J. Paranko et I. Salonen, CALICIN IN HUMAN SPERM FERTILIZING ZONA-FREE HAMSTER EGGS IN-VITRO, Reproduction, fertility and development, 7(1), 1995, pp. 97-105
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.