Abstract
Mammalian sperm capacitation is an essential prerequisite to fertilization. Although progress is being made in understanding the physiology and biochemistry of capacitation, little has been yet explored about the potential role(s) of individual sperm cell protein during this process. Therefore elucidation of the role of different sperm proteins in the process of capacitation might be of great importance to understand the process of fertilization. The present work describes the partial characterization of a 14-kDa protein (p14) detected in goat spermatozoa using an antibody directed against the purified protein. Confocal microscopic analysis reveals that the protein is present in both the intracellular and extracellular regions of the acrosomal and postacrosomal portion of caudal sperm head. Though subcellular localization shows that p14 is mainly cytosolic, however it is also seen to be present in peripheral plasma membrane and soluble part of acrosome. Immuno-localization experiment shows change in the distribution pattern of this protein upon induction of capacitation in sperm cells. Increased immunolabeling in the anterior head region of live spermatozoa is also observed when these cells are incubated under capacitating conditions, whereas most sperm cells challenged with the calcium ionophore A23187 to acrosome react, lose their labeling almost completely. Intracellular distribution of p14 also changes significantly during acrosome reaction. Interestingly, on the other hand the antibody raised against this 14-kDa sperm protein enhances the forward motility of caprine sperm cells. Rose-Bengal staining method shows that this anti-p14 antibody also decreases the number of acrosome reacted cells if incubated with capacitated sperm cells before induction of acrosome reaction. All these results taken together clearly indicate that p14 is intimately involved and plays a critical role in the acrosomal membrane fusion event.
Highlights
After leaving the testis, mammalian spermatozoa from many species are morphologically differentiated but have acquired neither progressive motility nor the ability to fertilize a metaphase II-arrested egg
We have examined the presence of p14 by Western blot analysis in caprine epididymis and epididymal spermatozoa using a polyclonal anti-p14 antibody raised in rabbit in our laboratory
Mammalian sperm-egg interactions are mediated by specific complementarity of proteins, glycoproteins, and carbohydrates
Summary
Mammalian spermatozoa from many species are morphologically differentiated but have acquired neither progressive motility nor the ability to fertilize a metaphase II-arrested egg. The physiological changes that confer on the sperm the ability to fertilize are collectively called capacitation [1]. Capacitation includes several cellular changes in the sperm in the distribution and composition of certain glycoproteins, protein tyrosine phosphorylation, intracellular Ca2+ and cAMP concentrations, as well as motility pattern [2,3]. This phenomenon is an absolute prerequisite that spermatozoa must undergo in order to interact efficiently with the zona pellucida and to accomplish one of the last steps leading to fertilization, namely the acrosome reaction (AR) [4]
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