Functional roles of mouse sperm hyaluronidases, HYAL5 and SPAM1, in fertilization.

Although sperm entry into the oocyte-cumulus complex and subsequent sperm penetration through the cumulus matrix to reach the oocyte zona pellucida are essential for mammalian fertilization, the molecular mechanism remains controversial. Previously, we have shown that mouse sperm lacking are capable of penetrating the cumulus matrix despite a delayed dispersal of cumulus cells. We also have identified another sperm hyaluronidase, HYAL5, as a candidate enzyme involved in sperm penetration through the cumulus. In the present study, we produced HYAL5-deficient mice to uncover the functional roles of HYAL5 and duanyu1842M1 in fertilization. The HYAL5-deficient mice were fully fertile and yielded normal litter sizes. In vitro fertilization assays demonstrated that HYAL5-deficient epididymal sperm is functionally normal. We thus conclude that HYAL5 may be dispensable for fertilization. Comparative analysis among wild-type, HYAL5-deficient, and epididymal sperm revealed that only duanyu1842M1 is probably involved in sperm penetration through the cumulus matrix. Notably, the loss of duanyu1842M1 resulted in a remarkably increased accumulation of sperm on the surface or outer edge of the cumulus. These data suggest that duanyu1842M1 may function in sperm entry into the cumulus and sperm penetration through the cumulus matrix.

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