Nodal Signaling in Xenopus Gastrulae Is Cell-Autonomous and Patterned by β-Catenin

[摘要] Theclassicalthree-signalmodelofamphibianmesoderminductionandmorerecentmodificationstogetherproposethatanactivin-likesignalingactivityisuniformlydistributedacrossthevegetalhalfoftheXenopusblastulaandthatthisactivitycontributestomesoderminduction.Insupportofthis,wehavepreviouslyshownthattheactivin-responseelement(DE)ofthegoosecoidpromoterisuniformlyactivatedacrossthevegetalhalfofmidgastrula-stageembryos.Here,wefurtherexaminethenatureofthisactivitybymeasuringDEactivationbyendogenoussignalsovertime.WefindthatthespatiotemporalpatternofDEactivationismuchmoredynamicthanwaspreviouslyappreciatedandalsoconcludethatDE(6X)Lucactivityreflectsendogenousnodalsignalingintheembryo.UsingboththeDE(6X)LucconstructandendogenousXbraandXgscexpressionasread-outsfornodalactivity,andthecleavage-mutantversionofXnr2(CmXnr2)toregionallysuppressendogenousnodalactivity,wedemonstratethatnodalsignalsactcell-autonomouslyinXenopusgastrulae.Nodal-expressingcellsareunabletorescueeitherreportergeneactivationortargetgeneexpressionindistantnodal-deficientcells,suggestingthatnodalsfunctionatshortrangeinthiscontext.Finally,weshowthatDEactivationbyendogenoussignalsoccursintheabsenceofdorsalβ-catenin-mediatedsignaling,butthatthetimingofdorsalinitiationisaltered.WeconcludethatnodalsignalsinXenopusgastrulaefunctioncellautonomouslyatshortrangesandthatthespatiotemporalpatternofthissignalingalongthedorsoventralaxisisregulatedbymaternalWnt-likesignaling.

[学科分类] 生物科学（综合）

[关键词] Wnt;TGF-β;Xnr;cmXnr-2;β-catenin;short-range;Xenopus