Polar lobe formation and cytokinesis in fertilized eggs of Ilyanassa obsoleta: II. Large bleb formation caused by high concentrations of exogenous calcium ions☆

[摘要] FertilizedeggsofthemolluskIlyanassaobsoleta(Nassariusobsoletus)formlargeblebsresemblingpolarlobeswithin12minofexposuretosolutionsofisotonicCaCl2,whereascontroleggsinseawaterremainspherical.Underidenticalconditions,fertilizedeggsoftheseaurchin,Strongylocentrotuspurpuratus,anorganismwhichnormallydoesnotformpolarlobes,donotformblebsuponexposuretosolutionsofisotonicCaCl2.Thecalcium-inducedblebbinginIlyanassastilloccursifothercationssuchasNa+,Mg2+,orMn2+arepresentinadditiontoCa2+,butnotifcomparableconcentrationsofK+arepresent.CytochalasinBpreventsthecalcium-inducedblebbing,whereascolchicinedoesnot.CytokinesisinbothIlyanassaandStrongylocentrotusandnormalpolarlobeformationinIlyanassaappeartorequireexogenousK+butnotexogenousCa2+.PreliminaryelectronmicroscopyofIlyanassaeggsexposedtoisotonicsolutionsofCaCl2hasshownmicrofilamentsinthecorticalcytoplasmintheregionoftheblebconstrictionbutnomicrofilamentsinsphericalcontroleggsinseawater.ThesedatasuggestthathighconcentrationsofexogenousCa2+triggerthepolymerizationandcontractionofaringofmicrofilamentsinthecorticalcytoplasmoftheIlyanassaeggwhichresultsintheformationofalobelikeblebofcytoplasm.TheobservationthatK+antagonizesthisCa2+-inducedblebbinghasledtotheformulationofatheorywhichpostulatesthattheratioofintracellularCa2+tointracellularK+iscriticalinthecontrolofpolarlobeformationandcytokinesis.

[学科分类] 生物科学（综合）