Species-specific Differences in Apoptotic Cell Localization in Granulosa and Theca Interna Cells during Follicular Atresia in Porcine and Bovine Ovaries.

Species-specific differences in the process of apoptosis in granulosa and theca layers during follicular atresia in porcine and bovine ovaries were investigated by in situ DNA 3’end-labeling (TUNEL) at the level of individual cells. In porcine ovaries, granulosa cells located on the inner surface of the granulosa layer appeared to undergo apoptosis at the first stage, followed by neighboring granulosa cells. In the contrast, granulosa cells located on the middle region appeared to undergo apoptosis at the first stage in bovine ovaries. In both porcine and bovine ovaries, detachment and degeneration of the granulosa cell layer and fragmentation of basement membrane occurred in the follicles at advanced stage of atresia. In the ovaries of both species, theca interna cells were still intact at the stage of early atresia and then apoptotic cells appeared in the late to final stages of atresia, but no apoptotic cells were observed in theca externa layers during follicular atresia. The present findings indicated that apoptosis occurring in granulosa cells is an initial symptom of follicular atresia in the ovaries of both species, and that the apoptosis inducing factor(s) and/or survival factor(s) for the granulosa cells may be different between porcine and bovine ovaries.