The mitochondrial cloud of Xenopus oocytes: The source of germinal granule material

摘要

ThemitochondrialcloudisaprominentmassinthecytoplasmofprevitellogenicoocytesofXenopuslaevis.Itisshownherethatthecloudcontainsbothmitochondriaandelectron-densegranulofibrillarmaterial(GFM).Usingacombinationoflightmicroscopical,fluorescence,time-lapsefilming,andelectronmicroscopicaltechniques,theontogenyofthesecomponentsisreportedandtheirfateisstudied.ItwasfoundthatthecloudisstationaryinprevitellogenicstagesandfragmentsintoislandsofmitochondriaandGFMduringstageII(usingthestagingsystemofJ.N.Dumont(1972)J.Morphol.136,153a€“180).TheseislandsbecomelocalizedintheperipheralcytoplasmatonepoleofthestageIIIoocyte.Bystudyingsuccessivestages,GFMwasfollowedthroughoogenesisanditwasfoundlocalizedonlyatthevegetalpoleofstageIVandVoocytes.Furthermore,itwasfoundthatitbearsastrikingresemblanceinposition,appearance,andassociationswithmitochondriatothea€?germinalgranulesa€?ofunfertilizedeggs.Germinalgranuleshavebeenshownbyotherstobecomeincorporatedintogerm-linecells.ItisconcludedthattheGFMistheprecursorofthismaterialandthatthemitochondrialcloudisthesiteofitsaccumulationandlocalizationintheprevitellogenicoocyte.