Granulosa Cells Express Integrin α6: Possible Involvement of Integrin α6 in Folliculogenesis

Abstract

To identify differentiation antigens of granulosa cells, we have raised two monoclonal antibodies against porcine granulosa cells (POG-2 antibody) and human granulosa cells (OG-1 antibody). Analysis of N-terminal amino acid sequences of purified OG-1 and POG-2 antigens revealed that they were identical to human integrin α6 and its porcine homolog, respectively. An immunohistochemical study showed that integrin α6 was highly expressed on granulosa cells in preovulatory follicles in the human ovary, whereas it was highly expressed on granulosa cells in small follicles in the porcine ovary. As a common characteristic of integrin α6 expression in both ovaries, granulosa cells located in inner layers, which are not in contact with the basal lamina, expressed integrin α6 on the cell surface. This expression profile suggests that the interaction between integrin and extracellular matrices occurs in the granulosa cells located in inner layers. This cell surface interaction is reported to modulate soluble signals to the cells. Since the expression of integrin α6 on inner-layer granulosa cells is related to stages of differentiation, this interaction may be involved in folliculogenesis.