Drosophila IRBP bZIP heterodimer binds P-element DNA and affects hybrid dysgenesis.

In Drosophila, P-element transposition causes mutagenesis and genome instability during hybrid dysgenesis. The P-element 31-bp terminal inverted repeats (TIRs) contain sequences essential for transposase cleavage and have been implicated in DNA repair via protein-DNA interactions with cellular proteins. The identity and function of these cellular proteins were unknown. Biochemical characterization of proteins that bind the TIRs identified a heterodimeric basic leucine zipper (bZIP) complex between an uncharacterized protein that we termed "Inverted Repeat Binding Protein (IRBP) 18" and its partner Xrp1. The reconstituted IRBP18/Xrp1 heterodimer binds sequence-specifically to its dsDNA-binding site within the P-element TIRs. Genetic analyses implicate both proteins as critical for repair of DNA breaks following transposase cleavage in vivo. These results identify a cellular protein complex that binds an active mobile element and plays a more general role in maintaining genome stability.

Allelic expression imbalance of the schizophrenia susceptibility gene CHI3L1: evidence of cis-acting variation and tissue specific regulation.

OBJECTIVE: To identify cis-acting regulatory variants influencing the expression of the schizophrenia susceptibility gene chitinase 3-like 1 gene (CHI3L1) in human lymphoblasts and post-mortem brain tissue. METHODS: To investigate the role of cis-acting regulatory variants in controlling gene expression of CHI3L1 we quantified relative allelic abundance in individuals heterozygous for the transcribed polymorphism rs880633. Allelic quantification was performed using RNA derived from 45 individuals from the HapMap CEU panel and 41 postmortem brain samples. Association of allelic imbalance with genetic variants was determined at a gene-wide level for the HapMap samples using available genotyping data. RESULTS: Expression of the CHI3L1 transcript is under the control of potently acting cis-variation in lymphoblasts. Polymorphisms in the promoter region of CHI3L1 were significantly associated with this allelic imbalance. In the single postmortem brain tissue investigated, only moderate allelic imbalance was detected and was restricted to a small number of individuals. CONCLUSION: CHI3L1 contains common cis-acting regulatory variants that affect gene expression in lymphoblasts. A previously identified schizophrenia susceptibility variant was significantly associated with allelic imbalance in lymphoblasts. These findings do not support the notion that the schizophrenia-associated CHI3L1 variants influence gene expression in BA46 of the adult brain. We confirm that CHI3L1 contains cis-acting variation but is subject to tissue-specific regulation.

Functional assessment of a promoter polymorphism in S100B, a putative risk variant for bipolar disorder.

Calcium-binding protein S100B has been implicated in the pathology of bipolar affective disorder (BPAD) and schizophrenia (SZ). S100B protein levels are elevated in serum of patients with both disorders compared to controls. We previously reported genetic association of a SNP in the promoter of S100B, rs3788266, with a psychotic form of BPAD. To test for genotypic effects of rs3788266 in vivo, S100B serum protein levels were measured in 350 Irish and German subjects of known S100B genotype. The functional effect of rs3788266 on S100B promoter activity was studied using the luciferase reporter system in U373MG glioblastoma and SH-SY5Y neuroblastoma cell lines. Allelic effects of rs3788266 on protein complex formation at the S100B promoter were investigated by an electrophoretic mobility shift assay. Higher mean serum S100B levels were associated with the risk G allele of rs3788266 in BPAD cases (P = 0.0001), unaffected relatives of BPAD cases (P < 0.0001) and unrelated controls (P < 0.0001). Consistent with the in vivo findings, luciferase gene expression was significantly increased in the presence of the G allele compared to the A allele in SH-SY5Y (P = <0.0001), and in U373MG (P = <0.0008) cell lines. The binding affinity of both SH-SY5Y and U373MG protein complexes for the S100B promoter was significantly stronger in the presence of G allele compared to the A allele promoter fragments. These data support rs3788266 as a functional promoter variant in the S100B gene where the presence of the G allele promotes increased gene expression and is associated with increased serum levels of the protein.

European collaborative study of early-onset bipolar disorder: Evidence for genetic heterogeneity on 2q14 according to age at onset.

Bipolar disorder has a genetic component, but the mode of inheritance remains unclear. A previous genome scan conducted in 70 European families led to detect eight regions linked to bipolar disease. Here, we present an investigation of whether the phenotypic heterogeneity of the disorder corresponds to genetic heterogeneity in these regions using additional markers and an extended sample of families. The MLS statistic was used for linkage analyses. The predivided sample test and the maximum likelihood binomial methods were used to test genetic homogeneity between early-onset bipolar type I (cut-off of 22 years) and other types of the disorder (later onset of bipolar type I and early-onset bipolar type II), using a total of 138 independent bipolar-affected sib-pairs. Analysis of the extended sample of families supports linkage in four regions (2q14, 3p14, 16p23, and 20p12) of the eight regions of linkage suggested by our previous genome scan. Heterogeneity testing revealed genetic heterogeneity between early and late-onset bipolar type I in the 2q14 region (P = 0.0001). Only the early form of the bipolar disorder but not the late form appeared to be linked to this region. This region may therefore include a genetic factor either specifically involved in the early-onset bipolar type I or only influencing the age at onset (AAO). Our findings illustrate that stratification according to AAO may be valuable for the identification of genetic vulnerability polymorphisms. © 2010 Wiley-Liss, Inc.

Support for tryptophan hydroxylase-2 as a susceptibility gene for bipolar affective disorder.

Bipolar affective disorder (BPAD) is a highly inherited genetic disorder and may be caused in part by deficits in serotonergic neurotransmission. We investigated whether variants within the tryptophan hydroxylase-2 (TPH2) gene, which is required for the synthesis of serotonin (5-HT), are associated with susceptibility to developing BPAD. Thirteen single nucleotide polymorphisms (SNPs) within TPH2 were genotyped in a collection of 151 Irish BPAD type I trios and were tested for association using the transmission disequilibrium test. SNPs rs1386482 and rs1386486, which are in very strong linkage disequilibrium, were associated with BPAD (P=0.006). The association retained significance after a correction for multiple testing. The associated SNPs are in perfect linkage disequilibrium with SNPs previously associated with BPAD (rs4290270) and impulsivity (rs1386483), a core trait of BPAD. These results strongly support a role for TPH2 in the aetiology of BPAD.