A Regulatory Gene Network That Directs Micromere Specification in the Sea Urchin Embryo

Developmental Biology

Eric H. Davidson¹  Paola Oliveri¹  Deanna M. Carrick¹ 

[1] Division of Biology 156-29, California Institute of Technology, Pasadena, California, 91125

关键词: sea urchin embryo;    homeodomain;    pmar1;    tbrain;    delta;    gene regulatory network;   

DOI  :  10.1006/dbio.2002.0627

学科分类：生物科学（综合）

来源: Academic Press

【 摘 要 】

Micromeresandtheirimmediatedescendantshavethreeknowndevelopmentalfunctionsinregularlydevelopingseaurchins:immediatelyaftertheirinitialsegregation,theyarethesourceofanunidentifiedsignaltotheadjacentveg2cellsthatisrequiredfornormalendomesodermalspecification;afewcleavageslater,theyexpressDelta,aNotchligandwhichtriggerstheconditionalspecificationofthecentralmesodermaldomainofthevegetalplate;andtheyexclusivelygiverisetotheskeletogenicmesenchymeofthepostgastrularembryo.Wedemonstratethekeycomponentsofthezygoticregulatorygenenetworkthataccountsformicromerespecificity.ThisnetworkisasubelementoftheoverallendomesodermspecificationnetworkoftheStrongylocentrotuspurpuratusembryo.Acentralroleisplayedbyanewlydiscoveredgeneencodingapairedclasshomeodomaintranscriptionfactorwhichinmicromeresactsasarepressorofarepressor:thegeneisnamedpmar1(paired-classmicromereanti-repressor).pmar1isexpressedonlyduringcleavageandearlyblastulastages,andexclusivelyinmicromeres.Itisinitiallyactivatedassoonasthemicromeresareformed,inresponsetoOtxandβ-Catenin/Tcfinputs.Therepressivenatureoftheinteractionsmediatedbythepmar1geneproductwasshownbytheidenticaleffectofintroducingmRNAencodingthePmar1factor,andmRNAencodinganEngrailed-Pmar1(En-Pmar1)repressordomainfusion.Inbothcases,theeffectsarederepression:ofthedeltagene;andofskeletogenicgenes,includingseveraltranscriptionfactorsnormallyexpressedonlyinmicromeredescendants,andalsoasetofdownstreamskeletogenicdifferentiationgenes.ThespatialphenotypeofembryosbearingexogenousmRNAencodingPmar1factororEn-Pmar1isexpansionofthedomainsofexpressionofthedownstreamgenesovermostoralloftheembryo.Thisresultsintransformationofmuchoftheembryointoskeletogenicmesenchymecellsthatexpressskeletogenicmarkers.Thenormalroleofpmarlistoprevent,exclusivelyinthemicromeres,theexpressionofarepressorthatisotherwiseoperativethroughouttheembryo.Thisfunctionaccountsforthelocalizationofdeltatranscriptioninmicromeres,andtherebyfortheconditionalspecificationofthevegetalplatemesoderm.Italsoexplainswhyskeletogenicdifferentiationgenebatteriesnormallyfunctiononlyinmicromeredescendants.Moregenerally,theregulatorynetworksubelementemergingfromthisworkshowshowthespecificityofmicromerefunctiondependsoncontinuingglobalregulatoryinteractions,aswellasonearlylocalizedinputs.

【 授权许可】

Unknown