Project description:Transcriptional networks have been shown to evolve very rapidly, prompting questions as to how such changes arise and are tolerated. Recent comparisons of transcriptional networks across species have implicated variations in the cis-acting DNA sequences near genes as the main cause of divergence. What is less clear is how these changes interact with trans-acting changes occurring elsewhere in the genetic circuit. Here, we report the discovery of a system of compensatory trans and cis mutations in the yeast AP-1 transcriptional network that allows for conserved transcriptional regulation despite continued genetic change. We pinpoint a single species, the fungal pathogen Candida glabrata, in which a trans mutation has occurred very recently in a single AP-1 family member distinguishing it from its Saccharomyces ortholog. Comparison of chromatin immunoprecipitation profiles between Candida and Saccharomyces shows that, despite their different DNA binding domains, the AP-1 orthologs regulate a conserved block of genes. This conservation is enabled by concomitant changes in the cis-regulatory motifs upstream of each gene. Thus, both trans and cis mutations have perturbed the yeast AP-1 regulatory system in such a way as to compensate for one another. This demonstrates an example of “co-evolution” between a DNA-binding transcription factor and its cis-regulatory site, reminiscent of the co-evolution of protein binding partners. 3 Experiments were performed. Three replicates CgAp1-TAP was ChIPped under MMS treatment (GSM397447..GSM397449), two replicates each of ScYap1R79K and ScYap4K252R (GSM594724..GSM594727), were ChIPped under MMS treatment.
Project description:Transcriptional networks have been shown to evolve very rapidly, prompting questions as to how such changes arise and are tolerated. Recent comparisons of transcriptional networks across species have implicated variations in the cis-acting DNA sequences near genes as the main cause of divergence. What is less clear is how these changes interact with trans-acting changes occurring elsewhere in the genetic circuit. Here, we report the discovery of a system of compensatory trans and cis mutations in the yeast AP-1 transcriptional network that allows for conserved transcriptional regulation despite continued genetic change. We pinpoint a single species, the fungal pathogen Candida glabrata, in which a trans mutation has occurred very recently in a single AP-1 family member distinguishing it from its Saccharomyces ortholog. Comparison of chromatin immunoprecipitation profiles between Candida and Saccharomyces shows that, despite their different DNA binding domains, the AP-1 orthologs regulate a conserved block of genes. This conservation is enabled by concomitant changes in the cis-regulatory motifs upstream of each gene. Thus, both trans and cis mutations have perturbed the yeast AP-1 regulatory system in such a way as to compensate for one another. This demonstrates an example of “co-evolution” between a DNA-binding transcription factor and its cis-regulatory site, reminiscent of the co-evolution of protein binding partners.
Project description:Gene expression is regulated both by cis elements, which are DNA segments closely linked to the genes they regulate, and by trans activating factors, which are usually proteins capable of diffusing to unlinked genes. Understanding the patterns and sources of regulatory variation is crucial for understanding phenotypic and genome evolution. Here, we investigate the global patterns of gene expression evolution in Saccharomyces cerivisiae. We report statistical methods useful in quantifying cis and trans regulation using next generation sequencing data. Using these methods, measured genome-wide allele-specific expression by deep sequencing to investigate the genetic architecture of gene regulatory variation between two strains of Saccharomyces cerevisiae. We find that expression polymorphism in yeast is common for both cis and trans regulation, though trans variation is more common. Our detailed analyses of the effects of functional constraint on expression variation as indicated by measures such as protein connectivity, gene essentiality, and the ratio of nonsynonymous substitutions to synonymous substitutions clearly reveal that both classes of variation are under purifying selection, but trans variation is more sensitive to selective constraint. Comparing interspecific expression divergence between S. cerevisiae and S. paradoxus to our intraspecific variation suggests that natural selection strongly influences the patterns of variation we observe. Further analyses revealed that cis divergence is more frequently mediated by positive Darwinian selection than trans divergence, which is compatible with neutral evolution. Study the gene expression patterns in two strains of yeast (BY and RM)
Project description:Gene expression differences between species are driven by both cis and trans effects. Whereas cis effects on gene expression are due to nearby genetic variants, trans effects are due to distal genetic variants that affect diffusible elements such as transcription factors. However, as previous studies have mostly assessed the impacts of cis and trans effects at the gene level, how cis and trans effects differentially impact regulatory elements such as enhancers and promoters remains poorly understood. Here, we used massively parallel reporter assays to directly measure cis and trans effects between human and mouse embryonic stem cells at thousands of individual regulatory elements, including enhancers as well as promoters of both protein-coding and long non-coding RNA genes. Our approach revealed that cis effects are widespread across regulatory elements, and the strongest cis effects are associated with the disruption of motifs recognized by strong transcriptional activators. Conversely, we found that trans effects are rare but stronger in enhancers than promoters, and can be attributed to a subset of transcription factors that are differentially expressed between human and mouse. While previous gene-based studies have found extensive co-occurrence of cis and trans effects in opposite directions that stabilize gene expression between species—or compensatory cis-trans effects—we find that cis-trans compensation is uncommon within individual regulatory elements. Moreover, regulatory elements that do show compensatory cis-trans effects are often less redundant than regulatory elements lacking compensatory cis-trans effects. Thus, our results are consistent with a model wherein compensatory cis-trans effects occur more often through crosstalk between multiple redundant regulatory elements than within a single individual regulatory element. Together, these results indicate that studying the evolution of individual regulatory elements is pivotal to understand the tempo and mode of gene expression evolution.
Project description:Two inbred mouse strains, C57BL/6J and CAST/EiJ, were crossed to generate both initial and reciprocal F1 crosses. For each genetically distinct class of mice (F0 C57BL/6J, F0 CAST/EiJ, F1i - C57BL/6J x CAST/EiJ, F1r - CAST/EiJ x C57BL/6J, where the male parent is listed first), samples were collected from a single lobe of the liver from 6 male mice between the ages of 4 and 6 months. The 24 samples were then processed to generate strand-specific RNA-seq libraries, which were sequenced on the Illumina GAII platform using 72bp paired-end reads.
Project description:Gene expression is regulated both by cis elements, which are DNA segments closely linked to the genes they regulate, and by trans activating factors, which are usually proteins capable of diffusing to unlinked genes. Understanding the patterns and sources of regulatory variation is crucial for understanding phenotypic and genome evolution. Here, we investigate the global patterns of gene expression evolution in Saccharomyces cerivisiae. We report statistical methods useful in quantifying cis and trans regulation using next generation sequencing data. Using these methods, measured genome-wide allele-specific expression by deep sequencing to investigate the genetic architecture of gene regulatory variation between two strains of Saccharomyces cerevisiae. We find that expression polymorphism in yeast is common for both cis and trans regulation, though trans variation is more common. Our detailed analyses of the effects of functional constraint on expression variation as indicated by measures such as protein connectivity, gene essentiality, and the ratio of nonsynonymous substitutions to synonymous substitutions clearly reveal that both classes of variation are under purifying selection, but trans variation is more sensitive to selective constraint. Comparing interspecific expression divergence between S. cerevisiae and S. paradoxus to our intraspecific variation suggests that natural selection strongly influences the patterns of variation we observe. Further analyses revealed that cis divergence is more frequently mediated by positive Darwinian selection than trans divergence, which is compatible with neutral evolution.
Project description:Gene-expression divergence between species shapes morphological evolution, but the molecular basis is largely unknown. Here we show cis- and trans-regulatory elements and chromatin modifications on gene-expression diversity in genetically tractable Arabidopsis allotetraploids. In Arabidopsis thaliana and Arabidopsis arenosa, both cis and trans with predominant cis-regulatory effects mediate gene-expression divergence. The majority of genes with both cis- and trans-effects are subjected to compensating interactions and stabilizing selection. Interestingly, chromatin modifications correlate with cis - and trans -regulation. In F1 allotetraploids, Arabidopsis arenosa trans factors predominately affect allelic expression divergence. Arabidopsis arenosa trans factors tend to upregulate Arabidopsis thaliana alleles, whereas Arabidopsis thaliana trans factors up- or down-regulate Arabidopsis arenosa alleles. In resynthesized and natural allotetraploids, trans effects drive expression of both homoeologous loci into the same direction. We provide evidence for natural selection and chromatin regulation in shaping gene-expression diversity during plant evolution and speciation. Examination of gene expression in 5 tetraploid Arabidopsis using mRNA-seq