Gap junction of stratum granulosum cells of mouse follicles: immunohistochemistry and electron microscopy.

The gap junction (GJ) of stratum granulosum cells was investigated in growing and mature follicles of the mouse by means of light- and electron-microscopic immunohistochemistry, freeze-fracturing and deep-etching methods. GJ increased in number and size in concert with the progress of follicular maturation and decreased rapidly in the preovulatory mature follicle. GJ membrane showed invagination, most remarkably at 5 h after hCG injection, within the cytoplasm of the granulosum cell. Two types of internalization seemed possible, annular internalization and highly convoluted tubular invagination, both by an actin-mediated mechanism. At least, a part of the internalized GJ membrane seemed to be degraded by a certain lysosomal enzyme (s). Connexin43 (derived from rat cardiac muscle GJ) was indicated to be a constituent of GJ protein in the mouse stratum granulosum cell. There was no GJ particle coexisting with tight junctional strands; by contrast, a formation plaque appeared quite often on granulosum cells at various stages. Such a plaque is presumed to represent a precursor structure of the new GJ of these cells. So far examined, however, the formation plaque failed to show positive reaction against anti-Cx43 antibody.