Abstract
The oocyte faces a particular challenge in terms of gene regulation. When oocytes resume meiosis at the end of the growth phase and prior to ovulation, the condensed chromatin state prevents the transcription of genes as they are required. Transcription is effectively silenced from the late germinal vesicle (GV) stage until embryonic genome activation (EGA) following fertilisation. Therefore, during its growth, the oocyte must produce the mRNA transcripts needed to fulfil its protein requirements during the active period of meiotic completion, fertilisation, and the maternal-to zygote-transition (MZT). After meiotic resumption, gene expression control can be said to be transferred from the nucleus to the cytoplasm, from transcriptional regulation to translational regulation. Maternal RNA-binding proteins (RBPs) are the mediators of translational regulation and their role in oocyte maturation and early embryo development is vital. Understanding these mechanisms will provide invaluable insight into the oocyte’s requirements for developmental competence, with important implications for the diagnosis and treatment of certain types of infertility. Here, we give an overview of post-transcriptional regulation in the oocyte, emphasising the current knowledge of mammalian RBP mechanisms, and develop the roles of these mechanisms in the timely activation and elimination of maternal transcripts.
Highlights
For correct and timely function, each cell regulates the expression of its genes to suit its specific protein requirements at any given moment
We showed that Patl2 invalidation leads to subfertility in females with oocytes showing dysregulation of a number of key transcripts expressed at various stages of oocyte maturation [40]
It is clear that RNA-binding proteins (RBPs) play an indispensable role in oocyte maturation and developmental competence across species
Summary
For correct and timely function, each cell regulates the expression of its genes to suit its specific protein requirements at any given moment. Post-transcriptional regulation is an essential component of the cell’s ability to regulate protein expression as it represents a secondary layer of control that is independent from the transcription machinery This type of regulation allows for rapid response to external stimuli [4] and becomes the prominent form of regulation in cases where transcription is not possible, i.e., due to compact/inaccessible chromatin. Post-transcriptional regulation can be global, through modulation of key components of the protein synthesis machinery, but it can be RNA-specific, through the presence of cis-regulatory elements typically within the 30 UTR of the mRNA sequence. The unique challenge of the oocyte is the synthesis and preservation of all transcripts necessary during this period of intense activity as well as their timely and selective translation and degradation To meet these requirements, a number of specialised RBPs exist, making up a specialised and multi-layered mRNA processing system. We give particular attention to the mechanisms that exist in mammalian ( mouse) oocytes
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