Heads or tails? Structural events and molecular mechanisms that promote mammalian sperm acrosomal exocytosis and motility

Abstract

Sperm structure has evolved to be very compact and compartmentalized to enable the motor (the flagellum) to transport the nuclear cargo (the head) to the egg. Furthermore, sperm do not exhibit progressive motility and are not capable of undergoing acrosomal exocytosis immediately following their release into the lumen of the seminiferous tubules, the site of spermatogenesis in the testis. These cells require maturation in the epididymis and female reproductive tract before they become competent for fertilization. Here we review aspects of the structural and molecular mechanisms that promote forward motility, hyperactivated motility, and acrosomal exocytosis. As a result, we favor a model articulated by others that the flagellum senses external signals and communicates with the head by second messengers to affect sperm functions such as acrosomal exocytosis. We hope this conceptual framework will serve to stimulate thinking and experimental investigations concerning the various steps of activating a sperm from a quiescent state to a gamete that is fully competent and committed to fertilization. The three themes of compartmentalization, competence, and commitment are key to an understanding of the molecular mechanisms of sperm activation. Comprehending these processes will have a considerable impact on the management of fertility problems, the development of contraceptive methods, and, potentially, elucidation of analogous processes in other cell systems.

Odorant receptor-mediated sperm activation in disease vector mosquitoes

“…3D). Both cAMP and cyclic guanosine monophosphate (cGMP) are important second messengers that regulate flagellar beating in response to activators and chemoattractants of mammalian and marine invertebrate sperm (33,34). The cAMP activation of A. gambiae sperm was unaffected by VUANT, suggesting the presence of a second messenger-mediated activation pathway that is either independent of Orco or performs downstream of Orco in A. gambiae (Fig.…”

“…The activation of insect sperm via ionotropic Ors is reminiscent of capacitation of mammalian sperm, which has been linked to signaling pathways mediated by metabotropic ORs (23,26,27) as well as the activity of several ionotropic channels (58,59). These include calcium channels, most notably the sperm cation channels, CatSpers (60)(61)(62)(63), potassium channels such as Kcnu1 (64,65) as well as sodium, proton, bicarbonate, and chloride channels that are localized along the sperm flagella and speculated to act downstream of receptors for diverse extracellular ligands (33,59). The modulation of insect and mammalian sperm via proteins of distinct evolutionary origins yet that encompass conserved modes of signal transduction represents a potent example of convergent evolution impacting upon a singularly essential biological process.…”

Cl− Channels and Transporters in Sperm Physiology

“…This process, called the AR, is now believed to occur in multiple steps. As multiple fusion points between the acrosomal and plasma membrane are involved in the AR, plasma membrane-outer acrosome hybrid vesicles are liberated, resulting in the release of the acrosomal content (Buffone et al 2012 ). The fusion machinery involved in this reaction is regulated by Ca 2+ and similar to that found in many neuroendocrinal secretory cells (Bello et al 2012 ;Castillo Bennett et al 2010 ).…”

Changing of the ejaculate parameters and sperm structure in men with overweight

“…Любая патология приводит к ухудшению подвижности сперматозои-да и, как следствие, снижению его способности к оплодотворению яйцеклетки. Не менее важна роль жгутика и в контроле акросомальной реакции -не-обходимого условия оплодотворения [21]. Кроме того, имеются данные о связи между патологией жгутика и изменении кариотипа: 99% сперматозои-дов с множественными жгутиками являются анеу-плоидными [22].…”