GM1 DYNAMICS INDICATE MEMBRANE CHANGES ASSOCIATED WITH CAPACITATION IN MURINE SPERMATOZOA

Abstract

We previously showed that in live murine and bovine sperm heads, the ganglioside GM1 localizes to the sterol-rich plasma membrane overlying the acrosome (APM). Labeling GM1 using the pentameric cholera toxin subunit B (CTB) induced a dramatic redistribution of signal from the APM to the sterol-poor post-acrosomal plasma membrane (PAPM) upon sperm death. We now show a similar phenomenon in the flagellum where CTB induced GM1 redistribution to sterol-poor membrane sub-domains of the annulus and flagellar zipper. Because sterol efflux from the plasma membrane is required for capacitation, we next examined whether GM1 localization might be useful to detect membrane changes associated with capacitation and/or acrosomal exocytosis. First, incubation of murine sperm with their respective stimuli for capacitation did not change GM1 distribution in live cells. However, incubation with specific stimuli for capacitation, followed by the use of specific fixation conditions, induced reproducible, stimulus-specific patterns of GM1 distribution. By assessing changes in GM1 distribution in response to progesterone-induced acrosomal exocytosis, we show that these patterns reflect the response of sperm populations to capacitating stimuli. These data suggest that GM1 localization can be used as a diagnostic tool for evaluating sperm response to stimuli for capacitation and/or acrosomal exocytosis. Such information could be useful when deciding between technologies of assisted reproduction, or when screening for male fertility. Furthermore, stimulus-specific changes in GM1 distribution showed that sperm could respond to NaHCO3 or mediators of sterol efflux independently, thereby refining existing models of capacitation. (poster)