Immunocytochemical characterization of porcine zona pellucida during follicular development

Sections of bovine ovaries fixed in Bouin's fluid or methanol-acetic acid and embedded in paraffin were incubated with chicken polyclonal antibodies to HPLC-purified zona glycoproteins ZP3 alpha and ZP3 beta. Oocytes of primordial follicles as well as of primary follicles showed weak labelling with anti-ZP3 alpha and anti-ZP3 beta. No immunostaining could be observed in the follicle cells. The ZP of primary follicles displayed distinct immunoreactivity for both ZP3 alpha and ZP3 beta. In secondary follicles, distinct labelling with anti-ZP3 beta and weak labelling with anti-ZP3 alpha could be seen in the oocyte. The ZP showed immunoreactivity with antibodies to ZP3 alpha and ZP3 beta. Both antibodies labelled single follicle cells. In tertiary follicles, the oocytes were weakly labelled with anti-ZP3 alpha and anti-ZP3 beta. Some granulosa cells showed staining for ZP3 alpha and ZP3 beta. The ZP displayed strong immunoreactivity for ZP3 beta and ZP3 alpha. Cells of the corona radiata were strongly immunopositive for ZP3 alpha and ZP3 beta. Similar histotopography of immunoreactive cells could be seen in preovulatory follicles. The characteristic pattern observed for the distribution of ZP3 alpha and ZP3 beta strongly suggests that in the porcine ovary both the oocyte and the follicle cells contribute to the synthesis of the ZP, perhaps in sequence.