CALMODULIN DURING HUMAN SPERM INCORPORATION INTO HAMSTER OOCYTE - AN IMMUNOGOLD ELECTRON-MICROSCOPE STUDY

In the present study, immunogold labeling of ultrathin sections of hum an sperm, before and after incorporation into hamster oocyte, was used to obtain insight into the ultrastructural localization and possible function of calmodulin during fertilization. In heads of ejaculated, c apacitated, and acrosome-reacted fixed human sperm, calmodulin was mai nly found in two compartments, the subacrosomal layer and the postacro some. After sperm-egg fusion, the subacrosomal calmodulin was unaltere d and surrounded by the fertilization cone in which actin was abundant . There was no co-localization of calmodulin and actin. In contrast, p ostacrosomal calmodulin disappeared as soon as the sperm head was inco rporated into egg cytoplasm. These unique localizations and redistribu tions are in agreement with the concept of a calmodulin targeting from acrosome toward postacrosome through the subacrosomal layer during sp ermatogenesis (Weinman et al., 1986b: J Histochem Cytochem 34:118). Mo reover, they strongly suggest a role for calmodulin both in sperm-egg fusion and in the initial pulse of Ca2+ occurring during fertilization . (C) 1994 Wiley-Liss, Inc.