Oocyte activation induced by spermatids and the spermatozoa

It has been reported that a sperm factor (SF) found in spermatozoa plays a critical role in fertilization. However, particulars of the oocyte-activati ng and Ca2+ oscillation (Ca-Os)-inducing abilities of this SF remain unknow n. We examined these abilities of spermatids in mouse, hamster and human by a mouse test (injection of spermatids into mouse oocytes). In mice, the ro und spermatids (ROS), elongated spermatids (ELS) and spermatozoa activated 0%, 93% and 92% of the oocytes, respectively. ROS injection resulted in no Ca-Os (type C). ELS induced a normal oscillation (type A) at 0% and an abno rmal oscillation (type B) at 94%. Mouse spermatozoa induced type A Ca-Os at 90%. For mice, oocyte-activating and Ca2+ oscillation-inducing ability aro se in different phases of spermiogenesis. We also observed this differentia l timing for hamster spermatids. Hamster ROS activated 74% of oocyte (ELS: 90%, sperm: 86%). Human ROS activated 64% of oocytes (sperm: 100%), but onl y 35% of the oocytes showed type A Ca-Os. These results indicate that oocyt e activation generally occurs between the ROS and ELS phases, although thes e phases differ among species. They also indicate that oocyte activation is not necessarily accompanied by Ca-Os. These findings suggest the existence of different thresholds at which the SF induces oocyte activation and Ca2 oscillation, or of different factors that induce oocyte activation and Ca- Os. We found SF to be clinically impaired in 0.9% of ICSI patients. A combi nation of artificial oocyte activation and ICSI proved effective with such patients.