Nonequivalence of Maternal Centrosomes/Centrioles in Starfish Oocytes: Selective Casting-Off of Reproductive Centrioles into Polar Bodies

摘要

Itisbelievedthatinmostanimalsonlythepaternalcentrosomeprovidesthedivisionpolesformitosisinzygotes.Thispaternalinheritanceofthecentrosomesdependsontheselectivelossofthematernalcentrosome.Inordertounderstandthemechanismofcentrosomeinheritance,thebehaviorofallmaternalcentrosomes/centrioleswasinvestigatedthroughoutthemeioticandmitoticcyclesbyusingstarfisheggsthathadpolarbody(PB)formationsuppressed.Instarfishoocytes,thecentriolesdonotduplicateduringmeiosisII.Hence,eachcentrosomeofthemeiosisIIspindlehasonlyonecentriole,whereasinmeiosisI,eachhasapairofcentrioles.WhentwopairsofmeiosisIcentrioleswereretainedinthecytoplasmofoocytesbycompletesuppressionofPBextrusion,theyseparatedintofoursinglecentriolesinmeiosisII.However,aftercompletionofthemeioticprocess,onlytwoofthefoursinglecentrioleswerefoundinadditiontothepronucleus.WhenthetwosinglecentriolesofameiosisIIspindlewereretainedintheoocytecytoplasmbysuppressingtheextrusionofthesecondPB,onlyonecentriolewasfoundwiththepronucleusafterthecompletionofthemeioticprocess.WhenthesePB-suppressedeggswereartificiallyactivatedtodrivethemitoticcycles,allthesurvivingsinglecentriolesduplicatedrepeatedlytoformpairsofcentrioles,whichcouldorganizemitoticspindles.Theseresultsindicatethatthematernalcentriolesarenotequivalentintheirintrinsicstabilityandreproductivecapacity.ThecentrosomeswiththereproductivecentriolesareselectivelycastoffintothePBs,resultinginthematureegginheritinganonreproductivecentriole,whichwoulddegradeshortlyafterthecompletionofmeiosis.