Even after several decades of quiescent storage in the ovary, the female germ cell is capable of reinitiating transcription to build the reserves that are essential to support early embryonic development. In the current model of mammalian oogenesis, there exists bilateral communication between the gamete and the surrounding cells that is limited to paracrine signaling and direct transfer of small molecules via gap junctions existing at the end of the somatic cells' projections that are in contact with the oolemma. The purpose of this work was to explore the role of cumulus cell projections as a means of conductance of large molecules, including RNA, to the mammalian oocyte. By studying nascent RNA with confocal and transmission electron microscopy in combination with transcript detection, we show that the somatic cells surrounding the fully grown bovine oocyte contribute to the maternal reserves by actively transferring large cargo, including mRNA and long noncoding RNA. This occurrence was further demonstrated by the reconstruction of cumulus-oocyte complexes with transfected cumulus cells transferring a synthetic transcript. We propose selective transfer of transcripts occurs, the delivery of which is supported by a remarkable synapselike vesicular trafficking connection between the cumulus cells and the gamete. This unexpected exogenous contribution to the maternal stores offers a new perspective on the determinants of female fertility.

So far, the characteristics of a good quality egg have been elusive, similar to the nature of the physiological, cellular, and molecular cues leading to its production both in vivo and in vitro. Current understanding highlights a strong and complex interdependence between the follicular cells and the gamete. Secreted factors induce cellular responses in the follicular cells, and direct exchange of small molecules from the cumulus cells to the oocyte through gap junctions controls meiotic arrest. Studying the interconnection between the cumulus cells and the oocyte, we previously demonstrated that the somatic cells also contribute transcripts to the gamete. Here, we show that these transcripts can be visualized moving down the transzonal projections (TZPs) to the oocyte, and that a time course analysis revealed progressive RNA accumulation in the TZPs, indicating that RNA transfer occurs before the initiation of meiosis resumption under a timetable fitting with the acquisition of developmental competence. A comparison of the identity of the nascent transcripts trafficking in the TZPs, with those in the oocyte increasing in abundance during maturation, and that are present on the oocyte's polyribosomes, revealed transcripts common to all three fractions, suggesting the use of transferred transcripts for translation. Furthermore, the removal of potential RNA trafficking by stripping the cumulus cells caused a significant reduction in maturation rates, indicating the need for the cumulus cell RNA transfer to the oocyte. These results offer a new perspective to the determinants of oocyte quality and female fertility, as well as provide insight that may eventually be used to improve in vitro maturation conditions.

Although the oocyte is the largest cell in the body and an unavoidable phase in life, its physiology is still poorly understood, and other cell types provide little insight into its unique nature. Even basic cellular functions in the oocyte such as energy metabolism are not yet fully understood. It is known that the mitochondria of the female gamete exhibit an immature form characterized by limited energy production from glucose and oxidative phosphorylation. We show that the bovine oocyte uses alternative means to maintain ATP production during maturation, namely, the adenosine salvage pathway. Meiosis resumption is triggered by destruction of cyclic AMP by phosphodiesterases producing adenosine monophosphate that is converted into ATP by adenylate kinases and creatine kinases. Inhibition of these enzymes decreased ATP production, and addition of their substrates restored ATP production in denuded oocytes. Addition of phosphocreatine to the oocyte maturation medium influenced the phenotype of the resulting blastocysts. We propose a model in which adenylate kinases and creatine kinases act as drivers of ATP production from added AMP during oocyte maturation.

Now recognised as part of the cellular transcriptome, the function of long non-coding (lnc) RNA remains unclear. Previously, we found that some lncRNA molecules in bovine embryos are highly responsive to culture conditions. In view of a recent demonstration that lncRNA may play a role in regulating important functions, such as maintenance of pluripotency, modification of epigenetic marks and activation of transcription, we sought evidence of its involvement in embryogenesis. Among the numerous catalogued lncRNA molecules found in oocytes and early embryos of cattle, three candidates chosen for further characterisation were found unexpectedly in the cytoplasmic compartment rather than in the nucleus. Transcriptomic survey of subcellular fractions found these candidates also associated with polyribosomes and one of them spanning transzonal projections between cumulus cells and the oocyte. Knocking down this transcript in matured oocytes increased developmental rates, leading to larger blastocysts. Transcriptome and methylome analyses of these blastocysts showed concordant data for a subset of four genes, including at least one known to be important for blastocyst survival. Functional characterisation of the roles played by lncRNA in supporting early development remains elusive. Our results suggest that some lncRNAs play a role in translation control of target mRNA. This would be important for managing the maternal reserves within which is embedded the embryonic program, especially before embryonic genome activation.

No abstract

Previous studies have shown that patients with a low socioeconomic position undergoing various surgical procedures are at higher risk for postoperative complications and worse survival outcomes than patients with a high socioeconomic position. Complication and mortality rates are also higher for individuals from lower social classes treated for myocardial infarction, certain cancers, and other serious conditions. Some studies suggest an association between socioeconomic position and postsurgical complications among women undergoing hysterectomy.This register-based cohort study was designed to determine whether there is an association between socioeconomic position and risk of complications following hysterectomy and to investigate the role of lifestyle factors and comorbidity on this association. Participants included nearly all Danish women (n = 22,150) with a benign elective hysterectomy registered in the Danish Hysterectomy Database between 2004 and 2008. The association between 3 selected measures of socioeconomic position (education, employment, and income) and complications was assessed using multiple logistic regression models. The risk of infection, hospitalization, readmission, and reoperation after hysterectomy was also examined in women of different socioeconomic status.Complications following hysterectomy occurred in 17% of the women. The risk of infection, complications, and readmission was higher among women with less high school education and unemployed women than women with more than high school education and employed women. Unemployment (but not low education) was associated with higher odds of hospitalization of more than 4 days. Most of the social differences appeared to be due to lifestyle factors (smoking and body mass index) and comorbidity. However, the association between low education and the overall rate of complications remained unexplained. The higher odds of infection, complications, and hospitalization of more than 4 days among unemployed women could only be partially explained by differences in lifestyle and comorbidity status.These findings show that the risk of complications following hysterectomy is significantly higher in women with a low socioeconomic position than in women with a high socioeconomic position. Differences in complications among women with low socioeconomic status can be partially explained by unhealthy lifestyle and presence of comorbidity. EDITORIAL COMMENT(Most readers of the Survey are aware of the sociodemographic disparities in access to care, screening rates, and outcomes across a wide range of conditions facing women in the United States. Hysterectomy risk factors, rates, routes, postoperative complications, and long-term outcomes have been found to vary substantially across groups of different race/ethnicity, household income, educational attainment, insurance status, and occupation. These explanatory factors are associated with each other, making it hard to determine which factors contribute the most to racial/ethnic differences.The authors of the study...

The period beginning with the signal for ovulation, when a fully‐grown oocyte progresses through meiosis to become a mature egg that is fertilized and develops as a preimplantation embryo, is crucial for healthy development. The early preimplantation embryo is unusually sensitive to cell volume perturbations, with even moderate decreases in volume or dysregulation of volume‐regulatory mechanisms resulting in developmental arrest. To prevent this, early embryos possess mechanisms of cell volume control that are apparently unique to them. These rely on the accumulation of glycine and betaine (N, N, N‐trimethylglycine) as organic osmolytes—compounds that can provide intracellular osmotic support without the deleterious effects of inorganic ions. Preimplantation embryos also have the same mechanisms as somatic cells that mediate rapid responses to deviations in cell volume, which rely on inorganic ion transport. Both the unique, embryo‐specific mechanisms that use glycine and betaine and the inorganic ion‐dependent mechanisms undergo major changes during meiotic maturation and preimplantation development. The most profound changes occur immediately after ovulation is triggered. Before this, oocytes cannot regulate their volume, since they are strongly attached to their rigid extracellular matrix shell, the zona pellucida. After ovulation is triggered, the oocyte detaches from the zona pellucida and first becomes capable of independent volume regulation. A complex set of developmental changes in each cell volume‐regulatory mechanism continues through egg maturation and preimplantation development. The unique cell volume‐regulatory mechanisms in eggs and preimplantation embryos and the developmental changes they undergo appear critical for normal healthy embryo development.

The fully grown mammalian oocyte is tightly attached to its extracellular matrix shell, the zona pellucida (ZP), but the oocyte detaches from the ZP shortly after ovulation is signaled. The mechanism by which the oocyte detaches from the ZP is unknown. Because ZP proteins are initially secreted as transmembrane proteins, we hypothesized that attachment of the oocyte to the ZP is mediated by transmembrane ZP proteins and that detachment occurs when these proteins are cleaved by peptidases. To identify potential candidates for the type of peptidase, we used mouse oocyte transcriptome data sets to identify candidate peptidases localized to the exterior of the oocyte. Screening with a set of small molecule inhibitors that broadly target the families of peptidases represented by the candidates, we found that only inhibitors of the M10 and M12 families of metallopeptidases prevented detachment. Using more selective inhibitors indicated that detachment was prevented by an inhibitor, GI254023X, developed to be selective for ADAM10 in the M12 family but not by those considered selective for the M10 family or for other M12 metallopeptidases expressed in oocytes. Using an antibody that binds to an epitope just distal to the likely cleavage site of murine ZP3 showed that this site was gradually lost from the oocyte surface during the period when detachment occurs, and that inhibiting metallopeptidase activity prevented the loss of this epitope. Taken together, these results indicate that detachment of the oocyte from the ZP is mediated by a metallopeptidase.