Expression of Bcl-2 and 3-beta hydroxysteroid dehydrogenase protein duringoocyte and follicle development in fetal and post-natal pig ovaries

The fetal and post-natal development of the pig ovary involves both prolife ration and apoptotic loss of germ cells, follicle formation and growth, and the initiation of oocyte meiotic maturation. The present study measured th e expression of the proto-oncogene Bcl-2 immunohistochemically on paraffin sections of pig ovaries to determine its relationship with folliculogenesis on Days 50 and 80 post coitum (p,c.) and on Days 1, 21, and 56 post partum (p.p.). The expression of the steroidogenic enzyme 3 beta-hydroxysteroid d ehydrogenase (3 beta HSD) was used to determine the lineages of the cells f orming the ovarian follicles, and the expression of the cell proliferation- associated nuclear antigen Ki-67 was used to determine germ cell proliferat ion and the initiation of follicle growth. Expression of Ki-67 showed that many oogonia were proliferating on Days 50 and 80 p.c. Granulosa cells were more proliferative on Day 56 p.p. than at any other stage; Ki-67 was expre ssed in 70% of growing follicles and granulosa cells had a 3% mean staining index per section. Less than 4% of germ cells and follicles had morphologi cal signs of degeneration during the period of the study. Bcl-2 was most ab undant on Days 21 p.p. and 56 p.p.; staining was localized to stromal cells among follicles and in small clusters in the cortical-medullary junction ( CMJ). 3 beta HSD staining on Day 50 p,c. was seen in cords of stromal cells within the medulla of the ovary, and in the stromal cells investing the oo gonial nests. On Days 80 p.c., 1 p.p., 21 p.p., and 56 p.p., 3 beta HSD was expressed in the granulosa cells of primary or primordial follicles at the CMJ. Production of Bcl-2 by somatic cells may support germ cell and preant ral follicle survival.