Several millions single nucleotide polymorphisms (SNPs) have already been collected and deposited in public databases and these are important resources not only for use as markers to identify ...disease-associated genes, but also to understand the mechanisms that underlie the genome diversification.
A spectrum analysis of SNP density distribution in the genomic regions around transcription start sites (TSSs) revealed a remarkable periodicity of 146 nucleotides. This periodicity was observed in the regions that were associated with CpG islands (CGIs), but not in the regions without CpG islands (nonCGIs). An analysis of the sequence divergence of the same genomic regions between humans and chimpanzees also revealed a similar periodical pattern in CGI. The occurrences of any mono- or di-nucleotide sequences in these regions did not reveal such a periodicity, thus indicating that an interpretation of this periodicity solely based on the sequence-dependent susceptibility to mutation is highly unlikely.
The periodical patterns of nucleotide variability suggest the location of nucleosomes that are phased at TSS, and can be viewed as the genetic footprint of the chromatin state that has been maintained throughout mammalian evolutionary history. The results suggest the possible involvement of the nucleosome structure in the promoter function, and also a fundamental functional/structural difference between the two promoter classes, i.e., those with and without CGIs.
Coelacanths are known as “living fossils” because their morphology has changed very little from that in the fossil record. To elucidate why coelacanths have evolved so slowly is thus of primary ...importance in evolutionary biology. In the present study, we determined the entire sequence of the HOX cluster of the Tanzanian coelacanth (Latimeria chalumnae) and compared it with that of the Indonesian coelacanth (L. menadoensis), which was available in the literature. The most intriguing result was the extremely small genetic divergence between the two coelacanths. The synonymous divergence of the HOX coding region between the two coelacanths was estimated to be 0.07%, which is ~11-fold smaller than that of human–chimp. When we applied the estimated divergence time of the two coelacanths of 6million years ago (MYA) and 30MYA, which were proposed in independent mitochondrial DNA analyses, the synonymous substitution rate of the coelacanth HOX cluster was estimated to be ~11-fold and 56-fold smaller than that of human–chimp, respectively. Thus, the present study implies that the reduction of the nucleotide substitution rate in coelacanth HOX genes may account for the conservation of coelacanth morphology during evolution.
► We sequenced the HOX cluster of the Tanzanian coelacanth. ► The genetic divergence between two coelacanth species is very small. ► The slow substitution rate may account for the slow rate of coelacanth evolution.
Activation-induced cytidine deaminase (AID) is the essential enzyme for imprinting immunological memory through class switch recombination (CSR) and somatic hypermutation (SHM) of the immunoglobulin ...(Ig) gene. AID-dependent reduction of Topoisomerase 1 (Top1) promotes DNA cleavage that occurs upon Ig gene diversification, whereas the mechanism behind AID-induced Top1 reduction remains unclear. Here, we clarified the contribution of the microRNA-Ago2 complex in AID-dependent Top1 decrease. Ago2 binds to Top1 3'UTR with two regions of AID-dependent Ago2-binding sites (5'- and 3'dABs). Top1 3'UTR knockout (3'UTRKO) in B lymphoma cells leads to decreases in DNA break efficiency in the IgH gene accompanied by a reduction in CSR and SHM frequencies. Furthermore, AID-dependent Top1 protein reduction and Ago2-binding to Top1 mRNA are down-regulated in 3'UTRKO cells. Top1 mRNA in the highly translated fractions of the sucrose gradient is decreased in an AID-dependent and Top1 3'UTR-mediated manner, resulting in a decrease in Top1 protein synthesis. Both AID and Ago2 localize in the mRNA-binding protein fractions and they interact with each other. Furthermore, we found some candidate miRNAs which possibly bind to 5'- and 3'dAB in Top1 mRNA. Among them, miR-92a-3p knockdown induces the phenotypes of 3'UTRKO cells to wild-type cells whereas it does not impact on 3'UTRKO cells. Taken together, the Ago2-miR-92a-3p complex will be recruited to Top1 3'UTR in an AID-dependent manner and posttranscriptionally reduces Top1 protein synthesis. These consequences cause the increase in a non-B-DNA structure, enhance DNA cleavage by Top1 in the Ig gene and contribute to immunological memory formation.
To elucidate the genetics of coronary artery disease (CAD) in the Japanese population, we conducted a large-scale genome-wide association study of 168,228 individuals of Japanese ancestry (25,892 ...cases and 142,336 controls) with genotype imputation using a newly developed reference panel of Japanese haplotypes including 1,781 CAD cases and 2,636 controls. We detected eight new susceptibility loci and Japanese-specific rare variants contributing to disease severity and increased cardiovascular mortality. We then conducted a trans-ancestry meta-analysis and discovered 35 additional new loci. Using the meta-analysis results, we derived a polygenic risk score (PRS) for CAD, which outperformed those derived from either Japanese or European genome-wide association studies. The PRS prioritized risk factors among various clinical parameters and segregated individuals with increased risk of long-term cardiovascular mortality. Our data improve the clinical characterization of CAD genetics and suggest the utility of trans-ancestry meta-analysis for PRS derivation in non-European populations.
The single strand conformation polymorphism (SSCP) method is a sensitive technique used to detect subtle sequence differences in PCR-amplified DNA fragments as separated peaks in electrophoretic ...analysis. In this chapter, we focus on SSCP analysis for quantifying polymorphic alleles rather than scanning for mutations. Short fragments carrying single nucleotide polymorphisms are amplified from individual and pooled DNA samples, then the products are labeled with fluorescent dyes and analyzed by automated capillary electrophoresis under nondenaturing conditions. Dedicated software, QSNPlite, interprets trace data of the electrophoresis to identify alleles of individuals and quantify these alleles in the pool. The software can also incorporate sequencing data to assign alleles at the nucleotide level. The procedures described here are being used in association studies that compare allele frequencies between cases and controls to identify genes responsible for common diseases.
We show that single-nucleotide polymorphisms (SNPs) of moderate to high heterozygosity (minor allele frequencies >10%) can be efficiently detected, and their allele frequencies accurately estimated, ...by pooling the DNA samples and applying a capillary-based SSCP analysis. In this method, alleles are separated into peaks, and their frequencies can be reliably and accurately quantified from their peak heights (SD <1.8%). We found that as many as 40% of publicly available SNPs that were analyzed by this method have widely differing allele frequency distributions among groups of different ethnicity (parents of Centre d'Etude Polymorphisme Humaine families vs. Japanese individuals). These results demonstrate the effectiveness of the present pooling method in the reevaluation of candidate SNPs that have been collected by examination of limited numbers of individuals. The method should also serve as a robust quantitative technique for studies in which a precise estimate of SNP allele frequencies is essential—for example, in linkage disequilibrium analysis.
Complete hydatidiform moles (CHMs) are tissues carrying duplicated haploid genomes derived from single sperms, and detecting copy number variations (CNVs) in CHMs is assumed to be sensitive and ...straightforward methods. We genotyped 108 CHM genomes using Affymetrix SNP 6.0 (GEO#: GSE18642) and Illumina 1M-duo (GEO#: GSE54948). After quality control, we obtained 84 definitive haplotype consisting of 1.7million SNPs and 2339 CNV regions. The results are presented in the database of our web site (http://orca.gen.kyushu-u.ac.jp/cgi-bin/gbrowse/humanBuild37D4_1/).
MicroRNAs (miRNAs) and circulating cell-free mitochondrial DNA (ccf-mtDNA) have attracted interest as biological markers of affective disorders. In response to stress, it is known that miRNAs in ...mitochondria diffuse out of the cytoplasm alongside mtDNA; however, this process has not yet been identified. We hypothesized that miRNAs derived from specific cell nuclei cause mitochondrial damage and mtDNA fragmentation under MDD-associated stress conditions.
A comprehensive analysis of the plasma miRNA levels and quantification of the plasma ccf-mtDNA copy number were performed in 69 patients with depression to determine correlations and identify genes and pathways interacting with miRNAs. The patients were randomly assigned to receive either selective serotonin reuptake inhibitors (SSRI) or mirtazapine. Their therapeutic efficacy over four weeks was evaluated in relation to miRNAs correlated with ccf-mtDNA copy number.
The expression levels of the five miRNAs showed a significant positive correlation with the ccf-mtDNA copy number after correcting for multiple testing. These miRNAs are involved in gene expression related to thyroid hormone synthesis, the Hippo signaling pathway, vasopressin-regulated water reabsorption, and lysine degradation. Of these five miRNAs, miR-6068 and miR-4708-3p were significantly associated with the SSRI and mirtazapine treatment outcomes, respectively.
This study did not show comparison with a healthy group.
The expression levels of specific miRNAs were associated with ccf-mtDNA copy number in untreated depressed patients; moreover, these miRNAs were linked to antidepressant treatment outcomes. These findings are expected to lead to the elucidation of new pathological mechanism of depression.
•Five microRNAs were associated with mitochondrial DNA in patients with depression.•These miRNAs showed positive correlation.•These were associated with genes on pathways such as thyroid hormone synthesis.•miR-6068 and miR-4708-3p were associated with antidepressant treatment outcome.
Epilepsy is a common neurological disorder, and mutations in genes encoding ion channels or neurotransmitter receptors are frequent causes of monogenic forms of epilepsy. Here we show that abnormal ...expansions of TTTCA and TTTTA repeats in intron 4 of SAMD12 cause benign adult familial myoclonic epilepsy (BAFME). Single-molecule, real-time sequencing of BAC clones and nanopore sequencing of genomic DNA identified two repeat configurations in SAMD12. Intriguingly, in two families with a clinical diagnosis of BAFME in which no repeat expansions in SAMD12 were observed, we identified similar expansions of TTTCA and TTTTA repeats in introns of TNRC6A and RAPGEF2, indicating that expansions of the same repeat motifs are involved in the pathogenesis of BAFME regardless of the genes in which the expanded repeats are located. This discovery that expansions of noncoding repeats lead to neuronal dysfunction responsible for myoclonic tremor and epilepsy extends the understanding of diseases with such repeat expansion.
The majority of complete hydatidiform moles (CHMs) harbor duplicated haploid genomes that originate from sperm. This makes CHMs more advantageous than conventional diploid cells for determining ...haplotypes of SNPs and copy-number variations (CNVs), because all of the genetic variants in a CHM genome are homozygous. Here we report SNP and CNV haplotype structures determined by analysis of 100 CHMs from Japanese subjects via high-density DNA arrays. The obtained haplotype map should be useful as a reference for the haplotype structure of Asian populations. We resolved common CNV regions (merged CNV segments across the examined samples) into CNV events (clusters of CNV segments) on the basis of mutual overlap and found that the haplotype backgrounds of different CNV events within the same CNV region were predominantly similar, perhaps because of inherent structural instability.
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