Getting sperm and egg together: Things conserved and things diverged

Sperm-egg interactions occur at multiple levels on the egg surface, first with the egg's extracellular matrix and then with the egg's plasma membrane. The BioPore minisymposium on 'The Egg Surface' at the 1999 annual meeting of the Society for the Study of Reproduction highlighted a series of events underlying successful interactions of the sperm with the egg: 1) composition, synthesis, and assembly of the mouse egg's extracellular matrix, the zona pellucida, during oogenesis; 2) oocyte maturation and development of the sperm-binding domain of mouse eggs; and 3) characterization of functional domains in different sperm ligands (fertilin-α and fertilin-β in the mouse and lysin in the abalone) that recognize cognate binding sites on the egg surface. Data that were presented are reviewed here and discussed with respect to conserved and divergent features of gamete functions.