GM1 Dynamics as a Marker for Membrane Changes Associated With the Process of Capacitation in Murine and Bovine Spermatozoa

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Abstract
We previously showed that in live murine and bovine sperm heads, the ganglioside G(M1) localizes to the sterol-rich plasma membrane overlying the acrosome (APM). Labeling G(M1) using the pentameric cholera toxin subunit B (CTB) induced a dramatic redistribution of signal from the APM to the sterol-poor postacrosomal plasma membrane (PAPM) upon sperm death. We now show a similar phenomenon in the flagellum where CTB induces G(M1) redistribution to sterol-poor membrane subdomains of the annulus and flagellar zipper. Because sterol efflux from the plasma membrane is required for capacitation, we examined whether G(M1) localization might be useful to detect membrane changes associated with capacitation and/or acrosomal exocytosis. First, incubation of murine and bovine sperm with their respective stimuli for capacitation did not change G(M1) distribution in live cells. However, incubation of sperm of both species with specific stimuli for capacitation, followed by the use of specific fixation conditions, induced reproducible, stimulus-specific patterns of G(M1) distribution. By assessing changes in G(M1) distribution in response to progesterone-induced AE, we show that these patterns reflect the response of murine sperm populations to capacitating stimuli. These data suggest that G(M1) localization can be used as a diagnostic tool for evaluating sperm response to stimuli for capacitation and/or AE. Such information could be useful when deciding between technologies of assisted reproduction or when screening for male fertility. Furthermore, stimulus-specific changes in G(M1) distribution showed that sperm could respond to NaHCO(3) or mediators of sterol efflux independently, thereby refining existing models of capacitation.