Lower rate of genomic variation identified in the trans-membrane domain of monoamine sub-class of Human G-Protein Coupled Receptors: The Human GPCR-DB Database

BACKGROUND: We have surveyed, compiled and annotated nucleotide variations in 338 human 7-transmembrane receptors (G-protein coupled receptors). In a sample of 32 chromosomes from a Nordic population, we attempted to determine the allele frequencies of 80 non-synonymous SNPs, and found 20 novel polymorphic markers. GPCR receptors of physiological and clinical importance were prioritized for statistical analysis. Natural variation and rare mutation information were merged and presented online in the Human GPCR-DB database . RESULTS: The average number of SNPs per 1000 bases of exonic sequence was found to be twice the average number of SNPs per Kilobase of intronic regions (2.2 versus 1.0). Of the 338 genes, 111 were single exon genes, that is, were intronless. The average number of exonic-SNPs per single-exon gene was 3.5 (n = 395) while that for multi-exon genes was 0.8 (n = 1176). The average number of variations within the different protein domain (N-terminus, internal- and external-loops, trans-membrane region, C-terminus) indicates a lower rate of variation in the trans-membrane region of Monoamine GPCRs, as compared to Chemokine- and Peptide-receptor sub-classes of GPCRs. CONCLUSIONS: Single-exon GPCRs on average have approximately three times the number of SNPs as compared to GPCRs with introns. Among various functional classes of GPCRs, Monoamine GPRCs have lower number of natural variations within the trans-membrane domain indicating evolutionary selection against non-synonymous changes within the membrane-localizing domain of this sub-class of GPCRs

Genetics of neurological disorders

Neurological diseases are defined as an inappropriate function of the peripheral or central nervous system due to impaired electrical impulses throughout the brain and/or nervous system that may present with heterogeneous symptoms according to the parts of the system involved in these pathologic processes. Growing evidence on genetic components of neurological disease have been collected during recent years. Genetic studies have opened the way for understanding the underlying pathology of many neurological disorders. The outcome of current intense research into the genetics of neurological disorders will hopefully be the introduction of new diagnostic tools and the discovery of potential targets for new and more effective medications and preventive measures

The influence of 5 ' codon context on translation termination in Saccharomyces cerevisiae

Translation termination in vivo was studied in the yeast Saccharomyces cerevisiae using a translation-assay system. Codon changes that were made at position -2-relative to the stop codon, gave a 3.5-fold effect on termination in a release-factor-defective (sup45) mutant strain, in line with the effect observed in a wild-type strain. The influence of the -2 codon could be correlated to the charge of the corresponding amino acid residue in the nascent peptide; an acidic residue favoring efficient termination. Thus, the C-terminal end of the nascent peptide influences translation termination both in the bacterium Escherichia coil and to a lesser extent in the yeast S. cerevisiae. However, the sensitivity to the charge of the penultimate amino acid is reversed when the E. coli and S. cerevisiae are compared. Changing -1 (P-site) codons in yeast gave a 10-fold difference in effect on the efficiency of termination. This effect could not be related to any property of the encoded last amino acid in the nascent peptide. Iso-codons read by the same tRNA (AAA/G, GAA/G) gave similar readthrough values. Codons for glutamine (CAA/G), glutamic acid (GAA/G) and isoleucine (AUA/C) that are read by different isoaccepting tRNAs are associated with an approximately twofold difference in each case in termination efficiency. This suggests that the P-site tRNAis able to influence termination at UGAC in yeast

Analysis of 5-hydroxytryptamine 2c receptor gene promoter variants as alcohol-dependence risk factors

To examine whether polymorphic variants of the HTR2C gene are associated with diagnosis of alcohol dependence. We compared allele frequencies of five HTR2C promoter polymorphisms in a Nordic population of alcohol dependent individuals (Males: n = 309; Females: n = 127) and ethnically matched controls (Males: n = 83; Females: n = 190) in whom alcohol dependence was established, or any diagnosis of substance disorder was excluded, respectively. Patients were further subtyped into Type I (late onset) and Type II (early onset) alcoholics. None of the individual polymorphisms indicated significant association with alcohol dependence. A common promoter haplotype (GAGG) exhibited different distribution frequencies between males and females (Type I), however on Bonferroni's multiple-testing correction, this observation proved to be insignificant. Although we report a lack of association between alcohol dependence and five common promoter polymorphisms, and the constituted haplotypes, the analysis tends to indicate gender and sub-type differences. We suggest that a follow up study with larger sample numbers should be performed to improve the power to detect the genetic influences of HTR2C in alcohol dependence

Identification of functional SNPs in the 5-prime flanking sequences of human genes

Background: Over 4 million single nucleotide polymorphisms (SNPs) are currently reported to exist within the human genome. Only a small fraction of these SNPs alter gene function or expression, and therefore might be associated with a cell phenotype. These functional SNPs are consequently important in understanding human health. Information related to functional SNPs in candidate disease genes is critical for cost effective genetic association studies, which attempt to understand the genetics of complex diseases like diabetes, Alzheimer's, etc. Robust methods for the identification of functional SNPs are therefore crucial. We report one such experimental approach. Results: Sequence conserved between mouse and human genomes, within 5 kilobases of the 5-prime end of 176 GPCR genes, were screened for SNPs. Sequences flanking these SNPs were scored for transcription factor binding sites. Allelic pairs resulting in a significant score difference were predicted to influence the binding of transcription factors (TFs). Ten such SNPs were selected for mobility shift assays (EMSA), resulting in 7 of them exhibiting a reproducible shift. The full-length promoter regions with 4 of the 7 SNPs were cloned in a Luciferase based plasmid reporter system. Two out of the 4 SNPs exhibited differential promoter activity in several human cell lines. Conclusions: We propose a method for effective selection of functional, regulatory SNPs that are located in evolutionary conserved 5-prime flanking regions (5'-FR) regions of human genes and influence the activity of the transcriptional regulatory region. Some SNPs behave differently in different cell types.Medicine, Faculty ofMolecular Medicine and Therapeutics, Centre forNon UBCReviewedFacult

Nonsynonymous SNPs: validation characteristics, derived allele frequency patterns, and suggestive evidence for natural selection

We experimentally investigated more than 1,200 entries in dbSNP that would change amino-acids (nsSNPs), using various subsets of DNA samples drawn from 18 global populations (approximately 1,000 subjects in total). First, we mined the data for any SNP features that correlated with a high validation rate. Useful predictors of valid SNPs included multiple submissions to dbSNP, having a dbSNP validation statement, and being present in a low number of ESTs. Together, these features improved validation rates by almost 10-fold. Higher-abundance SNPs (e.g., T/C variants) also validated more frequently. Second, we considered derived alleles and noted a considerably (approximately 10%) increased average derived allele frequency (DAF) in Europeans vs. Africans, plus a further increase in some other populations. This was not primarily due to an SNP ascertainment bias, nor to the effects of natural selection. Instead, it can be explained as a drift-based, progressive increase in DAF that occurs over many generations and becomes exaggerated during population bottlenecks. This observation could be used as the basis for novel DAF-based tests for comparing demographic histories. Finally, we considered individual marker patterns and identified 37 SNPs with allele frequency variance or FST values consistent with the effects of population-specific natural selection. Four particularly striking clusters of these markers were apparent, and three of these coincide with genes/regions from among only several dozen such domains previously suggested by others to carry signatures of selection