The oocyte-to-embryo transition (OET) arguably initiates with formation of a primordial follicle and culminates with reprogramming of gene expression during the course of zygotic genome activation. This transition results in converting a highly differentiated cell, i.e. oocyte, to undifferentiated cells, i.e. initial blastomeres of a preimplantation embryo. A plethora of changes occur during the OET and include, but are not limited to, changes in transcription, chromatin structure, and protein synthesis; accumulation of macromolecules and organelles that will comprise the oocyte's maternal contribution to the early embryo; sequential acquisition of meiotic and developmental competence to name but a few. This review will focus on transcriptional and post-transcriptional changes that occur during OET in mouse because such changes are likely the major driving force for OET. We often take a historical and personal perspective, and highlight how advances in experimental methods often catalyzed conceptual advances in understanding the molecular bases for OET. We also point out questions that remain open and therefore represent topics of interest for future investigation.

• MeSH
• Cell Differentiation physiology   MeSH
• Embryonic Development physiology   MeSH
• Genome MeSH
• Mice MeSH
• Oocytes physiology   MeSH
• Ovarian Follicle physiology   MeSH
• Gene Expression Regulation, Developmental MeSH
• Animals MeSH
• Check Tag
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Research Support, N.I.H., Intramural MeSH

At the end of the growth phase, mouse antral follicle oocytes acquire full developmental competence. In the mouse, this event is marked by the transition from the so-called non-surrounded nucleolus (NSN) chromatin configuration into the transcriptionally quiescent surrounded nucleolus (SN) configuration, which is named after a prominent perinucleolar condensed chromatin ring. However, the SN chromatin configuration alone is not sufficient for determining the developmental competence of the SN oocyte. There are additional nuclear and cytoplamic factors involved, while a little is known about the changes occurring in the cytoplasm during the NSN/SN transition. Here, we report functional analysis of maternal ELAVL2 an AU-rich element binding protein. Elavl2 gene encodes an oocyte-specific protein isoform (denoted ELAVL2°), which acts as a translational repressor. ELAVL2° is abundant in fully grown NSN oocytes, is ablated during the NSN/SN transition and remains low during the oocyte-to-embryo transition (OET). ELAVL2° overexpression during meiotic maturation causes errors in chromosome segregation, indicating the significance of naturally reduced ELAVL2° levels in SN oocytes. On the other hand, during oocyte growth, prematurely reduced Elavl2 expression results in lower yields of fully grown and meiotically matured oocytes, suggesting that Elavl2 is necessary for proper oocyte maturation. Moreover, Elavl2 knockdown showed stimulating effects on translation in fully grown oocytes. We propose that ELAVL2 has an ambivalent role in oocytes: it functions as a pleiotropic translational repressor in efficient production of fully grown oocytes, while its disposal during the NSN/SN transition contributes to the acquisition of full developmental competence.

• Keywords
• ARE, ELAVL2, NSN, SN, chromatin, oocyte,
• MeSH
• Cell Line MeSH
• ELAV-Like Protein 2 genetics   metabolism   MeSH
• Gene Knockdown Techniques MeSH
• Humans MeSH
• Meiosis physiology   MeSH
• Mice, Inbred BALB C MeSH
• Mice, Inbred C57BL MeSH
• Mice, Transgenic MeSH
• Oocytes cytology   metabolism   MeSH
• Ovarian Follicle cytology   metabolism   MeSH
• Protein Isoforms genetics   metabolism   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• ELAV-Like Protein 2 MeSH
• Elavl2 protein, mouse MeSH Browser
• Protein Isoforms MeSH

BACKGROUND: RNA interference (RNAi) is a powerful approach to study a gene function. Transgenic RNAi is an adaptation of this approach where suppression of a specific gene is achieved by expression of an RNA hairpin from a transgene. In somatic cells, where a long double-stranded RNA (dsRNA) longer than 30 base-pairs can induce a sequence-independent interferon response, short hairpin RNA (shRNA) expression is used to induce RNAi. In contrast, transgenic RNAi in the oocyte routinely employs a long RNA hairpin. Transgenic RNAi based on long hairpin RNA, although robust and successful, is restricted to a few cell types, where long double-stranded RNA does not induce sequence-independent responses. Transgenic RNAi in mouse oocytes based on a shRNA offers several potential advantages, including simple cloning of the transgenic vector and an ability to use the same targeting construct in any cell type. RESULTS: Here we report our experience with shRNA-based transgenic RNAi in mouse oocytes. Despite optimal starting conditions for this experiment, we experienced several setbacks, which outweigh potential benefits of the shRNA system. First, obtaining an efficient shRNA is potentially a time-consuming and expensive task. Second, we observed that our transgene, which was based on a common commercial vector, was readily silenced in transgenic animals. CONCLUSIONS: We conclude that, the long RNA hairpin-based RNAi is more reliable and cost-effective and we recommend it as a method-of-choice when a gene is studied selectively in the oocyte.

• MeSH
• Genetic Vectors genetics   MeSH
• Gene Knockdown Techniques economics   methods   MeSH
• HeLa Cells MeSH
• Cloning, Molecular MeSH
• Crosses, Genetic MeSH
• Humans MeSH
• RNA, Small Interfering metabolism   MeSH
• Mice, Transgenic MeSH
• Mice MeSH
• Oocytes metabolism   MeSH
• Plasmids genetics   MeSH
• Polymerase Chain Reaction MeSH
• Proto-Oncogene Proteins c-mos genetics   metabolism   MeSH
• RNA Interference * MeSH
• Transgenes genetics   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Male MeSH
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• RNA, Small Interfering MeSH
• Proto-Oncogene Proteins c-mos MeSH

In mammalian somatic cells, several pathways that converge on deadenylation, decapping, and 5'-3' degradation are found in cytoplasmic foci known as P-bodies. Because controlled mRNA stability is essential for oocyte-to-zygote transition, we examined the dynamics of P-body components in mouse oocytes. We report that oocyte growth is accompanied by loss of P-bodies and a subcortical accumulation of several RNA-binding proteins, including DDX6, CPEB, YBX2 (MSY2), and the exon junction complex. These proteins form transient RNA-containing aggregates in fully grown oocytes with a surrounded nucleolus chromatin configuration. These aggregates disperse during oocyte maturation, consistent with recruitment of maternal mRNAs that occurs during this time. In contrast, levels of DCP1A are low during oocyte growth, and DCP1A does not colocalize with DDX6 in the subcortical aggregates. The amount of DCP1A markedly increases during meiosis, which correlates with the first wave of destabilization of maternal mRNAs. We propose that the cortex of growing oocytes serves as an mRNA storage compartment, which contains a novel type of RNA granule related to P-bodies.

• MeSH
• Cell Differentiation physiology   MeSH
• Cytoplasmic Granules metabolism   MeSH
• Endoribonucleases MeSH
• Intracellular Space MeSH
• Protein Conformation MeSH
• Multiprotein Complexes metabolism   MeSH
• Mice, Inbred C57BL MeSH
• Mice MeSH
• Oocytes metabolism   MeSH
• Ovary growth & development   metabolism   MeSH
• RNA-Binding Proteins physiology   MeSH
• Ribonucleoproteins metabolism   MeSH
• RNA Caps metabolism   MeSH
• RNA, Messenger, Stored metabolism   MeSH
• Trans-Activators metabolism   MeSH
• Gene Expression Regulation, Developmental physiology   MeSH
• Structure-Activity Relationship MeSH
• Animals MeSH
• Check Tag
• Mice MeSH
• Female MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Endoribonucleases MeSH
• Multiprotein Complexes MeSH
• RNA-Binding Proteins MeSH
• Ribonucleoproteins MeSH
• RNA Caps MeSH
• RNA, Messenger, Stored MeSH
• smad4-interacting protein SMIF, mouse MeSH Browser
• Trans-Activators MeSH