Article

Polycomb function during oogenesis is required for mouse embryonic development

Friedrich Miescher Institute for Biomedical Research, CH-4058 Basel, Switzerland.
Genes & development (Impact Factor: 10.8). 04/2012; 26(9):920-32. DOI: 10.1101/gad.188094.112
Source: PubMed

ABSTRACT

In mammals, totipotent embryos are formed by fusion of highly differentiated gametes. Acquisition of totipotency concurs with chromatin remodeling of parental genomes, changes in the maternal transcriptome and proteome, and zygotic genome activation (ZGA). The inefficiency of reprogramming somatic nuclei in reproductive cloning suggests that intergenerational inheritance of germline chromatin contributes to developmental proficiency after natural conception. Here we show that Ring1 and Rnf2, components of Polycomb-repressive complex 1 (PRC1), serve redundant transcriptional functions during oogenesis that are essential for proper ZGA, replication and cell cycle progression in early embryos, and development beyond the two-cell stage. Exchange of chromosomes between control and Ring1/Rnf2-deficient metaphase II oocytes reveal cytoplasmic and chromosome-based contributions by PRC1 to embryonic development. Our results strongly support a model in which Polycomb acts in the female germline to establish developmental competence for the following generation by silencing differentiation-inducing genes and defining appropriate chromatin states.

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    • "Because PRC1 and PRC2 directly regulate the repression of a large set of common target genes, different models of functional dependency between these complexes have been proposed over the years (Gao et al., 2012; Scelfo et al., 2014) that suggest a dominant role for the PRC1 repressive activity (Blackledge et al., 2014; Cooper et al., 2014). Whereas Ring1a and Ring1b can be redundant during development (del Mar Lorente et al., 2000; Voncken et al., 2003), the Ring1a/b double KO embryos are impaired at the two-cell stage (Posfai et al., 2012), highlighting the requirement to inactivate both proteins to fully uncover PRC1 biological roles. Despite the extensive literature on the role of PRC1 in regulating gene transcription, embryonic stem cell (ESC) differentiation , and development, the role of PRC1 activity in adult stem cells is still largely unexplored. "
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    ABSTRACT: Polycomb repressive complexes (PRCs) are among the most important gatekeepers of establishing and maintaining cell identity in metazoans. PRC1, which plays a dominant role in this context, executes its functions via multiple subcomplexes, which all contribute to H2AK119 mono-ubiquitination (H2Aubq). Despite our comprehensive knowledge of PRC1-dependent H2Aubq in embryonic stem cells and during early development, its role in adult stem cells still remains poorly characterized. Here we show that PRC1 activity is required for the integrity of the intestinal epithelium, regulating stem cell self-renewal via a cell-autonomous mechanism that is independent from Cdkn2a expression. By dissecting the PRC1-dependent transcription program in intestinal stem cells, we demonstrate that PRC1 represses a large number of non-lineage-specific transcription factors that directly affect β-catenin/Tcf transcriptional activity. Our data reveal that PRC1 preserves Wnt/β-catenin activity in adult stem cells to maintain intestinal homeostasis and supports tumor formation induced by the constitutive activation of this pathway.
    No preview · Article · Nov 2015 · Cell stem cell
    • "pCHK1 staining was almost absent in controls (n=30) but was observed in 48% of Bcas2 mNull twocell embryos (n=25) (Fig. 5G). In addition to DNA damage checkpoints, malfunction of zygotic genome activation (ZGA) also causes two-cell stage arrest (Bultman et al., 2006;Posfai et al., 2012;Wu et al., 2003). When the expression of ZGA genes (Zeng et al., 2004;Zeng and Schultz, 2005) was examined by quantitative RT-PCR, the mRNA levels of ZGA genes such as Tdpoz1, Tdpoz3, Tdpoz4 increased. "
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    ABSTRACT: Mammalian early embryos maintain accurate genome integrity for proper development within a programmed timeline despite constant assaults on their DNA by replication, DNA demethylation and genetic defects transmitted from germ cells. However, how genome integrity is safeguarded during mammalian early embryonic development remains unclear. BCAS2 (Breast Carcinoma Amplified Sequence 2), a core component of the PRP19 complex involved in pre-mRNA splicing, plays an important role in the DNA damage response through the RPA complex, a key regulator in the maintenance of genome integrity. Currently, the physiological role of BCAS2 in mammals is unknown. We now report that BCAS2 responds to endogenous and exogenous DNA damage in mouse zygotes. Maternal depletion of BCAS2 compromises the DNA damage response in early embryos, leading to developmental arrest at the two- to four-cell stage accompanied by the accumulation of damaged DNA and micronuclei. Furthermore, BCAS2 mutants that are unable to bind RPA1 fail in DNA repair during the zygotic stage. In addition, phosphorylated RPA2 cannot localize to the DNA damage sites in mouse zygotes with disrupted maternal BCAS2. These data suggest that BCAS2 may function through the RPA complex during DNA repair in zygotes. Altogether, our results reveal that maternal BCAS2 maintains the genome integrity of early embryos and is essential for female mouse fertility.
    No preview · Article · Oct 2015 · Development
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    • "On irradiated cells, PRC1 subunits migrate to sites of induced DNA damage (Chou et al., 2010; Ginjala et al., 2011) to participate at the earliest signalling and amplification steps of the DDR pathways (Bergink et al., 2006; Lukas et al., 2011; Vissers et al., 2012). Defects in DNA replication have also been observed in double RING1A-and RING1B-deficient two-cell embryos and immortalised fibroblasts (Piunti et al., 2014; Posfai et al., 2012), but the involved processes are poorly characterised. Here, we address the contributions of RING1A and RING1B to DNA replication by immunolocalisation studies in unperturbed cells, shortly after conditional inactivation. "
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    ABSTRACT: Functions of Polycomb products extend beyond their well known activity as transcriptional regulators to include genome duplication processes. Polycomb activities in DNA replication and DNA damage repair are unclear, particularly without induced replicative stress. We have used a cellular model of conditionally inactive Polycomb E3 ligases (RING1A and RING1B) that monoubiquitylate lysine 119 of histone H2A (H2AK119Ub) to examine DNA replication in unperturbed cells. We identify slow elongation and fork stalling during DNA replication, associated to the accumulation of mid and late S cells. Signs of replicative stress and colocalization of double strand breaks with chromocenters, the sites of coalesced pericentromeric heterocromatic (PCH) domains, were enriched in cells at mid S, the stage at which PCH is replicated. Altered replication was rescued by targeted monoubiquitylation of PCH through methyl-CpG binding domain protein 1. The acute senescence associated to the depletion of RING1 proteins, mediated by CDKN1A/p21 upregulation, could be uncoupled from a response to DNA damage. These findings link cell proliferation and Polycomb RING1A/B to S phase progression through a specific function in PCH replication. © 2015. Published by The Company of Biologists Ltd.
    Full-text · Article · Aug 2015 · Journal of Cell Science
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