Cytokeratin-like proteins in the sheep oocyte

In immunoblotting analysis of fully grown oocyte proteins separated by sodium dodecyl sulfate polyacrylamide (SDS-PAGE) gel electrophoresis, four polypeptides reacted specifically with cytokeratin antibodies: Mr 66,000, IEP 5.6; Mr 64,000, IEP 5.4; Mr 59,000, IEP 5.3; Mr 55,00, IEP 5.2. These proteins remained insoluble after extraction in high salt buffer and Triton X-100. In oocytes isolated from small antral follicles, only two polypeptides of Mr 66,000 and Mr 55,000 were detected. Immunofluorescence microscopy revealed a bright granular staining throughout the oocyte with an accumulation of granules in the perinuclear and cortical regions. Using electron microscopy and immunogold staining after treatment with cytokeratin antibody, gold particles were found on discrete amorphous material distributed throughout the cell. In the subcortical region of the oocyte, dense aggregates, whose diameters ranged from 3 to 8 microns, were also covered with gold particles. From these results it appears that cytokeratin-like proteins are present in sheep oocytes in a non-fibrillar form.