Localization of a developmentally regulated protein in porcine follicles identified by a monoclonal antibody

In the present study we employed a monoclonal antibody (Mab 3D8) obtained against a rat ovarian antigen and identified a 76 kDa protein in porcine ovarian follicles.

The localization of this antigen was studied by light and electron-microscopic immunocytochemistry and further characterized by polyacrylamide gel electrophoresis and immunoblotting on nitrocellulose membranes.

We found that the antigen recognized by Mab 3D8 is localized in granulosa cells (GCs) and oocytes. The expression of the 76 kDa protein apparently depends on the developmental stage. A particularly strong reaction was observed in cumulus cells and oocytes in early and late antral follicles. In granulosa cells the reaction product was localized in rough endoplasmic reticulum (RER), cis and trans faces of the Golgi stack, the outer nuclear envelope and in numerous transport vesicles budding from the endoplasmic reticulum. In the oocyte the reaction product was localized in structures related to specific endocytosis - small pits at the cell surface, two subsets of endosomes, endocytic carrier vesicles and the prelysosomal compartment (PLC).

The results obtained suggest that porcine oocytes possess the cellular structures, which allow them to bind and internalize this protein, which is most probably produced by granulosa cells. During oocyte development the intracellular site of accumulation of the 76 kDa protein varies, which implies that it is under developmental control. follicle