On the number and rate of formation of sperm-zona bonds in the mouse.

In mammalian fertilization, sperm bind to the zona pellucida, a glycoprotein matrix forming a shell surrounding the oocyte. Subsequently, one of the bound sperm penetrates the zona and fertilizes the egg. The adhesion between sperm and zona is mediated by complementary receptor-ligand pairs. Recent biochemical evidence has identified likely candidates for these molecules in the mouse. Biophysical studies have predicted that very few (possibly as few as one) bonds are needed to tether a motile sperm to the zona. We have used the data characterizing the putative receptors of the mouse sperm to predict the number of bonds they can form with the zona ligands. Our calculations indicate that few bonds probably form between the sperm and zona during the initial contact when the sperm is captured, supporting the hypothesis that fertilization depends on the action of a very few sperm-zona bonds.