Amphibians sperm binding

Until now, no experimental results support the hypothesis of a carbohydrate-mediated species-speeifie sperm binding for amphibians, similar to that demonstrated for mammalians. Further studies will probably indicate if the pattern of glycan structures found in each amphibian species represent the support for a specifie recognition of the ovule by the spermatozoon. 

Induction of the acrosome reaction is a key event that occurs in sea urchins, starfish, ascidians and mammals. However, it is not clear that in the amphibian Xenopus sperm undergo the same type of acrosome reaction, because thus far it has not been possible to detect a morphologically identifiable acrosome vesicle in these sperm. The acrosome reaction in echinoderms and in mammals has been well studied. During the acrosome reaction the acrosomal vesicle fuses with the plasma membrane and the acrosomal components are externalized. Several proteolytic activities thought to be involved in penetration through the extracellular matrix of the egg are deteeted in the acrosomal contents. In addition, exposure of egg coat binding molecules on the surface of the sperm occurs (see below). 

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