Paul Robert Buckland

Cis-acting variation in the expression of a high proportion of genes in human brain

Much of the genetic component of human phenotypic diversity, including susceptibility to disease, is proposed to be the result of cis-acting influences on gene expression. If this hypothesis is correct, it implies that cis-acting regulatory variation is a common phenomenon. However, direct evidence in support of this view is scarce. We have applied highly quantitative measures of allele-specific expression in order to screen an average of 19 informative subjects (range 8–26) for the presence of common cis-acting influences on the expression of 15 genes by using RNA derived from human brain. We found that, in seven of the 15 assayed genes, at least one individual exhibited relative differences in allelic expression of 20% or more and, in one gene (DTNBP1), allelic expression differences exceeded 50%. These results suggest that cis-acting variation in gene expression commonly occurs in native tissue and hence provide empirical support for the hypothesis that this is potentially an important mechanism underlying human phenotypic diversity.

A family based association study of T102C polymorphism in 5HT2A and schizophrenia plus identification of new polymorphisms in the promoter.

Several studies have shown an association between schizophrenia and the C allele of a T-C polymorphism at nucleotide 102 and the 5HT2A receptor gene. In the present study we observed this association in a sample of 63 parent/offspring trios where the proband received a diagnosis of DSM-III-R schizophrenia using TDT analysis (χ2 = 6.26, P = 0.006,χ2 = 9.00, P = 0.001 when one affected offspring was selected at random from each family, suggesting that the results are due to association rather than linkage). There was no significant difference between the transmission of C102 from heterozygous fathers and mothers, which fails to support a role for genomic imprinting in this effect. T102C does not result in an alteration of the amino acid sequence of the protein. We therefore screened the promoter of 5HT2A for polymorphisms using single-strand confirmation polymorphism analysis. An A-G polymorphism at −1438 that creates an HpaII restriction site was identified. This was found to be in complete linkage disequilibrium with T102C and is hence a candidate for the pathogenic variant in schizophrenia. Functional analysis of A-1438G using luciferase assay demonstrated significant basal promoter activity in 5HT2A expressing HeLa cells by both the A and G variants. However, comparison of the A and G variants showed no significant differences in basal activity nor when promoter activity was induced by cAMP and protein kinase C-dependent mechanisms.

Cheap, accurate and rapid allele frequency estimation of single nucleotide polymorphisms by primer extension and DHPLC in DNA pools

Abstract. At present, the cost of genotyping single nucleotide polymorphisms (SNPs) in large numbers of subjects poses a formidable problem for molecular genetic approaches to complex diseases. We have tested the possibility of using primer extension and denaturing high performance liquid chromatography to estimate allele frequencies of SNPs in pooled DNA samples. Our data show that this method should allow the accurate estimation of absolute allele frequencies in pooled samples of DNA and also of the difference in allele frequency between different pooled DNA samples. This technique therefore offers an efficient and cheap method for genotyping SNPs in large case-control and family-based association samples.

Evidence that interaction between neuregulin 1 and its receptor erbB4 increases susceptibility to schizophrenia.

There is now strong evidence that Neuregulin 1 (NRG1) is a susceptibility gene for schizophrenia. NRG1 mediates some of its effects through the tyrosine kinase receptor erbB4, and analysis of gene knock‐out animals suggests that the functional interaction of NRG1 and erbB4 mediates behaviors that may model some aspects of the schizophrenia phenotype in mice. Given these findings, we have sought evidence for association between schizophrenia and erbB4. Mutation screening of erbB4 in 14 DSMIV schizophrenics revealed 15 SNPs, none of which were nonsynonymous. Analysis of the allele frequencies of each SNP in pools of 368 DSMIV schizophrenics and 368 controls provided modest evidence for association with two of the SNPs, although individual genotyping in an extended sample of 680 cases did not confirm this. However, we did find evidence for a significant interaction between the NRG1 “Icelandic” schizophrenia risk haplotype and erbB4 (P = 0.019). The NRG1 and erbB4 interacting marker was further genotyped in an independent sample of 290 cases and 634 controls from Dublin. Interaction between NRG1 and erbB4 remained significant in the combined sample of 970 cases and 1,341 controls, OR = 2.98 (CI: 1.16–7.64), P = 0.01, although it only showed a trend in the Dublin sample alone (P = 0.11, two tailed). Our data require independent replication, but tentatively suggest that NRG1 may mediate its effects on schizophrenia susceptibility through functional interaction with erbB4, and that genetic interaction between variants at the two loci increases susceptibility to schizophrenia.

Support for RGS4 as a susceptibility gene for schizophrenia

BACKGROUND The gene encoding the regulator of G-protein signaling 4 has recently been associated with susceptibility to schizophrenia. This finding is particularly interesting, because it was replicated within the same study and also because there are functional, positional, and expression data to support the regulator of G-protein signaling 4 as a schizophrenia candidate gene. Although the original report was highly suggestive, a limitation was that the study was conducted on rather small samples. METHODS We have examined a large case (n = 709) control (n = 710) sample for association between schizophrenia using four markers investigated in the earlier study, denoted single nucleotide polymorphisms 1, 4, 7, and 18. RESULTS We were able to replicate the associations with single nucleotide polymorphisms 4 and 18 that had previously been reported individually and have also identified significant association with haplotypes constructed from single nucleotide polymorphisms 1 and 4. CONCLUSIONS Our data give modest support for the hypothesis that the regulator of G-protein signaling 4 is a susceptibility gene for schizophrenia.

The serotonin-2A receptor gene locus does not contain common polymorphism affecting mRNA levels in adult brain

The serotonin-2A (HTR2A) receptor is a molecule of particular interest in biological psychiatry, as it is an important target for psychotropic drugs,1,2 and altered HTR2A expression has been found in several neuropsychiatric conditions, including depression3 and schizophrenia.4 Genetic association has been reported between a synonymous 102T/C polymorphism in the gene encoding HTR2A and a number of clinical phenotypes, including schizophrenia,5,6 clozapine response,7 psychotic symptoms in Alzheimers disease8 and certain features of depression.9 Given that there are no known effects of the 102T/C polymorphism on the structure of the receptor, attention has switched to the possibility that the observations of both altered expression and genetic association point to functional sequence variants that alter expression of the HTR2A gene.10 Moreover, data have been presented recently suggesting that mRNAs containing the 102T- and C-alleles are differentially expressed.11 This suggests a direct effect of the variant itself on mRNA levels, or the influence of a distinct regulatory variant, such as the −1438A/G promoter polymorphism, with which it is in perfect linkage disequilibrium.12 The present study tested this hypothesis by employing a highly accurate quantitative allele- specific primer extension assay13 to measure the relative expression of brain mRNAs carrying each allele in 23 individuals heterozygous for the 102T/C polymorphism. Comparison between allele ratios derived from genomic DNA and mRNA from several cortical regions revealed that the 102C- and T-alleles are expressed identically. Furthermore, the absence of any interindividual variability in relative mRNA allele ratio suggests that the HTR2A locus is unlikely to contain common polymorphisms or epigenetic modification that alter HTR2A mRNA levels in adult brain, and essentially exclude such phenomena as a potential explanation for the altered expression and genetic associations that have been reported to date.

Changes in dopamine D1, D2 and D3 receptor mRNA levels in rat brain following antipsychotic treatment

The effects of administration of antipsychotic drugs (1–32 days, twice per day) on the rat brain mRNA levels of dopamine D1, D2 and D3 receptors has been assessed by a novel procedure utilising solution hybridisation with oligonucleotides. Saline and sulpiride (10 mg/kg/injection) had no effect on D1, D2 and D3 receptor mRNA levels. Haloperidol (1.5 mg/kg/injection) elicited increases in D1, D2 and D3 receptor mRNA levels of 100%, 100% and 300%, respectively, after 32 days and loxapine (2 mg/kg/injection) elicited increases of 450%, 150% and 550%, respectively. These results indicate that the up-regulation of dopamine receptors may be associated with the occurrence of tardive dyskinesia but not the clinical mode of action of antipsychotics.

Polymorphically duplicated genes: their relevance to phenotypic variation in humans

A number of disorders are known to be caused by duplication of genes, but these are all rare events. However, there is evidence that polymorphic gene duplication may be common and a growing number of genes are known to be duplicated in a polymorphic manner although phenotypes cannot be associated with most of these. Gene duplication occurring due to cytogenetic abnormalities such as Down syndrome predisposes the patients to a variety of complex disorders. It is possible therefore that many complex disorders and variable phenotypes are associated with duplication of genes.

Bi-directional changes in the levels of messenger RNAs encoding γ-aminobutyric acidA receptor α subunits after flurazepam treatment

Changes in γ-aminobutyric acidA (GABAA) receptor function have been observed following chronic benzodiazepine administration. The molecular mechanisms responsible are unknown, but one possibility is that benzodiazepines induce alterations in the expression of genes which encode subunits of the GABAA receptor complex, resulting in changes in the receptor structure and function. We have investigated this hypothesis by evaluating the effect of flurazepam 40 mg/kg i.p. on brain levels of the mRNAs which encode the α1, α2, α3, α5, and α6 subunits of the GABAA receptor complex. Rats were treated with flurazepam or vehicle for up to 32 days. No changes were found in the levels of α1 and α2 mRNA. A rapid decrease was found in the level of α5 mRNA; α3 mRNA was increased by 4 days of treatment and this was followed by an increase in α6 levels. These results support the hypothesis that the alteration in GABAA receptor function after benzodiazepine administration results from changes in subunit gene expression. Furthermore, the predicted consequences of the pattern of mRNA changes we have observed suggest that altered gene expression may be important in the genesis of benzodiazepine tolerance.

Photo-affinity labelling of the thyrotropin receptor

The thyrotropin (TSH) receptor is an important but poorly characterised component of the thyroid cell surface [l] and in this paper we describe an analysis of the receptor using affinity labelling [2]. Detergent solubilised porcine and human TSH receptors have been partially purified by Sepharose -TSH affinity chromatography [3] and then covalently crosslinked to 125 I-labelled TSH. Analysis of the TSH-TSH receptor complexes by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) suggests that both porcine and human TSH receptors contain a similar basic unit of two peptide chains linked by one or more disulphide bridges. These basic units bind one molecule of TSH and have relative molecular masses (M,) of 87 000 in the case of the porcine TSH receptor and 100 000 in the case of the human TSH receptor.