Conserved Mechanism of Dorsoventral Axis Determination in Equal-Cleaving Spiralians

Developmental Biology

Jonathan J. Henry¹ 

[1] Marine Biological Laboratory, Woods Hole, Massachusetts, 02543

关键词: induction;    cell interactions;    unequal cleavage;    Nemertea;   

DOI  :  10.1006/dbio.2002.0741

学科分类：生物科学（综合）

来源: Academic Press

【 摘 要 】

Manymembersofthespiralianphyla(i.e.,annelids,echiurans,vestimentiferans,molluscs,sipunculids,nemerteans,polycladturbellarians,gnathostomulids,mesozoans)exhibitearly,equalcleavagedivisions.Inthecaseoftheequal-cleavingmolluscs,animal–vegetalinductiveinteractionsbetweenthederivativesofthefirstquartetmicromeresandthevegetalmacromeresspecifywhichmacromerebecomesthe3Dcellduringtheintervalbetweenfifthandsixthcleavage.The3Dmacromereservesasadorsalorganizerandgivesrisetothe4dmesentoblast.EventhoughithasbeenarguedthatthissituationrepresentstheancestralconditionamongtheSpiralia,theseinductiveeventshaveonlybeendocumentedinequal-cleavingmolluscs.EmbryosofthenemerteanCerebratuluslacteusalsoundergoequal,spiralcleavage,andthefatemapoftheseembryosissimilartothatofotherspiralians.Theroleofanimalfirstquartetmicromeresintheestablishmentofthedorsal(D)cellquadrantwasexaminedinC.lacteusbyremovingspecificcombinationsofmicromeresattheeight-cellstage.Tofollowthedevelopmentofvariouscellquadrants,onequadrantwaslabeledwithDiIatthefour-cellstage,andspecificfirstquartetmicromereswereremovedfromdiscretepositionsrelativetothelocationofthelabeledquadrant.Theresultsindicatethatthefirstquartetisrequiredfornormaldevelopment,asremovalofallfourmicromerespreventeddorsoventralaxisformation.Inmostcases,wheneitheroneortwoadjacentfirstquartetmicromereswereremovedfromonesideoftheembryo,thecellquadrantontheoppositeside,withitsmacromerecenteredunderthegreatestnumberoftheremaininganimalmicromeres,ultimatelybecametheDquadrant.Twinscontainingduplicateddorsoventralaxesweregeneratedbyremovaloftwoopposingfirstquartetmicromeres.Thus,anycellquadrantcanbecometheDquadrant,andthedorsoventralaxisisestablishedaftertheeight-cellstage.WhileitisnotyetclearexactlywhenkeyinductiveinteractionstakeplacethatestablishtheDquadrantinC.lacteus,contactsbetweentheprogenyofanimalmicromeresandvegetalmacromeresareestablishedduringtheintervalbetweenthefifthandsixthroundofcleavagedivisions(i.e.,32-to64-cellstages).Thesefindingsarguethatthismechanismofcellandaxisdeterminationhasbeenconservedamongequal-cleavingspiralians.

【 授权许可】

Unknown