Role of cumulus oophorus in increasing efficiency of fertilization in mouse oocytes in vitro

The functional role of the cumulus oophorus during fertilization was examined. It was found that the sperm concentration necessary for successful fertilization was markedly different between cumulus-intact and cumulus-free oocytes; only 5 sperm/μl were required for the maxi-mum level of fertilization of cumulus-intact oocytes, while 150 sperm/μl were needed for cumu-lus-free oocytes. Fertilization rate did not increase by co-culturing cumulus-free oocytes with detached cumulus cells in the fertilization medium. On the other hand, supplementing the fertili-zation medium with soluble factor(s) vortexed out of cumulus-oocyte complexes significantly improved the rate of fertilization (56% in the treated group vs 36% in controls; P