Comparative cytochemistry of the developing ovarian follicles of the dog,rabbit, and mouse: Origin of the zona pellucida

The reactivity of the glycoproteins of ovarian follicles of the dog, rabbit, and mouse were compared, using the Alcian blue (pH 0.5) and Alcian yellow (pH 2.5) technique at the light-microscope level and the periodic acid-chromic acid-silver methenamine technique at the electron-microscope level. In paraffin sections, the rabbit and mouse show the appearance of both zona pellucida and follicular fluid in the earliest growing follicles. In the dog, there is a sequence of development with the follicular fluid appearing late, after much of the zona has been secreted. The zona and follicular fluid are highly sulfated in all animals. Zonae pellucidae of atresia appear to lose all traces of sulfation and become highly acidic. At the electronmicroscope level, oocytes contain little if any reactive glycoprotein material which can be related to zona pellucida formation. The initial appearance of the zona material occurs between follicle cell membranes extending outwards and away from the oocyte. Follicle cells of all species consistently contain a variety of reactive Golgi bodies and granules, with exocytotic vesicles, suggesting active synthesis and secretion of zona material. Our observations suggest that in the early stages of oogenesis, the follicular epithelium is responsible for at least part of the synthesis of the zona pellucida. It is possible therefore that both the oocyte and its follicle cells participate, probably on the sequential basis, in the synthesis of the mammalian zona pellucida.