Guraya S S
Department of Zoology, College of Basic Sciences and Humanities, Punjab Agricultural University, Ludhiana, India.
Int Rev Cytol. 2000;199:1-64. doi: 10.1016/s0074-7696(00)99001-6.
A comparative account is given of advances in cellular and molecular biology of capacitation and acrosome reaction in spermatozoa by comparing and contrasting their biochemical and physiological changes in response to various factors in vivo and in vitro. It can now be stated that phenomena of sperm capacitation and acrosome reaction are endogenous molecular events occurring at the membrane level which can be modulated by external environmental factors. The molecular mechanisms and the signal transduction pathways mediating the process of capacitation and acrosome reaction are only partially defined and appear to involve modification of intracellular Ca2+ and other ions, lipid transfer, and phospholipid remodeling in the sperm plasma membrane as well as changes in protein phosphorylation. Evidences for the involvement of cAMP-dependent kinase pathway in the acrosome reaction are discussed. The mediation of one or more external signals by the sperm plasma membrane appears to activate this pathway after or simultaneously with the influx of Ca2+. Concurrent with or following entry of Ca2+, adenylate cyclase is activated, leading to increased concentrations of cAMP-activation of cAMP-dependent kinase and protein phosphorylation; the identity of such proteins and their role in the acrosome reaction must be determined. The roles of biological effectors of the acrosome reaction, such as ZP3 and follicular fluid are still to be defined at the molecular level. The gaps in our knowledge about the cellular and molecular aspects of capacitation and acrosome reaction are emphasized.
通过比较和对比精子在体内和体外对各种因素作出反应时的生化和生理变化，对精子获能和顶体反应的细胞与分子生物学进展进行了比较阐述。现在可以指出，精子获能和顶体反应现象是发生在膜水平的内源性分子事件，可受外部环境因素调节。介导获能和顶体反应过程的分子机制和信号转导途径仅部分明确，似乎涉及细胞内Ca2+和其他离子的修饰、脂质转移、精子质膜中的磷脂重塑以及蛋白质磷酸化的变化。讨论了cAMP依赖性激酶途径参与顶体反应的证据。精子质膜对一种或多种外部信号的介导似乎在Ca2+流入之后或同时激活该途径。在Ca2+进入的同时或之后，腺苷酸环化酶被激活，导致cAMP浓度增加——激活cAMP依赖性激酶和蛋白质磷酸化；此类蛋白质的身份及其在顶体反应中的作用必须加以确定。顶体反应的生物效应物，如ZP3和卵泡液，在分子水平上的作用仍有待确定。强调了我们在获能和顶体反应的细胞与分子方面知识的空白。
