Ectodermal interactions during neurogenesis in the glossiphoniid leech Helobdella triserialis☆

[摘要] MorphogeneticcellinteractionsduringdevelopmentwerestudiedbycombiningcellablationandcelllineagetracingtechniquesinembryosoftheleechHelobdellatriserialis.Ablationofanidentifiedectodermalteloblast,orteloblastprecursorblastomere,ononesideofanearlyembryowasoftenfoundtoresultinthelaterabnormalmigrationoftheprogenycellsofthecorrespondingcontralateral,nonablatedteloblasttotheablatedsideoftheembryo;suchabnormalmigrationwastermed“midlineviolation.”Twodifferentkindsofmidlineviolationwereobserved.Crossover:afterablationofanNteloblastindividualstemcellprogenyofthecontralateralNteloblastsometimescrosstheventralmidlineofthegerminalplateoftheembryo.Switching:afterablationofanOPQteloblastprecursorbandletsofstemcellsproducedbythecontralateralO,P,orQteloblastssometimesswitchtothegerminalbandoftheablatedsideatthesiteoforiginofthegerminalbands.Theoccurrenceofcrossoverandswitchingshowsthattheeventualsiteoccupiedbyaprogenycellofaparticularteloblastisnotautomaticallydeterminedbyitslineage,butalsodependsoninteractionswithothercells.MidlineviolationintheleechembryoCNSdoesnotconstitutetrueregulation,however,sincetherestorationofneuronstotheablatedsideisaccompaniedbyaneurondeficitonthenonablatedside.Theoccurrenceofthetwodistinctkindsofmidlineviolation,crossoverandswitching,maybeexplainedbytherelativepositionofthestemcellbandletswithinthegerminalbands,andbythegeometricalfeaturesoftheformationofthegerminalplatefromthegerminalbands.

[学科分类] 生物科学（综合）