Interestingly, not all granulosa cells from early antral follicles exhibited immunostaining for pro-hibitin. As the follicles matured to the large antral follicle stage, granulosa cells in the follicular wall, but not those surrounding the oocyte, expressed P450scc (Fig. 3F). A gradient-like pattern of prohibitin expression was also observed in the large antral follicle (Fig. 3E).
To determine the prohibitin expression patterns associated with follicular atresia and cell death, ovarian serial sections from rats treated with eCG plus anti-eCG antiserum were localized by in situ TUNEL and prohibitin immunohisto-chemistry, respectively. Consistent with our previous reports, apoptotic granulosa cells were present in preantral, early antral, and large antral atretic follicles (Fig. 4, A, C, and E, and Table 1). Prohibitin immunostaining was evident in preantral, early antral, and large antral atretic follicles (Fig. 4, B, D, and F). Interestingly, prohibitin appeared to be translocated from the cytoplasm to the nucleus in some cells of follicles undergoing atresia and was markedly visible in early and large antral follicle cells (Fig. 4, B, D, and F, arrow). This observation is not an artifact, because we focused at higher magnification on the focal plane intersecting the nuclear compartment.