concept-of-stem-cell.ppt

concept-of-stem-cell.ppt

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干细胞总论（GENERALIDEAONSTEMCELLS）,南京医科大学第一附属医院汪承亚,一、干细胞的概念,“Stemcells”isatermtodescribenormalprecursorcellsthatcangiverisetomultipletissuetypes.Stemcellpotentials:

SelfrenewalProliferationDifferentiation,二、干细胞的特征1.形态特征和生化特征形态特征圆形或椭圆形，核质比大；生化特征较高的端粒酶活性。

2.生长特征增殖的缓慢性,G0增殖的自稳性（区别与肿瘤细胞的本质特征，库量一定）自我复制多向分化和分化的不可逆性,三、干细胞的类型,ByDifferentiationpotentialTotipotentstemcellsarecellsthatcangiverisetoafullyfunctionalorganismaswellastoeverycelltypeofthebody.e.g.EmbryonicStemCellswheninsertedintoanearlyembryo,theyjointhehostcellstocreateanormalmouse.Pluripotentstemcellsarecapableofgivingrisetovirtuallyanytissuetype,butnottoafunctioningorganism.Definitionsof“pluripotent”generallyincludethepotentialofthecelltoformderivativesfromallthreegermlayers:

endoderm（givingrisetothegut）,themesoderm（givingrisetocartilage,bone,andsmoothandstriatedmuscle）,andectoderm（givingrisetothenervoussystemandotherepithelialtissue）.Multipotentstemcellsaremoredifferentiatedcells（thatis,theirpossiblelineagesarelessplastic/moredetermined）andthuscangiveriseonlytoalimitednumberoftissues.Forexample,HSC,MSC（mesenchymalstemcell）hasbeenshowntoproducebone,muscle,cartilage,fat,andotherconnectivetissues.Committedstemcellsneuralstemcelltoproduceneron,三、干细胞的类型（续）,bypotentialsourcesforstemcells:

Embryonicstemcellsderivedfromtheinnercellmassofablastocyst（averyearlyembryo）.Adultstemcellsstemcellsfoundinadulttissuesarereferredtoasadultstemcells.certaintissuesofthebody,frompost-embryonicdevelopmentthroughthenormallifeofanyorganism,requirestemcellsfornormalturnoverandrepair.agoodexampleisblood,butthisistrueformuscleandotherconnectivetissueaswell,andmaybetrueforatleastsomenervoussystemcells.,CellCycleandStemCellSelfRenewalorDifferentiation,Althoughitisstillnotclearwhatcontrolsthedecisiontoeitherself-renewordifferentiate,orhowthefateofadifferentiatingdaughtercellisdetermined,theregulationofthecellcycleappearstoplayakeyroleintheseprocesses.TheeukaryoticcellcycleconsistsofalternatingroundsofDNAreplication（Sphase）andcelldivision（Mphase）separatedbythegapphasesG1andG2.,SCsexhibitslowcellcycle:

G1arrest,extendingcellcycleprogression,Progressionthroughthecellcycleiscontrolledbytheperiodicactivationofcyclin-dependentkinases（Cdks）.MultipleCdkshavebeenidentifiedinmammaliancells.Ingeneral,Cdkscanberegulatedbyatleastthreeindependentmechanisms.First,Cdkkinaseactivityisdependentonitsassociationwithdistinctcyclinproteins,andformationofthesecomplexesisdrivenbycyclesofcyclinsynthesisanddegradation.Second,phosphorylationofCdkkinaseataconservedthreonineresiduebyCdkactivatingkinase（CAK）isrequiredforactivity,whereasinhibitoryphosphorylationwithintheATP-bindingsiteisregulatedbythecombinedactionoftheWee1kinaseandCdc25phosphatase.Finally,CdkactivitycanberegulatedbybindingtoaspecificclassofCdkinhibitors（CKIs）.,Progressionthroughthecellcycledependsoncyclin-dependentkinase（Cdk）-mediatedphosphorylationevents,InearlyG1,D-typecyclinsaresynthesizedandpartnerwithCdk4AndCdk6.LateG1ischaracterizedbyE-typecyclinexpressionandCdk2activity.Theactivationofthesekinasesresultsinthephosphorylationofcrucialregulatorsofcell-cycleprogression,suchaspRb,whichliberatesactivatingE2FstodriveS-phaseentry.ThecrucialroleforCDKactivationinthedecisiontocommittocelldivisionindicatestheimportanceoffinelytunedmechanismsbywhichtomodulatethesekinases.Indeed,inadditiontotheregulatedsynthesisanddestructionofcyclins,Cdkactivitycanbeadjustedbyothermechanisms,includingphosphorylationanddirectregulationbyaclassofproteinsknownascyclindependentkinaseinhibitors（CKIs）.,Figure2.ThedecisiontocommittoDNAreplicationismadeattheG1-to-StransitionbyphosphorylationoftheRbpocketprotein（green）,resultingintheliberationofE2Fs（green）toactivategeneexpressionrequiredforS-phaseentry.Rbphosphorylation,inturn,dependsonthecoordinateregulationofcyclins（blue）,cyclin-dependentkinases（blue）,andCdkinhibitors（yellow）.,1.DNADAMAGE-DEPENDENTCHECKPOINTInmosteukaryoticcells,DNAdamagedelayscellcycleprogressionbyinhibitingCdkkinaseactivationateithertheG2-to-MorG1-to-S-phasetransition.Inmulticellularorganisms,DNAdamageactivatesacheckpointcontrolpathwaythatleadstoeithercellcyclearrestinG1orG2,orprogrammedcelldeath,i.e.,apoptosis.AkeyregulatorisP53.P53isasequence-specificDNA-bindingproteinthatactivatesthetranscriptionofavarietyofdownstreameffectorgenes.P53isrequiredforcellcyclearrestinG1,orapoptosisfromG1orG2MammaliancellsalsoarrestthecellcycleinG2inresponsetoDNAdamage.P53canthentrans-activateanumberofgenes,includingIPT1/WAF1/p21,apotentinhibitorofCDKactivitiesrequiredfortheG1toSphasetransition.Theproposedroleforp21incellcyclearrestistwofold;inadditiontoblockingCDKactivity,p21isalsoknowntobindproliferatingcellnuclearantigen（PCNA）,aproteinrequiredforbothDNAreplicationandDNArepair.OtherpotentialcandidatesthatmightparticipateinP53-dependentG1arrestincludetheGadd45,WIP1CyclinD1,andABLgenes.,CellCycleCheckpoints,DNADAMAGE-DEPENDENTCHECKPOINT（continue）Itisstillamysteryastowhy,inmulticellularorganisms,somecellsarrestthecellcycleinresponsetoDNAdamagewhereasothersundergoapoptosis.Althoughthebasisforthisdifferenceispoorlyunderstood,P53hasbeenshowntobeessentialforbothG1arrestfollowingDNAdamageandapoptosisfromG1orG2.ApoptosisoccursthroughapathwayP53isknowntoinduceexpressionofgenesthatpromoteapoptosis,includingBax,FAS,andinsulin-likegrowthfactor-1-bindingprotein-3（IGF-BP3）.Onemodelproposesthatlow-levelDNAdamagemaysignalcellcyclearrestviatheATM-dependentcheckpoint,whereasmoreextensivedamagemayactivateP53byanalternativepathway,thelatterleadingtoapoptosis.Finally,theDNAdamagecheckpointcanalsoinhibitDNAreplicationinitiationandS-phaseprogression.,P53andwaf1expression:

nanyixuebao1997,3:

234,Vaco411（wtp53）SW480（mup53）24hr6hr0hr6hr0hr,Northernblotanalysisshowingtheeffectof5Gyofrirradiationontheexpressionofp53andWAF1incolontumorcelllines,2.THESPINDLECHECKPOINTFailuretoalignchromosomesonthemitoticspindleduringmetaphasetriggersacheckpointthatblockschromosomesegregationandexitfrommitosis.Twopathwaysareactivatedinresponsetodetachedchromosomes.ThefirstpathwayrequirestheproductsoftheBub1,Bub3,Mps1,andMad13genes.TheseproteinsfunctioninasignaltransductionpathwaythatinhibitsAPCcdc20,whichnormallytargetsthemetaphase-to-anaphaseinhibitorPds1fordegradation.ThesecondpathwayrequiresByr4andBub2,whichfunctionasatwo-componentGAP（GTPaseactivatingprotein）thatmaintainstheTem1-GTPaseinaninactive（GDP）form,therebypreventingreleaseofCdc14fromthenucleolus.IntheabsenceofCdc14activity,APCcdh1remainsinaphosphorylatedinactivestate,andthereforecellsareprohibitedfromexitingmitosis.,CellCycleCheckpoints（continue）,3.CELLCYCLECHECKPOINTSINACHANGINGCELLCYCLEMulticellularorganismsappeartouseawidevarietyofcheckpointcontrolstomaintaingenomestabilityduringdevelopment.Environmentalregulationofcellcycleprogression:

StemCells（SCs）alsorespondtoenvironmentalfactorbyundergoingcellcyclearrestoractivation,nutritionalstarvationcausescellstoarrestintheG1phase.Thebindingofpheromonetoacell-surfacereceptoractivatesamitogen-activated（MAP）kinasecascade.Surprisinglylittleisknownaboutthemolecularmechanismsthatregulatecellproliferation.,CellCycleCheckpoints（continue）,2）Organismal-levelSignals:

ActivationorincreaseinSCdivisionhasbeenshowntotakeplaceundervariousconditions:

transplantationintoirradiatedhosts;depletionofcyclingcellsbycytotoxins;inresponsetodevelopmentalprogramming;andevenasaresultofphysicalactivity.Thebest-characterizedexampleisthatprimitiveHSCcelldivisionmustdramaticallyincreaseupontransplantation.3）MolecularSignaling:

StudiesinvitrohaveshownthattherateofcelldivisionoffreshlyisolatedG0/G1primitiveHSCsortheamplificationofHSC-likecellsincreasesuponadditionofspecificcytokines.SCF,LIF,TPOetcdirectlylinkedtotheincreaseinHSCmitoticactivity;Epidermalgrowthfactor（EGF）andbasicfibroblastgrowthfactorandtheirsignalingpathwaystoincreaseordecreasemammalianneuroblasts;inaddition,inhibitionofsignalingbyDPP,atransforminggrowthfactorlikemolecule,resultsinslowercellcyclesingerm-lineSCs,Post-HSCTdonorSCdivisioncouldberegulatedbyOrganismal-levelSignals,miRNAslinktostemcellsbiology,Micro-RNAs（mi-RNAs）areendogenousnon-codingsmallRNAmolecules,around20nucleutidesinsize,whichnegativelyregulategeneexpressionpost-transcriptionallythroughmRNAcleavage,mRNAdecayortranslationalrepression.Over600distinctmiRNAshavebeendiscoveredinthehumangenome,andeachispredictedtoregulateseveralhundredtargetmRNAs.ItisalsosupposedthatonemRNAberegulatedbymorethanonemiRNA.TheEnormousregulatorypotentialofmiRNAsmayevensurpassthatoftranscriptionfactornetworks.,Fig.SchematicoverviewofthebiogenesisandmodeofactionofmammalianmicroRNAs.,Fig.1SchematicoverviewofthebiogenesisandmodeofactionofmammalianmicroRNAs.MicroRNAgenesaretranscribedbyRNApolymeraseIIeitherfromtheirownpromoterorfromthepromoterofthegeneinwhichthey