Gene expression during the oocyte‐to‐embryo transition in mammals

Abstract

The seminal question in modern developmental biology is the origins of new life arising from the unification of sperm and egg. The roots of this question begin from 19 th -20 th century embryologists studying fertilization and embryogenesis. Although the revolution of molecular biology has yielded significant insight into the complexity of this process, the overall orchestration of genes, molecules, and cells, is still not fully formed. Early mammalian development, specifically the oocyte-to-embryo transition, is essentially under "maternal command" from factors deposited in the cytoplasm during oocyte growth, independent of de novo transcription from the nascent embryo. Many of the advances in understanding this developmental period occurred in tandem with application of new methods and techniques from molecular biology, from protein electrophoresis to sequencing and assemblies of whole genomes. From this bed of knowledge, it appears that precise control of mRNA translation is a key regulator coordinating the molecular and cellular events occurring during oocyte-to-embryo transition. Notably, oocyte transcriptomes share, yet retain some uniqueness, common genetic motifs among all chordates. The common genetic motifs typically define fundamental processes critical for cellular maintenance, whereas the unique genetic features may be a source of variation and a substrate for sexual selection, genetic drift, or gene flow. One purpose for this complex interplay among genes, proteins, and cells may allow for evolution to transform and act upon the underlying processes, at molecular, structural and organismal levels, to increase diversity, which is the ultimate goal of sexual reproduction.

Characterization of Maternal Antigen That Embryos Require (MATER/NLRP5) Gene and Protein in Pig Somatic Tissues and Germ Cells

“…Processing of the sperm nucleus, organization of the two pronuclei and the first cell divisions, as well as activation of the embryonic genome are regulated by pre-existing factors in the egg cytoplasm encoded by maternal genes [19]. The NLRP5 gene has one of the earliest effects on embryogenesis; fertilized oocytes from NLRP5 knock-out mice do not progress beyond the 2-cell stage [15].…”

“…An increasing amount of data indicates that the embryonic genome activation is crucial for the success of preimplantation embryo development [16]. To ensure maternal-embryo transition (MET) of gene expression, oocytes have to reach a sufficiently advanced level of developmental competence during differentiation and maturation [17][18][19]. Maternally expressed genes are implicated in this process, and some of them are associated with developmental competence [20,21].…”

Competition between target sites of regulators shapes post-transcriptional gene regulation

“…Pronounced changes in the transcriptome of a cell can also occur without transcription. An extreme example is the fertilization of an oocyte, the reprogramming of which into a totipotent zygote is independent of transcription in all studied animals [22][23][24] . In Caenorhabditis elegans, thousands of mRNAs are turned over within ~30 minutes 25 .…”

Proteomic Analysis of Eggs from Mytilus edulis Females Differing in Mitochondrial DNA Transmission Mode

“…The study of the molecular basis of DUI might thus be advanced by transcriptomic and proteomic studies of these cells. The potential for such maternal effects are supported by evidence that maternal factors deposited in the oocyte are entirely responsible for its development and that of the early embryo (35). Oocytes show a high level of transcriptional activity to provide mRNAs required for growth of the embryo, including a network of transcriptional regulators (36).…”

“…However transcript levels do not necessarily reflect protein levels because of measurement errors and biological factors such as protein turnover rates and variable half-life (38,39). Thus proteomics approaches are important to complement transcriptomic studies in oocytes (35,40). For example, comparison of germinal vesicle and metaphase II murine oocytes using 2-DE and silver staining successfully revealed 12 (41) and 63 (42) protein expression differences, many known to be associated with meiosis and murine maturation.…”