ABSTRACT: Next-generation sequencing for MHC class I genes typing reveals trans-species polymorphism in Eutropis multifasciata and other species of Scincidae
Project description:Gene expression evolution can be caused by changes in cis- or trans-regulatory elements or both. As cis and trans regulation operate through different molecular mechanisms, cis and trans mutations may show different inheritance patterns and may be subjected to different selective constraints. To investigate these issues, we obtained and analyzed gene expression data from two Saccharomyces cerevisiae strains and their hybrid, using high-throughput sequencing. Our data indicate that compared to other types of genes, those with antagonistic cis-trans interactions are more likely to exhibit over- or under-dominant inheritance of expression level. Moreover, in accordance with previous studies, genes with trans variants tend to have a dominant inheritance pattern while cis variants are enriched for additive inheritance. In addition, cis regulatory differences contribute more to expression differences between species than within species, whereas trans regulatory differences show a stronger association between divergence and polymorphism. Our data indicate that in the trans component of gene expression differences genes subjected to weaker selective constraints tend to have an excess of polymorphism over divergence compared to those subjected to stronger selective constraints. In contrast, in the cis component, this difference between genes under stronger and weaker selective constraint is mostly absent. To explain these observations, we propose that purifying selection more strongly shapes trans polymorphism than cis polymorphism. Study the gene expression patterns in two strains of yeast (BY and RM)
Project description:Gene expression evolution can be caused by changes in cis- or trans-regulatory elements or both. As cis and trans regulation operate through different molecular mechanisms, cis and trans mutations may show different inheritance patterns and may be subjected to different selective constraints. To investigate these issues, we obtained and analyzed gene expression data from two Saccharomyces cerevisiae strains and their hybrid, using high-throughput sequencing. Our data indicate that compared to other types of genes, those with antagonistic cis-trans interactions are more likely to exhibit over- or under-dominant inheritance of expression level. Moreover, in accordance with previous studies, genes with trans variants tend to have a dominant inheritance pattern while cis variants are enriched for additive inheritance. In addition, cis regulatory differences contribute more to expression differences between species than within species, whereas trans regulatory differences show a stronger association between divergence and polymorphism. Our data indicate that in the trans component of gene expression differences genes subjected to weaker selective constraints tend to have an excess of polymorphism over divergence compared to those subjected to stronger selective constraints. In contrast, in the cis component, this difference between genes under stronger and weaker selective constraint is mostly absent. To explain these observations, we propose that purifying selection more strongly shapes trans polymorphism than cis polymorphism.
Project description:The adaptive immune system distinguishes self from non-self by surveying peptides generated from degradation of intracellular proteins that are loaded onto MHC Class I molecules for display on the cell surface. While early studies reported that the bulk of cell surface MHC Class I complexes require the ubiquitin-proteasome system (UPS) for their generation, this conclusion has been challenged. To better understand MHC Class I peptide origins, we sought to carry out a comprehensive, quantitative census of the MHC Class I peptide repertoire in the presence and absence of UPS activity. We introduce optimized methodology to enrich for authentic Class I-bound peptides in silico and then quantify by mass spectrometry their relative amounts upon perturbation of the ubiquitin-proteasome system. Whereas most peptides are dependent on the proteasome and ubiquitination for their generation, a surprising 30% of the MHC Class I repertoire, enriched in peptides of mitochondrial origin, appears independent of these pathways. A further ~10% of Class I-bound peptides were found to be dependent on the proteasome but independent of ubiquitination for their generation. Notably, clinically achievable partial inhibition of the proteasome resulted in display of novel peptide antigens. Our results suggest that generation of MHC Class I/peptide complexes is more complex than previously recognized, with UPS-dependent and UPS-independent components; paradoxically, a smaller number of atypical peptides increase in presentation when canonical pathways are impaired.
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