Egg exudate-induced reduction of sperm lysin sensitivity in the vitelline coat after fertilization of Bufo japonicus and its participation in polyspermy block.
The jellyless eggs of Bufo japonicus or those from which the vitelline coats (VCs) had been removed (denuded eggs) were electrically activated. The exudate that accompanied egg activation (AEX) was collected to study its role in preventing polyspermy. When dejellied (but VC intact) eggs were treated with AEX, the eggs lost not only fertilizability but also the sensitivity of their VCs to the sperm lysin. By contrast, denuded eggs treated with AEX were fertilizable; even activated eggs were highly fertilizable, provided they were deprived of their VCs and inseminated 30 min after activation. The loss of sensitivity to sperm lysin occurred in VCs 3-5 min after activation either in De Boer's or 1/20 De Boer's solution. The activity of AEX to reduce the sensitivity of VCs to sperm lysin was heat-sensitive and dependent on Ca2+, but it was not affected at all by the variety of protease inhibitors used. The activity was lost by the preincubation of AEX with fragmented VCs in the presence of Ca2+, suggesting Ca(2+)-dependent binding of AEX molecules to the VC at fertilization. Immunocytochemical studies employing anti-AEX rabbit serum showed that the pertinent antigens were localized in the cortical granules of unfertilized eggs and in both the inner surface of VCs and the perivitelline space of fertilized eggs. We conclude that the AEX-induced loss of lysin sensitivity in VCs and the deposition of cortical granule materials on the inner wall of VCs constitute a slow and permanent block to polyspermy.
Yamasaki
H
H
Zoological Institute, Faculty of Science, Hokkaido University, Sapporo, Japan.
Katagiri
C
C
D000818:Animals; D002025:Bufonidae; D002118:Calcium / Q000502:physiology; D004558:Electric Stimulation; D005122:Exudates and Transudates / Q000502:physiology*; D005306:Fertilization / Q000502:physiology*; D007700:Kinetics; D009088:Mucoproteins / Q000378:metabolism; D014817:Vitelline Membrane / Q000502:physiology*
D009088:Mucoproteins; C010393:lysin, gastropoda; D002118:Calcium