Sperm binding to the oocyte leads to increased cytoplasmic calcium which triggers the acrosome reaction [46]. Both μ- and m-calpain have recently been detected in rodent sperm [47] and oocytes [45]. m-calpain was implicated in the acrosome reaction [47] which correlated with a translocation of m-calpain to the cortical membrane in oocytes where it might participate in the release of cortical granule contents required to prevent polyspermy [45]. m-calpain also relocalized to the oocyte meiotic spindle after fertilization, were it could be involved in chromosome segregation [45]. Polyspermy or defective chromosome segregation would both have lethal effects on early embryonic development.