Shapiro B M, Cook S, Quest A F, Oberdorf J, Wothe D
Department of Biochemistry SJ-70, University of Washington, Seattle 98195.
J Reprod Fertil Suppl. 1990;42:3-8.
Several mechanisms are used to control the behaviour of sea urchin spermatozoa while fertilizing eggs. These include discrete regulatory steps that modulate the sperm activation sequence from spawning to gamete membrane fusion. After release from the testis, sperm motility is instantaneously activated, by using intracellular pH as a throttle mechanism to control the rate of the dynein motor that catalyses axonemal bending. To support motility, energy is transported from the mitochondrion to the tail, by using a shuttle mechanism involving phosphocreatine diffusion. This shuttle employs a novel, endotriplicated, creatine kinase of Mr 140,000 in the flagellar axoneme as its terminus. The steering mechanism that determines where the spermatozoon swims is unknown, but may involve an egg peptide-induced guanylate cyclase activation, mediated by a cGMP-dependent Ca2+ channel, and attenuated by a plasma membrane cGMP phosphodiesterase. Upon arriving at the egg, which is identified by virtue of its proteoglycan coat (egg jelly), the spermatozoon undergoes a univesicular secretion that prepares it to fuse with the egg. This acrosome reaction involves several altered ionic fluxes in its mechanism, terminating in a massive Ca2+ uptake. If the spermatozoon is fortunate enough to fuse with an egg, a new member of the species is generated; if the acrosome reaction occurs without gamete fusion, the spermatozoon rapidly dies. All of these activation processes involve changes in the intracellular ionic milieu that are co-ordinated with altered enzyme activities, often in a causal fashion. Even with our current imperfect understanding of the process, a few of the steps in sperm activation may be defined by biochemical pathways that include specific modulatory control points.
在使卵子受精的过程中，有几种机制用于控制海胆精子的行为。这些机制包括离散的调节步骤，可调节从精子排放到配子膜融合的精子激活序列。从睾丸释放后，精子活力立即被激活，通过利用细胞内pH作为节流机制来控制催化轴丝弯曲的动力蛋白的速率。为了支持运动，能量通过涉及磷酸肌酸扩散的穿梭机制从线粒体运输到尾部。这种穿梭机制采用一种新型的、内膜三倍化的、分子量为140,000的肌酸激酶，位于鞭毛轴丝的末端。决定精子游动方向的导向机制尚不清楚，但可能涉及由cGMP依赖性Ca2+通道介导的、由卵肽诱导的鸟苷酸环化酶激活，并由质膜cGMP磷酸二酯酶减弱。到达卵子（通过其蛋白聚糖外衣（卵黄膜）识别）时，精子会经历单泡分泌，为与卵子融合做好准备。这种顶体反应在其机制中涉及几种改变的离子通量，最终导致大量Ca2+摄取。如果精子有幸与卵子融合，就会产生该物种的一个新个体；如果顶体反应在没有配子融合的情况下发生，精子会迅速死亡。所有这些激活过程都涉及细胞内离子环境的变化，这些变化通常以因果关系与改变的酶活性相协调。即使我们目前对这个过程的理解并不完美，精子激活过程中的一些步骤可能由包括特定调节控制点的生化途径来定义。
