Allelic expression imbalance of the schizophrenia susceptibility gene CHI3L1: evidence of cis-acting variation and tissue specific regulation
ABSTRACT 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.
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.
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.
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.
- [Show abstract] [Hide abstract]
ABSTRACT: The evolutionarily conserved 18-glycosyl-hydrolase family contains true chitinases and chitinase-like proteins that lack enzymatic activity. Acidic mammalian chitinase has recently been associated with animal models of asthma. The related chitinase-like protein, YKL-40 (also called human cartilage glycoprotein 39 [HCgp-39] and chitinase 3-like 1), can be readily measured in the serum. However, its relationship to asthma has not been evaluated. We quantified serum YKL-40 levels in three cohorts of patients with asthma--one recruited from the patient population at Yale University, one from the University of Paris, and one from the University of Wisconsin--as well as in controls from the surrounding communities. In the Paris cohort, immunohistochemical analysis and morphometric quantitation were used to evaluate the locus of expression of YKL-40 in the lung. The clinical characteristics of the patients with high serum or lung YKL-40 levels were also evaluated. Serum YKL-40 levels were significantly elevated in patients with asthma as compared with controls. In the Paris cohort, lung YKL-40 levels were elevated and were correlated with circulating YKL-40 levels (r=0.55, P<0.001) and with airway remodeling (measured as the thickness of the subepithelial basement membrane) (r=0.51, P=0.003). In all three cohorts, serum YKL-40 levels correlated positively with the severity of asthma and inversely with the forced expiratory volume in 1 second. Patients with elevated levels of YKL-40 had significantly more frequent rescue-inhaler use, greater oral corticosteroid use, and a greater rate of hospitalization than patients with lower levels. YKL-40 is found in increased quantities in the serum and lungs in a subgroup of patients with asthma, in whom expression of chitinase in both compartments correlates with the severity of asthma. The recovery of YKL-40 from these patients indicates either a causative or a sentinel role for this molecule in asthma.New England Journal of Medicine 11/2007; 357(20):2016-27. DOI:10.1056/NEJMoa073600 · 54.42 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The gene encoding catechol-O-methyltransferase (COMT) is a strong candidate for schizophrenia susceptibility, owing to the role of COMT in dopamine metabolism, and the location of the gene within the deleted region in velocardiofacial syndrome, a disorder associated with high rates of schizophrenia. Recently, a highly significant association was reported between schizophrenia and a COMT haplotype in a large case-control sample (Shifman et al. 2002). In addition to a functional valine-->methionine (Val/Met) polymorphism, this haplotype included two noncoding single-nucleotide polymorphisms (SNPs) at either end of the COMT gene. Given the role of COMT in dopamine catabolism and that deletion of 22q11 (containing COMT) is associated with schizophrenia, we postulated that the susceptibility COMT haplotype is associated with low COMT expression. To test this hypothesis, we have applied quantitative measures of allele-specific expression using mRNA from human brain. We demonstrate that COMT is subject to allelic differences in expression in human brain and that the COMT haplotype implicated in schizophrenia (Shifman et al. 2002) is associated with lower expression of COMT mRNA. We also show that the 3' flanking region SNP that gave greatest evidence for association with schizophrenia in that study is transcribed in human brain and exhibits significant differences in allelic expression, with lower relative expression of the associated allele. Our results indicate that COMT variants other than the Val/Met change are of functional importance in human brain and that the haplotype implicated in schizophrenia susceptibility is likely to exert its effect, directly or indirectly, by down-regulating COMT expression.The American Journal of Human Genetics 07/2003; 73(1):152-61. DOI:10.1086/376578 · 10.99 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: Cis-regulatory variation is considered to be an important determinant of human phenotypic variability, including susceptibility to complex disease. Recent studies have shown that the effects of cis-regulatory polymorphism on gene expression can differ widely between tissues. In the present study, we tested whether the effects of cis-regulatory variation can also differ between regions of the adult human brain. We used relative allelic expression to measure cis-effects on the RNA expression of five candidate genes for neuropsychiatric illness (ZNF804A, NOS1, RGS4, AKT1 and TCF4) across multiple discrete brain regions within individual subjects. For all five genes, we observed significant differences in allelic expression between brain regions in several individual subjects, suggesting regional differences in the effects of cis-regulatory polymorphism to be a common phenomenon. As well as highlighting an important caveat for studies of regulatory polymorphism in the brain, our findings indicate that it is possible to delineate brain areas in which cis-regulatory variants are active. This may provide important insights into the fundamental biology of neuropsychiatric phenotypes with which such variants are associated.Human Molecular Genetics 11/2010; 19(22):4490-6. DOI:10.1093/hmg/ddq380 · 6.68 Impact Factor