Ultrastructural and lectin binding changes during the formation of the animal dimple in oocytes of Discoglossus pictus (Anura)

摘要

InDiscoglossuspictuseggs,theanimaldimpleistheonlyplacewherefertilizationcanoccur.Thecarbohydratecompositionofthedimplemembranewasinvestigatedusingfluorescent-labeledlectins.Receptorsforsoybeanagglutinin(SBA)andwheatgermagglutinin(WGA)arespecificallylocalizedonthedimplewalls,whereasfucose-likeresiduesareonlypresentatthebottomofthedimple.Thislectinbindingpatternistransientsinceitonlyappearswhenthedimpleiscompletelyformedanddisappearsimmediatelyafterfertilization.Theformationofthedimplerequiresanincreaseinsurface.Ourultrastructuralstudiessuggestthatmembranegrowthoccursthroughtheinsertionofvesiclesintotheplasmamembrane.Wehypothesizethatthelectin-bindingglycocomponentsthatweobservedareinsertedalongwiththevesicleswhichfuseintothemembrane.Thesevesiclesmostprobablyoriginatefromtheannulatelamellaeandcisternalstackspresentinfull-grownoocytes.Thepossibilitythatthesurfacefeaturesofthedimple,suchasthemicrovilli,thecomplexglycocalyx,andparticularytheneutralcarbohydrateresidues(fucose-like),mightfavorsperm-eggfusionisdiscussed.