Hyaluronan-degrading activity of mouse sperm hyaluronidase is not required for fertilization?

Sperm hyaluronidase has long been believed to participate in sperm penetration through the cumulus matrix. However, our previous works using male mice lacking either one of two sperm hyaluronidases, SPAM1 and HYAL5, conclusively showed that neither of these hyaluronidases is essential for fertilization. In this study, we examined whether the hyaluronan-degrading activity of mouse epididymal sperm is indeed required for the fertilization process. When the oocyte-cumulus complex was incubated with sperm protein extracts or capacitated epididymal sperm in the presence of the hyaluronidase inhibitor apigenin, dispersal of cumulus cells from the cumulus was effectively inhibited. Despite the presence of apigenin, capacitated epididymal sperm normally entered the oocyte-cumulus complex, traversed the cumulus matrix and reached the oocyte zona pellucida. Importantly, epididymal sperm were also capable of normally fertilizing the metaphase II-arrested oocytes in the presence of apigenin. These data suggest that the hyaluronan-degrading activity of sperm hyaluronidase may not be required for fertilization, at least in the mouse.