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Epigenetics and Chromatin

, 9:44

First Online: 19 October 2016Received: 27 July 2016Accepted: 05 October 2016

Abstract

BackgroundIn C. elegans, in order to equalize gene expression between the sexes and balance X and autosomal expression, two steps are believed to be required. First, an unknown mechanism is hypothesized to upregulate the X chromosome in both sexes. This mechanism balances the X to autosomal expression in males, but creates X overexpression in hermaphrodites. Therefore, to restore the balance, hermaphrodites downregulate gene expression twofold on both X chromosomes. While many studies have focused on X chromosome downregulation, the mechanism of X upregulation is not known.

ResultsTo gain more insight into X upregulation, we studied the effects of chromatin condensation and histone acetylation on gene expression levels in male C. elegans. We have found that the H4K16 histone acetyltransferase MYS-1-Tip60 mediates dramatic decondensation of the male X chromosome as measured by FISH. However, RNA-seq analysis revealed that MYS-1 contributes only slightly to upregulation of gene expression on the X chromosome. These results suggest that the level of chromosome decondensation does not necessarily correlate with the degree of gene expression change in vivo. Furthermore, the X chromosome is more sensitive to MYS-1-mediated decondensation than the autosomes, despite similar levels of H4K16ac on all chromosomes, as measured by ChIP-seq. H4K16ac levels weakly correlate with gene expression levels on both the X and the autosomes, but highly expressed genes on the X chromosome do not contain exceptionally high levels of H4K16ac.

ConclusionThese results indicate that H4K16ac and chromosome decondensation influence regulation of the male X chromosome; however, they do not fully account for the high levels of gene expression observed on the X chromosomes.

KeywordsCaenorhabditis elegans Dosage compensation Gene expression Epigenetics Chromosome territories Chromatin Histone acetylation AbbreviationsDCCdosage compensation complex

HAThistone acetyltransferase

H4K16achistone H4 lysine 16 acetylation

FISHfluorescent in situ hybridization

YACyeast artificial chromosome

IFimmunofluorescence

MSLmale-specific lethal

NSLnon-specific lethal

TSStranscription start site

TTStranscription termination site

Electronic supplementary materialThe online version of this article doi:10.1186-s13072-016-0097-x contains supplementary material, which is available to authorized users.

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Autor: Alyssa C. Lau - Kevin P. Zhu - Elizabeth A. Brouhard - Michael B. Davis - Györgyi Csankovszki

Fuente: https://link.springer.com/



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