CALICIN IN HUMAN SPERM FERTILIZING ZONA-FREE HAMSTER EGGS IN-VITRO

Calicin, a basic cytoskeletal protein has been proposed to be involved in the formation and maintenance of the highly regular organization o f the postacrosomal perinuclear theca, the calyx of mammalian spermato zoa. The fate of human sperm calicin in the zona-free hamster egg fert ilized in vitro has been analysed at the light and electron microscope level using polyclonal mouse anti-calicin antibodies. Calicin was loc alized in the postacrosomal dense lamina of the capacitated acrosome-r eacted spermatozoa attached on the surface of the egg as well as in th e spermatozoa at an early stage of ooplasmic incorporation. As determi ned by the aid of the DNA-specific fluorescent dye 4,6-diamidino-2-phe nylindole (DAPI), the pattern of staining with anti-calicin changed fr om a funnel-shape into a ring soon after the onset of the nuclear deco ndensation. Later, no anti-calicin labelling could be detected around the more decondensed sperm nuclei. Because the residual, ring-like acc umulation of calicin was associated with the least decondensed chromat in, it appears that the degradation of calicin-containing perinuclear theca is intimately involved with the posteriorly advancing nuclear di sintegration. The ring formation also suggests that the calyx of human spermatozoa is not structurally homogeneous at least in terms of sens itivity to ooplasmic degradation. Calicin appears to be unaffected by lytic enzymes of the acrosome. The present study further shows that DA PI can be effectively used to analyse sperm nuclear decondensation in vitro.