Investigating single nucleotide polymorphism (SNP) density in the human genome and its implications for molecular evolution

Variation within the non-coding genome influences genetic and epigenetic regulation of the human leukocyte antigen genes

Variation within the non-coding genome may influence the regulation and expression of important genes involved in immune control such as the human leukocyte antigen (HLA) system. Class I and Class II HLA molecules are essential for peptide presentation which is required for T lymphocyte activation. Single nucleotide polymorphisms within non-coding regions of HLA Class I and Class II genes may influence the expression of these genes by affecting the binding of transcription factors and chromatin modeling molecules. Furthermore, an interplay between genetic and epigenetic factors may also influence HLA expression. Epigenetic factors such as DNA methylation and non-coding RNA, regulate gene expression without changing the DNA sequence. However, genetic variation may promote or allow genes to escape regulation by epigenetic factors, resulting in altered expression. The HLA system is central to most diseases, therefore, understanding the role of genetics and epigenetics on HLA regulation will tremendously impact healthcare. The knowledge gained from these studies may lead to novel and cost-effective diagnostic approaches and therapeutic interventions. This review discusses the role of non-coding variants on HLA regulation. Furthermore, we discuss the interplay between genetic and epigenetic factors on the regulation of HLA by evaluating literature based on polymorphisms within DNA methylation and miRNA regulatory sites within class I and Class II HLA genes. We also provide insight into the importance of the HLA non-coding genome on disease, discuss ethnic-specific differences across the HLA region and provide guidelines for future HLA studies.

Identification of Insertion and Deletion (InDel) Markers for Chickpea (Cicer arietinum L.) Based on Double-Digest Restriction Site-Associated DNA Sequencing

Enhancing the marker repository and the development of breeder-friendly markers in chickpeas is important in relation to chickpea genomics-assisted breeding applications. Insertion-deletion (InDel) markers are widely distributed across genomes and easily observed with specifically designed primers, leading to less time, cost, and labor requirements. In light of this, the present study focused on the identification and development of InDel markers through the use of double-digest restriction site-associated DNA sequencing (ddRADSeq) data from 20 chickpea accessions. Bioinformatic analysis identified 20,700 InDel sites, including 15,031 (72.61%) deletions and 5669 (27.39%) insertions, among the chickpea accessions. The InDel markers ranged from 1 to 25 bp in length, while single-nucleotide-length InDel markers were found to represent the majority of the InDel sites and account for 79% of the total InDel markers. However, we focused on InDel markers wherein the length was greater than a single nucleotide to avoid any read or alignment errors. Among all of the InDel markers, 96.1% were less than 10 bp, 3.6% were between 10 and 20 bp, and 0.3% were more than 20 bp in length. We examined the InDel markers that were 10 bp and longer for the development of InDel markers based on a consideration of the genomic distribution and low-cost genotyping with agarose gels. A total of 29 InDel regions were selected, and primers were successfully designed to evaluate their efficiency. Annotation analysis of the InDel markers revealed them to be found with the highest frequency in the intergenic regions (82.76%), followed by the introns (6.90%), coding sequences (6.90%), and exons (3.45%). Genetic diversity analysis demonstrated that the polymorphic information content of the markers varied from 0.09 to 0.37, with an average of 0.20. Taken together, these results showed the efficiency of InDel marker development for chickpea genetic and genomic studies using the ddRADSeq method. The identified markers might prove valuable for chickpea breeders.

Translation Rates and Protein Folding

The mRNA coding sequence defines not only the amino acid sequence of the protein, but also the speed at which the ribosomes move along the mRNA while making the protein. The non-uniform local kinetics - denoted as translational rhythm - is similar among mRNAs coding for related protein folds. Deviations from this conserved rhythm can result in protein misfolding. In this review we summarize the experimental evidence demonstrating how local translation rates affect cotranslational protein folding, with the focus on the synonymous codons and patches of charged residues in the nascent peptide as best-studied examples. Alterations in nascent protein conformations due to disturbed translational rhythm can persist off the ribosome, as demonstrated by the effects of synonymous codon variants of several disease-related proteins. Charged amino acid patches in nascent chains also modulate translation and cotranslational protein folding, and can abrogate translation when placed at the N-terminus of the nascent peptide. During cotranslational folding, incomplete nascent chains navigate through a unique conformational landscape in which earlier intermediate states become inaccessible as the nascent peptide grows. Precisely tuned local translation rates, as well as interactions with the ribosome, guide the folding pathway towards the native structure, whereas deviations from the natural translation rhythm may favor pathways leading to trapped misfolded states. Deciphering the 'folding code' of the mRNA will contribute to understanding the diseases caused by protein misfolding and to rational protein design.

Genome Assembly and Structural Variation Analysis of Luffa acutangula Provide Insights on Flowering Time and Ridge Development

Luffa spp. is an important worldwide cultivated vegetable and medicinal plant from the Cucurbitaceae family. In this study, we report a high-quality chromosome-level genome of the high-generation inbred line SG261 of Luffa acutangula. The genomic sequence was determined by PacBio long reads, Hi-C sequencing reads, and 10× Genomics sequencing, with an assembly size of 739.82 Mb, contig N50 of 18.38 Mb, and scaffold N50 of 56.08 Mb. The genome of L. acutangula SG261 was predicted to contain 27,312 protein-coding genes and 72.56% repetitive sequences, of which long terminal repeats (LTRs) were an important form of repetitive sequences, accounting for 67.84% of the genome. Phylogenetic analysis reveals that L. acutangula evolved later than Luffa cylindrica, and Luffa is closely related to Momodica charantia. Comparing the genome of L. acutangula SG261 and L. cylindrica with PacBio data, 67,128 high-quality structural variations (SVs) and 55,978 presence-absence variations (PAVs) were identified in SG261, resulting in 2424 and 1094 genes with variation in the CDS region, respectively, and there are 287 identical genes affected by two different structural variation analyses. In addition, we found that the transcription factor FY (FLOWERING LOCUS Y) families had a large expansion in L. acutangula SG261 (flowering in the morning) compared to L. cylindrica (flowering in the afternoon), which may result in the early flowering time in L. acutangula SG261. This study provides valuable reference for the breeding of and pan-genome research into Luffa species.

Whole genome sequences of 70 indigenous Ethiopian cattle

Indigenous animal genetic resources play a crucial role in preserving global genetic diversity and supporting the livelihoods of millions of people. In Ethiopia, the majority of the cattle population consists of indigenous breeds. Understanding the genetic architecture of these cattle breeds is essential for effective management and conservation efforts. In this study, we sequenced DNA samples from 70 animals from seven indigenous cattle breeds, generating about two terabytes of pair-end reads with an average coverage of 14X. The sequencing data were pre-processed and mapped to the cattle reference genome (ARS-UCD1.2) with an alignment rate of 99.2%. Finally, the variant calling process produced approximately 35 million high-quality SNPs. These data provide a deeper understanding of the genetic landscape, facilitate the identification of causal mutations, and enable the exploration of evolutionary patterns to assist cattle improvement and sustainable utilization, particularly in the face of unpredictable climate changes.

Elevated incidence of somatic mutations at prevalent genetic sites

The common loci represent a distinct set of the human genome sites that harbor genetic variants found in at least 1% of the population. Small somatic mutations occur at the common loci and non-common loci, i.e. csmVariants and ncsmVariants, are presumed with similar probabilities. However, our work revealed that within the coding region, common loci constituted only 1.03% of all loci, yet they accounted for 5.14% of TCGA somatic mutations. Furthermore, the small somatic mutation incidence rate at these common loci was 2.7 times that observed in the non-common. Notably, the csmVariants exhibited an impressive recurrent rate of 36.14%, which was 2.59 times of the ncsmVariants. The C-to-T transition at the CpG sites accounted for 32.41% of the csmVariants, which was 2.93 times for the ncsmVariants. Interestingly, the aging-related mutational signature contributed to 13.87% of the csmVariants, 5.5 times that of ncsmVariants. Moreover, 35.93% of the csmVariants contexts exhibited palindromic features, outperforming ncsmVariant contexts by 1.84 times. Notably, cancer patients with higher csmVariants rates had better progression-free survival. Furthermore, cancer patients with high-frequency csmVariants enriched with mismatch repair deficiency were also associated with better progression-free survival. The accumulation of csmVariants during cancerogenesis is a complex process influenced by various factors. These include the presence of a substantial percentage of palindromic sequences at csmVariants sites, the impact of aging and DNA mismatch repair deficiency. Together, these factors contribute to the higher somatic mutation incidence rates of common loci and the overall accumulation of csmVariants in cancer development.

Comparative Genomic Analysis of Warthog and Sus Scrofa Identifies Adaptive Genes Associated with African Swine Fever

BACKGROUND

As warthogs (Phacochoerus africanus) have innate immunity against African swine fever (ASF), it is critical to understand the evolutionary novelty of warthogs to explain their specific ASF resistance.

METHODS

Here, we present two completed new genomes of one warthog and one Kenyan domestic pig as fundamental genomic references to elucidate the genetic mechanisms of ASF tolerance.

RESULTS

Multiple genomic variations, including gene losses, independent contraction, and the expansion of specific gene families, likely molded the warthog genome to adapt to the environment. Importantly, the analysis of the presence and absence of genomic sequences revealed that the DNA sequence of the warthog genome had an absence of the gene lactate dehydrogenase B (LDHB) on chromosome 2 compared with the reference genome. The overexpression and siRNA of LDHB inhibited the replication of the African swine fever virus. Combined with large-scale sequencing data from 42 pigs worldwide, the contraction and expansion of tripartite motif-containing (TRIM) gene families revealed that TRIM family genes in the warthog genome are potentially responsible for its tolerance to ASF.

CONCLUSION

Our results will help improve the understanding of genetic resistance to ASF in pigs.

Genome diversity of Leishmania aethiopica

Leishmania aethiopica is a zoonotic Old World parasite transmitted by Phlebotomine sand flies and causing cutaneous leishmaniasis in Ethiopia and Kenya. Despite a range of clinical manifestations and a high prevalence of treatment failure, L. aethiopica is one of the most neglected species of the Leishmania genus in terms of scientific attention. Here, we explored the genome diversity of L. aethiopica by analyzing the genomes of twenty isolates from Ethiopia. Phylogenomic analyses identified two strains as interspecific hybrids involving L. aethiopica as one parent and L. donovani and L. tropica respectively as the other parent. High levels of genome-wide heterozygosity suggest that these two hybrids are equivalent to F1 progeny that propagated mitotically since the initial hybridization event. Analyses of allelic read depths further revealed that the L. aethiopica - L. tropica hybrid was diploid and the L. aethiopica - L. donovani hybrid was triploid, as has been described for other interspecific Leishmania hybrids. When focusing on L. aethiopica, we show that this species is genetically highly diverse and consists of both asexually evolving strains and groups of recombining parasites. A remarkable observation is that some L. aethiopica strains showed an extensive loss of heterozygosity across large regions of the nuclear genome, which likely arose from gene conversion/mitotic recombination. Hence, our prospection of L. aethiopica genomics revealed new insights into the genomic consequences of both meiotic and mitotic recombination in Leishmania.

Evolution of weedy giant ragweed (Ambrosia trifida): Multiple origins and gene expression variability facilitates weediness

Agricultural weeds may originate from wild populations, but the origination patterns and genetics underlying this transition remain largely unknown. Analysis of weedy-wild paired populations from independent locations may provide evidence to identify key genetic variation contributing to this adaptive shift. We performed genetic variation and expression analyses on transcriptome data from 67 giant ragweed samples collected from different locations in Ohio, Iowa, and Minnesota and found geographically separated weedy populations likely originated independently from their adjacent wild populations, but subsequent spreading of weedy populations also occurred locally. By using eight closely related weedy-wild paired populations, we identified thousands of unique transcripts in weedy populations that reflect shared or specific functions corresponding, respectively, to both convergently evolved and population-specific weediness processes. In addition, differential expression of specific groups of genes was detected between weedy and wild giant ragweed populations using gene expression diversity and gene co-expression network analyses. Our study suggests an integrated route of weedy giant ragweed origination, consisting of independent origination combined with the subsequent spreading of certain weedy populations, and provides several lines of evidence to support the hypothesis that gene expression variability plays a key role in the evolution of weedy species.

Refining the Camelus dromedarius Myostatin Gene Polymorphism through Worldwide Whole-Genome Sequencing

Myostatin (MSTN) is a highly conserved negative regulator of skeletal muscle in mammals. Inactivating mutations results in a hyper-muscularity phenotype known as "double muscling" in several livestock and model species. In Camelus dromedarius, the gene structure organization and the sequence polymorphisms have been previously investigated, using Sanger and Next-Generation Sequencing technologies on a limited number of animals. Here, we carried out a follow-up study with the aim to further expand our knowledge about the sequence polymorphisms at the myostatin locus, through the whole-genome sequencing data of 183 samples representative of the geographical distribution range for this species. We focused our polymorphism analysis on the ±5 kb upstream and downstream region of the MSTN gene. A total of 99 variants (77 Single Nucleotide Polymorphisms and 22 indels) were observed. These were mainly located in intergenic and intronic regions, with only six synonymous Single Nucleotide Polymorphisms in exons. A sequence comparative analysis among the three species within the Camelus genus confirmed the expected higher genetic distance of C. dromedarius from the wild and domestic two-humped camels compared to the genetic distance between C. bactrianus and C. ferus. In silico functional prediction highlighted: (i) 213 differential putative transcription factor-binding sites, out of which 41 relative to transcription factors, with known literature evidence supporting their involvement in muscle metabolism and/or muscle development; and (ii) a number of variants potentially disrupting the canonical MSTN splicing elements, out of which two are discussed here for their potential ability to generate a prematurely truncated (inactive) form of the protein. The distribution of the considered variants in the studied cohort is discussed in light of the peculiar evolutionary history of this species and the hypothesis that extremely high muscularity, associated with a homozygous condition for mutated (inactivating) alleles at the myostatin locus, may represent, in arid desert conditions, a clear metabolic disadvantage, emphasizing the thermoregulatory and water availability challenges typical of these habitats.

Molecular Markers: An Overview of Data Published for Fungi over the Last Ten Years

Fungi are amongst the most abundant and diverse organisms. Despite being widely known for their adverse role in food spoilage or as pathogens for humans, animals, or plants, they also present several beneficial effects. Fungi contribute to human well-being due to their role as decomposers, degrading decay matter into smaller molecules which can be easily used by other ecosystem members. These organisms can produce medicinal compounds or modulate protective immune responses in human intestine. Fungi intervene in diverse food processes or act as a food supply. Due to fungal diversity, the unequivocal identification of these organisms is crucial to increasing their practical applications and decreasing their adverse effects. The process of identification could be achieved through the integral sequencing of fungi genomes. However, this procedure would be time-consuming and rather cost-inefficient. Therefore, several molecular markers have been developed to overcome these limitations. The chronology of DNA-based molecular markers development can be divided into three main steps: (1) prior to the development of the PCR technique (RFLP); (2) after the development of the PCR technique (RAPD, AFLP, ISSR, VNTR, SNP, InDels, and DNA barcoding); (3) after the development of the massive parallel sequencing technique (Metabarcoding and WGS). Therefore, the present review covers an overview of the most recently developed molecular markers used for fungal detection and identification.

Development of a High-Density 665 K SNP Array for Rainbow Trout Genome-Wide Genotyping

Single nucleotide polymorphism (SNP) arrays, also named « SNP chips », enable very large numbers of individuals to be genotyped at a targeted set of thousands of genome-wide identified markers. We used preexisting variant datasets from USDA, a French commercial line and 30X-coverage whole genome sequencing of INRAE isogenic lines to develop an Affymetrix 665 K SNP array (HD chip) for rainbow trout. In total, we identified 32,372,492 SNPs that were polymorphic in the USDA or INRAE databases. A subset of identified SNPs were selected for inclusion on the chip, prioritizing SNPs whose flanking sequence uniquely aligned to the Swanson reference genome, with homogenous repartition over the genome and the highest Minimum Allele Frequency in both USDA and French databases. Of the 664,531 SNPs which passed the Affymetrix quality filters and were manufactured on the HD chip, 65.3% and 60.9% passed filtering metrics and were polymorphic in two other distinct French commercial populations in which, respectively, 288 and 175 sampled fish were genotyped. Only 576,118 SNPs mapped uniquely on both Swanson and Arlee reference genomes, and 12,071 SNPs did not map at all on the Arlee reference genome. Among those 576,118 SNPs, 38,948 SNPs were kept from the commercially available medium-density 57 K SNP chip. We demonstrate the utility of the HD chip by describing the high rates of linkage disequilibrium at 2–10 kb in the rainbow trout genome in comparison to the linkage disequilibrium observed at 50–100 kb which are usual distances between markers of the medium-density chip.

Exploring genetic variation and population structure in a threatened species, Noturus placidus, with whole-genome sequence data

The Neosho madtom (Noturus placidus) is a small catfish, generally less than 3 inches in length, unique to the Neosho-Spring River system within the Arkansas River Basin. It was federally listed as threatened in 1990, largely due to habitat loss. For conservation efforts, we generated whole-genome sequence data from 10 Neosho madtom individuals originating from 3 geographically separated populations to evaluate genetic diversity and population structure. A Neosho madtom genome was de novo assembled, and genome size and content were assessed. Single nucleotide polymorphisms were assessed from de Bruijn graphs, and via reference alignment with both the channel catfish (Ictalurus punctatus) reference genome and Neosho madtom reference genome. Principal component analysis and structure analysis indicated weak population structure, suggesting fish from the 3 locations represent a single population. Using a novel method, genome-wide conservation and divergence between the Neosho madtom, channel catfish, and zebrafish (Danio rerio) was assessed by pairwise contig alignment, which demonstrated that genes important to embryonic development frequently had conserved sequences. This research in a threatened species with no previously published genomic resources provides novel genetic information to guide current and future conservation efforts and demonstrates that using whole-genome sequencing provides detailed information of population structure and demography using only a limited number of rare and valuable samples.

circTAF8 Regulates Myoblast Development and Associated Carcass Traits in Chicken

Recent studies have shown that circular RNAs (circRNAs) play important roles in skeletal muscle development. CircRNA biogenesis is dependent on the genetic context. Single-nucleotide polymorphisms in the introns flanking circRNAs may be intermediate-inducible factors between circRNA expression and phenotypic traits. Our previous study showed that circTAF8 is an abundantly and differentially expressed circRNA in leg muscle during chicken embryonic development. Here, we aimed to investigate circTAF8 function in muscle development and the association of the SNPs in the circTAF8 flanking introns with carcass traits. In this study, we observed that overexpression of circTAF8 could promote the proliferation of chicken primary myoblasts and inhibit their differentiation. In addition, the SNPs in the introns flanking the circTAF8 locus and those associated with chicken carcass traits were analyzed in 335 partridge chickens. A total of eight SNPs were found associated with carcass traits such as leg muscle weight, live weight, and half and full-bore weight. The association analysis results of haplotype combinations were consistent with the association analysis of a single SNP. These results suggest that circTAF8 plays a regulatory role in muscle development. These identified SNPs were found correlated with traits to muscle development and carcass muscle weight in chickens.

HNF1A：From Monogenic Diabetes to Type 2 Diabetes and Gestational Diabetes Mellitus

Diabetes, a disease characterized by hyperglycemia, has a serious impact on the lives and families of patients as well as on society. Diabetes is a group of highly heterogeneous metabolic diseases that can be classified as type 1 diabetes (T1D), type 2 diabetes (T2D), gestational diabetes mellitus (GDM), or other according to the etiology. The clinical manifestations are more or less similar among the different types of diabetes, and each type is highly heterogeneous due to different pathogenic factors. Therefore, distinguishing between various types of diabetes and defining their subtypes are major challenges hindering the precise treatment of the disease. T2D is the main type of diabetes in humans as well as the most heterogeneous. Fortunately, some studies have shown that variants of certain genes involved in monogenic diabetes also increase the risk of T2D. We hope this finding will enable breakthroughs regarding the pathogenesis of T2D and facilitate personalized treatment of the disease by exploring the function of the signal genes involved. Hepatocyte nuclear factor 1 homeobox A (HNF1α) is widely expressed in pancreatic β cells, the liver, the intestines, and other organs. HNF1α is highly polymorphic, but lacks a mutation hot spot. Mutations can be found at any site of the gene. Some single nucleotide polymorphisms (SNPs) cause maturity-onset diabetes of the young type 3 (MODY3) while some others do not cause MODY3 but increase the susceptibility to T2D or GDM. The phenotypes of MODY3 caused by different SNPs also differ. MODY3 is among the most common types of MODY, which is a form of monogenic diabetes mellitus caused by a single gene mutation. Both T2D and GDM are multifactorial diseases caused by both genetic and environmental factors. Different types of diabetes mellitus have different clinical phenotypes and treatments. This review focuses on HNF1α gene polymorphisms, HNF1A-MODY3, HNF1A-associated T2D and GDM, and the related pathogenesis and treatment methods. We hope this review will provide a valuable reference for the precise and individualized treatment of diabetes caused by abnormal HNF1α by summarizing the clinical heterogeneity of blood glucose abnormalities caused by HNF1α mutation.

Whole Genome DNA Methylation Variations in Mammary Gland Tissues from Holstein Cattle Producing Milk with Various Fat and Protein Contents

Milk fat and protein contents are among key elements of milk quality, and they are attracting more attention in response to consumers' demand for high-quality dairy products. To investigate the potential regulatory roles of DNA methylation underlying milk component yield, whole genome bisulfite sequencing was employed to profile the global DNA methylation patterns of mammary gland tissues from 17 Canada Holstein cows with various milk fat and protein contents. A total of 706, 2420 and 1645 differentially methylated CpG sites (DMCs) were found between high vs. low milk fat (HMF vs. LMF), high vs. low milk protein (HMP vs. LMP), and high vs. low milk fat and protein (HMFP vs. LMFP) groups, respectively (q value < 0.1). Twenty-seven, 56 and 67 genes harboring DMCs in gene regions (denoted DMC genes) were identified for HMF vs. LMF, HMP vs. LMP and HMFP vs. LMFP, respectively. DMC genes from HMP vs. LMP and HMFP vs. LMFP comparisons were significantly overrepresented in GO terms related to aerobic electron transport chain and/or mitochondrial ATP (adenosine triphosphate) synthesis coupled electron transport. A total of 83 (HMF vs. LMF), 708 (HMP vs. LMP) and 408 (HMFP vs. LMFP) DMCs were co-located with 87, 147 and 158 quantitative trait loci (QTL) for milk component and yield traits, respectively. In conclusion, the identified methylation changes are potentially involved in the regulation of milk fat and protein yields, as well as the variation in reported co-located QTLs.

MP3RNA-seq: Massively parallel 3' end RNA sequencing for high-throughput gene expression profiling and genotyping

Transcriptome deep sequencing (RNA-seq) has become a routine method for global gene expression profiling. However, its application to large-scale experiments remains limited by cost and labor constraints. Here we describe a massively parallel 3' end RNA-seq (MP3RNA-seq) method that introduces unique sample barcodes during reverse transcription to permit sample pooling immediately following this initial step. MP3RNA-seq allows for handling of hundreds of samples in a single experiment, at a cost of about $6 per sample for library construction and sequencing. MP3RNA-seq is effective for not only high-throughput gene expression profiling, but also genotyping. To demonstrate its utility, we applied MP3RNA-seq to 477 double haploid lines of maize. We identified 19,429 genes expressed in at least 50% of the lines and 35,836 high-quality single nucleotide polymorphisms for genotyping analysis. Armed with these data, we performed expression and agronomic trait quantitative trait locus (QTL) mapping and identified 25,797 expression QTLs for 15,335 genes and 21 QTLs for plant height, ear height, and relative ear height. We conclude that MP3RNA-seq is highly reproducible, accurate, and sensitive for high-throughput gene expression profiling and genotyping, and should be generally applicable to most eukaryotic species.

RNA-Seq Data for Reliable SNP Detection and Genotype Calling: Interest for Coding Variant Characterization and Cis-Regulation Analysis by Allele-Specific Expression in Livestock Species

In addition to their common usages to study gene expression, RNA-seq data accumulated over the last 10 years are a yet-unexploited resource of SNPs in numerous individuals from different populations. SNP detection by RNA-seq is particularly interesting for livestock species since whole genome sequencing is expensive and exome sequencing tools are unavailable. These SNPs detected in expressed regions can be used to characterize variants affecting protein functions, and to study cis-regulated genes by analyzing allele-specific expression (ASE) in the tissue of interest. However, gene expression can be highly variable, and filters for SNP detection using the popular GATK toolkit are not yet standardized, making SNP detection and genotype calling by RNA-seq a challenging endeavor. We compared SNP calling results using GATK suggested filters, on two chicken populations for which both RNA-seq and DNA-seq data were available for the same samples of the same tissue. We showed, in expressed regions, a RNA-seq precision of 91% (SNPs detected by RNA-seq and shared by DNA-seq) and we characterized the remaining 9% of SNPs. We then studied the genotype (GT) obtained by RNA-seq and the impact of two factors (GT call-rate and read number per GT) on the concordance of GT with DNA-seq; we proposed thresholds for them leading to a 95% concordance. Applying these thresholds to 767 multi-tissue RNA-seq of 382 birds of 11 chicken populations, we found 9.5 M SNPs in total, of which ∼550,000 SNPs per tissue and population with a reliable GT (call rate ≥ 50%) and among them, ∼340,000 with a MAF ≥ 10%. We showed that such RNA-seq data from one tissue can be used to (i) detect SNPs with a strong predicted impact on proteins, despite their scarcity in each population (16,307 SIFT deleterious missenses and 590 stop-gained), (ii) study, on a large scale, cis-regulations of gene expression, with ∼81% of protein-coding and 68% of long non-coding genes (TPM ≥ 1) that can be analyzed for ASE, and with ∼29% of them that were cis-regulated, and (iii) analyze population genetic using such SNPs located in expressed regions. This work shows that RNA-seq data can be used with good confidence to detect SNPs and associated GT within various populations and used them for different analyses as GTEx studies.

Mechanistic insights on nsSNPs on binding site of renin and cytochrome P450 proteins: A computational perceptual study for pharmacogenomics evaluation

Past several decades, therapeutic investigations lead to the discovery of numerous antihypertensive drugs. Although it has been proved for their potency, altered efficacy is common norms in several conditions due to genetic variations. Cytochrome P450 plays a crucial role in drug metabolism and responsible for the pharmacokinetic and pharmacodynamic properties of the drug molecules. Here, we report the deleterious point mutations in the genes associated with the altered response of antihypertensive drug molecules and their metabolizers. Missense variants were filtered as potential nonsynonymous single nucleotide polymorphisms among the available data for the target genes (REN, CYP2D6, CYP3A4). The key objective of the work is to identify the deleterious single nucleotide polymorphisms (SNPs) responsible for the drug response and metabolism for the application of personalized medication. The molecular docking studies revealed that Aliskiren and other clinically approved drug molecules have a high binding affinity with both wild and mutant structures of renin, CYP2D6, and CYP3A4 proteins. The docking (Glide XP) score was observed to have in the range of -8.896 to -11.693 kcal/mol. The molecular dynamics simulation studies were employed to perceive the structural changes and conformational deviation through various analyses. Each studied SNPs was observed to have disparate scoring in the binding affinity to the specific drug molecules. As a prospective plan, we assume this study might be applied to identify the risky SNPs associated with hypertension from the patients to recommend the suitable drug for personalized hypertensive treatment. Further, extensive clinical pharmacogenomics studies are required to support the findings.

Novel Structural Variation and Evolutionary Characteristics of Chloroplast tRNA in Gossypium Plants

Cotton is one of the most important fiber and oil crops in the world. Chloroplast genomes harbor their own genetic materials and are considered to be highly conserved. Transfer RNAs (tRNAs) act as "bridges" in protein synthesis by carrying amino acids. Currently, the variation and evolutionary characteristics of tRNAs in the cotton chloroplast genome are poorly understood. Here, we analyzed the structural variation and evolution of chloroplast tRNA (cp tRNA) based on eight diploid and two allotetraploid cotton species. We also investigated the nucleotide evolution of chloroplast genomes in cotton species. We found that cp tRNAs in cotton encoded 36 or 37 tRNAs, and 28 or 29 anti-codon types with lengths ranging from 60 to 93 nucleotides. Cotton chloroplast tRNA sequences possessed specific conservation and, in particular, the Ψ-loop contained the conserved U-U-C-X3-U. The cp tRNAs of Gossypium L. contained introns, and cp tRNA^Ile contained the anti-codon (C-A-U), which was generally the anti-codon of tRNA^Met. The transition and transversion analyses showed that cp tRNAs in cotton species were iso-acceptor specific and had undergone unequal rates of evolution. The intergenic region was more variable than coding regions, and non-synonymous mutations have been fixed in cotton cp genomes. On the other hand, phylogeny analyses indicated that cp tRNAs of cotton were derived from several inferred ancestors with greater gene duplications. This study provides new insights into the structural variation and evolution of chloroplast tRNAs in cotton plants. Our findings could contribute to understanding the detailed characteristics and evolutionary variation of the tRNA family.

SNP-Density Crossover Maps of Polymorphic Transposable Elements and HLA Genes Within MHC Class I Haplotype Blocks and Junction

The genomic region (~4 Mb) of the human major histocompatibility complex (MHC) on chromosome 6p21 is a prime model for the study and understanding of conserved polymorphic sequences (CPSs) and structural diversity of ancestral haplotypes (AHs)/conserved extended haplotypes (CEHs). The aim of this study was to use a set of 95 MHC genomic sequences downloaded from a publicly available BioProject database at NCBI to identify and characterise polymorphic human leukocyte antigen (HLA) class I genes and pseudogenes, MICA and MICB, and retroelement indels as haplotypic lineage markers, and single-nucleotide polymorphism (SNP) crossover loci in DNA sequence alignments of different haplotypes across the Olfactory Receptor (OR) gene region (~1.2 Mb) and the MHC class I region (~1.8 Mb) from the GPX5 to the MICB gene. Our comparative sequence analyses confirmed the identity of 12 haplotypic retroelement markers and revealed that they partitioned the HLA-A/B/C haplotypes into distinct evolutionary lineages. Crossovers between SNP-poor and SNP-rich regions defined the sequence range of haplotype blocks, and many of these crossover junctions occurred within particular transposable elements, lncRNA, OR12D2, MUC21, MUC22, PSORS1A3, HLA-C, HLA-B, and MICA. In a comparison of more than 250 paired sequence alignments, at least 38 SNP-density crossover sites were mapped across various regions from GPX5 to MICB. In a homology comparison of 16 different haplotypes, seven CEH/AH (7.1, 8.1, 18.2, 51.x, 57.1, 62.x, and 62.1) had no detectable SNP-density crossover junctions and were SNP poor across the entire ~2.8 Mb of sequence alignments. Of the analyses between different recombinant haplotypes, more than half of them had SNP crossovers within 10 kb of LTR16B/ERV3-16A3_I, MLT1, Charlie, and/or THE1 sequences and were in close vicinity to structurally polymorphic Alu and SVA insertion sites. These studies demonstrate that (1) SNP-density crossovers are associated with putative ancestral recombination sites that are widely spread across the MHC class I genomic region from at least the telomeric OR12D2 gene to the centromeric MICB gene and (2) the genomic sequences of MHC homozygous cell lines are useful for analysing haplotype blocks, ancestral haplotypic landscapes and markers, CPSs, and SNP-density crossover junctions.

Evaluating Genetic Diversity of Agaricus bisporus Accessions through Phylogenetic Analysis Using Single-Nucleotide Polymorphism (SNP) Markers

Agaricus bisporus, commonly known as the button mushroom, is widely cultivated throughout the world. To breed new strains with more desirable traits and improved adaptability, diverse germplasm, including wild accessions, is a valuable genetic resource. To better understand the genetic diversity available in A. bisporus and identify previously unknown diversity within accessions, a phylogenetic analysis of 360 Agaricus spp. accessions using single-nucleotide polymorphism genotyping was performed. Genetic relationships were compared using principal coordinate analysis (PCoA) among accessions with known origins and accessions with limited collection data. The accessions clustered into four groups based on the PCoA with regard to genetic relationships. A subset of 67 strains, which comprised a core collection where repetitive and uninformative accessions were not included, clustered into 7 groups following analysis. Two of the 170 accessions with limited collection data were identified as wild germplasm. The core collection allowed for the accurate analysis of A. bisporus genetic relationships, and accessions with an unknown pedigree were effectively grouped, allowing for origin identification, by PCoA analysis in this study.

Genetic variation in the chemokine receptor 5 gene and course of HIV infection; review on genetics and immunological aspect

Chemokines are small protein molecules associated with various physiological events precisely in immune modulation via chemokine receptors. The chemokine receptors are G-protein coupled receptors express mainly on the cell surface of immune cells. Retroviruses, including HIV in the early stage of infection, primarily target chemokines receptors and get internalized easily into immune cells; T cell and escape from immune surveillance. HIV glycoprotein selectively develops an affinity for the extracellular domain of chemokines receptors and allows the pathogen to internalize via CCR-5. Now, CCR-5 remains a crucial signaling pathway that can be translated into the therapeutic target by changing the receptor protein environment. Many populations have a mutation in coding and promoter regions of CCR-5, tuning a resistance for HIV infection. Natively, there are several mechanisms where the human genome remains in the dynamic state by changing its composition and acquiring variations. Single nucleotide polymorphism is spontaneous phenomenon responsible for precise and point mutation at the genome. Several studies have demonstrated that European and African American populations are enriched in significant CCR5 promoter SNP (CCR5Δ32) in the coding and promoter region as well. Now, such SNP can be an early-stage biomarker in studying HIV and other similar infections. Here, in this study, we have elucidated the role of SNP (both the promoter and coding region) and the fate of HIV infections. We also empathized with the genetics of such SNPs, mostly frequency and its immunological impact.

Association of PCSK1 gene polymorphisms with abdominal fat content in broilers

Protein proteolytic enzymes (Proprotein Convertase, PC) is a Ca²⁺ -dependent serine protease family, whose main function is to cleave precursors of biologically inactive proteins or peptide chains into active functional molecules. Proprotein convertase subtilisin/kexin type 1 (PCSK1) gene is mainly expressed in nerve and endocrine tissues. In this study, PCSK1 was selected as an important candidate gene for abdominal fat content in broilers. We cloned the exon region of chicken PCSK1 gene and found six single-nucleotide polymorphisms (SNPs). Association analysis was carried out and we found that the polymorphisms of these six SNPs were significantly associated with abdominal fat content in G19 and G20 populations. Five of these SNPs were significantly associated with abdominal fat content in G19 and G20 combined population. The polymorphism of these five SNPs was significantly correlated with the abdominal fat content of AA broilers. Together, our study demonstrated that c.927T>C, c.1880C>T, c.*900G>A, and c.*1164C>T were significantly associated with abdominal fat content in populations used in this study, which means that these SNPs in PCSK1 gene could be used as candidate markers to select lean broiler lines.

Whole genome detection of sequence and structural polymorphism in six diverse horses

The domesticated horse has played a unique role in human history, serving not just as a source of animal protein, but also as a catalyst for long-distance migration and military conquest. As a result, the horse developed unique physiological adaptations to meet the demands of both their climatic environment and their relationship with man. Completed in 2009, the first domesticated horse reference genome assembly (EquCab 2.0) produced most of the publicly available genetic variations annotations in this species. Yet, there are around 400 geographically and physiologically diverse breeds of horse. To enrich the current collection of genetic variants in the horse, we sequenced whole genomes from six horses of six different breeds: an American Miniature, a Percheron, an Arabian, a Mangalarga Marchador, a Native Mongolian Chakouyi, and a Tennessee Walking Horse, and mapped them to EquCab3.0 genome. Aside from extreme contrasts in body size, these breeds originate from diverse global locations and each possess unique adaptive physiology. A total of 1.3 billion reads were generated for the six horses with coverage between 15x to 24x per horse. After applying rigorous filtration, we identified and functionally annotated 17,514,723 Single Nucleotide Polymorphisms (SNPs), and 1,923,693 Insertions/Deletions (INDELs), as well as an average of 1,540 Copy Number Variations (CNVs) and 3,321 Structural Variations (SVs) per horse. Our results revealed putative functional variants including genes associated with size variation like LCORL gene (found in all horses), ZFAT in the Arabian, American Miniature and Percheron horses and ANKRD1 in the Native Mongolian Chakouyi horse. We detected a copy number variation in the Latherin gene that may be the result of evolutionary selection impacting thermoregulation by sweating, an important component of athleticism and heat tolerance. The newly discovered variants were formatted into user-friendly browser tracks and will provide a foundational database for future studies of the genetic underpinnings of diverse phenotypes within the horse.

The domesticated horse played a unique role in human history, serving not just as a source of dietary animal protein, but also as a catalyst for long-distance migration and military conquest. As a result, the horse developed unique physiological adaptations to meet the demands of both their climatic environment and their relationship with man. Although the completion of the horse reference genome allowed for the discovery of many genetic variants, the remarkable diversity across breeds of horse calls for additional effort to quantify the complete span of genetic polymorphism within this unique species. In this work, we present genome re-sequencing and variant detection analysis for six horses belonging to six different breeds representing different morphology, origins and vary in their physiological demands and response. We identified and annotated not just single nucleotide polymorphisms (SNPs), but also insertions and deletions (INDELs), copy number variations (CNVs) and structural variations (SVs). Our results illustrate novel sources of polymorphism and highlight potentially impactful variations for phenotypes of body size and conformation. We also detected a copy number loss in the Latherin gene that could be the result of an evolutionary selection affecting thermoregulation through sweating. Our newly discovered variants were formatted into easy-to-use tracks that can be easily accessed by researchers around the globe.

SNP Diversity in CD14 Gene Promoter Suggests Adaptation Footprints in Trypanosome Tolerant N'Dama (Bos taurus) but not in Susceptible White Fulani (Bos indicus) Cattle

Immune response to infections has been shown to be mediated by genetic diversity in pattern recognition receptors, leading to disease tolerance or susceptibility. We elucidated naturally occurring variations within the bovine CD14 gene promoter in trypanosome-tolerant (N'Dama) and susceptible (White Fulani) cattle, with genomic and computational approaches. Blood samples were collected from White Fulani and N'Dama cattle, genomic DNA extracted and the entire promoter region of the CD14 gene amplified by PCR. We sequenced this region and performed in silico computation to identify SNP variants, transcription factor binding sites, as well as micro RNAs in the region. CD14 promoter sequences were compared with the reference bovine genome from the Ensembl database to identify various SNPs. Furthermore, we validated three selected N'Dama specific SNPs using custom Taqman SNP genotyping assay for genetic diversity. In all, we identified a total of 54 and 41 SNPs at the CD14 promoter for N'Dama and White Fulani respectively, including 13 unique SNPs present in N'Dama only. The significantly higher SNP density at the CD14 gene promoter region in N'Dama may be responsible for disease tolerance, possibly an evolutionary adaptation. Our genotype analysis of the three loci selected for validation show that mutant alleles (A/A, C/C, and A/A) were adaptation profiles within disease tolerant N'Dama. A similar observation was made for our haplotype analysis revealing that haplotypes H1 (ACA) and H2 (ACG) were significant combinations within the population. The SNP effect prediction revealed 101 and 89 new transcription factor binding sites in N'Dama and White Fulani, respectively. We conclude that disease tolerant N'Dama possessing higher SNP density at the CD14 gene promoter and the preponderance of mutant alleles potentially confirms the significance of this promoter in immune response, which is lacking in susceptible White Fulani. We, therefore, recommend further in vitro and in vivo study of this observation in infected animals, as the next step for understanding genetic diversity relating to varying disease phenotypes in both breeds.

Genetic variants of TSPAN12 gene in patients with retinopathy of prematurity

Genetic susceptibility to retinopathy of prematurity (ROP) has been reported. However, no virulence genes are currently known for ROP. This study aimed to assess FZD4, LRP5, TSPAN12, and NDP, which are known virulence genes involved in familial exudative vitreoretinopathy, an ailment that shares some symptoms with ROP. After approval from the parents of diseased infants, blood samples from 29 Han patients with ROP were collected for genomic DNA extraction. Direct sequencing was used to assess the four candidate genes, namely FZD4, LRP5, TSPAN12, and NDP. Finally, genetic mutations were screened. Changes of three nucleotide sequences were found in the four candidate genes; notably, a c.954G>A hybrid mutation in the TSPAN12 gene was predicted to cause protein structure and function alterations. The molecular pathogenesis of ROP is complex, and likely involves the c.954G>A mutation in TSPAN12.

Gene expression variation and parental allele inheritance in a Xiphophorus interspecies hybridization model

Understanding the genetic mechanisms underlying segregation of phenotypic variation through successive generations is important for understanding physiological changes and disease risk. Tracing the etiology of variation in gene expression enables identification of genetic interactions, and may uncover molecular mechanisms leading to the phenotypic expression of a trait, especially when utilizing model organisms that have well-defined genetic lineages. There are a plethora of studies that describe relationships between gene expression and genotype, however, the idea that global variations in gene expression are also controlled by genotype remains novel. Despite the identification of loci that control gene expression variation, the global understanding of how genome constitution affects trait variability is unknown. To study this question, we utilized Xiphophorus fish of different, but tractable genetic backgrounds (inbred, F₁ interspecies hybrids, and backcross hybrid progeny), and measured each individual’s gene expression concurrent with the degrees of inter-individual expression variation. We found, (a) F₁ interspecies hybrids exhibited less variability than inbred animals, indicting gene expression variation is not affected by the fraction of heterozygous loci within an individual genome, and (b), that mixing genotypes in backcross populations led to higher levels of gene expression variability, supporting the idea that expression variability is caused by heterogeneity of genotypes of cis or trans loci. In conclusion, heterogeneity of genotype, introduced by inheritance of different alleles, accounts for the largest effects on global phenotypical variability.

Phenotypical variability is a multi-factorial phenomenon. Although it has been shown that inheriting certain gene is associated with lower phenotypical variability, how genome complexity affect phenotypical variability is still unclear. To study this question, we used inbred Xiphophorus fish, backcross interspecies hybrids, and F₁ interspecies hybrids between select Xiphophorus species to model genetic composition with minimum, medium, and maximum heterozygosity respectively, and measured their global gene expression variability. We found gene expression variation is not affected by the percentage of heterozygous loci in individual genome, but instead related to heterogeneity of genotype at local or remote loci.

Evidence of evolutionary history and selective sweeps in the genome of Meishan pig reveals its genetic and phenotypic characterization

Background

Meishan is a pig breed indigenous to China and famous for its high fecundity. The traits of Meishan are strongly associated with its distinct evolutionary history and domestication. However, the genomic evidence linking the domestication of Meishan pigs with its unique features is still poorly understood. The goal of this study is to investigate the genomic signatures and evolutionary evidence related to the phenotypic traits of Meishan via large-scale sequencing.

Results

We found that the unique domestication of Meishan pigs occurred in the Taihu Basin area between the Majiabang and Liangzhu Cultures, during which 300 protein-coding genes have underwent positive selection. Notably, enrichment of the FoxO signaling pathway with significant enrichment signal and the harbored gene IGF1R were likely associated with the high fertility of Meishan pigs. Moreover, NFKB1 exhibited strong selective sweep signals and positively participated in hyaluronan biosynthesis as the key gene of NF-kB signaling, which may have resulted in the wrinkled skin and face of Meishan pigs. Particularly, three population-specific synonymous single-nucleotide variants occurred in PYROXD1, MC1R, and FAM83G genes; the T305C substitution in the MCIR gene explained the black coat of the Meishan pigs well. In addition, the shared haplotypes between Meishan and Duroc breeds confirmed the previous Asian-derived introgression and demonstrated the specific contribution of Meishan pigs.

Conclusions

These findings will help us explain the unique genetic and phenotypic characteristics of Meishan pigs and offer a plausible method for their utilization of Meishan pigs as valuable genetic resources in pig breeding and as an animal model for human wrinkled skin disease research.

Haplotyping of Heterozygous SNPs in Genomic DNA Using Long-Range PCR

To study meiotic recombination products, cis- or trans-association of disease polymorphisms, or allele-specific expression patterns, it is necessary to phase heterozygous polymorphisms separated by several kilobases. Haplotyping using long-range polymerase chain reaction (PCR) is a powerful, cost-effective method to directly obtain the phase of multiple heterozygous sites with standard laboratory equipment in a handful of loci for many samples. The method is based on the amplification of large genomic DNA regions (up to ~40 kb) with a reaction mixture that combines a proofreading polymerase with allele-specific primer pairs that preferentially amplify matched templates. The analysis of two heterozygous SNPs requires four reactions, each containing one of the four possible allele-specific primer combinations (two forward and two reverse primers), with the mismatches occurring at the 3' ends of the primers. The two correct primer combinations will more efficiently elongate the matching alleles than the alternative alleles, and the difference in amplification efficiency can be monitored with real-time PCR.

Polymorphism related to cardiovascular risk in hemodialysis subjects: a systematic review

Cardiovascular disease (CVD) is one of the leading causes of mortality in hemodialysis (HD) subjects. In addition to the traditional risk factors that are common in these individuals, genetic factors are also involved, with emphasis on single nucleotide polymorphs (SNPs). In this context, the present study aims to systematically review the studies that investigated the polymorphisms associated with cardiovascular risk in this population. In general, the SNPs present in HD individuals are those of genes related to inflammation, oxidative stress and vascular calcification, also able of interfering in the cardiovascular risk of this population. In addition, polymorphisms in genes related to recognized risk factors for CVD, such as dyslipidemia, arterial hypertension and left ventricular hypertrophy, also influence cardiovascular morbidity and mortality.

Comparative assessment of SSR and SNP markers for inferring the population genetic structure of the common fungus Armillaria cepistipes

During the last years, simple sequence repeats (SSRs, also known as microsatellites) and single-nucleotide polymorphisms (SNPs) have become the most popular molecular markers for describing neutral genetic variation in populations of a wide range of organisms. However, only a limited number of studies has focused on comparing the performance of these two types of markers for describing the underlying genetic structure of wild populations. Moreover, none of these studies targeted fungi, the group of organisms with one of the most complex reproductive strategies. We evaluated the utility of SSRs and SNPs for inferring the neutral genetic structure of Armillaria cepistipes (basidiomycetes) at different spatial scales. For that, 407 samples were collected across a small (150 km²) area in the Ukrainian Carpathians and a large (41 000 km²) area in the Swiss Alps. All isolates were analyzed at 17 SSR loci distributed throughout the whole genome and at 24 SNP loci located in different single-copy conserved genes. The two markers showed different patterns of structure within the two spatial scales studied. The multi-allelic SSR markers seemed to be best suited for detecting genetic structure in indigenous fungal populations at a rather small spatial scale (radius of ~50-100 km). The pattern observed at SNP markers rather reflected ancient divergence of distant (~1000 km) populations that in addition are separated by mountain ranges. Despite these differences, both marker types were suitable for detecting the weak genetic structure of the two A. cepistipes populations investigated.

An evolutionary medicine perspective on Neandertal extinction

The Eurasian sympatry of Neandertals and anatomically modern humans - beginning at least 45,000 years ago and possibly lasting for more than 5000 years - has sparked immense anthropological interest into the factors that potentially contributed to Neandertal extinction. Among many different hypotheses, the "differential pathogen resistance" extinction model posits that Neandertals were disproportionately affected by exposure to novel infectious diseases that were transmitted during the period of spatiotemporal sympatry with modern humans. Comparisons of new archaic hominin paleogenome sequences with modern human genomes have confirmed a history of genetic admixture - and thus direct contact - between humans and Neandertals. Analyses of these data have also shown that Neandertal nuclear genome genetic diversity was likely considerably lower than that of the Eurasian anatomically modern humans with whom they came into contact, perhaps leaving Neandertal innate immune systems relatively more susceptible to novel pathogens. In this study, we compared levels of genetic diversity in genes for which genetic variation is hypothesized to benefit pathogen defense among Neandertals and African, European, and Asian modern humans, using available exome sequencing data (three individuals, or six chromosomes, per population). We observed that Neandertals had only 31-39% as many nonsynonymous (amino acid changing) polymorphisms across 73 innate immune system genes compared to modern human populations. We also found that Neandertal genetic diversity was relatively low in an unbiased set of balancing selection candidate genes for primates, those genes with the highest 1% genetic diversity genome-wide in non-human hominoids (apes). In contrast, Neandertals had similar or higher levels of genetic diversity than humans in 12 major histocompatibility complex (MHC) genes. Thus, while Neandertals may have been relatively more susceptible to some novel pathogens and differential pathogen resistance could be considered as one potential contributing factor in their extinction, the expectations of this model are not universally met.

Variations at regulatory regions of the milk protein genes are associated with milk traits and coagulation properties in the Sarda sheep

Regulatory variation at the ovine casein genes could have important effects on the composition and coagulation properties of milk. Herewith, we have partially resequenced the promoters and the 3'-UTR of the four casein genes in 25 Sarda sheep. Alignment of these sequences allowed us to identify a total of 29 SNPs. This level of polymorphism (one SNP every 250 bp) is remarkably high if compared with SNP densities estimated in human genic regions (approximately one SNP per bp). The 29 SNPs identified in our resequencing experiment, plus three previously reported SNPs mapping to the lactalbumin, alpha (LALBA) and β-lactoglobulin (BLG, also known as progestagen-associated endometrial protein, PAEP) genes, were genotyped with a multiplex TaqMan Open Array Real-Time PCR assay in 760 Sarda sheep with records for milk composition and coagulation properties. Association analysis revealed the existence of significant associations of CSN1S2 and CSN3 genotypes with milk protein and casein contents. Moreover, genotypes at CSN1S1 were significantly associated with rennet coagulation time, curd firming time and curd firmness, whereas CSN2 was associated with curd firming time. These results suggest that SNPs mapping to the promoters and 3'-UTRs of ovine casein genes may exert regulatory effects on gene expression and that they could be used for improving sheep milk quality and technological traits at the population level through marker assisted selection.

FetalQuantSD: accurate quantification of fetal DNA fraction by shallow-depth sequencing of maternal plasma DNA

Noninvasive prenatal testing using massively parallel sequencing of maternal plasma DNA has been rapidly adopted in clinical use worldwide. Fetal DNA fraction in a maternal plasma sample is an important parameter for accurate interpretations of these tests. However, there is a lack of methods involving low-sequencing depth and yet would allow a robust and accurate determination of fetal DNA fraction in maternal plasma for all pregnancies. In this study, we have developed a new method to accurately quantify the fetal DNA fraction by analysing the maternal genotypes and sequencing data of maternal plasma DNA. Fetal DNA fraction was calculated based on the proportion of non-maternal alleles at single-nucleotide polymorphisms where the mother is homozygous. This new approach achieves a median deviation of 0.6% between predicted fetal DNA fraction and the actual fetal DNA fraction using as low as 0.03-fold sequencing coverage of the human genome. We believe that this method will further enhance the clinical interpretations of noninvasive prenatal testing using genome-wide random sequencing.

Evaluating the impact of sequencing error correction for RNA-seq data with ERCC RNA spike-in controls

Sequencing errors are a major issue for several next-generation sequencing-based applications such as de novo assembly and single nucleotide polymorphism detection. Several error-correction methods have been developed to improve raw data quality. However, error-correction performance is hard to evaluate because of the lack of a ground truth. In this study, we propose a novel approach which using ERCC RNA spike-in controls as the ground truth to facilitate error-correction performance evaluation. After aligning raw and corrected RNA-seq data, we characterized the quality of reads by three metrics: mismatch patterns (i.e., the substitution rate of A to C) of reads aligned with one mismatch, mismatch patterns of reads aligned with two mismatches and the percentage increase of reads aligned to reference. We observed that the mismatch patterns for reads aligned with one mismatch are significantly correlated between ERCC spike-ins and real RNA samples. Based on such observations, we conclude that ERCC spike-ins can serve as ground truths for error correction beyond their previous applications for validation of dynamic range and fold-change response. Also, the mismatch patterns for ERCC reads aligned with one mismatch can serve as a novel and reliable metric to evaluate the performance of error-correction tools.

Role of +405C>G and +936C>T polymorphisms of the vascular endothelial growth factor gene and risk of esophageal cancer in the Kashmiri population

BACKGROUND

The gene for the vascular endothelial growth factor (VEGF), which promotes angiogenesis and permeability, is polymorphic. The aim of the present study was to evaluate the relationship between +936C>T and +404C>G polymorphism of VEGF with risk of esophageal cancer in the Kashmiri population in India.

MATERIALS AND METHODS

150 esophageal cancer patients and 150 unrelated healthy controls were genotyped for two VGEF SNPs (+405C/G, and +936C/T) using DNA extracted from prospectively collected blood samples by the PCR-RFLP method.

RESULTS

For the VEGF +936C>T polymorphism a significant association of CT and combined CT+TT genotypes was observed with increased risk of esophageal cancer (p=0.021; 0.024). For the +405C>G polymorphism we observed significantly increased frequency of GG genotype in cases as compared to controls and also the +405 GG Genotype was observed to have a two fold risk(OR=2.7356; 95%CI=1.1409- 6.5593; p=0.020). The combined genotypes of GG-CC and GG-CT of +405C>G and +936C>T were found to be significantly associated with increased risk of esophageal cancer (p=0.0376; 0.0099).

CONCLUSIONS

From the results of the present study a significant association of +936C>T and +405C>G polymorphisms with increased esophageal cancer risk exists in the Kashmiri population.

Signatures of selection in tilapia revealed by whole genome resequencing

Natural selection and selective breeding for genetic improvement have left detectable signatures within the genome of a species. Identification of selection signatures is important in evolutionary biology and for detecting genes that facilitate to accelerate genetic improvement. However, selection signatures, including artificial selection and natural selection, have only been identified at the whole genome level in several genetically improved fish species. Tilapia is one of the most important genetically improved fish species in the world. Using next-generation sequencing, we sequenced the genomes of 47 tilapia individuals. We identified a total of 1.43 million high-quality SNPs and found that the LD block sizes ranged from 10–100 kb in tilapia. We detected over a hundred putative selective sweep regions in each line of tilapia. Most selection signatures were located in non-coding regions of the tilapia genome. The Wnt signaling, gonadotropin-releasing hormone receptor and integrin signaling pathways were under positive selection in all improved tilapia lines. Our study provides a genome-wide map of genetic variation and selection footprints in tilapia, which could be important for genetic studies and accelerating genetic improvement of tilapia.

Allele frequency distribution of CYP2C19*2 allelic variants associated with clopidogrel resistance in cardiac patients

Drug resistance is a phenomenon that has become a critical issue in medical practice. Such is the case in the response to clopidogrel treatment, which is variable inter-individually and inter-ethnically due to genetic polymorphisms in the cytochrome P40 (CYP) gene. Clopidogrel is an anti-platelet agent administered to cardiac patients in the form of a prodrug, which is further metabolized into an active form by CYP enzymes. There are many allelic variants of the CYP gene that are involved in clopidogrel resistance, of which CYP2C19*2 has been demonstrated to be one of the most significant loss-of-function alleles. In the present study, 100 cardiac patients with percutaneous coronary intervention (PCI) or acute coronary syndrome (ACS) who were undergoing treatment with clopidogrel were selected and the patients were analyzed for CYP2C19*2 allelic variants using an allele-specific primer extension polymerase chain reaction method. The variant amplicons were visualized on gel and validated by Sanger sequencing. The observed allelic frequency distribution of CYP2C19*2 variants was 18% heterozygous for CYP2C19*2 A/C/G variants, 35% heterozygous for A/G variants, 13% heterozygous for C/G variants, 6% heterozygous for A/C variants, 7% homozygous for A variant, 5% homozygous for C variant and 16% homozygous for G wild-type. Furthermore, tri-allelic single nucleotide polymorphisms (SNPs) were identified in the CYP2C19*2 allele in cardiac patients for the first time, to the best of our knowledge; these were CYP2C19*2 A/C/G SNPs (18%). The overall frequency observed for new allelic variant C of CYP2C19*2 was 42%. These results suggested that there are significant inter-ethnic variations in the allelic frequencies of CYP2C19*2, which may be responsible for the variable clopidogrel response in cardiac patients.

Single nucleotide variations: biological impact and theoretical interpretation

Genome-wide association studies (GWAS) and whole-exome sequencing (WES) generate massive amounts of genomic variant information, and a major challenge is to identify which variations drive disease or contribute to phenotypic traits. Because the majority of known disease-causing mutations are exonic non-synonymous single nucleotide variations (nsSNVs), most studies focus on whether these nsSNVs affect protein function. Computational studies show that the impact of nsSNVs on protein function reflects sequence homology and structural information and predict the impact through statistical methods, machine learning techniques, or models of protein evolution. Here, we review impact prediction methods and discuss their underlying principles, their advantages and limitations, and how they compare to and complement one another. Finally, we present current applications and future directions for these methods in biological research and medical genetics.

Association of +405C>G and +936C>T polymorphisms of the vascular endothelial growth factor gene with sporadic breast cancer in North Indians

BACKGROUND

Vascular endothelial growth factor (VEGF), an endothelial cell specific mitogen, has been implicated as a critical factor influencing tumor related angiogenesis. The aim of present study was to evaluate the relationship between VEGF +936C>T and +405C>G polymorphisms of VEGF with risk of breast cancer in Punjab, India.

MATERIALS AND METHODS

We screened DNA samples of 192 sporadic breast cancer patients and 192 unrelated healthy, gender and age matched control individuals for VEGF +936C>T and +405C>G polymorphisms using the PCR-RFLP method.

RESULTS

For the VEGF +405C>G polymorphism, we observed significantly increased frequency of GG genotype in cases as compared to controls and strong association of +405GG genotype was observed with three fold risk for breast cancer (OR=3.07; 95%CI 1.41-6.65; p=0.003). For the +936C>T polymorphism, significant associations of CT and combined CT+TT genotypes were observed with elevated risk of breast cancer (p=0.021; 0.023). The combined genotype combinations of GG-CC and GG- CT of +405C>G and +936C>T polymorphisms were found to be significantly associated with increased risk of breast cancer (p=0.04; 0.0064).

CONCLUSIONS

The findings of the present study indicated significant associations of VEGF +936C>T and +405C>G polymorphisms with increased breast cancer risk in patients from Punjab, North India.

SNP-guided identification of monoallelic DNA-methylation events from enrichment-based sequencing data

Monoallelic gene expression is typically initiated early in the development of an organism. Dysregulation of monoallelic gene expression has already been linked to several non-Mendelian inherited genetic disorders. In humans, DNA-methylation is deemed to be an important regulator of monoallelic gene expression, but only few examples are known. One important reason is that current, cost-affordable truly genome-wide methods to assess DNA-methylation are based on sequencing post-enrichment. Here, we present a new methodology based on classical population genetic theory, i.e. the Hardy–Weinberg theorem, that combines methylomic data from MethylCap-seq with associated SNP profiles to identify monoallelically methylated loci. Applied on 334 MethylCap-seq samples of very diverse origin, this resulted in the identification of 80 genomic regions featured by monoallelic DNA-methylation. Of these 80 loci, 49 are located in genic regions of which 25 have already been linked to imprinting. Further analysis revealed statistically significant enrichment of these loci in promoter regions, further establishing the relevance and usefulness of the method. Additional validation was done using both 14 whole-genome bisulfite sequencing data sets and 16 mRNA-seq data sets. Importantly, the developed approach can be easily applied to other enrichment-based sequencing technologies, like the ChIP-seq-based identification of monoallelic histone modifications.

DNA clustering and genome complexity

Early global measures of genome complexity (power spectra, the analysis of fluctuations in DNA walks or compositional segmentation) uncovered a high degree of complexity in eukaryotic genome sequences. The main evolutionary mechanisms leading to increases in genome complexity (i.e. gene duplication and transposon proliferation) can all potentially produce increases in DNA clustering. To quantify such clustering and provide a genome-wide description of the formed clusters, we developed GenomeCluster, an algorithm able to detect clusters of whatever genome element identified by chromosome coordinates. We obtained a detailed description of clusters for ten categories of human genome elements, including functional (genes, exons, introns), regulatory (CpG islands, TFBSs, enhancers), variant (SNPs) and repeat (Alus, LINE1) elements, as well as DNase hypersensitivity sites. For each category, we located their clusters in the human genome, then quantifying cluster length and composition, and estimated the clustering level as the proportion of clustered genome elements. In average, we found a 27% of elements in clusters, although a considerable variation occurs among different categories. Genes form the lowest number of clusters, but these are the longest ones, both in bp and the average number of components, while the shortest clusters are formed by SNPs. Functional and regulatory elements (genes, CpG islands, TFBSs, enhancers) show the highest clustering level, as compared to DNase sites, repeats (Alus, LINE1) or SNPs. Many of the genome elements we analyzed are known to be composed of clusters of low-level entities. In addition, we found here that the clusters generated by GenomeCluster can be in turn clustered into high-level super-clusters. The observation of 'clusters-within-clusters' parallels the 'domains within domains' phenomenon previously detected through global statistical methods in eukaryotic sequences, and reveals a complex human genome landscape dominated by hierarchical clustering.

Vascular endothelial growth factor (VEGF) gene polymorphisms and breast cancer risk in Punjabi population from North West India

The purpose of this study was to evaluate the association of seven VEGF promoter polymorphisms with breast cancer risk in Punjabi population from North West India. We screened DNA samples of 102 sporadic breast cancer patients and 102 unrelated healthy, gender, and age-matched individuals for seven VEGF promoter polymorphisms [-417 C/T (rs833062), -172 C/A (rs59260042), -165 C/T (rs79469752), -160 C/T, -152 G/A (rs13207351), -141 A/C (rs28357093) and -116 G/A (rs1570360)] by direct sequencing. The frequency of GG, GA, and AA genotype of -152 G/A polymorphism was 26.47 vs 38.34%, 46.08 vs 51.96%, and 27.45 vs 9.80%, in patients and controls, respectively. VEGF -152 AA genotype was significantly associated with increased risk for breast cancer (OR = 4.04, 95%CI, 1.69-9.68, p = 0.001; recessive model OR = 3.48, 95%CI, 1.59-7.63, p = 0.001). For VEGF -116 G/A polymorphism, G and A allele frequencies were 65.2 vs 76.47% and 34.8 vs 23.53% in patients and controls, respectively. Individuals having -116 AA genotype (OR = 3.40; 95%CI, 1.24-9.37; p = 0.014) and A allele (OR = 1.73; 95%CI, 1.12-2.67; p = 0.012) were associated with increased risk for breast cancer. VEGF -165 C/T and -141 A/C polymorphisms were associated with reduced risk for breast cancer. There was significantly decreased frequency of CT genotype (4.90 vs 18.63%; p = 0.002) and T allele (2.45 vs 9.31%; p = 0.003) of -165 C/T polymorphism among breast cancer patients as compared to controls. VEGF -141 A and C allele frequency were 96.57 vs 91.18% and 3.43 vs 8.82% in patients and controls, respectively. Significant reduced risk for breast cancer was observed with AC genotype (OR = 0.34, 95%CI, 0.14-0.86; p = 0.019) and C allele (OR = 0.37; 95%CI, 0.15-0.89; p = 0.023) of -141 A/C polymorphism. We did not observe association of VEGF -417 T/C, -172 C/A, -160 C/T polymorphisms with breast cancer risk in the studied subjects (p > 0.05). The VEGF -152 G/A and -116 G/A polymorphisms were found to be significantly associated with increased risk for breast cancer while -165 C/T and -141 A/C polymorphisms were found to be associated with decreased risk for breast cancer in Punjabi population from North West India.

Prevalent RNA recognition motif duplication in the human genome

The sequence-specific recognition of RNA by proteins is mediated through various RNA binding domains, with the RNA recognition motif (RRM) being the most frequent and present in >50% of RNA-binding proteins (RBPs). Many RBPs contain multiple RRMs, and it is unclear how each RRM contributes to the binding specificity of the entire protein. We found that RRMs within the same RBP (i.e., sibling RRMs) tend to have significantly higher similarity than expected by chance. Sibling RRM pairs from RBPs shared by multiple species tend to have lower similarity than those found only in a single species, suggesting that multiple RRMs within the same protein might arise from domain duplication followed by divergence through random mutations. This finding is exemplified by a recent RRM domain duplication in DAZ proteins and an ancient duplication in PABP proteins. Additionally, we found that different similarities between sibling RRMs are associated with distinct functions of an RBP and that the RBPs tend to contain repetitive sequences with low complexity. Taken together, this study suggests that the number of RBPs with multiple RRMs has expanded in mammals and that the multiple sibling RRMs may recognize similar target motifs in a cooperative manner.

Gene-level integrated metric of negative selection (GIMS) prioritizes candidate genes for nephrotic syndrome

Nephrotic syndrome (NS) gene discovery efforts are now occurring in small kindreds and cohorts of sporadic cases. Power to identify causal variants in these groups beyond a statistical significance threshold is challenging due to small sample size and/or lack of family information. There is a need to develop novel methods to identify NS-associated variants. One way to determine putative functional relevance of a gene is to measure its strength of negative selection, as variants in genes under strong negative selection are more likely to be deleterious. We created a gene-level, integrated metric of negative selection (GIMS) score for 20,079 genes by combining multiple comparative genomics and population genetics measures. To understand the utility of GIMS for NS gene discovery, we examined this score in a diverse set of NS-relevant gene sets. These included genes known to cause monogenic forms of NS in humans as well as genes expressed in the cells of the glomerulus and, particularly, the podocyte. We found strong negative selection in the following NS-relevant gene sets: (1) autosomal-dominant Mendelian focal segmental glomerulosclerosis (FSGS) genes (p= 0.03 compared to reference), (2) glomerular expressed genes (p = 4×10^-23), and (3) predicted podocyte genes (p = 3×10^-9). Eight genes causing autosomal dominant forms of FSGS had a stronger combined score of negative selection and podocyte enrichment as compared to all other genes (p=1 x 10^-3). As a whole, recessive FSGS genes were not enriched for negative selection. Thus, we also created a transcript-level, integrated metric of negative selection (TIMS) to quantify negative selection on an isoform level. These revealed transcripts of known autosomal recessive disease-causing genes that were nonetheless under strong selection. We suggest that a filtering strategy that includes measuring negative selection on a gene or isoform level could aid in identifying NS-related genes. Our GIMS and TIMS scores are available at http://glom.sph.umich.edu/GIMS/.