Selection for translation efficiency on synonymous polymorphisms in recent human evolution

Assessing Mechanisms of Potential Local Adaptation Through a Seascape Genomic Approach in a Marine Gastropod, Littoraria flava

Understanding the combined effects of environmental heterogeneity and evolutionary processes on marine populations is a primary goal of seascape genomic approaches. Here, we utilized genomic approaches to identify local adaptation signatures in Littoraria flava, a widely distributed marine gastropod in the tropical West Atlantic population. We also performed molecular evolution analyses to investigate potential selective signals across the genome. After obtaining 6,298 and 16,137 single nucleotide polymorphisms derived from genotyping-by-sequencing and RNA sequencing, respectively, 69 from genotyping-by-sequencing (85 specimens) and four from RNA sequencing (40 specimens) candidate single nucleotide polymorphisms were selected and further evaluated. The correlation analyses support different evolutionary pressures over transcribed and non-transcribed regions. Thus, single nucleotide polymorphisms within transcribed regions could account for the genotypic and possibly phenotypic divergences in periwinkles. Our molecular evolution tests based on synonymous and non-synonymous ratio (kN/kS) showed that genotype divergences containing putative adaptive single nucleotide polymorphisms arose mainly from synonymous and/or UTR substitutions rather than polymorphic proteins. The distribution of genotypes across different localities seems to be influenced by marine currents, pH, and temperature variations, suggesting that these factors may impact the species dispersion. The combination of RNA sequencing and genotyping-by-sequencing derived datasets provides a deeper understanding of the molecular mechanisms underlying selective forces responses on distinct genomic regions and could guide further investigations on seascape genomics for non-model species.

Detection of two SNPs of the LIPE gene in Holstein-Friesian cows with divergent milk production

The LIPE gene (lipase E, hormone-sensitive type), also known as hormone-sensitive lipase, acts as a primary regulator of lipid metabolism during lactation in cows. We studied a total of two hundred Holstein-Friesian cows and performed sequencing analysis that revealed two synonymous nucleotide changes within the LIPE gene: a transition change, c.276 T > C in exon 2 (g.50631651 T > C; position 351 of GenBank: ON638900) and a transversion change, c.219C > A in exon 6 (g.50635369C > A; position 1070 of GenBank: ON638901). The observed genotypes were TC and CC for the c.276 T > C SNP and CC and CA for the c.219C > A SNP. Notably, the heterozygous TC genotype of the T351C SNP exhibited a significant association with high milk yield. Furthermore, the T351C SNP displayed significant associations with various milk parameters, including temperature, freezing point, density and the percentages of fat, protein, lactose, solids and solids-not-fat, with the homozygous CC genotype showing higher values. The c.219C > A SNP also demonstrated a significant association with milk composition, with heterozygous genotypes (CA) exhibiting higher percentages of fat, protein, and lactose compared to homozygous genotypes (CC). This effect was consistent among both high and low milk producers for fat and lactose percentages, while high milk producers exhibited a higher protein percentage than low milk producers. These findings highlight the importance of considering the detected SNPs in marker-assisted selection and breeding programs for the identification of high milk-producing Holstein-Friesian cows and potentially other breeds. Moreover, this study strongly supports the fundamental role of the LIPE gene in milk production and composition in lactating animals.

Influence of FMO3 and CYP3A4 Polymorphisms on the Pharmacokinetics of Teneligliptin in Humans

Teneligliptin, a dipeptidyl peptidase-4 inhibitor, is used to treat type 2 diabetes mellitus. FMO3 and CYP3A4 metabolize teneligliptin into teneligliptin sulfoxide. This study examined the effects of FMO3 (rs909530, rs1800822, rs2266780, and rs2266782) and CYP3A4 (rs2242480) polymorphisms on teneligliptin pharmacokinetics at a steady state among 23 healthy participants administered 20 mg teneligliptin daily for 6 days. Subjects with FMO3 rs909530, rs2266780, and rs2266782 polymorphisms exhibited a significant gene dosage-dependent increase in maximum steady-state plasma drug concentration (Cmax,ss) and area under the drug concentration vs time curve (AUC) (p<0.05). However, the Cmax values significantly decreased but the AUC values did not significantly vary in subjects with CYP3A4 polymorphism (rs2242480). These results suggest that FMO3 and CYP3A4 polymorphisms affect teneligliptin pharmacokinetics in humans. The findings of this study provide a scientific basis for the inter-individual variation in teneligliptin disposition.

A novel age-informed approach for genetic association analysis in Alzheimer's disease

BACKGROUND

Many Alzheimer's disease (AD) genetic association studies disregard age or incorrectly account for it, hampering variant discovery.

METHODS

Using simulated data, we compared the statistical power of several models: logistic regression on AD diagnosis adjusted and not adjusted for age; linear regression on a score integrating case-control status and age; and multivariate Cox regression on age-at-onset. We applied these models to real exome-wide data of 11,127 sequenced individuals (54% cases) and replicated suggestive associations in 21,631 genotype-imputed individuals (51% cases).

RESULTS

Modeling variable AD risk across age results in 5-10% statistical power gain compared to logistic regression without age adjustment, while incorrect age adjustment leads to critical power loss. Applying our novel AD-age score and/or Cox regression, we discovered and replicated novel variants associated with AD on KIF21B, USH2A, RAB10, RIN3, and TAOK2 genes.

CONCLUSION

Our AD-age score provides a simple means for statistical power gain and is recommended for future AD studies.

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.

Polymorphisms in Glycolysis-Related Genes Are Associated with Clinical Outcomes of Paclitaxel-Cisplatin Chemotherapy in Non-Small Cell Lung Cancer

OBJECTIVE

This study was conducted to investigate whether polymorphisms in glycolysis-related genes are associated with clinical outcomes of patients with advanced-stage non-small cell lung cancer (NSCLC) undergoing chemotherapy.

METHODS

A total of 377 patients with NSCLC were enrolled. Sixty-five single-nucleotide polymorphisms in 26 genes involved in the glycolytic pathway were evaluated. The associations of the variants with the chemotherapy response and overall survival (OS) were analyzed.

RESULTS

Among the 65 variants investigated, PFKL rs2073436C>G and GPI rs7248411C>G significantly correlated with clinical outcomes after chemotherapy in multivariate analyses. PFKL rs2073436C>G was significantly associated with both a worse response to chemotherapy (adjusted odds ratio [aOR] = 0.64, 95% CI = 0.45-0.90, p = 0.01) and a worse OS (adjusted hazard ratio [aHR] = 1.35, 95% CI = 1.14-1.61, p = 0.001). GPI rs7248411C>G was significantly associated with both a better chemotherapy response (aOR = 1.58, 95% CI = 1.07-2.23, p = 0.02) and a better OS (aHR = 0.80, 95% CI = 0.66-0.98, p = 0.03). When stratified by tumor histology, PFKL rs2073436C>G was significantly associated with OS only in squamous cell carcinoma, whereas GPI rs7248411C>G exhibited a significant association with the chemotherapy response and OS only in adenocarcinoma.

CONCLUSION

This result suggests that the PFKL rs2073436C>G and GPI rs7248411C>G are useful for predicting the clinical outcome of first-line paclitaxel-cisplatin chemotherapy in NSCLC.

Trace amine-associated receptor gene polymorphism increases drug craving in individuals with methamphetamine dependence

BACKGROUND

Methamphetamine (MA) is a potent agonist at the trace amine-associated receptor 1 (TAAR1). This study evaluated a common variant (CV) in the human TAAR1 gene, synonymous single nucleotide polymorphism (SNP) V288V, to determine the involvement of TAAR1 in MA dependence.

METHODS

Participants (n = 106) with active MA dependence (MA-ACT), in remission from MA dependence (MA-REM), with active polysubstance dependence, in remission from polysubstance dependence, and with no history of substance dependence completed neuropsychiatric symptom questionnaires and provided blood samples. In vitro expression and function of CV and wild type TAAR1 receptors were also measured.

RESULTS

The V288V polymorphism demonstrated a 40% increase in TAAR1 protein expression in cell culture, but message sequence and protein function were unchanged, suggesting an increase in translation efficiency. Principal components analysis resolved neuropsychiatric symptoms into four components, PC1 (depression, anxiety, memory, and fatigue), PC2 (pain), PC3 (drug and alcohol craving), and PC4 (sleep disturbances). Analyses of study group and TAAR1 genotype revealed a significant interaction for PC3 (craving response) (p = 0.003). The control group showed no difference in PC3 associated with TAAR1, while adjusted mean craving for the MA-ACT and MA-REM groups, among those with at least one copy of V288V, was estimated to be, respectively, 1.55 (p = 0.036) and 1.77 (p = 0.071) times the adjusted mean craving for those without the TAAR1 SNP.

CONCLUSIONS

Neuroadaptation to chronic MA use may be altered by TAAR1 genotype and result in increased dopamine signaling and craving in individuals with the V288V genotype.

Targeted sequencing reveals expanded genetic diversity of human transfer RNAs

Transfer RNAs are required to translate genetic information into proteins as well as regulate other cellular processes. Nucleotide changes in tRNAs can result in loss or gain of function that impact the composition and fidelity of the proteome. Despite links between tRNA variation and disease, the importance of cytoplasmic tRNA variation has been overlooked. Using a custom capture panel, we sequenced 605 human tRNA-encoding genes from 84 individuals. We developed a bioinformatic pipeline that allows more accurate tRNA read mapping and identifies multiple polymorphisms occurring within the same variant. Our analysis identified 522 unique tRNA-encoding sequences that differed from the reference genome from 84 individuals. Each individual had ~66 tRNA variants including nine variants found in less than 5% of our sample group. Variants were identified throughout the tRNA structure with 17% predicted to enhance function. Eighteen anticodon mutants were identified including potentially mistranslating tRNAs; e.g., a tRNA^Ser that decodes Phe codons. Similar engineered tRNA variants were previously shown to inhibit cell growth, increase apoptosis and induce the unfolded protein response in mammalian cell cultures and chick embryos. Our analysis shows that human tRNA variation has been underestimated. We conclude that the large number of tRNA genes provides a buffer enabling the emergence of variants, some of which could contribute to disease.

Contrasting Patterns of Rapid Molecular Evolution within the p53 Network across Mammal and Sauropsid Lineages

Cancer is a threat to multicellular organisms, yet the molecular evolution of pathways that prevent the accumulation of genetic damage has been largely unexplored. The p53 network regulates how cells respond to DNA-damaging stressors. We know little about p53 network molecular evolution as a whole. In this study, we performed comparative genetic analyses of the p53 network to quantify the number of genes within the network that are rapidly evolving and constrained, and the association between lifespan and the patterns of evolution. Based on our previous published data set, we used genomes and transcriptomes of 34 sauropsids and 32 mammals to analyze the molecular evolution of 45 genes within the p53 network. We found that genes in the network exhibited evidence of positive selection and divergent molecular evolution in mammals and sauropsids. Specifically, we found more evidence of positive selection in sauropsids than mammals, indicating that sauropsids have different targets of selection. In sauropsids, more genes upstream in the network exhibited positive selection, and this observation is driven by positive selection in squamates, which is consistent with previous work showing rapid divergence and adaptation of metabolic and stress pathways in this group. Finally, we identified a negative correlation between maximum lifespan and the number of genes with evidence of divergent molecular evolution, indicating that species with longer lifespans likely experienced less variation in selection across the network. In summary, our study offers evidence that comparative genomic approaches can provide insights into how molecular networks have evolved across diverse species.

Identification of a synonymous variant in TRIM59 gene for gastric cancer risk in a Chinese population

Tripartite motif 59 (TRIM59) is a novel oncogenic driver in gastric cancer (GC) that is implicated in disease progression as well as dismal survival. Genetic variants in peculiar gene are likely candidates for conferring hereditary susceptibility. The role of TRIM59 polymorphism in predicting the risk of malignant diseases and its relevance to TRIM59 expression have not been discussed. Using a HapMap tagSNPs approach, we screened three tag TRIM59 single nucleotide polymorphisms (SNPs) (rs1141023G>A, rs7629A>G, rs11706810T>C) which were genotyped in 602 GC patients and 868 healthy controls. Our study provided convincing result that carries of variant rs1141023A allele markedly increased GC risk (P=0.006). In comparison with the GG homozygotes, the variant GA heterozygotes demonstrated 1.50-fold elevated risk of GC (p=0.014, 95% confidence interval [CI] = 1.09–2.08). Subjects who carried the (GA+AA) genotypes of rs1141023 were associated with remarkable increased GC risk compared with the common genotype (P = 0.013, adjusted OR = 1.50, 95% CI = 1.09–2.05). Further stratified analyses displayed that the relationship between mutant genotype of rs1141023 and GC risk was more profound in male individuals. Intriguingly, there is no significant distinction of TRIM59 mRNA expression between rs1141023GA genotype and GG genotype in 44 normal gastric tissues. Taken together, our results suggest that rs1141023 polymorphism contributes to increased predisposition to GC and thus may be responsible for predicting early GC.

Donors FMO3 polymorphisms affect tacrolimus elimination in Chinese liver transplant patients

AIM

Flavin-containing monooxygenase (FMO) variants were potentially involved in tacrolimus metabolism in kidney transplantion. The influences of FMO3 genotypes on tacrolimus elimination in Chinese liver transplant patients remained unclear.

PATIENTS & METHODS

FMO3 SNPs and CYP3A5 rs776746 were analyzed in 110 Chinese patients.

RESULTS

Donor FMO3 rs1800822 allele T and rs909530 allele T were associated with fast tacrolimus elimination. Combination of polymorphisms of donor FMO3 rs1800822 and rs909530 genotype impacted on tacrolimus elimination (p = 0.0221). The number of donor rs1800822 allele T and rs909530 allele T was confirmed to be an independent predictor of the tacrolimus concentration-to-dose ratios for weeks 2, 3 and 4 in the multivariate analysis.

CONCLUSION

Donor's FMO3 polymorphisms might affect tacrolimus elimination.

Explosive genetic evidence for explosive human population growth

The advent of next-generation sequencing technology has allowed the collection of vast amounts of genetic variation data. A recurring discovery from studying larger and larger samples of individuals had been the extreme, previously unexpected, excess of very rare genetic variants, which has been shown to be mostly due to the recent explosive growth of human populations. Here, we review recent literature that inferred recent changes in population size in different human populations and with different methodologies, with many pointing to recent explosive growth, especially in European populations for which more data has been available. We also review the state-of-the-art methods and software for the inference of historical population size changes that lead to these discoveries. Finally, we discuss the implications of recent population growth on personalized genomics, on purifying selection in the non-equilibrium state it entails and, as a consequence, on the genetic architecture underlying complex disease and the performance of mapping methods in discovering rare variants that contribute to complex disease risk.

Genetic polymorphisms in glycolytic pathway are associated with the prognosis of patients with early stage non-small cell lung cancer

This study was conducted to investigate whether polymorphisms of genes involved in glycolysis are associated with the prognosis of patients with non-small cell lung cancer (NSCLC) after surgical resection. Forty-four single nucleotide polymorphisms (SNPs) of 17 genes in glycolytic pathway were investigated in a total of 782 patients with NSCLC who underwent curative surgical resection. The association of the SNPs with overall survival (OS) and disease free survival (DFS) were analyzed. Among the 44 SNPs investigated, four SNPs (ENO1 rs2274971A > G, PFKM rs11168417C > T, PFKP rs1132173C > T, PDK2 rs3785921G > A) were significantly associated with survival outcomes in multivariate analyses. When stratified by tumor histology, three SNPs (ENO1 rs2274971A > G, PFKM rs11168417C > T, and PDK2 rs3785921G > A) were significantly associated with OS and/or DFS only in squamous cell carcinoma, whereas PFKP rs1132173C > T exhibited a significant association with survival outcomes only in adenocarcinoma. When the four SNPs were combined, OS and DFS decreased as the number of bad genotypes increased (Ptrend = 8 × 10⁻⁴ and 3 × 10⁻⁵, respectively). Promoter assays showed that ENO1 rs2274971G allele had significantly higher promoter activity compared to the rs2274971A allele. The four SNPs, especially ENO1 rs2274971A > G, may be useful for the prediction of prognosis in patients with surgically resected NSCLC.

Association analysis of DACT1 genetic variants and gastric cancer risk in a Chinese Han population: a case-control study

Purpose

Disheveled-binding antagonist of beta-catenin 1 (DACT1) is involved in tumorigenesis through influencing cell apoptosis and proliferation. We aimed to investigate the effect of three tag single-nucleotide polymorphisms (SNPs) in DACT1 (rs863091 C>T, rs17832998 C>T, and rs167481 C>T) on the occurrence of gastric cancer (GC), their association with specific clinical characteristics, and consideration of the functional relevance of GC-related SNPs.

Subjects and methods

In this hospital-based case–control study, the genotypes were acquired using the TaqMan-MGB method consisting of 602 cases and 602 controls. DACT1 messenger RNA level was evaluated in 76 paired tumoral and normal tissues using quantitative reverse transcription–polymerase chain reaction. Logistic regression was used to evaluate the associations among the DACT1 SNPs and GC.

Results

We found a significant association between the variant genotypes of rs863091 and decreased risk of GC (TT vs CC: P=0.009, adjusted odds ratio =0.34, 95% confidence interval =0.15–0.77; CT + TT vs CC: P=0.030, adjusted odds ratio =0.74, 95% confidence interval =0.57–0.97). In further stratified analyses, rs863091 variant genotypes were associated with a reduced risk of GC in younger individuals (<60 years) and males. No overall significant association with GC risk was observed in SNP rs17832998 or rs167481. Additionally, we assessed DACT1 messenger RNA levels in GC and found that DACT1 expressions of individuals carrying CT and TT genotypes were much higher than those with CC genotype.

Conclusion

Our findings suggest that the DACT1 rs863091 C>T polymorphism may be associated with a decreased risk of GC in the Chinese Han population and influence DACT1 expression.

The functional relevance of somatic synonymous mutations in melanoma and other cancers

Recent technological advances in sequencing have flooded the field of cancer research with knowledge about somatic mutations for many different cancer types. Most cancer genomics studies focus on mutations that alter the amino acid sequence, ignoring the potential impact of synonymous mutations. However, accumulating experimental evidence has demonstrated clear consequences for gene function, leading to a widespread recognition of the functional role of synonymous mutations and their causal connection to various diseases. Here, we review the evidence supporting the direct impact of synonymous mutations on gene function via gene splicing; mRNA stability, folding, and translation; protein folding; and miRNA-based regulation of expression. These results highlight the functional contribution of synonymous mutations to oncogenesis and the need to further investigate their detection and prioritization for experimental assessment.

Association Study Between SLC15A4 Polymorphisms and Haplotypes and Systemic Lupus Erythematosus in a Han Chinese Population

Objective: The gene SLC15A4 (solute carrier family 15 [oligopeptide transporter], member 4) has been reported as contributing to the pathogenesis of systemic lupus erythematosus (SLE). We performed a case–control replication study to investigate further the association between single-nucleotide polymorphisms (SNPs) in the SLC15A4 gene and systemic SLE in a Han Chinese population. Methods: In Han Chinese SLE patients and healthy individuals (n = 355, 375, respectively), 18 SNPs in the SLC15A4 gene were genotyped using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and TaqMan SNP genotyping assays. Analyses of allele frequencies and genotypes using codominant, dominant, and recessive models were conducted, as well as a linkage disequilibrium analysis. P values < 0.05 were considered significant. Results: Allele frequencies of five of the analyzed SNPs were significantly associated with SLE. Under a codominant model the genotype frequencies of rs3765108 AG and rs7308691 AT were significantly higher in the SLE group than the control group (p = 0.019, 0.049, respectively). Under a dominant model the rs1385374 (TT+CT) SNP carried a higher risk of SLE than (CC) (p = 0.042). One SLC15A4 haplotype (TA), which consists of 2 SNPs (rs959989 and rs983492), was associated with SLE (p = 0.024). Conclusion: Our study determined that five SNPs (rs959989, rs1385374, rs983492, rs12298615, and rs10847697) are associated with SLE. Thus, SLC15A4 may be important in the pathogenesis of SLE in Han Chinese patients.

The Code of Silence: Widespread Associations Between Synonymous Codon Biases and Gene Function

Some mutations in gene coding regions exchange one synonymous codon for another, and thus do not alter the amino acid sequence of the encoded protein. Even though they are often called 'silent,' these mutations may exhibit a plethora of effects on the living cell. Therefore, they are often selected during evolution, causing synonymous codon usage biases in genomes. Comparative analyses of bacterial, archaeal, fungal, and human cancer genomes have found many links between a gene's biological role and the accrual of synonymous mutations during evolution. In particular, highly expressed genes in certain functional categories are enriched with optimal codons, which are decoded by the abundant tRNAs, thus enhancing the speed and accuracy of the translating ribosome. The set of genes exhibiting codon adaptation differs between genomes, and these differences show robust associations to organismal phenotypes. In addition to selection for translation efficiency, other distinct codon bias patterns have been found in: amino acid starvation genes, cyclically expressed genes, tissue-specific genes in animals and plants, oxidative stress response genes, cellular differentiation genes, and oncogenes. In addition, genomes of organisms harboring tRNA modifications exhibit particular codon preferences. The evolutionary trace of codon bias patterns across orthologous genes may be examined to learn about a gene's relevance to various phenotypes, or, more generally, its function in the cell.

Synonymous Polymorphisms in HOXB13 as a Protective Factor for Prostate Cancer

BACKGROUND

Genomic association and linkage studies, as well as epidemiological data have implicated both the HOXB13 gene and single nucleotide polymorphisms (SNPs) in the development of prostate cancer (PCa). The recent association between the G84E polymorphism in the HOXB13 gene and PCa has been shown to result in a more aggressive cancer with an earlier onset of the disease. We examined the frequency of this mutation and other recurrent HOXB13 SNPs in patients with PCa and those with benign prostatic hyperplasia (BPH) or no cancer.

METHODS

Reverse transcriptase-polymerase chain reaction (RT-PCR) was performed on exons 1 and 2 of HOXB13 gene, followed by bidirectional Sanger Sequencing on peripheral blood from 232 PCa (age 46-92) and 110 BPH (age 45-84) patients. Statistical analysis was used to correlate between recurrent SNPs and PCa.

RESULTS

The G84E mutation was found at a low frequency in randomly selected PCa and BPH (both 0.9%). Two recurrent, synonymous SNPs, rs8556 and rs900627, were also detected. rs8556 was detected in 48 PCa (20.7%) and 26 BPH (23.6%) subjects; rs9900627was detected in 27 PCa (11.6%) and 19 BPH (17.3%) subjects. Having both rs8556 and rs9900627 or being homozygous for either one was associated with being 2.9 times less likely to develop PCa (p=0.05).

CONCLUSIONS

Although a larger study in order to confirm our findings, our data suggests a significant negative correlation between two SNPs, rs8556 and rs9900627, and the presence of PCa.

Multiple roles of the coding sequence 5' end in gene expression regulation

The codon composition of the coding sequence's (ORF) 5′ end first few dozen codons is known to be distinct to that of the rest of the ORF. Various explanations for the unusual codon distribution in this region have been proposed in recent years, and include, among others, novel regulatory mechanisms of translation initiation and elongation. However, due to the fact that many overlapping regulatory signals are suggested to be associated with this relatively short region, its research is challenging. Here, we review the currently known signals that appear in this region, the theories related to the way they regulate translation and affect the organismal fitness, and the debates they provoke.

Effective population size does not predict codon usage bias in mammals

Synonymous codons are not used at equal frequency throughout the genome, a phenomenon termed codon usage bias (CUB). It is often assumed that interspecific variation in the intensity of CUB is related to species differences in effective population sizes (N_e), with selection on CUB operating less efficiently in species with small N_e. Here, we specifically ask whether variation in N_e predicts differences in CUB in mammals and report two main findings. First, across 41 mammalian genomes, CUB was not correlated with two indirect proxies of N_e (body mass and generation time), even though there was statistically significant evidence of selection shaping CUB across all species. Interestingly, autosomal genes showed higher codon usage bias compared to X-linked genes, and high-recombination genes showed higher codon usage bias compared to low recombination genes, suggesting intraspecific variation in N_e predicts variation in CUB. Second, across six mammalian species with genetic estimates of N_e (human, chimpanzee, rabbit, and three mouse species: Mus musculus, M. domesticus, and M. castaneus), N_e and CUB were weakly and inconsistently correlated. At least in mammals, interspecific divergence in N_e does not strongly predict variation in CUB. One hypothesis is that each species responds to a unique distribution of selection coefficients, confounding any straightforward link between N_e and CUB.

Impairment of translation in neurons as a putative causative factor for autism

BACKGROUND

A dramatic increase in the prevalence of autism and Autistic Spectrum Disorders (ASD) has been observed over the last two decades in USA, Europe and Asia. Given the accumulating data on the possible role of translation in the etiology of ASD, we analyzed potential effects of rare synonymous substitutions associated with ASD on mRNA stability, splicing enhancers and silencers, and codon usage.

PRESENTATION OF THE HYPOTHESIS

We hypothesize that subtle impairment of translation, resulting in dosage imbalance of neuron-specific proteins, contributes to the etiology of ASD synergistically with environmental neurotoxins.

TESTING THE HYPOTHESIS

A statistically significant shift from optimal to suboptimal codons caused by rare synonymous substitutions associated with ASD was detected whereas no effect on other analyzed characteristics of transcripts was identified. This result suggests that the impact of rare codons on the translation of genes involved in neuron development, even if slight in magnitude, could contribute to the pathogenesis of ASD in the presence of an aggressive chemical background. This hypothesis could be tested by further analysis of ASD-associated mutations, direct biochemical characterization of their effects, and assessment of in vivo effects on animal models.

IMPLICATIONS OF THE HYPOTHESIS

It seems likely that the synergistic action of environmental hazards with genetic variations that in themselves have limited or no deleterious effects but are potentiated by the environmental factors is a general principle that underlies the alarming increase in the ASD prevalence.

REVIEWERS

This article was reviewed by Andrey Rzhetsky, Neil R. Smalheiser, and Shamil R. Sunyaev.

Neutral genomic regions refine models of recent rapid human population growth

Human populations have experienced dramatic growth since the Neolithic revolution. Recent studies that sequenced a very large number of individuals observed an extreme excess of rare variants and provided clear evidence of recent rapid growth in effective population size, although estimates have varied greatly among studies. All these studies were based on protein-coding genes, in which variants are also impacted by natural selection. In this study, we introduce targeted sequencing data for studying recent human history with minimal confounding by natural selection. We sequenced loci far from genes that meet a wide array of additional criteria such that mutations in these loci are putatively neutral. As population structure also skews allele frequencies, we sequenced 500 individuals of relatively homogeneous ancestry by first analyzing the population structure of 9,716 European Americans. We used very high coverage sequencing to reliably call rare variants and fit an extensive array of models of recent European demographic history to the site frequency spectrum. The best-fit model estimates ∼ 3.4% growth per generation during the last ∼ 140 generations, resulting in a population size increase of two orders of magnitude. This model fits the data very well, largely due to our observation that assumptions of more ancient demography can impact estimates of recent growth. This observation and results also shed light on the discrepancy in demographic estimates among recent studies.

dbPSHP: a database of recent positive selection across human populations

The dbPSHP database (http://jjwanglab.org/dbpshp) aims to help researchers to efficiently identify, validate and visualize putative positively selected loci in human evolution and further discover the mechanism governing these natural selections. Recent evolution of human populations at the genomic level reflects the adaptations to the living environments, including climate change and availability and stability of nutrients. Many genetic regions under positive selection have been identified, which assist us to understand how natural selection has shaped population differences. Here, we manually collect recent positive selections in different human populations, consisting of 15,472 loci from 132 publications. We further compiled a database that used 15 statistical terms of different evolutionary attributes for single nucleotide variant sites from the HapMap 3 and 1000 Genomes Project to identify putative regions under positive selection. These attributes include variant allele/genotype properties, variant heterozygosity, within population diversity, long-range haplotypes, pairwise population differentiation and evolutionary conservation. We also provide interactive pages for visualization and annotation of different selective signals. The database is freely available to the public and will be frequently updated.

Evolution at two levels of gene expression in yeast

Despite the greater functional importance of protein levels, our knowledge of gene expression evolution is based almost entirely on studies of mRNA levels. In contrast, our understanding of how translational regulation evolves has lagged far behind. Here we have applied ribosome profiling—which measures both global mRNA levels and their translation rates—to two species of Saccharomyces yeast and their interspecific hybrid in order to assess the relative contributions of changes in mRNA abundance and translation to regulatory evolution. We report that both cis- and trans-acting regulatory divergence in translation are abundant, affecting at least 35% of genes. The majority of translational divergence acts to buffer changes in mRNA abundance, suggesting a widespread role for stabilizing selection acting across regulatory levels. Nevertheless, we observe evidence of lineage-specific selection acting on several yeast functional modules, including instances of reinforcing selection acting at both levels of regulation. Finally, we also uncover multiple instances of stop-codon readthrough that are conserved between species. Our analysis reveals the underappreciated complexity of post-transcriptional regulatory divergence and indicates that partitioning the search for the locus of selection into the binary categories of “coding” versus “regulatory” may overlook a significant source of selection, acting at multiple regulatory levels along the path from genotype to phenotype.

A silent exonic SNP in kdm3a affects nucleic acids structure but does not regulate experimental autoimmune encephalomyelitis

Defining genetic variants that predispose for diseases is an important initiative that can improve biological understanding and focus therapeutic development. Genetic mapping in humans and animal models has defined genomic regions controlling a variety of phenotypes known as quantitative trait loci (QTL). Causative disease determinants, including single nucleotide polymorphisms (SNPs), lie within these regions and can often be identified through effects on gene expression. We previously identified a QTL on rat chromosome 4 regulating macrophage phenotypes and immune-mediated diseases including experimental autoimmune encephalomyelitis (EAE). Gene analysis and a literature search identified lysine-specific demethylase 3A (Kdm3a) as a potential regulator of these phenotypes. Genomic sequencing determined only two synonymous SNPs in Kdm3a. The silent synonymous SNP in exon 15 of Kdm3a caused problems with quantitative PCR detection in the susceptible strain through reduced amplification efficiency due to altered secondary cDNA structure. Shape Probability Shift analysis predicted that the SNP often affects RNA folding; thus, it may impact protein translation. Despite these differences in rats, genetic knockout of Kdm3a in mice resulted in no dramatic effect on immune system development and activation or EAE susceptibility and severity. These results provide support for tools that analyze causative SNPs that impact nucleic acid structures.

Natural variation of salinity response, population structure and candidate genes associated with salinity tolerance in perennial ryegrass accessions

Natural variation in salinity response, effects of population structure on growth and physiological traits and gene-trait association were examined in 56 global collections of diverse perennial ryegrass (Lolium perenne L.) accessions. Three population structure groups were identified with 66 simple sequence repeat markers, which on average accounted for 9 and 11% of phenotypic variation for the control and salinity treatment at 300 mm NaCl. Group 1 (10 accessions) had greater plant height, leaf dry weight and water content, chlorophyll index, K(+) concentration and K(+) /Na(+) than group 2 (39 accessions) and group 3 (7 accessions) under salinity stress, while group 3 had higher Na(+) than groups 1 and 2. Eighty-seven single nucleotide polymorphisms were detected from four partial candidate genes encoding aquaporin and Na(+) /H(+) antiporter in both plasma and tonoplast membranes. Overall, rapid decay of linkage disequilibrium was observed within 500 bp. Significant associations were found between the putative LpTIP1 and Na(+) for the control and between the putative LpNHX1 and K(+) /Na(+) under the control and salinity treatments after controlling population structure. These results indicate that population structure influenced phenotypic traits, and allelic variation in LpNHX1 may affect salinity tolerance of perennial ryegrass.

Strong purifying selection at synonymous sites in D. melanogaster

Synonymous sites are generally assumed to be subject to weak selective constraint. For this reason, they are often neglected as a possible source of important functional variation. We use site frequency spectra from deep population sequencing data to show that, contrary to this expectation, 22% of four-fold synonymous (4D) sites in Drosophila melanogaster evolve under very strong selective constraint while few, if any, appear to be under weak constraint. Linking polymorphism with divergence data, we further find that the fraction of synonymous sites exposed to strong purifying selection is higher for those positions that show slower evolution on the Drosophila phylogeny. The function underlying the inferred strong constraint appears to be separate from splicing enhancers, nucleosome positioning, and the translational optimization generating canonical codon bias. The fraction of synonymous sites under strong constraint within a gene correlates well with gene expression, particularly in the mid-late embryo, pupae, and adult developmental stages. Genes enriched in strongly constrained synonymous sites tend to be particularly functionally important and are often involved in key developmental pathways. Given that the observed widespread constraint acting on synonymous sites is likely not limited to Drosophila, the role of synonymous sites in genetic disease and adaptation should be reevaluated.

Translational signatures and mRNA levels are highly correlated in human stably expressed genes

Background

Gene expression is one of the most relevant biological processes of living cells. Due to the relative small population sizes, it is predicted that human gene sequences are not strongly influenced by selection towards expression efficiency. One of the major problems in estimating to what extent gene characteristics can be selected to maximize expression efficiency is the wide variation that exists in RNA and protein levels among physiological states and different tissues. Analyses of datasets of stably expressed genes (i.e. with consistent expression between physiological states and tissues) would provide more accurate and reliable measurements of associations between variations of a specific gene characteristic and expression, and how distinct gene features work to optimize gene expression.

Results

Using a dataset of human genes with consistent expression between physiological states we selected gene sequence signatures related to translation that can predict about 42% of mRNA variation. The prediction can be increased to 51% when selecting genes that are stably expressed in more than 1 tissue. These genes are enriched for translation and ribosome biosynthesis processes and have higher translation efficiency scores, smaller coding sequences and 3^′ UTR sizes and lower folding energies when compared to other datasets. Additionally, the amino acid frequencies weighted by expression showed higher correlations with isoacceptor tRNA gene copy number, and smaller absolute correlation values with biosynthetic costs.

Conclusion

Our results indicate that human gene sequence characteristics related to transcription and translation processes can co-evolve in an integrated manner in order to optimize gene expression.

A common polymorphism in the LDL receptor gene has multiple effects on LDL receptor function

A common synonymous single nucleotide polymorphism in exon 12 of the low-density lipoprotein receptor (LDLR) gene, rs688, has been associated with increased plasma total and LDL cholesterol in several populations. Using immortalized lymphoblastoid cell lines from a healthy study population, we confirmed an earlier report that the minor allele of rs688 is associated with increased exon 12 alternative splicing (P < 0.05) and showed that this triggered nonsense-mediated decay (NMD) of the alternatively spliced LDLR mRNA. However, since synonymous single nucleotide polymorphisms may influence structure and function of the encoded proteins by co-translational effects, we sought to test whether rs688 was also functional in the full-length mRNA. In HepG2 cells expressing LDLR cDNA constructs engineered to contain the major or minor allele of rs688, the latter was associated with a smaller amount of LDLR protein at the cell surface (-21.8 ± 0.6%, P = 0.012), a higher amount in the lysosome fraction (+25.7 ± 0.3%, P = 0.037) and reduced uptake of fluorescently labeled LDL (-24.3 ± 0.7%, P < 0.01). Moreover, in the presence of exogenous proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that reduces cellular LDL uptake by promoting lysosomal degradation of LDLR, the minor allele resulted in reduced capacity of a PCSK9 monoclonal antibody to increase LDL uptake. These findings are consistent with the hypothesis that rs688, which is located in the β-propeller region of LDLR, has effects on LDLR activity beyond its role in alternative splicing due to impairment of LDLR endosomal recycling and/or PCSK9 binding, processes in which the β-propeller is critically involved.

Human coding synonymous single nucleotide polymorphisms at ramp regions of mRNA translation

According to the ramp model of mRNA translation, the first 50 codons favor rare codons and have slower speed of translation. This study aims to detect translational selection on coding synonymous single nucleotide polymorphisms (sSNP) to support the ramp theory. We investigated fourfold degenerate site (FFDS) sSNPs with A ↔ G or C ↔ T substitutions in human genome for distribution bias of synonymous codons (SC), grouped by CpG or non-CpG sites. Distribution bias of sSNPs between the 3(rd) ~50(th) codons and the 51(st) ~ remainder codons at non-CpG sites were observed. In the 3(rd) ~50(th) codons, G → A sSNPs at non-CpG sites are favored than A → G sSNPs [P = 2.89 × 10(-3)], and C → T at non-CpG sites are favored than T → C sSNPs [P = 8.50 × 10(-3)]. The favored direction of SC usage change is from more frequent SCs to less frequent SCs. The distribution bias is more obvious in synonymous substitutions CG(G → A), AC(C → T), and CT(C → T). The distribution bias of sSNPs in human genome, i.e. frequent SCs to less frequent SCs is favored in the 3(rd) ~50(th) codons, indicates translational selection on sSNPs in the ramp regions of mRNA templates.

Three independent determinants of protein evolutionary rate

One of the most widely accepted ideas related to the evolutionary rates of proteins is that functionally important residues or regions evolve slower than other regions, a reasonable outcome of which should be a slower evolutionary rate of the proteins with a higher density of functionally important sites. Oddly, the role of functional importance, mainly measured by essentiality, in determining evolutionary rate has been challenged in recent studies. Several variables other than protein essentiality, such as expression level, gene compactness, protein-protein interactions, etc., have been suggested to affect protein evolutionary rate. In the present review, we try to refine the concept of functional importance of a gene, and consider three factors-functional importance, expression level, and gene compactness, as independent determinants of evolutionary rate of a protein, based not only on their known correlation with evolutionary rate but also on a reasonable mechanistic model. We suggest a framework based on these mechanistic models to correctly interpret the correlations between evolutionary rates and the various variables as well as the interrelationships among the variables.

Cell-Type Specific Determinants of NRAMP1 Expression in Professional Phagocytes

The Natural resistance-associated macrophage protein 1 (Nramp1 or Solute carrier 11 member 1, Slc11a1) transports divalent metals across the membrane of late endosomes and lysosomes in professional phagocytes. Nramp1 represents an ancient eukaryotic cell-autonomous defense whereas the gene duplication that yielded Nramp1 and Nramp2 predated the origin of Sarcopterygians (lobe-finned fishes and tetrapods). SLC11A1 genetic polymorphisms associated with human resistance to tuberculosis consist of potential regulatory variants. Herein, current knowledge of the regulation of SLC11A1 gene expression is reviewed and comprehensive analysis of ENCODE data available for hematopoietic cell-types suggests a hypothesis for the regulation of SLC11A1 expression during myeloid development and phagocyte functional polarization. SLC11A1 is part of a 34.6 kb CTCF-insulated locus scattered with predicted regulatory elements: a 3' enhancer, a large 5' enhancer domain and four elements spread around the transcription start site (TSS), including several C/EBP and PU.1 sites. SLC11A1 locus ends appear mobilized by ETS-related factors early during myelopoiesis; activation of both 5' and 3' enhancers in myelo-monocytic cells correlate with transcription factor binding at the TSS. Characterizing the corresponding cis/trans determinants functionally will establish the mechanisms involved and possibly reveal genetic variation that impacts susceptibility to infectious or immune diseases.

Genic and nongenic contributions to natural variation of quantitative traits in maize

The complex genomes of many economically important crops present tremendous challenges to understand the genetic control of many quantitative traits with great importance in crop production, adaptation, and evolution. Advances in genomic technology need to be integrated with strategic genetic design and novel perspectives to break new ground. Complementary to individual-gene–targeted research, which remains challenging, a global assessment of the genomic distribution of trait-associated SNPs (TASs) discovered from genome scans of quantitative traits can provide insights into the genetic architecture and contribute to the design of future studies. Here we report the first systematic tabulation of the relative contribution of different genomic regions to quantitative trait variation in maize. We found that TASs were enriched in the nongenic regions, particularly within a 5-kb window upstream of genes, which highlights the importance of polymorphisms regulating gene expression in shaping the natural variation. Consistent with these findings, TASs collectively explained 44%–59% of the total phenotypic variation across maize quantitative traits, and on average, 79% of the explained variation could be attributed to TASs located in genes or within 5 kb upstream of genes, which together comprise only 13% of the genome. Our findings suggest that efficient, cost-effective genome-wide association studies (GWAS) in species with complex genomes can focus on genic and promoter regions.