Follicular Epithelial Cell-Oocyte Connection during Development of Hamster Ovarian Follicle

Abstract

Changes in follicular epithelial cell-oocyte connections during the development of hamster ovarian follicles were studied by scanning electron microscopy using the Osmium-Dimethylsulfoxide-Osmium (ODO) maceration method. Follicular development was also examined histologically. In primordial follicles, the flattened follicular epithelial cells were closely associated with the oocyte. In primary follicles, polyhedral follicular epithelial cells surrounding the oocyte possessed rarely microvillous processes. The zona pellucida (ZP) appeared between the oocyte and the surrounding follicular epithelial cells when they were proliferated by 3 layers. By ODO maceration for 1-2 days, the matrix of ZP in the growing preantral follicles was completely dissolved, thereby tortuous and ramified cytoplasmic processes of the follicular epithelial cells toward the oocyte were exposed. These processes increased progressively in thickness and in number as the follicle developed. In antral follicles, the cumulus cell processes were elongated, but still maintained. The ZP of the antral follicular oocyte showed increased resistance to ODO maceration compared to that of the growing follicular oocyte. Further, layered heterogeneity of the ZP was noticed in the solubility to ODO maceration, suggesting that subtle changes do occur in the properties of the ZP matrix during residence in the follicle. It is revealed three-dimensionally in the hamster ovarian follicles that the cytoplasmic processes of the follicular epithelial cells develop rapidly, coincidently with the ZP formation, at the early-growing follicle stage and they are maintained until the antral follicle stage.