Sperm Capacitation and Acrosome Reaction in Mammalian Sperm

Abstract

Physiological changes that endow mammalian sperm with fertilizing capacity are known as sperm capacitation. As part of capacitation, sperm develop an asymmetrical flagellar beating known as hyperactivation and acquire the ability to undergo the acrosome reaction. Together, these processes promote fertilizing competence in sperm. At the molecular level, capacitation involves a series of signal transduction events which include activation of cAMP-dependent phosphorylation pathways, removal of cholesterol, hyperpolarization of the sperm plasma membrane, and changes in ion permeability. In recent years, new technologies have aided in the study of sperm signaling molecules with better resolution, at both spatial and temporal levels, unraveling how different cascades integrate and cooperate to render a fertilizing sperm. Despite this new information, the molecular mechanisms connecting capacitation with acrosomal exocytosis and hyperactivation are not well understood. This review brings together results obtained in mammalian species in the field of sperm capacitation with special focus on those pathways involved in the preparation to undergo the acrosomal reaction.

Exposure to Cadmium Impairs Sperm Functions by Reducing CatSper in Mice

“…In mammals, the acrosome reaction is crucial for sperm to fuse with the oocyte [25]. Here, both spontaneous and progesterone-induced ARs were examined in cadmium-treated mice.…”

“…It has been previously proposed that the sperm-specific cation channel (CatSper) acts as the main intracellular Ca 2+ source and may cause several Ca 2+ -dependent responses (motility, chemotaxis, and the acrosome reaction) [22, 25-29], whereas the sperm-specific potassium channel (Slo3) accounts for hyperpolarization of the membrane potential [24, 30]. Further studies have also revealed that both CatSper and KSper are indispensable to male fertility and that any mutation of either channel will cause male infertility [30, 31].…”

CFTR/ENaC-dependent regulation of membrane potential during human sperm capacitation is initiated by bicarbonate uptake through NBC

“…During this time, sperm undergo several molecular and cellular changes in a process known as capacitation (1,2). At the cellular level, capacitation prepares sperm to develop hyperactivated motility and to undergo acrosomal exocytosis (3,4). At the molecular level, once sperm enter the seminal plasma and the female reproductive tract, they are exposed to higher HCO 3 -concentration (~15-25 mM) (5,6) which results in activation of the atypical soluble adenylyl cyclase (ADCY10) that in turn leads to cAMP synthesis and activation of PKA (7).…”

5’-AMP-Activated Protein Kinase Regulates Goat Sperm Functions via Energy Metabolism In Vitro

“…Hyperactivation is helpful to release of sperm from the oviduct reservoirs and to penetrate the extracellular matrix of the eggs [4]. When sperm approach the egg, they go through a process known as the acrosome reaction that removes plasma membrane in the area of acrosomal cap and exocytosing acrosomal content [5]. ATP is needed for both hyperactivation and acrosome reaction [6].…”