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Proc Natl Acad Sci U S A. 2015 Nov 24;112(47):14641-6. doi: 10.1073/pnas.1512775112. Epub 2015 Nov 6.

Histone chaperone CAF-1 mediates repressive histone modifications to protect preimplantation mouse embryos from endogenous retrotransposons.

Author information

1
RIKEN BioResource Center, Tsukuba, Ibaraki 305-0074, Japan;
2
RIKEN BioResource Center, Tsukuba, Ibaraki 305-0074, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan;
3
Tohoku University Graduate School of Medicine, Sendai, Miyagi 980-8575, Japan;
4
Department of Advanced Medical Initiatives, Faculty of Medicine, Kyushu University, Fukuoka, Fukuoka 812-8582, Japan;
5
Advanced Biological Information Research Division, Inamori Frontier Research Center, Kyushu University, Fukuoka, Fukuoka 819-0395, Japan;
6
RIKEN BioResource Center, Tsukuba, Ibaraki 305-0074, Japan; Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8572, Japan; Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Tokyo 113-0033, Japan ogura@rtc.riken.go.jp.

Abstract

Substantial proportions of mammalian genomes comprise repetitive elements including endogenous retrotransposons. Although these play diverse roles during development, their appropriate silencing is critically important in maintaining genomic integrity in the host cells. The major mechanism for retrotransposon silencing is DNA methylation, but the wave of global DNA demethylation that occurs after fertilization renders preimplantation embryos exceptionally hypomethylated. Here, we show that hypomethylated preimplantation mouse embryos are protected from retrotransposons by repressive histone modifications mediated by the histone chaperone chromatin assembly factor 1 (CAF-1). We found that knockdown of CAF-1 with specific siRNA injections resulted in significant up-regulation of the retrotransposons long interspersed nuclear element 1, short interspersed nuclear element B2, and intracisternal A particle at the morula stage. Concomitantly, increased histone H2AX phosphorylation and developmental arrest of the majority (>95%) of embryos were observed. The latter was caused at least in part by derepression of retrotransposons, as treatment with reverse transcriptase inhibitors rescued some embryos. Importantly, ChIP analysis revealed that CAF-1 mediated the replacement of H3.3 with H3.1/3.2 at the retrotransposon regions. This replacement was associated with deposition of repressive histone marks, including trimethylation of histone H3 on lysine 9 (H3K9me3), H3K9me2, H3K27me3, and H4K20me3. Among them, H4K20me3 and H3K9me3 seemed to play predominant roles in retrotransposon silencing, as assessed by knockdown of specific histone methyltransferases and forced expression of unmethylatable mutants of H3.1K9 and H4K20. Our data thus indicate that CAF-1 is an essential guardian of the genome in preimplantation mouse embryos by deposition of repressive histone modifications via histone variant replacement.

KEYWORDS:

CAF-1; embryo; histone variant; mouse; retrotransposon

PMID:
26546670
PMCID:
PMC4664303
DOI:
10.1073/pnas.1512775112
[Indexed for MEDLINE]
Free PMC Article

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