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【图文】cell division and establishment of asymmetry during embryo development
H.Schatten,Q.-Y.Sun/SeminarsinCell&DevelopmentalBiology21 (4
Fig.1.(a)Schematicrepresentationofatypicalmammaliancentrosomedisplayingtwoperpendicularlyorientedcentriolessurroundedbyameshworkofpericentriolarmaterial(PCM)thatnucleatesmicrotubules.(b)Schematicrepresentationofmicrotubulesassociatedwithcentrosomesdisplayingtranslocationofsubstrates,enzymesandorganellessuchasmitochondriaalongmicrotubulesaidedbydynein(whitecircles)andkinesin(blackcircles).ModifiedfromSchatten[106].
humans(reviewedby[108]).Thepresentreviewwillfocusonthecurrentstateofknowledgeontheroleofgermcellcentro-somesduringfertilization,formationofthezygotecentrosome,centrosomeduplicationandseparationduringfirstembryoniccelldivision,andasymmetriccelldivisionsduringcelldifferentiationandsubsequentembryodevelopment.Itwillalsoaddressasym-metriccelldivisioninstemcellsandformationoftheprimaryciliumduringembryodevelopment.
Thecompositionofthecentrosomehasbeendiscussedinpreviousreviews([109][11-14,106-108];andothers).TheschematicdiagraminFig.1aisshownasabriefintroductiontoatypicalcentrosomedisplayingtwocentrioles(motheranddaughtercentriolepair)eachca.0.3-0.6?minlengthandca.0.2?mindiameterthatareassociatedwitheachotherbyinterconnectingfibersandsurroundedbyameshworkofpericentriolarmaterial(PCM).Distalandsubdistalappendagesarecharacteristicfeaturesofthemothercentriolewhilethedaughtercentriolewilldevelopthesefeatureswhenbecomingamothercentrioleafterseparationandduringthenextduplicationcycle([15];reviewedin[10,13,14,16];andothers).ThePCMmaterialconsistsofafibrousscaffoldinglatticecontainingalargeamountofcoiled-coilcentrosomalproteinsthatareestimatedtobebetween50and100,dependingonmethodsemployedanddependingonspecificcellcyclestages.PCMcomponentsincludestructuralproteins,regulatorymolecules,centrosome-associatedproteins,aswellasheatshockproteins(reviewedin[106];reviewedbyRat-tner,thisissue).Uniquetothecentrosomeorganelleisthelackofaconfiningmembranewhichallowsrapidanddirectinteractionswithcellularcomponents.ThePCM’sthree-dimensionalarchi-tectureisprimarilymaintainedthroughspecificprotein-proteininteractions.KeyproteinsofthePCMincludethe?-tubulinringcomplex(?-TuRC),acomplexofthecentrosomecorestructurethatiscrucialformicrotubulenucleationalongwithpericentrinsPCNT1andPCNT2,poloandaurorakinases,themicrotubuleanchoringproteinsninein,centriolin,dynactinandnumerousothersthathavebeenhighlightedanddescribedindetailinseveralotherexcellentreviews([109]andarticlestherein).Centrinplaysanessentialroleincentrosomeduplication[17].Dysfunctionsofspe-cificcentrosomalproteinshavebeenlinkedtovariousdiseasesandinfertility([109]andarticlestherein).Microtubulesareanchoredwiththeirminusendstothecentrosomecorestructurewhiledistalmicrotubuleplus-endsfavoradditionoftubulinsubunitsandthereforemicrotubulegrowth[18];throughthesedynamicmicrotubuleformationscentrosomesbecomecriticalcentralsta-tionsforcellularcommunication.Fig.1brepresentsseveralaspectsofcentrosomefunctionsascentralstationfortheregulationoftraffickingalongmicrotubulerailroadswhichincludesmitochon-drialtranslocation,recruitmentofcellcycle-specificcentrosomeproteins,andvariousregulatorycomponents.PCMmaterialishighlydynamicandchangesshapetoformavarietyofdifferentconfigurationswhichisparticularlyimportanttoaccommodatetherapidandvariedrequirementsforsuccessfulfertilization,appositionoftheparentalgenomicmaterial,symmetricandasymmetriccelldivision,celldifferentiationandasymmetricdistributionofcellfatecomponentsduringcelldifferentiationandsubsequentdevelopment,aswewillseeinthefollowingsections.
SeveralmodelsystemshavebeenutilizedtogaininsightsintothebiologyofcentrosomesduringfertilizationandthefirstcellcycleincludingseaurchineggsthathadbeenusedinBoveri’soriginalstudies[6]butmorerecently,studiesonDrosophilaandCaenorhabditiselegans(C.elegans)havebeenusedtocontributeinformationoncentrosomesthattosomeextentcanbeextrap-olatedtoseveralmammaliancellsystems,asmanyhomologs
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