Acrosomal reaction, glycoproteins

Fertilization is the fusion of the sperm and ovum. The sperm head binds to the plasma membrane of the egg (oolemma), and the entire spermatozoon enters the cytoplasm of the ovum. Only capacitated spermatozoa with intact acrosomes can enter and pass through the cumulus oophorus. The acrosome is a membrane-bound, cap-like structure covering the anterior portion of the sperm nucleus. The acrosomal reaction is the release of materials that lyse the glycoprotein coat (zona pellucida) surrounding the ovum. This is necessary for fertilization to take place. Before undergoing the acrosomal reaction, sperm go through a type of hypermotility called hyperactivation. The... 

Sperm penetrate the zona pellucida only after completion of the acrosome reaction. A similar process occurs in nonmammalian species, where sperm must penetrate the vitelline coat. In abalone this is accomplished by release of lysin, an acrosomal protein that disperses the vitelline coat by a noncatalytic mechanism (Lewis et al., 1982 Shaw et al., 1993). In contrast, the generally accepted model for mammalian sperm penetration of the zona pellucida is the acrosin hypothesis in which proteolysis of zona pellucida matrix glycoproteins by acrosin, the acrosomal serine esterase, plays a trailblazing role in the sperm penetration process (Yanag-... 

Bleil, J.D. and Wassarman, P.M. (1983). Sperm-egg interactions in the mouse Sequence of events and induction of the acrosome reaction by a zona pellucida glycoprotein. Dev. Biol. 95 317-324. 

Trimmer, J.S., Trowbridge, I.S., and Vacquier, V.D. (1985). Monoclonal antibody to a membrane glycoprotein inhibits the acrosome reaction and associated Ca and H fluxes of sea urchin sperm. Cell 40 697-703. 

Keller, S. H., and Vacquier, V. D., 1994, The isolation of acrosome-reaction-inducing glycoproteins from sea urchin egg jelly, Dev. Biol. 162 304-312. 

Co-ARIS means cofactor for acrosome reaction-inducing substance. These saponins are present in the protective jelly of starfish eggs and induce the acrosome reaction depending on the pH and the calcium level of seawater. Associated with a sulfated glycoprotein called ARIS, Co-ARISes have a function similar to that of SAPs for the sea urchins (see Chapter 25 and Hoshi et al., 1988). 

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