Abstract
Gap junctional communication (GJC) plays a primordial role in oocyte maturation and meiotic resumption in mammals by directing the transfer of numerous molecules between cumulus cells and the oocyte. Gap junctions are made of connexins (Cx), proteins that regulate GJC in numerous ways. Understanding the dynamic regulation of connexin arrangements during in vitro maturation (IVM) could provide a powerful tool for controlling meiotic resumption and consequently in vitro development of fully competent oocytes. However, physiological events happening during the early hours of IVM may still be elucidated. The present study reports the dynamic regulation of connexin expression, degradation and localization during this stage. Cx43, Cx45 and Cx60 were identified as the main connexins expressed in swine COC. Cx43 and Cx45 transcripts were judged too static to be a regulator of GJC, while Cx43 protein expression was highly responsive to gonadotropins, suggesting that it might be the principal regulator of GJC. In addition, the degradation of Cx43 expressed after 4.5 h of IVM in response to equine chorionic gonadotropin appeared to involve the proteasomal complex. Cx43 localisation appeared to be associated with GJC. Taken together, these results show for the first time that gonadotropins regulate Cx43 protein expression, degradation and localisation in porcine COC during the first several hours of IVM. Regulation of Cx43 may in turn, via GJC, participate in the development of fully competent oocytes.
Highlights
Gap junctional communication (GJC) plays key roles in numerous tissues and cell types, including ovaries, follicles and cumulus oocyte complex (COC)
Using a conventional PCR approach to determine first which connexin transcripts were present in the oocyte and/or cumulus cells after 4.5 h of conventional in vitro maturation (IVM) (Fig. 1), we found that Cx43, Cx45 and Cx60 were strongly expressed, while Cx26 and Cx32 were weakly expressed
We have previously demonstrated that cumulus cells are crucial during the first 4 h of IVM in order for meiosis to resume properly
Summary
Gap junctional communication (GJC) plays key roles in numerous tissues and cell types, including ovaries, follicles and cumulus oocyte complex (COC). GJC plays a primordial role in oocyte maturation and meiotic resumption in mammals [6,7]. Gap junctions are channels that allow direct exchange of ions and small molecules (#1 kDa) between adjacent cells. Their formation results from mutual docking of plasma membrane hemichannels called connexons. Each connexon is composed of six trans-membrane protein molecules called connexins. Connexins are expressed ubiquitously in animal cells, except in differentiated skeletal muscle cells, erythrocytes, and mature sperm cells [8]. The ability of the cell to mix gap junction connexin content in this manner increases possibilities for the regulation of specific permeability [12,13]
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