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The genomic distribution of transposable elements is driven by spatially variable purifying selection

ABSTRACT: The genomic distribution of transposable elements is driven by spatially variable purifying selection

PROVIDER: PRJEB54573 | ENA |

REPOSITORIES: ENA

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			Action	DRS
	ERR9922530_1.fastq.gz	Fastqsanger.gz
	ERR9922530_2.fastq.gz	Fastqsanger.gz
	ERR9922540_1.fastq.gz	Fastqsanger.gz
	ERR9922540_2.fastq.gz	Fastqsanger.gz
	ERR9922521_1.fastq.gz	Fastqsanger.gz

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Variable chromatin structure revealed by in situ spatially correlated DNA cleavage mapping

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Purifying selection acting on the sequence of highly expressed proteins in the microevolution

Project description:Constraints on the rate of protein sequence evolution have been a central question in evolutionary biology. Orthology analysis between closely related species has revealed that the evolutionary speed is constrained by the expression level, with highly expressed proteins evolving slowly. This negative correlation between expression levels and evolutionary rates (known as the E-R anticorrelation) has already been widely observed in past macroevolution between species, for example, between Escherichia coli and Salmonella. However, it remains unclear whether this seemingly general law also governs microevolution, including past and de novo, within a species. To explore the ubiquitous impact of expression level on molecular evolution in bacteria, we analysed genome sequences for 99 strains of E. coli for microevolution in nature. We also analysed genomic mutations accumulated under laboratory conditions as a model of de novo microevolution. Here, we show that the E-R anticorrelation is significant in both past microevolution and de novo evolution in E. coli. Our data also indicate that purifying selection acting on highly expressed genes contributes to the ubiquity of the E-R anticorrelation. This study confirmed ongoing purifying selection acting on highly expressed genes, and implied that expression level has a ubiquitous impact on the speed of molecular diversification evolution in bacteria.

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Plant Y-chromosome degeneration is retarded by haploid purifying selection.

Project description:Plant Y-chromosome degeneration is retarded by haploid purifying selection.

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Long-term experimental evolution reveals purifying selection on piRNA-mediated control of transposable element expression.

Project description:BackgroundTransposable elements (TEs) are an almost universal constituent of eukaryotic genomes. In animals, Piwi-interacting small RNAs (piRNAs) and repressive chromatin often play crucial roles in preventing TE transcription and thus restricting TE activity. Nevertheless, TE content varies widely across eukaryotes and the dynamics of TE activity and TE silencing across evolutionary time is poorly understood.ResultsHere, we used experimentally evolved populations of C. elegans to study the dynamics of TE expression over 409 generations. The experimental populations were evolved at population sizes of 1, 10 and 100 individuals to manipulate the efficiency of natural selection versus genetic drift. We demonstrate increased TE expression relative to the ancestral population, with the largest increases occurring in the smallest populations. We show that the transcriptional activation of TEs within active regions of the genome is associated with failure of piRNA-mediated silencing, whilst desilenced TEs in repressed chromatin domains retain small RNAs. Additionally, we find that the sequence context of the surrounding region influences the propensity of TEs to lose silencing through failure of small RNA-mediated silencing.ConclusionsOur results show that natural selection in C. elegans is responsible for maintaining low levels of TE expression, and provide new insights into the epigenomic features responsible.

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Purifying selection shapes the coincident SNP distribution of primate coding sequences.

Project description:Genome-wide analysis has observed an excess of coincident single nucleotide polymorphisms (coSNPs) at human-chimpanzee orthologous positions, and suggested that this is due to cryptic variation in the mutation rate. While this phenomenon primarily corresponds with non-coding coSNPs, the situation in coding sequences remains unclear. Here we calculate the observed-to-expected ratio of coSNPs (coSNPO/E) to estimate the prevalence of human-chimpanzee coSNPs, and show that the excess of coSNPs is also present in coding regions. Intriguingly, coSNPO/E is much higher at zero-fold than at nonzero-fold degenerate sites; such a difference is due to an elevation of coSNPO/E at zero-fold degenerate sites, rather than a reduction at nonzero-fold degenerate ones. These trends are independent of chimpanzee subpopulation, population size, or sequencing techniques; and hold in broad generality across primates. We find that this discrepancy cannot fully explained by sequence contexts, shared ancestral polymorphisms, SNP density, and recombination rate, and that coSNPO/E in coding sequences is significantly influenced by purifying selection. We also show that selection and mutation rate affect coSNPO/E independently, and coSNPs tend to be less damaging and more correlated with human diseases than non-coSNPs. These suggest that coSNPs may represent a "signature" during primate protein evolution.

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Relaxed purifying selection in autopolyploids drives transposable element over-accumulation which provides variants for local adaptation.

Project description:Polyploidization is frequently associated with increased transposable element (TE) content. However, what drives TE dynamics following whole genome duplication (WGD) and the evolutionary implications remain unclear. Here, we leverage whole-genome resequencing data available for ~300 individuals of Arabidopsis arenosa, a well characterized natural diploid-autotetraploid plant species, to address these questions. Based on 43,176 TE insertions we detect in these genomes, we demonstrate that relaxed purifying selection rather than transposition bursts is the main driver of TE over-accumulation after WGD. Furthermore, the increased pool of TE insertions in tetraploids is especially enriched within or near environmentally responsive genes. Notably, we show that the major flowering-time repressor gene FLC is disrupted by a TE insertion specifically in the rapid-cycling tetraploid lineage that colonized mainland railways. Together, our findings indicate that tetrasomy leads to an enhanced accumulation of genic TE insertions, some of which likely contribute to local adaptation.

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The Role of Small RNA-Based Epigenetic Silencing for Purifying Selection on Transposable Elements in Capsella grandiflora.

Project description:To avoid negative effects of transposable element (TE) proliferation, plants epigenetically silence TEs using a number of mechanisms, including RNA-directed DNA methylation. These epigenetic modifications can extend outside the boundaries of TE insertions and lead to silencing of nearby genes, resulting in a trade-off between TE silencing and interference with nearby gene regulation. Therefore, purifying selection is expected to remove silenced TE insertions near genes more efficiently and prevent their accumulation within a population. To explore how effects of TE silencing on gene regulation shapes purifying selection on TEs, we analyzed whole genome sequencing data from 166 individuals of a large population of the outcrossing species Capsella grandiflora. We found that most TEs are rare, and in chromosome arms, silenced TEs are exposed to stronger purifying selection than those that are not silenced by 24-nucleotide small RNAs, especially with increasing proximity to genes. An age-of-allele test of neutrality on a subset of TEs supports our inference of purifying selection on silenced TEs, suggesting that our results are robust to varying transposition rates. Our results provide new insights into the processes affecting the accumulation of TEs in an outcrossing species and support the view that epigenetic silencing of TEs results in a trade-off between preventing TE proliferation and interference with nearby gene regulation. We also suggest that in the centromeric and pericentromeric regions, the negative aspects of epigenetic TE silencing are missing.

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Purifying selection acting on the sequence of highly expressed proteins in the microevolution

Project description:Purifying selection acting on the sequence of highly expressed proteins in the microevolution

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Small RNA accumulation in Transposable Element-silent and Transposable Element-active epigenomes

Project description:Background: The small RNAs that Transposable Elements generate are vastly different when they are transcriptionally silenced compared to when they are transcriptionally activated. We performed the deep sequencing of small RNAs in a number of small RNA biogenesis mutants in both Transposable Element-silenced and Transposable Element-active epigenome backgrounds. Results: We found that Transposable Elements generate large amounts of 21-22nt siRNAs only when they are transcriptionally active. These 21-22nt siRNAs are incorporated into the AGO6 protein. Conclusion: Ago6 is the key protein that bridges the post-transcriptional degradation of Transposable Element mRNAs and the establishment of DNA methylation. Examination of flower bud small RNAs from wild type and 5 single or double mutant combinations, many of which have biological replicates. In addition, IP purification of the AGO6 protein (and mock no-antigen controls) followed by sequencing of the incorporated small RNAs. Replicate A for Col and ddm1 are submitted in GSE41755

2014-11-14 | E-GEOD-57191 | biostudies-arrayexpress