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G_M1 Dynamics as a Marker for Membrane Changes Associated With the Process of Capacitation in Murine and Bovine Spermatozoa

VIMAL SELVARAJ^*,

DANIELLE E. BUTTKE^*,

ATSUSHI ASANO

JOHN L. MCELWEE

COLLIN A. WOLFF

JACQUELYN L. NELSON

ANGELA V. KLAUS

GARY R. HUNNICUTT

ALEXANDER J. TRAVIS

From the Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, New York; Department of Biology, Seton Hall University, South Orange, New Jersey; and the Population Council, The Rockefeller University, New York, New York.

Correspondence to: Alexander J Travis, Baker Institute for Animal Health, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853 (e-mail: ajt32{at}cornell.edu).

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 NaHCO₃ or mediators of sterol efflux independently, thereby refining existing models of capacitation.

     Key words: Rafts, ganglioside, cholesterol, cholera toxin, annulus