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Gene and protein domain-specific patterns of genetic variability within the G-protein coupled receptor superfamily.

INTRODUCTION: Guanine nucleotide binding proteins (G-proteins) represent the targets for >50% of all therapeutics. There is substantial interindividual variation in response to agonists and antagonists directed to these receptors, which may, in part, be due to genetic polymorphisms. As a class, the sequence variability of G-protein-coupled receptor (GPCR) genes has not been characterized. STUDY DESIGN: This variability was investigated by sequencing promoter, 5'- and 3'-UTR, coding blocks, and intron-exon boundaries, of 64 GPCR genes in an ethnically diverse group of 82 individuals. RESULTS: Of the 675 single-nucleotide variations found, 61% occurred in > or =1% of the population sample and the nature of these 412 single nucleotide polymorphisms (SNPs) was assessed. 5'-UTR (p = 0.002) and coding (p = 0.006) SNPs were observed more often in GPCR genes, compared with 309 non-GPCR genes similarly interrogated. The prevalence of non-synonymous coding SNPs was unexpectedly high, with 65% of GPCR genes having at least one. Intron-containing genes had half as many non-synonymous coding SNPs compared with intronless genes (p = 0.0009), suggesting that when introns are not available coding regions provide sites for variation. A distinct relationship between the prevalence of non-synonymous SNPs and receptor structural domains was evident (p = 0.0006 by ANOVA), with variability being most prominent in the transmembrane spanning domains (38%) and the intracellular loops (24%). Phosphoregulatory domains, particularly the carboxy terminus, often the site for agonist-promoted phosphorylation by G-protein coupled receptor kinases, were the least polymorphic (8%). CONCLUSIONS: There is substantial genetic variability in potentially pharmacologically relevant coding and noncoding regions of GPCRs. Such variability should be considered in the development of new agents, or optimization of existing agents, targeted to these receptors.

Analysis of Variance↗

Genomewide pattern of synonymous nucleotide substitution in two complete genomes of Mycobacterium tuberculosis.

Comparison of the pattern of synonymous nucleotide substitution between two complete genomes of Mycobacterium tuberculosis at 3298 putatively orthologous loci showed a mean percent difference per synonymous site of 0.000328 0.000022. Although 80.5% of loci showed no synonymous or nonsynonymous nucleotide differences, the level of polymorphism observed at other loci was greater than suggested by previous studies of a small number of loci. This level of nucleotide difference leads to the conservative estimate that the common ancestor of these two genotypes occurred approximately 35000 ago, which is twice as high as some recent estimates of the time of origin of this species. Our results suggest that a large number of loci should be examined for an accurate assessment of the level of nucleotide diversity in natural populations of pathogenic microorganisms.

Base Sequence↗

A two-stage approach identifies a Q344X mutation in the rhodopsin gene of a Chinese Singaporean family with autosomal dominant retinitis pigmentosa.

INTRODUCTION: Retinitis pigmentosa (RP) is a group of hereditary retinal diseases in which photoreceptor cells degenerate. It is both clinically and genetically heterogenous. Using a two-stage approach by combining linkage analysis with mutation detection, we have rapidly identified the gene locus and the mutation site of a Chinese Singaporean family with autosomal dominant RP. MATERIALS AND METHODS: Three Chinese Singaporean families were tested. One family showed autosomal dominant inheritance pattern, while the other two could be recessive or sporadic. Twelve di-nucleotide markers tightly linked to 6 genes known to be responsible for either autosomal dominant or recessive RP were selected for linkage analysis. Cosegregation of marker and disease inheritance pattern permits identification of the target candidate gene. RFLP (restriction fragment length polymorphism) markers were added to confirm the linkage result prior to the detailed mutation detection study. RESULTS: With this two-stage strategy, the autosomal dominant RP family showed the rhodopsin locus segregating concordantly with the disease. Mutation screening later identified a nonsense mutation 5261C>T in the last exon of rhodopsin gene. It predicted a Q344X changes at the C-terminus of the gene product, truncating it by 5 amino acids. CONCLUSION: This systematic approach facilitates molecular diagnosis of a genetically heterogenous disease like RP. This is the first report of an RP mutation in Singapore. This 5261C>T mutation has been reported in the Caucasian, but not the Chinese population. The relatively milder phenotype in this family showed similarity to the reported US family, indicating the correlation of mutation site to severity of disease regardless of ethnicity.

Asian People↗

Evidence for balancing selection from nucleotide sequence analyses of human G6PD.

Glucose-6-phosphate dehydrogenase (G6PD) mutations that result in reduced enzyme activity have been implicated in malarial resistance and constitute one of the best examples of selection in the human genome. In the present study, we characterize the nucleotide diversity across a 5.2-kb region of G6PD in a sample of 160 Africans and 56 non-Africans, to determine how selection has shaped patterns of DNA variation at this gene. Our global sample of enzymatically normal B alleles and A, A-, and Med alleles with reduced enzyme activities reveals many previously uncharacterized silent-site polymorphisms. In comparison with the absence of amino acid divergence between human and chimpanzee G6PD sequences, we find that the number of G6PD amino acid polymorphisms in human populations is significantly high. Unlike many other G6PD-activity alleles with reduced activity, we find that the age of the A variant, which is common in Africa, may not be consistent with the recent emergence of severe malaria and therefore may have originally had a historically different adaptive function. Overall, our observations strongly support previous genotype-phenotype association studies that proposed that balancing selection maintains G6PD deficiencies within human populations. The present study demonstrates that nucleotide sequence analyses can reveal signatures of both historical and recent selection in the genome and may elucidate the impact that infectious disease has had during human evolution.

Africa South of the Sahara↗

HLA-H: a pseudogene with increased variation due to balancing selection at neighboring loci.

The HLA complex includes the most polymorphic genes in the human genome. However, the HLA class Ib loci have little, if any, nucleotide variation, presumably due to their specialized functions or perhaps due to a lack of function. This population genetic study of HLA-H, a class I pseudogene, was initiated to determine the pattern of variation at neutral sites within the HLA complex. We found that the pattern of variation for HLA-H is consistent with the neutral model. However, the amount of variation in HLA-H is significantly greater than estimates for other silent sites within the human genome outside of the MHC (theta = 0.0144, P < 0.000001). Our study further indicates that other possible causes of increased variation such as a high mutation rate for HLA-H, interlocus gene conversion, increased diversity in the sample population in general, and selection acting directly on HLA-H are unlikely. Instead, these data suggest that HLA-H has increased variation as a result of balancing selection acting on nearby loci such as HLA-A.

Animals↗

Brain-derived neurotrophic factor variants are associated with childhood-onset mood disorder: confirmation in a Hungarian sample.

Brain-derived neurotrophic factor (BDNF) is a nerve growth factor that has been implicated in the neurobiology of depression. Our group has previously reported an association between a BDNF variant and childhood-onset mood disorder (COMD) in an adult sample from Pittsburgh. We hypothesize that variants at the BDNF locus are associated with COMD. Six BDNF polymorphisms were genotyped in 258 trios having juvenile probands with childhood-onset DSM-IV major depressive or dysthymic disorder. BDNF markers included the (GT)n microsatellite, Val66Met and four other single-nucleotide polymorphisms (SNPs) distributed across the BDNF gene. Family-based association and evolutionary haplotype analysis methods were used. Analysis of linkage disequilibrium (LD) revealed substantial LD among all six polymorphisms. Analyses of the Val66Met polymorphism demonstrated significant overtransmission of the val allele (chi2=7.12, d.f.=1, P=0.0076). Consistent with the pattern of LD, all other SNPs showed significant biased transmission. The (GT)n microsatellite alleles also indicated a trend towards biased transmission (170 bp: Z=2.095, P=0.036). Significant haplotypes involved Val66Met and BDNF2 (P=0.0029). In this Hungarian sample, we found all five BDNF SNPs tested and a haplotype containing the BDNF Val66Met Val allele to be associated with COMD. These results provide evidence that BDNF variants affect liability to juvenile-onset mood disorders, supported by data from two independent samples.

Adult↗

Positive selection on nucleotide substitutions and indels in accessory gland proteins of the Drosophila pseudoobscura subgroup.

Genes encoding reproductive proteins often diverge rapidly due to positive selection on nucleotide substitutions. While this general pattern is well established, the extent to which specific reproductive genes experience similar selection in different clades has been little explored, nor have possible targets of positive selection other than nucleotide substitutions, such as indels, received much attention. Here, we inspect for the signature of positive selection in the genes encoding five accessory gland proteins (Acps) (Acp26Aa, Acp32CD, Acp53Ea, Acp62F, and Acp70A) originally described from Drosophila melanogaster but with recognizable orthologues in the D. pseudoobscura subgroup. We compare patterns of selection within the D. psuedoobscura subgroup to those in the D. melanogaster subgroup. Similar patterns of positive selection were found in Acp26Aa and Acp62F in the two subgroups, while Acp53Ea and Acp70A experienced purifying selection in both subgroups. These proteins have thus remained targets for similar types of selection over long (>21-MY) periods of time. We also found several indel substitutions and polymorphisms in Acp26Aa and Acp32CD. These indels occur in the same regions as positively selected nucleotide substitutions for Acp26Aa in the D. pseudoobscura subgroup but not in the D. melanogaster subgroup. Rates of indel substitution within Acp26Aa in the D. pseudoobscura subgroup were up to several times those in noncoding regions of the Drosophila genome. This suggests that indel substitutions may be under positive selection and may play a key role in the divergence of some Acps.

Amino Acid Sequence↗

Angiotensin II type I receptor gene and myocardial infarction: tagging SNPs and haplotype based association study. The Beijing atherosclerosis study.

OBJECTIVES: The present study aimed to assess the effect of haplotype variation in angiotensin II type I receptor (AGTR1) gene on the risk of myocardial infarction (MI) in Chinese males. METHODS: We used 48 patients to identify the putative functional polymorphisms in AGTR1 gene by direct sequencing. The program tagSNPs was used to identify an optimal set of tagging single nucleotide polymorphisms (SNPs). These selected SNPs were then genotyped in 419 male patients with MI and 400 age-matched male controls. The program haplo.stats was used to investigate the relationship between the haplotypes and MI. RESULTS: Sixteen polymorphisms in AGTR1 gene were identified. Based on the linkage disequilibrium pattern among these SNPs, six polymorphisms, SNP1, SNP6-SNP7 and SNP13-SNP15, were selected as haplotype tagging SNPs and further genotyped. Single SNP analyses indicated that the SNP1, SNP6 and SNP13 were significantly associated with MI, adjusted for covariates. Haplotype-based association analyses identified the frequency of haplotype AGATAA was lower in cases than in controls (P = 0.006). In comparison, three haplotypes (AAATAA, TAGCAA and AAACAG) were found to significantly increase the risk of MI with adjusted odds ratio equal to 1.33, 1.75 and 2.64, respectively (P = 0.029, 0.026 and 0.015). CONCLUSIONS: Our study suggests that common genetic variations in the AGTR1 gene may affect the risk of MI in Chinese males, and that there might be several functional variants in AGTR1 gene and the combined effect of these variants seemed to have a larger effect on the risk of MI in Chinese males.

Adult↗

Linkage disequilibrium blocks, haplotype structure, and htSNPs of human CYP7A1 gene.

BACKGROUND: Cholesterol 7-alpha-hydroxylase (CYP7A1) is the rate limiting enzyme for converting cholesterol into bile acids. Genetic variations in the CYP7A1 gene have been associated with metabolic disorders of cholesterol and bile acids, including hypercholesterolemia, hypertriglyceridemia, arteriosclerosis, and gallstone disease. Current genetic studies are focused mainly on analysis of a single nucleotide polymorphism (SNP) at A-278C in the promoter region of the CYP7A1 gene. Here we report a genetic approach for an extensive analysis on linkage disequilibrium (LD) blocks and haplotype structures of the entire CYP7A1 gene and its surrounding sequences in Africans, Caucasians, Asians, Mexican-Americans, and African-Americans. RESULT: The LD patterns and haplotype blocks of CYP7A1 gene were defined in Africans, Caucasians, and Asians using genotyping data downloaded from the HapMap database to select a set of haplotype-tagging SNPs (htSNP). A low cost, microarray-based platform on thin-film biosensor chips was then developed for high-throughput genotyping to study transferability of the HapMap htSNPs to Mexican-American and African-American populations. Comparative LD patterns and haplotype block structure was defined across all test populations. CONCLUSION: A constant genetic structure in CYP7A1 gene and its surrounding sequences was found that may lead to a better design for association studies of genetic variations in CYP7A1 gene with cholesterol and bile acid metabolism.

Black or African American↗

Sequence variation of bradykinin receptors B1 and B2 and association with hypertension.

OBJECTIVE: To identify variants in the complete genomic sequence of the two subtypes of bradykinin receptors: B1 (BDKRB1) and B2 (BDKRB2) and to examine the association of these variants with essential hypertension. DESIGN: A case-control design comparing hypertensive and normotensive individuals was used. METHOD: A 64.4 kb genomic region containing the BDKRB1 and BDKRB2 genes was sequenced in 30 African-American individuals. A total of 282 single-nucleotide polymorphisms (SNPs) were identified. A total of 21 SNPs were genotyped in our complete cohorts of hypertensive and normotensive African-Americans (n = 218), American-Caucasians (n = 220) and Greek-Caucasians (n = 194). Pair-wise correlation coefficients were computed to assess linkage disequilibrium (LD) patterns among the SNPs. Chi-squared tests and logistic regression were used to assess association between the SNPs and hypertension status. RESULT: Pairwise LD demonstrated a general pattern of decline with increasing distance, which was consistent among the three groups with less LD in African-Americans. One SNP in the promoter region of BDKRB2 (rs1799722) was associated with hypertension (P = 0.044) in African-Americans. One SNP in BDKRB2 and three SNPs in BDKRB1 were associated with hypertension (P-values between 0.026 and 0.0004) in American-Caucasians. Haplotypes including those four SNPs and one SNP in B2, which results in an amino acid change, demonstrated a significant haplotype frequency difference between hypertensive and normotensive American-Caucasians (P = 0.025). CONCLUSION: These results support the hypothesis that the African-American population is an older population compared with the other samples and the two bradykinin receptors may play a role in blood pressure regulation.

Black or African American↗

Identifying signatures of selection at the enhancer of split neurogenic gene complex in Drosophila.

The Enhancer of split gene complex (E(spl)-C) is one of the more highly annotated gene regions in Drosophila, and the 12 genes within the complex help determine the spacing and patterning of adult bristles. Any E(spl)-C coding, transcribed, or cis-regulatory regions experiencing nonneutral evolution are strong candidates to harbor polymorphisms contributing to naturally occurring variation in bristle number. We confirm that the E(spl)-C is strongly conserved and show that 74% of regulatory elements previously identified in D. melanogaster are conserved in D. pseudoobscura. Regulatory elements in enhancer regions show lower nucleotide diversity and more rare polymorphisms compared with adjacent nonregulatory DNA, suggesting they are under purifying selection, and these effects are particularly pronounced when considering only conserved regulatory elements. The ratio of polymorphism to divergence was significantly different between binding sites and nonbinding sites for transcription factors within enhancer regions, suggesting the action of some form of selection. Too few polymorphisms in regions of the 3' UTR harboring regulatory motifs prevents adequate comparison of diversity and the polymorphism frequency spectrum between 3' UTR motif and nonmotif sequence. We identified at least two broad regions of the gene complex showing strong population subdivision among four populations, which is suggestive of local adaptation or background selection. Finally, two regions of the E(spl)-C exhibit low nucleotide diversity, a high level of rare polymorphisms, and an increase in linkage disequilibrium, which together suggest the action of positive selection. Notably, the gene m2 shows a significant deviation from neutrality by the McDonald-Kreitman test and resides in one of the two regions putatively experiencing a selective sweep. All sites in regions apparently visible to various selective forces are candidates for future work to determine their phenotypic effects.

3' Untranslated Regions↗

Mining for single nucleotide polymorphisms and insertions/deletions in maize expressed sequence tag data.

We have developed a computer based method to identify candidate single nucleotide polymorphisms (SNPs) and small insertions/deletions from expressed sequence tag data. Using a redundancy-based approach, valid SNPs are distinguished from erroneous sequence by their representation multiple times in an alignment of sequence reads. A second measure of validity was also calculated based on the cosegregation of the SNP pattern between multiple SNP loci in an alignment. The utility of this method was demonstrated by applying it to 102,551 maize (Zea mays) expressed sequence tag sequences. A total of 14,832 candidate polymorphisms were identified with an SNP redundancy score of two or greater. Segregation of these SNPs with haplotype indicates that candidate SNPs with high redundancy and cosegregation confidence scores are likely to represent true SNPs. This was confirmed by validation of 264 candidate SNPs from 27 loci, with a range of redundancy and cosegregation scores, in four inbred maize lines. The SNP transition/transversion ratio and insertion/deletion size frequencies correspond to those observed by direct sequencing methods of SNP discovery and suggest that the majority of predicted SNPs and insertion/deletions identified using this approach represent true genetic variation in maize.

Base Sequence↗

Screening of a RAPD marker tightly linked to Co gene in apple and the SCAR marker conversion.

A DNA marker linked to the columnar gene (Co) in apple (Malus domestica) was explored based on the population of 105 progenies of 'Spur Fuji' x 'Telamon' by bulk segregant analysis (BSA) and Random Amplified Polymorphic DNA (RAPD) technique. A total of 300 random primers were screened and a RAPD marker (S1142(682)) closely linked to Co gene (2.86 cM) was identified and then sequenced. Four specific PCR primers (two forward primers and two reverse primers) were designed,and the products of SCAR-PCR indicated that all the four pairs of primers could amplify polymorphic bands between columnar and non-columnar traits, so any of them could serve as the specific SCAR primers. One pair of these specific primers was chosen to amplify each individual in the population, and the result showed that the co-segregation pattern of this SCAR marker and Co gene was the same as that of the RAPD marker. Furthermore, it was found that the nucleotide sequence of the RAPD marker fragment contained an open reading frame (ORF) that could encode 68 deduced amino acid residues at the position of +45 - +251.

Amino Acid Sequence↗

Directional migration in the Hindu castes: inferences from mitochondrial, autosomal and Y-chromosomal data.

Genetic, ethnographic, and historical evidence suggests that the Hindu castes have been highly endogamous for several thousand years and that, when movement between castes does occur, it typically consists of females joining castes of higher social status. However, little is known about migration rates in these populations or the extent to which migration occurs between caste groups of low, middle, and high social status. To investigate these aspects of migration, we analyzed the largest collection of genetic markers collected to date in Hindu caste populations. These data included 45 newly typed autosomal short tandem repeat polymorphisms (STRPs), 411 bp of mitochondrial DNA sequence, and 43 Y-chromosomal single-nucleotide polymorphisms that were assayed in more than 200 individuals of known caste status sampled in Andrah Pradesh, in South India. Application of recently developed likelihood-based analyses to this dataset enabled us to obtain genetically derived estimates of intercaste migration rates. STRPs indicated migration rates of 1-2% per generation between high-, middle-, and low-status caste groups. We also found support for the hypothesis that rates of gene flow differ between maternally and paternally inherited genes. Migration rates were substantially higher in maternally than in paternally inherited markers. In addition, while prevailing patterns of migration involved movement between castes of similar rank, paternally inherited markers in the low-status castes were most likely to move into high-status castes. Our findings support earlier evidence that the caste system has been a significant, long-term source of population structuring in South Indian Hindu populations, and that patterns of migration differ between males and females.

Adult↗

Genotyping possible polymorphic variants of human mismatch repair genes in healthy Korean individuals and sporadic colorectal cancer patients.

The genotypic consequences of numerous single-nucleotide variants in human mismatch repair genes are mostly undetermined. We examined 27 reported single-nucleotide variants, rarely or ambiguously verified in a population-based study, to identify single-nucleotide polymorphisms (SNPs), haplotypes, and the genotype-phenotype association in Korean populations of 330 healthy individuals, 107 sporadic colorectal cancer patients, and 107 of their first-degree relatives. Real-time PCR 5'-nuclease assays (TaqMan) MGB assay) were used to determine 24 single-nucleotide variants, and restriction fragment length polymorphism (RFLP) assays were used to determine 3 variants. Of these 27 variants, 4 (hMSH2 gIVS12-6, hMLH1 655, hMLH1 1151, and hMSH2 1168, in descending order) were identified as SNPs occurring in 4.5 to 53.1% of healthy individuals, with polymorphism levels of 0.023-0.3 (mean, 0.092). East Asian populations had an ethnic predilection for the hMLH1 1151 SNP. The genotype distribution for all four SNPs showed no association with sporadic colorectal cancer. Twenty-three variants were not identified in the Korean population, suggesting that fifteen of these variants are colorectal cancer-related mutations and eight are SNPs. Two haplotype patterns existed exclusively, but with rare frequency, in sporadic colorectal cancer patients. The hMLH1 655 allele was closely correlated with hMLH1 protein expression (P = 0.02), but none of the four SNPs was associated with clinicopathologic variables. Among the 27 single nucleotide variants of mismatch repair genes, 12 were suggestive of nonfunctional SNPs and 15 may be colorectal cancer-related mutations. Further verification in other ethnic groups may provide the genotypic and phenotypic significance of single nucleotide variants found in mismatch repair genes.

Adaptor Proteins, Signal Transducing↗

Linkage analysis using single nucleotide polymorphisms.

We performed multipoint linkage analysis using 83 markers from the SNP Consortium (TSC) SNP linkage map in 3 regions covering 190 cM previously scanned with microsatellite markers and found to be linked to type 2 diabetes. Since the average linkage disequilibrium present in the TSC SNP marker clusters is relatively low, we assumed the intracluster genetic distances were a reasonable small nonzero distance (0.03 cM) and performed linkage analysis using GENEHUNTER PLUS and ASM linkage analysis software. We found that for the pedigree structures and missing data patterns in our samples the average information content in all three regions and the LOD score curves in two regions obtained from the TSC SNP markers were similar to results obtained from microsatellite marker maps with 10 cM average spacing. We also give an algorithm which extends the Lander-Green algorithm to permit multipoint linkage analysis of clusters of tightly linked markers with arbitrarily high levels of intracluster linkage disequilibrium.

Chromosome Mapping↗

Tag SNP selection for Finnish individuals based on the CEPH Utah HapMap database.

The pattern and nature of linkage disequilibrium in the human genome is being studied and catalogued as part of the International HapMap Project [:2003 Nature 426:789-796]. A key goal of the HapMap Project is to enable identification of tag single nucleotide polymorphisms (SNPs) that capture a substantial portion of common human genetic variability while requiring only a small fraction of SNPs to be genotyped [International HapMap Consortium, 2005: Nature 437:1299-1320]. In the current study, we examined the effectiveness of using the CEU HapMap database to select tag SNPs for a Finnish sample. We selected SNPs in a 17.9-Mb region of chromosome 14 based on pairwise linkage disequilibrium (r(2)) estimates from the HapMap CEU sample, and genotyped 956 of these SNPs in 1,425 Finnish individuals. An excess of SNPs showed significantly different allele frequencies between the HapMap CEU and the Finnish samples, consistent with population-specific differences. However, we observed strong correlations between the two samples for estimates of allele frequencies, r(2) values, and haplotype frequencies. Our results demonstrate that the HapMap CEU samples provide an adequate basis for tag SNP selection in Finnish individuals, without the need to create a map specifically for the Finnish population, and suggest that the four-population HapMap data will provide useful information for tag SNP selection beyond the specific populations from which they were sampled.

Chromosome Mapping↗

Plant disease resistance: commonality and novelty in multicellular innate immunity.

Pathogen avirulence genes encode for effector molecules that play a crucial role in the process of pathogen colonization of plant tissue. Successful host defense requires rapid and efficient detection of the pathogen avirulence factors. In the last few years, much progress has been made in delineating the plant molecular sentinels that participate in pathogen identification. Because this ability is genetic information that is 'hard-wired' into the genome, it is called 'innate immunity' and it draws its origins from a phylogenetically ancient form of immunity common to plants and animals. Conservation is shown in many of the functional molecular motifs of innate genes such as the Toll/interleukin 1 receptor domains, nucleotide binding domains and structures that contain leucine rich repeats. Novel plant molecular surveillance domains also include pathogen pattern recognition by coiled-coil domains and specialized kinases. The rapid evolution of plant innate immunity genes is readily detected in their sequence polymorphism, by their massive amplification and appearance in the genome in a clustered organization. By comparative biology of highly diverged innate immunity systems we can enhance our appreciation of the truly basic forces that have shaped its evolution in mutlicellular organisms.

Amino Acid Sequence↗