G M1 Dynamics as a Marker for Membrane Changes Associated With the Process of Capacitation in Murine and Bovine Spermatozoa

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.