Acrosome

PH-20, a guinea pig sperm protein of 64 kD, is present on both the plasma membrane and inner acrosomal membrane of sperm. It is essential for adhesion of sperm to the zona peUucida, the initial step in the fertilization process. Active immunization with PH-20 causes infertility in both male and female guinea pigs for a period ranging from 6 to 15 months (120). 

Tilney, L.G. Inoue, S. (1982). Acrosomal reaction or Thyone sperm. 11. The kinetics and possible mechanism of acrosomal process elongation. J. Cell Biol. 93, 820-827. 

Tumer KO, Syvanen M, Meizel S. 1997. The human acrosome reaction is highly sensitive to inhibition by cyclodiene insecticides. J Androl 18(6) 571-575. 

In addition, anandamide was found to parallel classical cannabinoid pharmacology in a series of nonbehavioral experimental systems. In isolated MVD, (Pertwee, 1992) and guinea pig ileum, it inhibited electrically evoked twitch responses (Pertwee, 1995). Moreover, anandamide was shown to decrease intraocular pressure in rabbits (Pate, 1995), to reduce sperm-fertilizing capacity in sea urchins by inhibition of the acrosome reaction (Schuel, 1994), and to produce hypotension in rats (Varga, 1995). 

Schurmann, A., et al. The glucose transport facilitator GLUT8 is predominantly associated with the acrosomal region of mature spermatozoa. Cell Tissue Res. 2002,... 

Mature males given weekly intraperitoneal injections of 20 or 50 mg Pb/kg BW as lead acetate for 6 weeks vs. 20 or 50 mg sodium acetate/kg BW as controls Dose-dependent increases in blood and sperm lead concentrations. Serum testosterone levels reduced in lead-exposed rats, possibly from generation of reactive oxygen species, and resulting in premature acrosome reaction and reduced sperm oocyte-penetrating capability 39... 

Clapper, D.L., J.A. Davis, PJ. Lamothe, C. Patton, and D. Epel. 1985a. Involvement of zinc in the regulation of pH, motility, and acrosome reactions in sea urchin sperm. Jour. Cell Biol. 100 1817-1824. 

In the case of vitamin D3, there is a membrane receptor that, after being bound to this compound, and by the mediation of a G-protein, activates the opening of channels for the entrance of calcium into the cell (Bouillon et al. 1995). There are also membrane receptors for progesterone that mediate, among other processes, the reaction of acrosomes in spermatozoa. Finally, evidence of extragenomic participation of estrogens in exocytosis does exist (Machado et al. 2002). 

Pursel, V. G. and Johnson, L. A. (1974). Glutaraldehyde fixation of boar spermatozoa for acrosome evaluation. 

ElJack A, Hrudka F. 1978. Morphogenesis of the acrosomic defects in the ram induced experimentally by ethylene dibromide [Abstract], Anat Histol Embryol 7 350. 

The spermatozoon consists of a head, a midpiece and a tail or flagellum. The head contains the nucleus and a vesicle known as the acrosome (Figure 19.4). It contains hydrolytic enzymes that are required during fertilisation of the ovum. 

Microfilaments of F actin traverse the microvilli in ordered bundles. The microfila-ments are attached to each other by actin-as-sociated proteins, particularly fimbrin and vil-lin. Calmodulin and a myosin-like ATPase connect the microfilaments laterally to the plasma membrane. Fodrin, another microfila-ment-associated protein, anchors the actin fibers to each other at the base, as well as attaching them to the cytoplasmic membrane and to a network of intermediate filaments. In this example, the microfilaments have a mainly static function. In other cases, actin is also involved in dynamic processes. These include muscle contraction (see p. 332), cell movement, phagocytosis by immune cells, the formation of microspikes and lamellipo-dia (cellular extensions), and the acrosomal process during the fusion of sperm with the egg cell. 

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.,... 

Sperm evaluations routinely include data on sperm number, morphology and motility (Berman etal., 1996). Testicular spermatid count or cauda epididymal weight are other useful measures of sperm production, but no surrogate measures are adequate to evaluate sperm morphology or motility. A number of other indices of sperm function have been employed (e.g., sperm-zona interactions, acrosome reaction, sperm swelling studies), but these have been of limited utility and infrequently used and have not been incorporated into any testing guidelines. 

Alves, A. P., Mulloy, B., Diniz, J. A., and Mourao, P. A. (1997). Sulfated polysaccharides from the egg jelly layer are species-specific inducers of acrosomal reaction in sperms of sea urchins. ]. Biol. Chem. 272, 6965-6971. 

The acrosomal process of some invertebrate sperm cells is an actin cable that sometimes forms almost instantaneously by polymerization of the actin monomers and shoots out to penetrate the outer layers of the egg during fertilization (Chapter 32). The stereocilia, the "hairs" of the hair cells in the inner ear, contain bundles of actin filaments.302 Motion of the stereocilia caused by sound produces changes in the membrane potential of the cells initiating a nerve impulse. In certain lizards each hair cell contains about 75 stereocilia of lengths up to 30 pm and diameter 0.8 pm and containing more than 3000 actin filaments in a semicrystalline array. Microvilli (Fig. 1-6) contain longitudinal arrays of actin filaments. 

Another remarkable example is extension of the acrosomal process from a sperm cell of the horseshoe crab Limulus polyphemus at fertilization. A bundle of actin filaments in a crystalline state lies coiled around the base of the nucleus. At fertilization the bundle uncoils and slides through a tunnel in the nucleus to form a 60 pm-long acrosomal process within a few seconds. The uncoiled bundle is also crystalline. The coiled bundle is apparently overtwisted and an actin crosslinking protein scrum mediates the conformational alteration that takes place.339 A somewhat related process maybe involved in contraction of bacteriophage tails (pp. 363,364)... 

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