Acrosome reaction zona pellucida

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... 

The acrosome reaction is the loss of the acrosomal and plasma membranes in the acrosome region and the release of acrosin, hyaluronidase and other enzymes that disperse the cumulus complex and allow the sperm to penetrate the zona pellucida. After capacitation and the acrosome reaction, sperm penetrate the extracellular cumulus matrix and bind with zona protein 3, a heavily glycosylated protein of the zona pellucida. The first segment of the sperm to make contact with the oolemma is usually the inner acrosomal membrane, followed by the postacrosomal region. The plasma membrane of the sperm attaches to microvilli on the oolemma. Sperm-egg fusion is apparent from reduced movement of the sperm tail (Yanagimachi, 1970,1988 Takano et al.,... 

Mammalian fertilization is the result of a precisely regulated series of cellular interactions. This process can be divided into a number of component stages, including the following (i) the early events that precede egg fusion, consisting of the preliminary event of sperm capacitation, sperm penetration of the cumulus oophorus, zona pellucida adhesion, initiation and completion of acrosome reactions, penetration of the zona pellucida, egg plasma membrane contact and fusion and (ii) the late events that occur within the egg that consist of sperm nuclear decondensation followed by pronuclear consolidation and syngamy. 

In conclusion, it is generally believed that the extracellular matrix of the cumulus oophorus functions as a selective filter permitting only those sperm that have not completed the acrosome reaction to penetrate to the zona pellucida. This matrix may also provide a unique microenvironment that regulates the final stages of capacitation. 

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-... 

Bailey, J.L. and Storey, B.T. (1994). Calcium influx into mouse spermatozoa activated by solubilized mouse zona pellucida, monitored with the calcium fluorescent indicator, fluo- 3. Inhibition of the influx by the influx by three inhibitors of the zona pellucida induced acrosome reaction Tyrphostin A48, pertussis toxin, and 3 -quinuclidinyl benzilate. Mol. Reprod. Dev. 39 297-308. 

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. 

Endo, Y., Lee, M.A., and Kopf, G.S. (1987). Evidence for a role of a guanine nucleotide-binding regulatory protein in the zona pellucida-induced mouse sperm acrosome reaction. Dev. Biol. 7 79 210-216. 

Florman, H.M. and First, N.L. (1988). The regulation of acrosomal exocytosis. I. Sperm capaeitation is required for the induction of acrosome reactions by the bovine zona pellucida in vitro. Dev.Biol. (28 453-463. 

Lu, Q. and Shur, B.D. (1997). Sperm from p 1,4-galactosyltransferase-null mice are refractory to ZP3-induced acrosome reactions and penetrate the zona pellucida poorly. Development 724 4121-4131. 

O Toole, C.M.B. and Florman, H.M. Cooperative regulation of intracellular Ca stores in sperm by pH and IP3 during the zona pellucida-induced acrosome reaction. (Unpublished.)... 

Storey, B.T., Hourani, C.M., and Kim, J.B. (1992). A transient rise in intracellular Ca is a precursor reaction to the zona pellucida-induced acrosome reaction in mouse sperm and is blocked by the induced acrosome reaction inhibitor 3-quinuclidinyl benzilate. Mol. Reprod. Dev. 52 41-50. 

Tesarik, J., Carreras, A., and Mendoza, C. (1993). Differential sensitivity of progesterone- and zona pellucida-induced acrosome reactions to pertussis toxin. Mol. Reprod. Dev. 54 183- 189. 

In Chapter 7, Florman and coauthors review the mechanisms of egg-regulated acrosome reactions of mammalian sperm. Among the aspects discussed are the nature of primary signal transducers and targets stimulated by binding of acrosome-intact sperm to receptors in the egg zona pellucida. In a detailed presentation, the potential roles of several sperm components including G proteins, cation channels, tyrosine kinases, calcium, and cellular pH are considered. 

Fulgham DL, Coddington CC, Johnson D, Kerr J, Alexander N, Hodgen GD. 1992. Human sperm acrosome reaction rate on zona pellucida a time course study. ARTA 3 25-34. 

Kligman I, Glassner M, Storey BT, Kopf GS. 1991. Zona-pellucida-mediated acrosomal exocytosis in mouse spermatozoa characterization of an intermediate stage prior to the completion of the acrosome reaction. Dev Biol 145 344—355. 

Lee MA, Kopf GS, Storey BT. 1987b. Effects of phorbol esters and a diacylglycerol on the mouse sperm acrosome reaction induced by the zona pellucida. Biol Reprod 36 611-621. 

Van Duin VM, Polman JEM, De Breet ITM, Van Ginneken K, Bunschoten H, Grootenhuis A, Brindle J, Aitken RJ. 1994. Recombinant human zona pellucida protein ZP3 produced by Chinese hamster ovary cells induces the human sperm acrosome reaction and promotes sperm-egg fusion. Biol Reprod 51 607-617. 

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