Mb deletion of 27 genes with mice engineered to contain a disruption of only one gene in the region, DGCR8. The ability to place both of these alterations on the same genetic background and then do head-to-head comparisons on a number of behavioral, neuropathological, and gene expression assays allows a clear assessment of which components of the mouse phenotype may be attributed specifically to DGCR8 haploinsufficiency. Perhaps not surprisingly, DGCR8 seems to play a role in some, but not all, of the behavioral and neuropathological changes seen in the animals with the 1.3 Mb deletion. The fact that the DGCR8 disruption was able to recapitulate certain elements of the full deletion in the mice does raise its profile as an important candidate gene for some of the neurocognitive elements of 22q11DS, and makes it a potential candidate gene for contributing to schizophrenia risk in individuals without 22q11DS.

Also of great interest is the known function of DGCR8. While the gene name simply stands for DiGeorge syndrome Critical Region gene 8, it is now known that this gene plays an important role in the biogenesis of microRNAs, small non-coding RNAs that regulate gene expression by targeting mRNAs for translational repression or degradation. As miRNAs have been predicted to regulate over 90 percent of genes in the human genome (Miranda et al., 2006), a disruption in a key miRNA processing step could have profound regulatory impacts. Indeed, as reported in the Stark et al. paper and elsewhere (Wang et al., 2007), homozygous deletion of DGCR8 function is lethal in mice. What perhaps seems to be the most surprising result is that haploinsufficiency of DGCR8 function does not induce a more profound phenotype, given the large number of genes that would be expected to be affected if miRNA processing were globally impaired. The Stark et al. paper determined that while the pre-processed form of miRNAs may be elevated in haploinsufficient mice, perhaps only 10-20 percent of all mature miRNAs show altered levels, suggesting that some type of compensatory mechanism may be involved in regulating the final levels of the other miRNAs. Still, the 20-70 percent decrease in the abundance of these altered miRNAs could have a profound effect on multiple cellular processes, given the regulatory nature of miRNAs. In the context of the recent evidence for altered levels of some miRNA in postmortem samples from individuals with schizophrenia (Perkins et al., 2007), the Stark et al. paper adds further support for studying miRNAs as potential candidate genes in all individuals with schizophrenia, not just those with 22q11DS. This paper should serve as an important reminder of how careful analysis of a biological subtype of a disorder can reveal important insights that will be relevant to a much broader set of affected individuals.

References:

1. 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 May 11; Abstract

2. Miranda KC, Huynh T, Tay Y, Ang YS, Tam WL, Thomson AM, Lim B, Rigoutsos I. A pattern-based method for the identification of MicroRNA binding sites and their corresponding heteroduplexes. Cell. 2006 Sep 22;126(6):1203-17. Abstract

3. Wang Y, Medvid R, Melton C, Jaenisch R, Blelloch R. DGCR8 is essential for microRNA biogenesis and silencing of embryonic stem cell self-renewal. Nat Genet. 2007 Mar 1;39(3):380-5. Abstract

4. Perkins DO, Jeffries CD, Jarskog LF, Thomson JM, Woods K, Newman MA, Parker JS, Jin J, Hammond SM. microRNA expression in the prefrontal cortex of individuals with schizophrenia and schizoaffective disorder. Genome Biol. 2007 Jan 1;8(2):R27. Abstract

View all comments by Linda Brzustowicz

Related News: Are Membrane Molecules Unmoored in 22q11DS Mouse?

Comment by:  Doron Gothelf
Submitted 27 October 2008
Posted 27 October 2008

The common theory held until recently regarding the genetic underpinning of neuropsychiatric disorders was based on the “common disease-common variant” model. According to that theory, multiple common alleles in the population contribute small-to-moderate additive or multiplicative effects to the predisposition to neuropsychiatric disorders. With the advances in genetic screening technologies this theory is now being challenged. Recent findings indicate that rare copy number variations (CNVs) may account for a substantial fraction of the overall genetic risk for neuropsychiatric disorders including schizophrenia and autism (Consortium, 2008; Stefansson et al., 2008; Mefford et al., 2008). The 22q11.2 microdeletion was the most common CNV identified in patients with schizophrenia in a recent large scale study of patients with schizophrenia (Consortium, 2008). The 22q11.2 microdeletion is also the most common microdeletion occurring in humans and up to one third of individuals with 22q11.2 deletion syndrome (22q11.2DS) develop schizophrenia by adulthood. Thus the syndrome serves as an important model from which to learn the path leading from a well defined genetic defect to brain development and eventually to the evolution of schizophrenia.

It is still uncertain whether the neuropsychiatric phenotype associated with 22q11.2DS is a result of a strong effect of haploinsufficiency of one or a few genes from the microdeletion region as some studies suggested (Gothelf et al., 2005; Paterlini et al., 2005; Raux et al., 2007; Vorstman et al., 2008), or the result of cumulative small effects of haploinsufficiency of multiple genes, each contributing a small effect, as other studies suggested (Maynard et al., 2003; Meechan et al., 2006).

The current very elegant study by Mukai and colleagues suggests that haploinsufficiency of a single gene from the 22q11.2 deleted region, Zdhhc8, is responsible for the microscopic neural hippocampal abnormalities present in a mouse model of the disease. Remarkably, these abnormalities were prevented with the reintroduction of enzymatically active ZDHHC8 protein. The works of Gogos and his colleagues (Paterlini et al., 2005; Stark et al., 2008) are consistently and brilliantly getting us closer to revealing the complex association between genes from the 22q11.2 region and the neuropsychiatric phenotype. If indeed haploinsuffiency of single genes like Zdhhc8, COMT, or Dgcr8 have a strong effect on abnormal brain development and the eruption of schizophrenia, it conveys an enormous potential for developing novel pathophysiologically based treatments for this refractory disease. Such treatments will target the enzymatic deficit conveyed by the genetic mutation.

References:

[No authors listed]. Rare chromosomal deletions and duplications increase risk of schizophrenia. Nature. 2008 Sep 11;455(7210):237-41. Abstract

Stefansson H, Rujescu D, Cichon S, Pietiläinen OP, Ingason A, Steinberg S, Fossdal R, Sigurdsson E, Sigmundsson T, Buizer-Voskamp JE, Hansen T, Jakobsen KD, Muglia P, Francks C, Matthews PM, Gylfason A, Halldorsson BV, Gudbjartsson D, Thorgeirsson TE, Sigurdsson A, Jonasdottir A, Jonasdottir A, Bjornsson A, Mattiasdottir S, Blondal T, Haraldsson M, Magnusdottir BB, Giegling I, Möller HJ, Hartmann A, Shianna KV, Ge D, Need AC, Crombie C, Fraser G, Walker N, Lonnqvist J, Suvisaari J, Tuulio-Henriksson A, Paunio T, Toulopoulou T, Bramon E, Di Forti M, Murray R, Ruggeri M, Vassos E, Tosato S, Walshe M, Li T, Vasilescu C, Mühleisen TW, Wang AG, Ullum H, Djurovic S, Melle I, Olesen J, Kiemeney LA, Franke B, Sabatti C, Freimer NB, Gulcher JR, Thorsteinsdottir U, Kong A, Andreassen OA, Ophoff RA, Georgi A, Rietschel M, Werge T, Petursson H, Goldstein DB, Nöthen MM, Peltonen L, Collier DA, St Clair D, Stefansson K, Kahn RS, Linszen DH, van Os J, Wiersma D, Bruggeman R, Cahn W, de Haan L, Krabbendam L, Myin-Germeys I. Large recurrent microdeletions associated with schizophrenia. Nature. 2008 Sep 11;455(7210):232-6. Abstract

Mefford HC, Sharp AJ, Baker C, Itsara A, Jiang Z, Buysse K, Huang S, Maloney VK, Crolla JA, Baralle D, Collins A, Mercer C, Norga K, de Ravel T, Devriendt K, Bongers EM, de Leeuw N, Reardon W, Gimelli S, Bena F, Hennekam RC, Male A, Gaunt L, Clayton-Smith J, Simonic I, Park SM, Mehta SG, Nik-Zainal S, Woods CG, Firth HV, Parkin G, Fichera M, Reitano S, Lo Giudice M, Li KE, Casuga I, Broomer A, Conrad B, Schwerzmann M, Räber L, Gallati S, Striano P, Coppola A, Tolmie JL, Tobias ES, Lilley C, Armengol L, Spysschaert Y, Verloo P, De Coene A, Goossens L, Mortier G, Speleman F, van Binsbergen E, Nelen MR, Hochstenbach R, Poot M, Gallagher L, Gill M, McClellan J, King MC, Regan R, Skinner C, Stevenson RE, Antonarakis SE, Chen C, Estivill X, Menten B, Gimelli G, Gribble S, Schwartz S, Sutcliffe JS, Walsh T, Knight SJ, Sebat J, Romano C, Schwartz CE, Veltman JA, de Vries BB, Vermeesch JR, Barber JC, Willatt L, Tassabehji M, Eichler EE. Recurrent rearrangements of chromosome 1q21.1 and variable pediatric phenotypes. N Engl J Med. 2008 Oct 16;359(16):1685-99. Abstract

Gothelf D, Eliez S, Thompson T, Hinard C, Penniman L, Feinstein C, Kwon H, Jin S, Jo B, Antonarakis SE, Morris MA, Reiss AL. COMT genotype predicts longitudinal cognitive decline and psychosis in 22q11.2 deletion syndrome. Nat Neurosci. 2005 Nov 1;8(11):1500-2. Abstract

Paterlini M, Zakharenko SS, Lai WS, Qin J, Zhang H, Mukai J, Westphal KG, Olivier B, Sulzer D, Pavlidis P, Siegelbaum SA, Karayiorgou M, Gogos JA. Transcriptional and behavioral interaction between 22q11.2 orthologs modulates schizophrenia-related phenotypes in mice. Nat Neurosci. 2005 Nov 1;8(11):1586-94. Abstract

Raux G, Bumsel E, Hecketsweiler B, van Amelsvoort T, Zinkstok J, Manouvrier-Hanu S, Fantini C, Brévière GM, Di Rosa G, Pustorino G, Vogels A, Swillen A, Legallic S, Bou J, Opolczynski G, Drouin-Garraud V, Lemarchand M, Philip N, Gérard-Desplanches A, Carlier M, Philippe A, Nolen MC, Heron D, Sarda P, Lacombe D, Coizet C, Alembik Y, Layet V, Afenjar A, Hannequin D, Demily C, Petit M, Thibaut F, Frebourg T, Campion D. Involvement of hyperprolinemia in cognitive and psychiatric features of the 22q11 deletion syndrome. Hum Mol Genet. 2007 Jan 1;16(1):83-91. Abstract

Vorstman JA, Chow EW, Ophoff RA, van Engeland H, Beemer FA, Kahn RS, Sinke RJ, Bassett AS. Association of the PIK4CA schizophrenia-susceptibility gene in adults with the 22q11.2 deletion syndrome. Am J Med Genet B Neuropsychiatr Genet. 2008 Jul 21; Abstract

Maynard TM, Haskell GT, Peters AZ, Sikich L, Lieberman JA, LaMantia AS. A comprehensive analysis of 22q11 gene expression in the developing and adult brain. Proc Natl Acad Sci U S A. 2003 Nov 25;100(24):14433-8. Abstract

Meechan DW, Maynard TM, Wu Y, Gopalakrishna D, Lieberman JA, LaMantia AS. Gene dosage in the developing and adult brain in a mouse model of 22q11 deletion syndrome. Mol Cell Neurosci. 2006 Dec 1;33(4):412-28. 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

View all comments by Doron Gothelf

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