Muscle lineage cytoplasm can change the developmental expression in epidermal lineage cells of ascidian embryos☆

摘要

Cytoplasmfrommusclelineageblastomeresofanascidianembryocancausecellsofanonmusclelineagetoproducelarvaltailmuscleacetylcholinesterase.Musclecytoplasmwaspartitionedmicrosurgicallyintoepidermallineageblastomeresattheeight-cellstage.Posteriorhalf-embryos(thetwoB3cells)ofAscidianigrawereobtainedfirstbyseparatingtheanteriorandposteriorblastomerepairsatthefour-cellstage.Atthirdcleavage,thetwoB3cellsdivideintoanectodermalcellpairthatgivesrisesolelytoepidermaltissues,andamesodermal-endodermalblastomerepairfromwhichthetailmusclecellsarederived.Whentheectodermalandmesendodermalblastomerepairswereisolatedfromoneanotherbymicrosurgeryandrearedaspartialembryos,onlycellsoriginatingfromthemesendodermalblastomeresproducedahistochemicalacetylcholinesterasereaction.ImmediatelyaftercleavageoftheisolatedB3cellsintoectodermalandmesendodermalcellpairs,thecleavagefurrowscouldbemadetodisappearbypressingfirmlyonthemesendodermalcellswithamicroneedle.Repeatedupanddownpressurewiththemicroneedleatanewpositionacrossthemesendodermalcellscausedfurrowstoreestablishinthenewposition,therebyincorporatingmesodermalcytoplasmandincreasingthesizeoftheectodermalcells.Thecytoplasmicallyalteredectodermalblastomerepairs,whichbecamedetachedfromthemesendodermalcellsbythismicrosurgicalprocedure,continuedtodivideandwererearedtoa€?larvala€?stages.One-thirdoftheseepidermalpartiallarvaeproducedpatchesofcellscontainingacetylcholinesterase.Theseresultslendfurthersupporttothetheorythatchoiceofparticulardifferentiationpathways(embryonicdetermination)inascidianembryosismediatedbysegregationofspecificeggcytoplasmicdeterminants.