Evidence that the fertilization envelope blocks sperm entry in eggs of Xenopus laevis: Interaction of sperm with isolated envelopes☆

摘要

ThecorticalreactionineggsofXenopuslaevisresultsinconversionofthevitellineenvelope(VE)intothefertilizationenvelope(FE).TheFEiscomposedoftheformerVEplusanewcomponent,thefertilizationlayer,thatformsasaconsequenceofthecorticalreaction.AninvitrotestsystemwasdevelopedtocomparetheVEandFEintermsoftheirpenetrabilitybysperm.VE'sandFE'swereisolatedfromunfertilizedeggsandcleavingembryos,respectively.Althoughtheyswellduringtheisolationprocedure,theisolatedVE'sandFE'sretainthemorphologicalcharacteristicsbywhichtheycanbedistinguishedinsitu.Penetrabilityofisolatedenvelopeswastestedbyexposingsuspensionsofenvelopestosperminasalinesolutiontowhichsolubilizedcomponentsfromthejellycoatoftheeggwereadded.IsolatedVE'swerepenetratedbyspermfrombothsides.Bycontrast,isolatedFE'sprovedimpenetrable:InnoinstancedidspermpenetrateeitherthefertilizationlayerortheVEcomponentoftheFE.WeconcludedthatthefertilizationenvelopeblocksspermentryinXenopuslaevis.