Ventralization of an indirect developing hemichordate by NiCl2 suggests a conserved mechanism of dorso-ventral (D/V) patterning in Ambulacraria (hemichordates and echinoderms)

摘要

Oneoftheearlieststepsinembryonicdevelopmentistheestablishmentofthefuturebodyaxes.MorphologicalandmoleculardataplacetheAmbulacraria(echinodermsandhemichordates)withintheDeuterostomiaandasthesistertaxontochordates.Extensiveworkoverthelastdecadesinechinoid(seaurchins)echinodermshasledtothecharacterizationofgeneregulatorynetworksunderlyinggermlayerspecificationandaxisformationduringembryogenesis.However,withtheexceptionofrecentstudiesfromadirectdevelopinghemichordate(emSaccoglossuskowalevskii/em),verylittleisknownaboutthemolecularmechanismunderlyingearlyhemichordatedevelopment.Unlikeechinoids,indirectdevelopinghemichordatesretainthelarvalbodyaxesandmajorlarvaltissuesaftermetamorphosisintotheadultworm.Inordertogaininsightintodorso-ventral(D/V)patterning,weusednickelchloride(NiClsub2/sub),apotentventralizingagentonechinodermembryos,ontheindirectdevelopingenteropneusthemichordate,emPtychoderaflava/em.OurpresentstudyshowsthatNiClsub2/subdisruptstheD/Vaxisandinducesformationofacircumferentialmouthwhentreatedbeforetheonsetofgastrulation.Molecularanalysis,usingnewlyisolatedtissue-specificmarkers,showsthattheventralectodermisexpandedatexpenseofdorsalectodermintreatedembryos,buthaslittleeffectongermlayeroranteriorndash;posteriormarkers.Theresultingventralizedphenotype,theeffectivedose,andtheNiClsub2/subsensitiveresponseperiodofemPtychoderaflava/em,isverysimilartotheeffectsofnickelonembryonicdevelopmentdescribedinlarvalechinoderms.ThesestrongsimilaritiesallowonetospeculatethataNiClsub2/subsensitivepathwayinvolvedindorso-ventralpatterningmaybesharedbetweenechinoderms,hemichordatesandaputativeambulacrarianancestor.Furthermore,nickeltreatmentsventralizethedirectdevelopinghemichordate,emS.kowalevskii/emindicatingthatacommonpathwaypatternsbothlarvalandadultbodyplansoftheambulacrarianancestorandprovidesinsightintotheoriginofthechordatebodyplan./p/div