Fabp7 maps to a quantitative trait locus for a schizophrenia endophenotype.

Deficits in prepulse inhibition (PPI) are a biological marker for schizophrenia. To unravel the mechanisms that control PPI, we performed quantitative trait loci (QTL) analysis on 1,010 F2 mice derived by crossing C57BL/6 (B6) animals that show high PPI with C3H/He (C3) animals that show low PPI. We detected six major loci for PPI, six for the acoustic startle response, and four for latency to response peak, some of which were sex-dependent. A promising candidate on the Chromosome 10-QTL was Fabp7 (fatty acid binding protein 7, brain), a gene with functional links to the N-methyl-D-aspartic acid (NMDA) receptor and expression in astrocytes. Fabp7-deficient mice showed decreased PPI and a shortened startle response latency, typical of the QTL's proposed effects. A quantitative complementation test supported Fabp7 as a potential PPI-QTL gene, particularly in male mice. Disruption of Fabp7 attenuated neurogenesis in vivo. Human FABP7 showed altered expression in schizophrenic brains and genetic association with schizophrenia, which were both evident in males when samples were divided by sex. These results suggest that FABP7 plays a novel and crucial role, linking the NMDA, neurodevelopmental, and glial theories of schizophrenia pathology and the PPI endophenotype, with larger or overt effects in males. We also discuss the results from the perspective of fetal programming.

Preliminary genome-wide association study of bipolar disorder in the Japanese population.

Recent progress in genotyping technology and the development of public databases has enabled large-scale genome-wide association tests with diseases. We performed a two-stage genome-wide association study (GWAS) of bipolar disorder (BD) in Japanese cohorts. First we used Affymetrix 100K GeneChip arrays in the analysis of 107 cases with bipolar I disorder and 107 controls, and selected markers that were nominally significant (P < 0.01) in at least one of the three models (1,577 markers in total). In the follow-up stage, we analyzed these markers using an Illumina platform (1,526 markers; 51 markers were not designable for the platform) and an independent sample set, which consisted of 395 cases (bipolar I + II) and 409 controls. We also assessed the population stratification of current samples using principal components analysis. After the two-stage analysis, 89 markers remained nominally significant (allelic P < 0.05) with the same allele being consistently over-represented in both the first and the follow-up stages. However, none of these were significant after correction for multiple-testing by false discovery rates. Sample stratification was virtually negligible. Collectively, this is the first GWAS of BD in the Japanese population. But given the small sample size and the limited genomic coverage, these results should be taken as preliminary.

T396I mutation of mouse Sufu reduces the stability and activity of Gli3 repressor.

Hedgehog signaling is primarily transduced by two transcription factors: Gli2, which mainly acts as a full-length activator, and Gli3, which tends to be proteolytically processed from a full-length form (Gli3FL) to an N-terminal repressor (Gli3REP). Recent studies using a Sufu knockout mouse have indicated that Sufu is involved in regulating Gli2 and Gli3 activator and repressor activity at multiple steps of the signaling cascade; however, the mechanism of specific Gli2 and Gli3 regulation remains to be elucidated. In this study, we established an allelic series of ENU-induced mouse strains. Analysis of one of the missense alleles, SufuT396I, showed that Thr396 residue of Sufu played a key role in regulation of Gli3 activity. SufuT396I/T396I embryos exhibited severe polydactyly, which is indicative of compromised Gli3 activity. Concomitantly, significant quantitative reductions of unprocessed Gli3 (Gli3FL) and processed Gli3 (Gli3REP) were observed in vivo as well as in vitro. Genetic experiments showed that patterning defects in the limb buds of SufuT396I/T396I were rescued by a constitutive Gli3REP allele (Gli3∆699), strongly suggesting that SufuT396I reduced the truncated Gli3 repressor. In contrast, SufuT396I qualitatively exhibited no mutational effects on Gli2 regulation. Taken together, the results of this study show that the Thr396 residue of Sufu is specifically required for regulation of Gli3 but not Gli2. This implies a novel Sufu-mediated mechanism in which Gli2 activator and Gli3 repressor are differentially regulated.

Genetic analysis of a functional GRIN2A promoter (GT)n repeat in bipolar disorder pedigrees in humans.

Hypofunction of glutamatergic neurotransmission has been hypothesized to underlie the pathophysiology of bipolar affective disorder, as well as schizophrenia. We examined the role of the N-methyl-D-aspartate receptor 2A subunit (GRIN2A) gene on 16p13.3, a region thought to be linked to bipolar disorder, (1) because in a prior study we identified a functional and polymorphic (GT)n repeat in the 5' regulatory region of the gene, with longer alleles showing lower transcriptional activity and an over representation in schizophrenia, and (2) because of the suggestion of a genetic overlap between affective disorder and schizophrenia. Family-based association tests detected a nominally significant preferential transmission of longer alleles in a panel of 96 multiplex bipolar pedigrees. These results support the hypothesis that a hypoglutamatergic state is involved in the pathogenesis of bipolar affective disorder.

ß-CateninC429S mice exhibit sterility consequent to spatiotemporally sustained Wnt signalling in the internal genitalia.

Wnt/ß-catenin signalling regulates numerous developmental and homeostatic processes. Ctnnb1 (also known as ß-catenin) is the only protein that transmits signals from various Wnt ligands to downstream genes. In this study, we report that our newly established mouse strain, which harbours a Cys429 to Ser missense mutation in the ß-catenin gene, exhibited specific organ defects in contrast to mice with broadly functioning Wnt/ß-catenin signalling. Both homozygous mutant males and females produced normal gametes but were infertile because of abnormal seminal vesicle and vaginal morphogenesis. An ins-TOPGAL transgenic reporter spatiotemporally sustained Wnt/ß-catenin signalling during the corresponding organogenesis. Therefore, ß-catenin(C429S) should provide new insights into ß-catenin as a universal component of Wnt/ß-catenin signal transduction.

Mouse mutagenesis and disease models for neuropsychiatric disorders.

In this chapter, mutant mouse resources which have been developed by classical genetics as well as by modern large-scale mutagenesis projects are summarized. Various spontaneous and induced mouse mutations have been archived since the rediscovery of Mendel's genetics in 1900. Moreover, genome-wide, large-scale mutagenesis efforts have recently been expanding the available mutant mouse resources. Forward genetics projects using ENU mutagenesis in the mouse were started in the mid-1990s. The widespread adoption of reverse genetics, using knockouts and conditional mutagenesis based on gene-targeting technology, followed. ENU mutagenesis has now evolved to provide a further resource for reverse genetics, with multiple point mutations in a single gene and this new approach is described. Researchers now have various options to obtain mutant mice: point mutations, transgenic mouse strains, and constitutional or conditional knockout mice. The established mutant strains have already contributed to modeling human diseases by elucidating the underlying molecular mechanisms as well as by providing preclinical applications. Examples of mutant mice, focusing on neurological and behavioral models for human diseases, are reviewed. Human diseases caused by a single gene or a small number of major genes have been well modeled by corresponding mutant mice. Current evidence suggests that quantitative traits based on polygenes are likely to be associated with a range of psychiatric diseases, and these are now coming within the range of modeling by mouse mutagenesis.

Expression analysis of actin-related genes as an underlying mechanism for mood disorders.

In this study, we explored the newly postulated 'disturbed cytoskeletal' theory of mood disorders. Firstly, we identified Cap1, a gene for important mediator of actin turnover, as a cogent quantitative trait gene for depressive trait of mice by combining the results of our prior genetic and current genome-wide expression analyses. Then we rigorously examined 'core' actin-related gene expression in the frontal cortex of C57BL/6 (B6) (prone to depression) and C3H/He (C3) (resistant to depression) mice. We confirmed that Cap1 was down-regulated at both transcript and protein levels in B6. Other differentially regulated genes included cofilin1 and profilin1 (up-regulated in B6), and a Rho-family GTPase member (Pak1) (down-regulated in B6). Thirdly, we investigated the 'core' actin-pathway components in human postmortem prefrontal cortices, and observed trend for CAP1 reduction in the bipolar brains. These data suggest that the balance of actin dynamics might be altered towards actin depolymerization in mood disorders.

Genetic association analyses of PHOX2B and ASCL1 in neuropsychiatric disorders: evidence for association of ASCL1 with Parkinson's disease.

We previously identified frequent deletion/insertion polymorphisms in the 20-alanine homopolymer stretch of PHOX2B (PMX2B), the gene for a transcription factor that plays important roles in the development of oculomotor nerves and catecholaminergic neurons and regulates the expression of both tyrosine hydroxylase and dopamine beta-hydroxylase genes. An association was detected between gene polymorphisms and overall schizophrenia, and more specifically, schizophrenia with ocular misalignment. These prior results implied the existence of other schizophrenia susceptibility genes that interact with PHOX2B to increase risk of the combined phenotype. ASCL1 was considered as a candidate interacting partner of PHOX2B, as ASCL1 is a transcription factor that co-regulates catecholamine-synthesizing enzymes with PHOX2B. The genetic contributions of PHOX2B and ASCL1 were examined separately, along with epistatic interactions with broader candidate phenotypes. These phenotypes included not only schizophrenia, but also bipolar affective disorder and Parkinson's disease (PD), each of which involve catecholaminergic function. The current case-control analyses detected nominal associations between polyglutamine length variations in ASCL1 and PD (P=0.018), but supported neither the previously observed weak association between PHOX2B and general schizophrenia, nor other gene-disease correlations. Logistic regression analysis revealed the effect of ASCL1 dominant x PHOX2B additive (P=0.008) as an epistatic gene-gene interaction increasing risk of PD. ASCL1 controls development of the locus coeruleus (LC), and accumulating evidence suggests that the LC confers protective effects against the dopaminergic neurodegeneration inherent in PD. The present genetic data may thus suggest that polyglutamine length polymorphisms in ASCL1 could influence predispositions to PD through the fine-tuning of LC integrity.

Identification of multiple genetic loci linked to the propensity for "behavioral despair" in mice.

The forced swim test (FST) and tail suspension test (TST) are widely used and well established screening paradigms for antidepressants. A variety of antidepressive agents are known to reduce immobility time in both FST and TST. To identify genetic determinants of immobility duration in both tests, we analyzed 560 F2 mice from an intercross between C57BL/6 (B6) and C3H/He (C3) strains. Composite interval mapping revealed five major loci (suggestive and significant linkage) affecting immobility in the FST, and four loci for the TST. The quantitative trait loci (QTL) on chromosomes 8 and 11 overlap between the two behavioral measures. Genome-wide interaction analysis, which was developed to identify locus pairs that may contribute epistatically to a phenotype, detected two pairs of chromosomal loci for the TST. The QTL on chromosome 11 and its associated epistatic TST-QTL on chromosome X encode gamma-aminobutyric acid type A (GABA(A)) receptor subunits as candidates. Sequence and expression analyses of these genes from the two parental strains revealed a significantly lower expression of the alpha1 subunit gene in the frontal cortex of B6 mice compared to C3 mice. The present quantitative trait study should open up avenues for identifying novel molecular targets for antidepressants and unraveling the complex genetic mechanisms of depressive and anxiety disorders.