[Show abstract][Hide abstract] ABSTRACT: Strong social relationships confer health and fitness benefits in a number of species, motivating the need to understand the processes through which they arise. In female cercopithecine primates, both kinship and dominance rank are thought to influence rates of affiliative behaviour and social partner preference. Teasing apart the relative importance of these factors has been challenging, however, as female kin often occupy similar positions in the dominance hierarchy. Here, we isolated the specific effects of rank on social relationships in female rhesus macaques by analysing grooming patterns in 18 social groups that did not contain close relatives, and in which dominance ranks were experimentally randomized. We found that grooming was asymmetrically directed towards higher-ranking females and that grooming bouts temporarily decreased the likelihood of aggression between grooming partners, supporting the idea that grooming is associated with social tolerance. Even in the absence of kin, females formed the strongest grooming relationships with females adjacent to them in rank, a pattern that was strongest for the highest-ranking females. Using simulations, we show that three rules for allocating grooming based on dominance rank recapitulated most of the relationships we observed. Finally, we evaluated whether a female's tendency to engage in grooming behaviour was stable across time and social setting. We found that one measure, the rate of grooming females provided to others (but not the rate of grooming females received), exhibited modest stability after accounting for the primary effect of dominance rank. Together, our findings indicate that dominance rank has strong effects on social relationships in the absence of kin, suggesting the importance of considering social status and social connectedness jointly when investigating their health and fitness consequences.
[Show abstract][Hide abstract] ABSTRACT: The genetic history of African populations is increasingly well documented, yet their patterns of epigenomic variation remain uncharacterized. Moreover, the relative impacts of DNA sequence variation and temporal changes in lifestyle and habitat on the human epigenome remain unknown. Here we generate genome-wide genotype and DNA methylation profiles for 362 rainforest hunter-gatherers and sedentary farmers. We find that the current habitat and historical lifestyle of a population have similarly critical impacts on the methylome, but the biological functions affected strongly differ. Specifically, methylation variation associated with recent changes in habitat mostly concerns immune and cellular functions, whereas that associated with historical lifestyle affects developmental processes. Furthermore, methylation variation—particularly that correlated with historical lifestyle—shows strong associations with nearby genetic variants that, moreover, are enriched in signals of natural selection. Our work provides new insight into the genetic and environmental factors affecting the epigenomic landscape of human populations over time.
Full-text · Article · Nov 2015 · Nature Communications
[Show abstract][Hide abstract] ABSTRACT: The innate immune system provides the first response to infection and is now recognized to be partially pathogen-specific. Mycobacterium tuberculosis (MTB) is able to subvert the innate immune response and survive inside macrophages. Curiously, only 5-10% of otherwise healthy individuals infected with MTB develop active tuberculosis (TB). We do not yet understand the genetic basis underlying this individual-specific susceptibility. Moreover, we still do not know which properties of the innate immune response are specific to MTB infection. To identify immune responses that are specific to MTB, we infected macrophages with eight different bacteria, including different MTB strains and related mycobacteria, and studied their transcriptional response. We identified a novel subset of genes whose regulation was affected specifically by infection with mycobacteria. This subset includes genes involved in phagosome maturation, superoxide production, response to vitamin D, macrophage chemotaxis, and sialic acid synthesis. We suggest that genetic variants that affect the function or regulation of these genes should be considered candidate loci for explaining TB susceptibility.
[Show abstract][Hide abstract] ABSTRACT: The bacterial composition of the human fecal microbiome is influenced by many lifestyle factors, notably diet. It is less clear, however, what role host genetics plays in dictating the composition of bacteria living in the gut. In this study, we examined the association of ~200K host genotypes with the relative abundance of fecal bacterial taxa in a founder population, the Hutterites, during two seasons (n = 91 summer, n = 93 winter, n = 57 individuals collected in both). These individuals live and eat communally, minimizing variation due to environmental exposures, including diet, which could potentially mask small genetic effects. Using a GWAS approach that takes into account the relatedness between subjects, we identified at least 8 bacterial taxa whose abundances were associated with single nucleotide polymorphisms in the host genome in each season (at genome-wide FDR of 20%). For example, we identified an association between a taxon known to affect obesity (genus Akkermansia) and a variant near PLD1, a gene previously associated with body mass index. Moreover, we replicate a previously reported association from a quantitative trait locus (QTL) mapping study of fecal microbiome abundance in mice (genus Lactococcus, rs3747113, P = 3.13 x 10-7). Finally, based on the significance distribution of the associated microbiome QTLs in our study with respect to chromatin accessibility profiles, we identified tissues in which host genetic variation may be acting to influence bacterial abundance in the gut.
[Show abstract][Hide abstract] ABSTRACT: DNA methylation is an epigenetic mark thought to be robust to environmental perturbations on a short time scale. Here, we challenge that view by demonstrating that the infection of human dendritic cells (DCs) with a live pathogenic bacteria is associated with rapid and active demethylation at thousands of loci, independent of cell division. We performed an integrated analysis of data on genome-wide DNA methylation, histone mark patterns, chromatin accessibility, and gene expression, before and after infection. We found that infection-induced demethylation rarely occurs at promoter regions and instead localizes to distal enhancer elements, including those that regulate the activation of key immune transcription factors. Active demethylation is associated with extensive epigenetic remodeling, including the gain of histone activation marks and increased chromatin accessibility, and is strongly predictive of changes in the expression levels of nearby genes. Collectively, our observations show that active, rapid changes in DNA methylation in enhancers play a previously unappreciated role in regulating the transcriptional response to infection, even in non-proliferating cells.
[Show abstract][Hide abstract] ABSTRACT: The recent discovery that methylated cytosines are converted to 5-hydroxymethylated cytosines (5hmC) by the family of ten-eleven translocation enzymes has sparked significant interest on the genomic location, the abundance in different tissues, the putative functions, and the stability of this epigenetic mark. 5hmC plays a key role in the brain, where it is particularly abundant and dynamic during development.
Here, we comprehensively characterize 5hmC in the prefrontal cortices of 24 subjects. We show that, although there is inter-individual variability in 5hmC content among unrelated individuals, approximately 8 % of all CpGs on autosomal chromosomes contain 5hmC, while sex chromosomes contain far less. Our data also provide evidence suggesting that 5hmC has transcriptional regulatory properties, as the density of 5hmC was highest in enhancer regions and within exons. Furthermore, we link increased 5hmC density to histone modification binding sites, to the gene bodies of actively transcribed genes, and to exon-intron boundaries. Finally, we provide several genomic regions of interest that contain gender-specific 5hmC.
Collectively, these results present an important reference for the growing number of studies that are interested in the investigation of the role of 5hmC in brain and mental disorders.
[Show abstract][Hide abstract] ABSTRACT: Social relationships have profound effects on health in humans and other primates, but the mechanisms that explain this relationship are not well understood. Using shotgun metagenomic data from wild baboons, we found that social group membership and social network relationships predicted both the taxonomic structure of the gut microbiome and the structure of genes encoded by gut microbial species. Rates of interaction directly explained variation in the gut microbiome, even after controlling for diet, kinship, and shared environments. They therefore strongly implicate direct physical contact among social partners in the transmission of gut microbial species. We identified 51 socially structured taxa, which were significantly enriched for anaerobic and non-spore-forming lifestyles. Our results argue that social interactions are an important determinant of gut microbiome composition in natural animal populations—a relationship with important ramifications for understanding how social relationships influence health, as well as the evolution of group living.
[Show abstract][Hide abstract] ABSTRACT: The optimal coordination of the transcriptional response of host cells to infection is essential for establishing appropriate immunological outcomes. In this context, the role of microRNAs (miRNAs) - important epigenetic regulators of gene expression - in regulating mammalian immune systems is increasingly well recognised. However, the expression dynamics of miRNAs, and that of their isoforms, in response to infection remains largely unexplored. Here, we characterized the genome-wide miRNA transcriptional responses of human dendritic cells, over time, to various mycobacteria differing in their virulence as well as to other bacteria outside the genus Mycobacterium, using small RNA-sequencing. We detected the presence of a core temporal response to infection, shared across bacteria, comprising 49 miRNAs, highlighting a set of miRNAs that may play an essential role in the regulation of basic cellular responses to stress. Despite such broadly shared expression dynamics, we identified specific elements of variation in the miRNA response to infection across bacteria, including a virulence-dependent induction of the miR-132/212 family in response to mycobacterial infections. We also found that infection has a strong impact on both the relative abundance of the miRNA hairpin arms and the expression dynamics of miRNA isoforms. That we observed broadly consistent changes in relative arm expression and isomiR distribution across bacteria suggests that this additional, internal layer of variability in miRNA responses represents an additional source of subtle miRNA-mediated regulation upon infection. Collectively, this study increases our understanding of the dynamism and role of miRNAs in response to bacterial infection, revealing novel features of their internal variability and identifying candidate miRNAs that may contribute to differences in the pathogenicity of mycobacterial infections.
[Show abstract][Hide abstract] ABSTRACT: The phagocytosis of apoptotic cells and associated vesicles (efferocytosis) by DCs is an important mechanism for both self tolerance and host defense. Although some of the engulfment ligands involved in efferocytosis have been identified and studied in vitro, the contributions of these ligands in vivo remain ill defined. Here, we determined that during Mycobacterium tuberculosis (Mtb) infection, the engulfment ligand annexin1 is an important mediator in DC cross-presentation that increases efferocytosis in DCs and intrinsically enhances the capacity of the DC antigen-presenting machinery. Annexin1-deficient mice were highly susceptible to Mtb infection and showed an impaired Mtb antigen-specific CD8+ T cell response. Importantly, annexin1 expression was greatly downregulated in Mtb-infected human blood monocyte-derived DCs, indicating that reduction of annexin1 is a critical mechanism for immune evasion by Mtb. Collectively, these data indicate that annexin1 is essential in immunity to Mtb infection and mediates the power of DC efferocytosis and cross-presentation.
Full-text · Article · Dec 2014 · Journal of Clinical Investigation
[Show abstract][Hide abstract] ABSTRACT: Chronic inflammatory and autoimmune diseases have been the focus of many genome-wide association studies (GWAS) because they represent a significant cause of illness and morbidity, and many are heritable. Almost a decade of GWAS studies suggests that the pathological inflammation associated with these diseases is controlled by a limited number of networked immune system genes. Chronic inflammatory and autoimmune diseases are enigmatic from an evolutionary perspective because they exert a negative affect on reproductive fitness. The persistence of these conditions may be partially explained by the important roles the implicated immune genes play in pathogen defense and other functions thought to be under strong natural selection in humans. The evolutionary reasons for chronic inflammatory and autoimmune disease persistence and uneven distribution across populations are the focus of this review.
No preview · Article · Oct 2014 · Current Opinion in Immunology
[Show abstract][Hide abstract] ABSTRACT: The evolutionary history of the human pygmy phenotype (small body size), a characteristic of African and Southeast Asian rainforest hunter-gatherers, is largely unknown. Here we use a genome-wide admixture mapping analysis to identify 16 genomic regions that are significantly associated with the pygmy phenotype in the Batwa, a rainforest hunter-gatherer population from Uganda (east central Africa). The identified genomic regions have multiple attributes that provide supporting evidence of genuine association with the pygmy phenotype, including enrichments for SNPs previously associated with stature variation in Europeans and for genes with growth hormone receptor and regulation functions. To test adaptive evolutionary hypotheses, we computed the haplotype-based integrated haplotype score (iHS) statistic and the level of population differentiation (FST) between the Batwa and their agricultural neighbors, the Bakiga, for each genomic SNP. Both |iHS| and FST values were significantly higher for SNPs within the Batwa pygmy phenotype-associated regions than the remainder of the genome, a signature of polygenic adaptation. In contrast, when we expanded our analysis to include Baka rainforest hunter-gatherers from Cameroon and Gabon (west central Africa) and Nzebi and Nzime neighboring agriculturalists, we did not observe elevated |iHS| or FST values in these genomic regions. Together, these results suggest adaptive and at least partially convergent origins of the pygmy phenotype even within Africa, supporting the hypothesis that small body size confers a selective advantage for tropical rainforest hunter-gatherers but raising questions about the antiquity of this behavior.
Full-text · Article · Aug 2014 · Proceedings of the National Academy of Sciences
[Show abstract][Hide abstract] ABSTRACT: The response of host immune cells to microbial stimuli is dependent on robust and coordinated gene expression programs involving the transcription of thousands of genes. The dysregulation of such regulatory programs is likely to significantly contribute to the marked differences in susceptibility to infectious diseases observed among individuals and between human populations. Although the specific factors leading to a dysfunctional immune response to infection remain largely unknown, we are increasingly appreciating the importance of genetic variants in altering the expression levels of immune-related genes, possibly via epigenetic changes. This review describes how recent technological advances have profoundly contributed to our current understanding of the genetic architecture and the epigenetic rules controlling immune responses to infectious agents and how genetic and epigenetic data can be combined to unravel the mechanisms associated with host variation in transcriptional responses to infection.
No preview · Article · Jun 2014 · Current Opinion in Immunology
[Show abstract][Hide abstract] ABSTRACT: The NKG2 family of NK receptors includes activating and inhibitory members. With the exception of the homodimer-forming NKG2D, NKG2 receptors recognize the nonclassical MHC class I molecule HLA-E, and they can be subdivided into two groups: those that associate with and signal through DAP12 to activate cells, and those that contain an ITIM motif to promote inhibition. The function of NKG2 family member NKG2E is unclear in humans, and its surface expression has never been conclusively established, largely because there is no Ab that binds specifically to NKG2E. Seeking to determine a role for this molecule, we chose to investigate its expression and ability to form complexes with intracellular signaling molecules. We found that NKG2E was capable of associating with CD94 and DAP12 but that the complex was retained intracellularly at the endoplasmic reticulum instead of being expressed on cell surfaces, and that this localization was dependent on a sequence of hydrophobic amino acids in the extracellular domain of NKG2E. Because this particular sequence has emerged and been conserved selectively among higher order primates evolutionarily, this observation raises the intriguing possibility that NKG2E may function as an intracellular protein.
Full-text · Article · Jun 2014 · The Journal of Immunology
[Show abstract][Hide abstract] ABSTRACT: Chiari-like malformation (CM) is a developmental abnormality of the craniocervical junction that is common in the Griffon Bruxellois (GB) breed with an estimated prevalence of 65%. This disease is characterized by overcrowding of the neural parenchyma at the craniocervical junction and disturbance of cerebrospinal fluid (CSF) flow. The most common clinical sign is pain either as a direct consequence of CM or neuropathic pain as a consequence of secondary syringomyelia. The etiology of CM remains unknown but genetic factors play an important role. To investigate the genetic complexity of the disease, a quantitative trait locus (QTL) approach was adopted. A total of 14 quantitative skull and atlas measurements were taken and were tested for association to CM. Six traits were found to be associated to CM and were subjected to a whole-genome association study using the Illumina canine high density bead chip in 74 GB dogs (50 affected and 24 controls). Linear and mixed regression analyses identified associated single nucleotide polymorphisms (SNPs) on 5 Canis Familiaris Autosomes (CFAs): CFA2, CFA9, CFA12, CFA14 and CFA24. A reconstructed haplotype of 0.53 Mb on CFA2 strongly associated to the height of the cranial fossa (diameter F) and an haplotype of 2.5 Mb on CFA14 associated to both the height of the rostral part of the caudal cranial fossa (AE) and the height of the brain (FG) were significantly associated to CM after 10 000 permutations strengthening their candidacy for this disease (P = 0.0421, P = 0.0094 respectively). The CFA2 QTL harbours the Sall-1 gene which is an excellent candidate since its orthologue in humans is mutated in Townes-Brocks syndrome which has previously been associated to Chiari malformation I. Our study demonstrates the implication of multiple traits in the etiology of CM and has successfully identified two new QTL associated to CM and a potential candidate gene.
[Show abstract][Hide abstract] ABSTRACT: Genome-wide scans for selection have identified multiple regions of the human genome as being targeted by positive selection. However, only a small proportion has been replicated across studies, and the prevalence of positive selection as a mechanism of adaptive change in humans remains controversial. Here we explore the power of two haplotype-based statistics - the integrated haplotype score (iHS) and the Derived Intra-allelic Nucleotide Diversity (DIND) test - in the context of next-generation sequencing data, and evaluate their robustness to demography and other selection modes. We show that these statistics are both powerful for the detection of recent positive selection, regardless of population history, and robust to variation in coverage, with DIND being insensitive to very low coverage. We apply these statistics to whole-genome sequence datasets from the 1000 Genomes Project and Complete Genomics. We found that putative targets of selection were highly significantly enriched in genic and non-synonymous SNPs, and that DIND was more powerful than iHS in the context of small sample sizes, low-quality genotype calling or poor coverage. As we excluded genomic confounders and alternative selection models, such as background selection, the observed enrichment attests to the action of recent, strong positive selection. Further support to the adaptive significance of these genomic regions came from their enrichment in functional variants detected by genome-wide association studies, informing the relationship between past selection and current benign and disease-related phenotypic variation. Our results indicate that hard sweeps targeting low-frequency standing variation have played a moderate, albeit significant, role in recent human evolution.