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Dual RNA 3’ end processing of H2A.X messenger RNA maintains DNA damage repair throughout the cell cycle

ABSTRACT: Replication-dependent (RD) histone mRNA are the only non-polyadenylated protein coding transcripts in humans. However, a subset of RD histone genes also expresses polyadenylated mRNA upon terminal differentiation to maintain histone proteins. We now show that even in cycling cells, RD histone genes express some poly(A) mRNA. The H2AFX gene, encoding the DNA damage signalling histone variant H2A.X, expresses both an S-phase-specific SL mRNA ending in the typical stem-loop (SL) structure and substantial amounts of an extended poly(A) mRNA. We show, by the selective removal of either mRNA isoform, that the S-phase-specific H2A.X SL mRNA can generate sufficient histone for deposition onto DNA damage responsive (DDR) chromatin in some cell types. In contrast, when cells have evolved to make predominantly H2A.X poly(A) mRNA they then require de novo H2A.X for efficient DDR. This highlights the importance of differential H2AFX mRNA 3’ end processing for the maintenance of effective DDR

ORGANISM(S): Homo sapiens

PROVIDER: GSE144323 | GEO | 2020/11/23

REPOSITORIES: GEO

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Project description:H2A.X is an H2A variant histone in eukaryotes, unique for its ability to respond to DNA damage, initiating the DNA repair pathway. H2A.X replacement within the histone octamer is mediated by the FAcilitates Chromatin Transactions (FACT) complex, a key chromatin remodeler. FACT is required for DEMETER (DME)-mediated DNA demethylation at certain loci in Arabidopsis thaliana female gametophytes during reproduction. Here, we sought to investigate whether H2A.X is involved in DME- and FACT-mediated DNA demethylation during reproduction. H2A.X is encoded by two genes in Arabidopsis genome, HTA3 and HTA5. We generated h2a.x double mutants, which displayed a normal growth profile, whereby flowering time, seed development, and root tip organization, S-phase progression and proliferation were all normal. However, h2a.x mutants were more sensitive to genotoxic stress, consistent with previous reports. H2A.X fused to Green Fluorescent Protein (GFP) under the H2A.X promoter was highly expressed especially in newly developing Arabidopsis tissues, including in male and female gametophytes, where DME is also expressed. We examined DNA methylation in h2a.x developing seeds and seedlings using whole genome bisulfite sequencing, and found that CG DNA methylation is decreased genome-wide in h2a.x mutant seeds. Hypomethylation was most striking in transposon bodies, and occurred on both parental alleles in the developing endosperm, but not the embryo or seedling. h2a.x-mediated hypomethylated sites overlapped DME targets, but also included other loci, predominately located in heterochromatic transposons and intergenic DNA. Our genome-wide methylation analyses suggest that H2A.X could function in preventing access of the DME demethylase to non-canonical sites. Alternatively, H2A.X may be involved in recruiting methyltransferases to those sites. Overall, our data show that H2A.X is required to maintain DNA methylation homeostasis in the unique chromatin environment of the Arabidopsis endosperm.

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Dual RNA 3’ end processing of H2A.X messenger RNA maintains DNA damage repair throughout the cell cycle

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