Changes in expression of connexin 43 gap junction messenger ribonucleic acid and protein during ovarianfollicular growth

Within the ovarian follicle, communication between granulosa cells and the oocyte via gap junction channels may be crucial for thedetermination of whether a given follicle continues its growth anddevelopment or becomes atretic. Numerous gap junction channels existbetween granulosa cells and between the oocyte and granulosa cells.This study addresses the potential hormonal regulation of the gapjunction gene during the processes of follicular growth, ovulation, andatresia. Because the ovary is an exceptionally heterogeneous tissue withnumerous follicles at different stages of development, in situhybridization and immunocytochemistry were used to localize gap junctiongene expression precisely to specific cells in the ovary. The resultsdemonstrated that only the granulosa cells of healthy, developing, preantral and antral follicles express large amounts of connexin 43(cx43) gap junction messenger RNA (mRNA) and protein. Theca cellscontained negligible levels of cx43 gap junction mRNA or protein. Very-little cx43 gap junction mRNA or protein was detected in folliclesundergoing atresia or in the corpora lutea.Additionally, during the night of proestrus, the level of cx43 gap junction mRNA and protein seen in the granulosa cells of the largepreovulatory follicles dramatically decreased after the ovulatory surgeof LH. This decrease was seen only in the preovulatory follicles andnot in less-developed follicles, thereby demonstrating a differentialresponse of the follicles to the preovulatory hormonal stimuli. Therefore, the expression of the gap junction gene may be hormonallyregulated during follicular growth and development, in preovulatoryfollicles in preparation for ovulation, and during the process of atresia.