Penetration by field vole spermatozoa of mouse and hamster zonae pellucidae without acrosome reaction.

Spermatozoa of the field vole (Microtus montebelli) that bound to the zona pellucida of field vole oocytes underwent the acrosome reaction before passing through it. In contrast, vole spermatozoa that bound to the zonae of mouse and hamster oocytes penetrated the zonae without any sign of the acrosome reaction. The presence or absence of proteinase/hyaluronidase inhibitors in the medium did not make any difference to zona penetration by acrosome-intact vole spermatozoa. These observations suggest that field vole spermatozoa can cross mouse and hamster zonae mechanically without assistance from zona-hydrolysing enzymes.