ATRX contributes to epigenetic asymmetry and silencing of major satellite transcripts in the maternal genome of the mouse embryo

Abstract

A striking proportion of human cleavage-stage embryos exhibit chromosome instability (CIN). Notably, until now, no experimental model has been described to determine the origin and mechanisms of complex chromosomal rearrangements. Here, we examined mouse embryos deficient for the chromatin remodeling protein ATRX to determine the cellular mechanisms activated in response to CIN. We demonstrate that ATRX is required for silencing of major satellite transcripts in the maternal genome, where it confers epigenetic asymmetry to pericentric heterochromatin during the transition to the first mitosis. This stage is also characterized by a striking kinetochore size asymmetry established by differences in CENP-C protein between the parental genomes. Loss of ATRX results in increased centromeric mitotic recombination, a high frequency of sister chromatid exchanges and double strand DNA breaks, indicating the formation of mitotic recombination break points. ATRX-deficient embryos exhibit a twofold increase in transcripts for aurora kinase B, the centromeric cohesin ESCO2, DNMT1, the ubiquitin-ligase (DZIP3) and the histone methyl transferase (EHMT1). Thus, loss of ATRX activates a pathway that integrates epigenetic modifications and DNA repair in response to chromosome breaks. These results reveal the cellular response of the cleavage-stage embryo to CIN and uncover a mechanism by which centromeric fission induces the formation of large-scale chromosomal rearrangements. Our results have important implications to determine the epigenetic origins of CIN that lead to congenital birth defects and early pregnancy loss, as well as the mechanisms involved in the oocyte to embryo transition.

Integrity of the human centromere DNA repeats is protected by CENP-A, CENP-C, and CENP-T

“…In U2OS cells, ATRX is deleted and telomere is maintained via the alternative lengthening of telomeres (ALT) pathway (30). It has been recently shown that C-SCE is enhanced in mouse embryos lacking ATRX, and suggested that this hyperrecombination may result in chromosome breakage at the centromere and fusion (25). Thus, it is likely that multiple mechanisms drive centromere instability in cancer cells.…”

“…Suppression of meiotic recombination at centromeres is established in eukaryotes, including human (19,21), whereas active mitotic recombination at the centromere has been reported in budding yeast, fission yeast, and mice (22)(23)(24)(25). In mice, DNA methylation by the DNA methyltransferases DNMT3a/b and chromatin remodeler α-thalassemia mental retardation X-linked protein (ATRX) contruibutes to suppression of centromereassociated sister chromatid exchanges (C-SCEs) (24,25), but it remains unclear whether human centromeres actively undergo recombination, and whether a direct mechanism exists to suppress illegitimate recombination within the core centromeric HOR.…”

Heterochromatin and the molecular mechanisms of ‘parent-of-origin’ effects in animals

“…It is known that either incorporation of mutant H3.3 or interference with expression of reverse major satellite RNAs affects CF and blocks development at the 2-cell stage (Santenard et al 2010;Casanova et al, 2013). Notably, DAXX also fails to be incorporated into constitutive heterochromatin at PNBs in ATRX-deficient zygotes (De La Fuente et al 2015) indicating that ATRX and DAXX act as a complex during CF, as they do at heterochromatic regions in other cell types (Voon et al 2015).…”

Dual spindle formation in zygotes keeps parental genomes apart in early mammalian embryos

“…Having an experimental method to induce mixing of the parental genomes in the zygote, put us in a position to test the hypothesis that nuclear compartmentalization plays a role in resolving epigenetic asymmetry in early development as proposed previously (Mayer, Smith et al 2000, Probst and Almouzni 2008, Duffie and Bourc'his 2013, De La Fuente, Baumann et al 2015.…”