Developmental expression and regulation of the gap junction protein and transcript in rat ovaries

The extensively developed network of cell-to-cell communication, generated by gap junctions, mediates transmission of small molecules between the cells of the ovarian follicle. Our study aimed at the analysis of the ontogeny and regulation of connexin43 (Cx43) the ovarian gap junction protein and its gene expression throughout folliculogenesis. Developmental analysis was performed using ovaries of immature rats at different ages and selected ovarian follicles of sexually mature female rats at different phases of their estrous cycle. In order to establish the effect of hormones involved in regulation of folliculogenesis on Cx43 modulation, the experimental animal model of sexually immature female rats administered with exogenous gonadotropins was employed. Developmental and hormonal modulations of Cx43 protein and its mRNA expression were studied by Western and Northern blot analysis, respectively. We found that Cx43 was undetectable in ovaries of rats on the first postnatal day, with a low level of this protein observed in 11-day-old rats ovaries. Some increase in the amount of Cx43 was observed at the age of 25 days with a dramatic elevation accompanied by phosphorylation of this protein that was specific to large antral follicles of sexually mature proestrous rats. Elimination of the protein was observed at estrus and could be prevented by cancellation of the preovulatory surge of luteinizing hormone (LH). This pattern of Cx43 modifications was mimicked by exogenous administration of hormones as follows: Pregnant mare's serum gonadotropin (PMSG) increased the Cx43 protein expression with a concurrent induction of its phosphorylation while a further human chorionic gonadotropin (hCG) injection resulted in a decrease of the signal. Analysis of the Cx43 mRNA showed a direct correlation between the Cx43 protein level and its gene expression. We conclude that: 1) At early folliculogenesis the ovarian gap junction protein Cx43 and its gene are developmentally regulated; and 2) After antrum formation, transcription, translation, and posttranslational modifications of Cx43 are regulated by gonadotropins.