Although there are many reports of sperm chromatin decondensation within eggs, only two reports have shown this observations with the use of the electromicroscopy. Nobody has shown the process of human sperm chromatin decondensationwith the continous observations of living ooplasma. Our previous report hasshown that calmodulin antagonist W-7 can stimulate the acrosome reaction of humansperm, and that these sperm are capable of penetrating zona-free hamster eggs. This study has shown the contious observations of chromatin decondensationof human sperm treated with W-7 by means of zona-free hamster eggs. Althoughvarious patterns of decondensation were recognized, almost all of the sperm showedthe following: 1) the brightness of the post acrosomal region was lost just beforedecondensation began, 2) chromatin dispersion began at the anterior, one-third ormid lateral region of the post acrosome, 3) the bright area origenated from thispost acrosomal region and gradually increased, 4) the decondensation of the postacrosomal region was more rapid than the acrosomal region, 5) the oval shapedring formation was shown to be a remaining chromatin mass by Nomarski InterferenceMicroscopy, and was recognized at the apex area of the acrosome, 6) the peripheralring formation, : appeared around the oval shaped ring formation which was fusingin the front and rear. This ring formation was observed for a period of approximately2 to 5 minutes after the oval shaped ring formation disappeared. From these observations, we suggest that the mechanism of human sperm chromatindecondensation does not resemble other mammalian sperm chromatin decondensationon the basis of such ring formation.
