Abstract
Several proteins present on the sperm membranes serve as signal transducers facilitating sperm maturation, capacitation,acrosome reaction and fertilization. Among them, guanylate cyclase (GC), the inositol trisphosphate receptor (IP3R) andcalmodulin have been reported rather extensively. Although biochemical data clearly suggest their roles in thefertilization process, the precise location of these proteins in the sperm membranes have not been adequately investigatedand need clarification. Using immunolocalization procedures we report that guanylate cyclase receptors (GCR) arelocalized on the apical region of the acrosome and on the postacrosomal plasmalemma, while IP3Rs are present in theneck region of the sperm and at lower density along the axonemal membrane. In contrast, calmodulin is restricted to thepostacrosomal, basal nuclear membrane and the neck region that corresponds to the redundant nuclear envelope and ERvesicles, with some reaction along the middle piece and tail membranes. Colocalization of these proteins on the spermmembrane together with biochemical data as reported previously provide further insight into their role in thespermatozoan motility and possibly the fertilization process.
Highlights
(Ramaroa and Garbers. 1985, Wedel and Garbers 2001, Revelli et al, 2002, Sharma 2002), and guanylate cyclase, the ubiquitous enzyme, catalyzes the conversion of GTP to cGMP mediated by nitric oxide (NO) [Bentley et al, 1986]
The major finding of the study is that there is a colocalization of signal transduction proteins on the sperm membranes
Close association of IP3R and guanylate cyclase receptors (GCR) in sperm membrane supports the suggestion made by Suarez and coworkers that IP3 mediated release of Ca2+ from calmodulin stores is related to the control of gated calcium channels during sperm motility and hyperactivated motility (Ho and Suarez, 2001, 2003)
Summary
(Ramaroa and Garbers. 1985, Wedel and Garbers 2001, Revelli et al, 2002, Sharma 2002), and guanylate cyclase, the ubiquitous enzyme, catalyzes the conversion of GTP to cGMP mediated by nitric oxide (NO) [Bentley et al, 1986]. 1985, Wedel and Garbers 2001, Revelli et al, 2002, Sharma 2002), and guanylate cyclase, the ubiquitous enzyme, catalyzes the conversion of GTP to cGMP mediated by nitric oxide (NO) [Bentley et al, 1986]. IP3 has been implicated in the regulation of Ca2+ from intracellular membrane stores during hyperactivated motility in several sperm species (Suarez and Osman, 1987, Ho and Suarez, 2001, 2003). IP3 may be implicated in the acrosome reactions in several species (Bird et al.; 1991). Increase in intracellular Ca2+ through IP3-gated channels may be associated with a signaling cascade leading to cell motility, the acrosome reaction, and capacitation (Brass and Joseph, 1985). The localization GCR, IP3R and calmodiulin on the sperm membranes in boar sperm will give us further insight into their role in the process leading to the various sperm functions
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