Motile cells lacking hyaluronidase can penetrate the hamster oocyte cumulus complex

Sperm hyaluronidase is thought to assist in penetration of the extracellular matrix (ECM) between the cumulus and corona radiata cells surrounding mammalian oocytes. The question was asked: Can motile cells which lack hyaluronidase penetrate the hamster oocyte cumulus complex (OCC)? Sea urchin (Strongylocentrotus purpuratus) and frog (Rana catesbeiana) sperm and the unicellular, biflagellated, green alga Chlamydomonas reinhardtii were extracted and found to contain no hyaluronidase activity. Moreover, none of these cells was able to disperse the cumulus cells of hamster OCC, nor did they affect the ultrastructure of the ECM between cells. Fresh hamster OCC were challenged with suspensions of each cell type. Frog and sea urchin sperm penetrated to the zona pellucida surface in less than 5 min. A cell wall-less mutant of Chlamydomonas also penetrated to the zona surface but required longer than 5 min. Wild-type Chlamydomonas penetrated only halfway to the zona, perhaps because its cell wall adhered to the ECM between the cumulus cells and retarded its movement. The motility of the frog and sea urchin sperm was not affected by the ECM of the OCC. Frog sperm exhibited slow lethargic motility yet had no difficulty penetrating to the zona; this indicates that hyperactivated motility is not required for penetration of the ECM. None of the challenge cells penetrated the zona pellucida, although the frog sperm did compress the weave of the zona. These data show that motile cells which lack the enzyme hyaluronidase can readily penetrate the ECM of the hamster cumulus and corona radiata and suggest that the significance of hyaluronidase in fertilization should be reevaluated.