Biochemical alterations in the oocyte in support of early embryonic development

Abstract

Notwithstanding the enormous reproductive potential encapsulated within a mature mammalian oocyte, these cells present only a limited window for fertilization before defaulting to an apoptotic cascade known as post-ovulatory oocyte aging. The only cell with the capacity to rescue this potential is the fertilizing spermatozoon. Indeed, the union of these cells sets in train a remarkable series of events that endows the oocyte with the capacity to divide and differentiate into the trillions of cells that comprise a new individual. Traditional paradigms hold that, beyond the initial stimulation of fluctuating calcium (Ca) required for oocyte activation, the fertilizing spermatozoon plays limited additional roles in the early embryo. While this model has now been drawn into question in view of the recent discovery that spermatozoa deliver developmentally important classes of small noncoding RNAs and other epigenetic modulators to oocytes during fertilization, it is nevertheless apparent that the primary responsibility for oocyte activation rests with a modest store of maternally derived proteins and mRNA accumulated during oogenesis. It is, therefore, not surprising that widespread post-translational modifications, in particular phosphorylation, hold a central role in endowing these proteins with sufficient functional diversity to initiate embryonic development. Indeed, proteins targeted for such modifications have been linked to oocyte activation, recruitment of maternal mRNAs, DNA repair and resumption of the cell cycle. This review, therefore, seeks to explore the intimate relationship between Ca release and the suite of molecular modifications that sweep through the oocyte to ensure the successful union of the parental germlines and ensure embryogenic fidelity.

Features of DNA Repair in the Early Stages of Mammalian Embryonic Development

“…During this time, they are exposed to exogenous and endogenous factors that cause damage to the DNA structure. DNA double strand breaks (DSBs) accumulate with age in primary follicle oocytes due to cellular metabolism and oxidative stress [ 6 ]. Factors such as γ-radiation, chemotherapy, and adverse environmental influences lead to the formation of DSBs in oocytes during the primary follicular stage [ 7 , 8 , 9 ].…”

Loss and Rebirth of the Animal Microtubule Organizing Center: How Maternal Expression of Centrosomal Proteins Cooperates with the Sperm Centriole in Zygotic Centrosome Reformation

“…During the same period it produces initially dormant mRNAs encoding PCM, centriolar and satellite proteins, to be able to hit the ground running after fertilization. Fast production of proteins during meiosis and after fertilization generally works via activation of maternal mRNAs stored in the egg, and does not require transcription of the nuclear genome . A key to elucidate assembly of zygotic centrioles may thus come from the analysis of protein expression patterns before and after fertilization.…”

“…Fast production of proteins during meiosis and after fertilization generally works via activation of maternal mRNAs stored in the egg, and does not require transcription of the nuclear genome. [104,105] A key to elucidate assembly of zygotic centrioles may thus come from the analysis of protein expression patterns before and after fertilization. Best studied in the Xenopus system, the respective maternal mRNAs include regulatory elements, which share obvious consensus elements and can be predicted with high reliability using bioinformatics tools.…”

“This is where it all started” – the pivotal role of PLCζ within the sophisticated process of mammalian reproduction: a systemic review

“…These oscillations release the oocyte from the MII phase arrest and initiate embryogenesis via meiotic resumption, cortical granule exocytosis, sperm nucleus decondensation, recruitment of maternal mRNA and pronuclear development – collectively known as “oocyte activation” [16, 17]. These processes involve multiple protein kinases, which are responsible for conveying Ca 2+ oscillation cues to achieve essential activation events, such as cytoskeletal reorganization and formation/extrusion of the second polar body, collectively leading to embryo development [18]. …”