Abstract
Mammalian oocyte maturation and embryo development are unique biological processes regulated by various modifications. Since de novo mRNA transcription is absent during oocyte meiosis, protein-level regulation, especially post-translational modification (PTM), is crucial. It is known that PTM plays key roles in diverse cellular events such as DNA damage response, chromosome condensation, and cytoskeletal organization during oocyte maturation and embryo development. However, most previous reviews on PTM in oocytes and embryos have only focused on studies of Xenopus laevis or Caenorhabditis elegans eggs. In this review, we will discuss the latest discoveries regarding PTM in mammalian oocytes maturation and embryo development, focusing on phosphorylation, ubiquitination, SUMOylation and Poly(ADP-ribosyl)ation (PARylation). Phosphorylation functions in chromosome condensation and spindle alignment by regulating histone H3, mitogen-activated protein kinases, and some other pathways during mammalian oocyte maturation. Ubiquitination is a three-step enzymatic cascade that facilitates the degradation of proteins, and numerous E3 ubiquitin ligases are involved in modifying substrates and thus regulating oocyte maturation, oocyte-sperm binding, and early embryo development. Through the reversible addition and removal of SUMO (small ubiquitin-related modifier) on lysine residues, SUMOylation affects the cell cycle and DNA damage response in oocytes. As an emerging PTM, PARlation has been shown to not only participate in DNA damage repair, but also mediate asymmetric division of oocyte meiosis. Each of these PTMs and external environments is versatile and contributes to distinct phases during oocyte maturation and embryo development.
Highlights
Oocyte maturation is a unique type of cell division that is different from mitosis
Besides the posttranslational modification (PTM) we reviewed above, a small number of studies found that other PTMs, such as glycosylation and acetylation, involved in oocyte maturation and embryo development
With a diagnosis of primary infertility of unknown causes, a four-generation family was included in a recent study (Sang et al, 2019)
Summary
Oocyte maturation is a unique type of cell division that is different from mitosis. It is defined as the reinitiation and completion of the first meiotic division (Trounson et al, 1998). The nucleosome is the basic structural unit of eukaryotic chromosomes consisting of a 147-bp segment of DNA wrapped against a histone octamer of H2A, H2B, H3, and H4 (Fodor et al, 2010) Histones such as H2A and H2B play important roles in oocyte maturation mainly by regulating the transcription process, and the C-terminal lysine residues of H2A and H2B can be ubiquitinated. During embryo development, it seems that H2Bub is not the upstream regulator of H3K79me and H3K4me3 At present, it is not well known how H2B dynamically modulates nucleosome stability and chromatin dynamics through ubiquitination and deubiquitination during the oocyte maturation and preimplantation process (Chandrasekharan et al, 2010; Fuchs et al, 2012). Ubc9mediated SUMOylation affects meiosis and preimplantation development mainly by regulating spindle organization and chromosome segregation
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