Modulation of cell cycle control during oocyte-to-embryo transitions

Abstract

Ex ovo omnia-all animals come from eggs-this statement made in 1651 by the English physician William Harvey marks a seminal break with the doctrine that all essential characteristics of offspring are contributed by their fathers, while mothers contribute only a material substrate. More than 360 years later, we now have a comprehensive understanding of how haploid gametes are generated during meiosis to allow the formation of diploid offspring when sperm and egg cells fuse. In most species, immature oocytes are arrested in prophase I and this arrest is maintained for few days (fruit flies) or for decades (humans). After completion of the first meiotic division, most vertebrate eggs arrest again at metaphase of meiosis II. Upon fertilization, this second meiotic arrest point is released and embryos enter highly specialized early embryonic divisions. In this review, we discuss how the standard somatic cell cycle is modulated to meet the specific requirements of different developmental stages. Specifically, we focus on cell cycle regulation in mature vertebrate eggs arrested at metaphase II (MII-arrest), the first mitotic cell cycle, and early embryonic divisions.

The sweet side of the cell cycle

“…The goal of meiosis is to generate haploid gametes, allowing for the formation of diploid offspring upon fertilization [47]. Meiosis involves two rounds of cell division (meiosis I and meiosis II) without an intervening round of DNA replication.…”

“…Meiosis involves two rounds of cell division (meiosis I and meiosis II) without an intervening round of DNA replication. In mammals, fully grown oocytes in the ovary are arrested in prophase I, and it is only upon hormonal stimulation at the time of ovulation that they will resume meiosis, progress through meiosis I, and then arrest at metaphase of meiosis II [47]. Then, it is only following fertilization that the second meiotic arrest will be released and zygotes will enter early embryonic mitotic divisions [47].…”

“…In mammals, fully grown oocytes in the ovary are arrested in prophase I, and it is only upon hormonal stimulation at the time of ovulation that they will resume meiosis, progress through meiosis I, and then arrest at metaphase of meiosis II [47]. Then, it is only following fertilization that the second meiotic arrest will be released and zygotes will enter early embryonic mitotic divisions [47]. Meiosis I includes homologous chromosome pairing, synapsis, and recombination and separation of homologous chromosomes.…”

Exploring the phosphoproteome profiles duringXenopusegg activation by calcium stimulation using a fully automated phosphopeptide purification system

“…Xenopus eggs have been used in studies on egg maturation, egg activation and other mechanisms, which facilitated the progress of developmental biology (1,2). It has been shown that signalling pathways including protein phosphorylation and dephosphorylation participate greatly in these regulation mechanisms (1,3,4).…”

“…It has been shown that signalling pathways including protein phosphorylation and dephosphorylation participate greatly in these regulation mechanisms (1,3,4). To clarify the complicated regulation mechanism of egg activation, comprehensive analysis of protein phosphorylation during egg activation is a powerful means.…”