Abstract
Changes in intercellular communication and structural integrity between oocyte and cumulus cells during oocyte maturation were examined in mice injected with pregnant mare serum gonadotropin and human chorionic gonadotropin (hCG). Three and 9 hr after hCG administration, dissolution of the germinal vesicle (GVBD) and progression to the second metaphase occurred in oocytes in both cases. Examination of the expansion of mouse cumulus-oocyte complexes with oocytes having undergone GVBD by electron microscopy revealed the deposition of intercellular materials between cumulus cells and the retraction of the cytoplasmic processes joining the cumulus cells to the oocyte. Cumulus to oocyte coupling decreased progressively with time after hCG administration, as assessed by a progressive reduction in transfer of lucifer yellow from the oocyte to the cumulus cells. Spread of lucifer yellow from the oocyte having undergone GVBD was limited to very few adjacent cumulus cells, but junctional apparatuses were still identified in the area where the processes of cumulus cells contact the oolemma. These results show that coupling occurs between the oocyte having undergone GVBD and its surrounding cumulus cells but that during oocyte maturation, coupling decreases, while materials are deposited in space between cumulus cells.
