Demonstration of cytokeratin intermediate filaments in oocytes of the developing and adult human ovary

The intermediate filaments (IF) present in the various cells of human ovaries were studied by immunolocalization using antibodies to cytokeratins (CKs), vimentin, desmin and alpha-smooth muscle (-SM) actin. Oocytes revealed a single paranuclear aggregate, which reacted with antibodies to CKs 8, 18 and 19 both in adult and fetal ovaries. The existence of this aggregate was also documented by electron microscopy. Ovarian surface epithelium and granulosa cells consistently coexpressed CKs 8, 18, 19 and vimentin. During follicle maturation vimentin remained unchanged in the granulosa layer while CKs content decreased, showing variation in the amount and distribution of the different CK-types. Thecal cells of secondary and mature follicles showed -SM actin positivity. These contractile fibres increased in mature follicles. Ordinary fibrous stromal cells showed isolated cells which were desmin and -SM actin positive. A similar pattern of IF expression and distribution existed in all stages of development in fetal and embryonic ovaries. These results indicate that CKs are present in human oocytes and that the coexpression of vimentin and CKs can be regarded as a peculiar feature of all ovarian cell types except oocytes and ordinary stromal cells. Contractile properties have been documented associated with a modification in expression of IF proteins. This is likely to represent an integral part of folliculogenesis along with the functional hormone-dependent changes.