TCF Is the Nuclear Effector of the β-Catenin Signal That Patterns the Sea Urchin Animal–Vegetal Axis

[摘要] Themechanismofanimalndash;vegetal(AV)axisformationintheseaurchinembryoisincompletelyunderstood.Specificationoftheaxisisthoughttoinvolveacombinationofcellndash;cellsignalsandasyetunidentifiedmaternaldeterminants.InXenopustheWntpathwayplaysacrucialroleindefiningtheembryonicaxes.RecentexperimentsinseaurchinshaveshownthatatleasttwocomponentsoftheWntsignalingpathway,GSK3βandβ-catenin,areinvolvedinembryonicAVaxispatterning.Theseresultssupportthenotionthatthedevelopmentalnetworkthatregulatesaxialpatterningindeuterostomesisevolutionarilyconserved.Tofurthertestthishypothesis,wehaveexaminedtheroleofβ-cateninnuclearbindingpartners,membersoftheTCFfamilyoftranscriptionalregulators,inseaurchinAVaxispatterning.TotesttheroleofTCFsinmediatingβ-cateninsignalsinseaurchinAVaxisdevelopmentweexaminedtheconsequencesofmicroinjectingRNAsencodingalteredformsofTCFonseaurchindevelopment.WeshowthatexpressionofadominantnegativeTCFresultsinaclassicldquo;animalizedrdquo;embryo.Incontrast,microinjectedRNAencodinganactivatedTCFproducesahighlyldquo;vegetalizedrdquo;embryo.WeshowthatthetransactivationalactivityofendogenousseaurchinTCFispotentiatedbyLiCltreatment,whichvegetalizesembryosbyinhibitingGSK3,consistentwithaninvivointeractionbetweenendogenousβ-cateninandTCF.Wealsoprovideevidenceindicatingthatallofβ-catenin'sactivityinpatterningtheseaurchinAVaxisismediatedbyTCF.Usingaglucocorticoid-responsiveTCF,weshowthatTCFtranscriptionalactivityaffectsspecificationalongtheAVaxisbetweenfertilizationandthe60-cellstage.