Disc1 is mutated in the 129S6/SvEv strain and modulates working memory in mice

Abstract

Disrupted-In-Schizophrenia (DISC1) is a leading candidate schizophrenia susceptibility gene. Here, we describe a deletion variant in mDisc1 specific to the 129S6͞SvEv strain that introduces a termination codon at exon 7, abolishes production of the full-length protein, and impairs working memory performance when transferred to the C57BL͞6J genetic background. Our findings provide insights into how DISC1 variation contributes to schizophrenia susceptibility in humans and the behavioral divergence between 129S6͞SvEv and C57BL͞6J mouse strains and have implications for modeling psychiatric diseases in mice.animal model ͉ gene mutation ͉ psychiatric disorder ͉ schizophrenia S chizophrenia is a common and genetically complex psychiatric disorder. Several leading candidate susceptibility genes have been identified (1), including DISC1. The position of this gene was initially pinpointed by a balanced translocation (1;11)(q42.1;q14.3) that was strongly linked to major neuropsychiatric diseases, including schizophrenia, depression, and bipolar disorder in a large Scottish family. The 1q breakpoint involves two genes, DISC1 and DISC2 (a noncoding, presumably regulatory RNA) (2) and truncates DISC1 immediately after exon 8. More recent large-scale linkage and follow-up association studies in families from Finland identified DISC1 as a positional candidate gene from the 1q42 locus (3). In addition, several polymorphisms in DISC1 were reported to be associated with schizophrenia-related cognitive endophenotypes (4 -6). Although the function of DISC1 is poorly understood, the gene is expressed the highest during early development, is associated with numerous cytoskeletal proteins, and could be involved in cell migration and neurite outgrowth and could play a role in centrosomal, microtubule and mitochondrial function, as well as in phosphodiesterase signaling (7-9). ResultsIn the process of a gene targeting experiment at the mDisc1 locus (see Supporting Methods, which is published as supporting information on the PNAS web site), we identified a 25-bp deletion in exon 6 of the 129S6͞SvEv mDisc1 allele. We used RT-PCR of mouse brain RNA from 129S6͞SvEv (Taconic Farms) and C57BL͞6J (The Jackson Laboratory) strains to examine sequences surrounding all mDisc1 exons. We confirmed the 25-bp deletion in exon 6 of 129S6͞SvEv mDisc1 transcript. The deletion was absent in the C57BL͞6J strain ( Fig. 1 a and b). We also confirmed by direct sequencing the presence of this deletion in genomic DNA isolated from tails of Taconic 129S6͞SvEv mice, as well as from ES cells (data not shown). We therefore conclude that this deletion represents a natural 129S6͞SvEv-specific polymorphism. As a control, we amplified exon 6 from genomic DNA from five other inbred strains (BALB͞cJ, CBA͞J, C3H͞HeJ, DBA͞2J, and AKR͞J strains). We did not detect this deletion variant in any strain (Fig. 1c), although we found that BALB͞cJ and C3H͞HeJ strains harbor a single, nonconservative (Glu529His) nucleotide polymorphism within the same 25-bp region. The identified 2...

Evidence that many of the DISC1 isoforms in C57BL/6J mice are also expressed in 129S6/SvEv mice

“…Evidence that many of the DISC1 isoforms in C57BL/6J mice are also expressed in 129S6/SvEv mice Recently, Koike et al 1 identified a 25-bp deletion in a coding exon of the Disrupted-In-Schizophrenia (DISC1) gene in the 129S6/SvEv strain, which was also confirmed at the genomic level for all extant 129 mouse inbred substrains. 2 This mutation could interfere with the production of the full-length DISC1 protein.…”

“…Immunoprecipitation with the mExon3 antibody followed by detection of the precipitates with the D27 antibody indicates that these two independent antibodies detect the same DISC1 molecule at 100 kDa, but an additional DISC1 band is detected by D27 at 105 kDa (Figure 1c). Therefore, this suggests that the antibody generated by Koike et al 1 might specifically detect a unique isoform of DISC1 at 100 kDa that is lost by the 25-bp deletion. Selective detection of this unique isoform in the immunoprecipitates with immunoglobulin G (IgG) from brain extracts of C57BL/6J, but not from those of 129S6/ SvEv, suggests that this isoform has a specific binding affinity to IgG (Supplementary Figure 4).…”

“…When the 129S6/SvEv-derived DISC1 gene was transferred to C57BL/6J genetic background, the resultant mice displayed a subtle behavioral abnormality in working memory, without any other major deficits in behavior and brain anatomy. 1 Several lines of evidence from animal models with RNA interference to DISC1, as well as studies in patient-derived lymphoblasts, suggest that loss of DISC1 function may be involved in the abnormalities underlying the pathophysiology of major mental conditions. 3 The minor behavioral abnormality resulting from the 25-bp deletion is in contrast to the results of three independent groups who have generated partial lossof-function models by expressing dominant-negative DISC1 constructs and obtained substantial changes in behavior, including deficits in prepulse inhibition, latent inhibition and working memory.…”

“…Subtle disturbance of an isoform(s) of susceptibility gene products may well account for the etiology of these disorders. In this sense, the mice reported by Koike et al 1 An article recently published in Molecular Psychiatry 1 reported that the cadherin gene (FAT) was associated with increased occurrence of bipolar affective disorder (BPAD) in four independent cohorts. The present investigation attempted to replicate these findings in a different cohort but found no significant association.…”

“…One proposed susceptibility locus occurs on chromosome 4q35. [2][3][4] Blair et al 1 undertook positional cloning, association tests and gene expression assays and found support for a role of the FAT gene, that resides within that chromosomal region, in relation to BPAD.…”