Topographical rearrangement of a plasma membrane antigen during capacitation of rat spermatozoa in vitro

摘要

Wehavepreviouslydescribedanantigen(termed2B1)onratspermatozoathatispresentontheplasmamembraneoverlyingthetaildomain.TheantigenismobilewithintheplaneoftheplasmamembraneandamAbtoitblocksfertilizationinvitro.Inthepresentstudywedescribesomedynamicpropertiesofthisantigeninrelationtoitstopographicaldistribution.Whenspermatozoawereincubatedinvitroinacapacitationmediumandstainedwith2B1mAb/FITC-rabbitanti-mouseF(aba€2)2,strongfluorescenceappearedovertheacrosomaldomain.Acuteexposureoffreshspermatozoatodissociatingreagents(1MNaClor5mM2-mercaptoethanol)orinducersoftheacrosomereaction(lysolecithin+Ca2+orA23187+Ca2+)failedtomimictheseeffects.SpermatozoaprelabeledwithFITC-2B1IgGandthencapacitatedinthepresenceofexcessa€?colda€?2B1IgGalsoshowedaccumulationoffluorescenceontheacrosomaldomain,suggestingthattheantigenhadmigratedfromthetail.MigrationwasselectiveandCa2+-andtemperature-dependentbutwasnotinhibitedbymetabolicpoisons(NaForNaN3).Motilitywasnotobligatoryformigration.Immunogold-labelingstudiesattheultrastructurallevelshowedthat2B1antigenwasrestrictedtothesurfacemembraneoverboththetailandtheacrosomaldomainsandthatduringmigrationitdidnotchangethetypeofmembraneintowhichitwasinserted.FromaquantitativeanalysisoffluorescenceonspermatozoaprelabeledwithFITC-2B1IgGandthencapacitated,theamountofantigenthatappearedontheacrosomaldomainwasapproximatelyequivalenttothatlostfromthemidpiecedomain.TheMrof2B1antigenextractedfromcapacitatedspermatozoawas300a€“500Dalessthanthatextractedfromnoncapacitatedcells,suggestingthatthemoleculehadumdergoneprocessingconcomitantwithmigration.Theseresultsarediscussedinrelationtomechanismsfortargetingantigenstositeswheretheybecomephysiologicallyactiveandarecorrectlypositionedtoparticipateingameterecognitionprocesses.