Expression of gap junctional proteins connexin 43, 32, and 26 throughout follicular development and atresia in cows.

Detection of connexin (Cx) proteins has been used as an indicator of the presence of structural and functional gap junctions in tissues. To examine the role of gap junctions during follicular growth and atresia, the presence of three major connexins, Cx43, Cx32, and Cx26, was evaluated in bovine ovaries by using immunohistochemistry and Western immunoblot analysis. Cx43 was not present in primordial follicles, but was present in granulosa cells of primary/secondary and antral follicles. Cx43 also was present on the borders between granulosa cells and the oocyte. Expression of Cx43 increased in healthy developing antral follicles, but decreased during follicular atresia. Cx32 was not present in healthy follicles but was present in granulosa cells of atretic antral, and especially small antral follicles. Cx26 was present in the oocyte of primordial and primary/secondary follicles, and in the granulosa and/or thecal cell layers of healthy antral follicles. The percentage of healthy antral follicles that expressed Cx26 also increased during follicular development, but decreased during atresia. Cx32 and Cx26 also were detected in ovarian blood vessels and in stromal tissues adjacent to the tunica albuginea in some ovaries. The pattern of expression of these Cx indicates that gap junctional proteins may be involved in the control of follicular growth and atresia in cows.