The influence of the metameric pattern in the mesoderm on migration of cranial neural crest cells in the chick embryo☆

[摘要] Inrecentstudiesofchickembryos,thecranialparaxialmesoblastwasfoundtobepatternedintosegmentalunitstermedsomitomeres.Anteriortothefirstsegmentalcleft,sevencontiguoussegmentsarealigned,withsomitomericinterfacesforminggroovesatrightanglestothemidline.Inthisstudy,themorphologicalrelationshipbetweenthemigratorypathwaysofcranialneuralcrestcellsandpatternedprimarymesenchymewasanalyzedwiththescanningelectronmicroscope,utilizingstereoimaging.Inaddition,thedevelopmentofneuromeresintheadjacentneuraltubewasmonitored.Itwasfoundthatcranialneuralcrestfirstappearsalongthedorsalmidlineasaridgeofcellswhichloosensfromthewalloftheneuraltubeandmigrateslaterallyasdiscretepopulations.Themesencephaliccrestappearsfirst,immediatelyfollowingneuraltubefusionatthatlevel,andmigratesoverthedorsalsurfaceoftheadjacentthirdsomitomereandintothegroovesformedbyitsjuncturewiththesecondandfourthsomitomeres.Later,theadditionofprosencephalicandrostralrhombencephaliccrestextendsthemesencephalicpopulationtoformashelfofcrestwhichspreadsoverthedorsalsurfaceofthefirstfoursomitomeres.Componentcellsofthismostcranialcrestshelfbecomeorientedandmimicthemetamericpatternofthesubjacentsomitomeres.Crestcellsadjacenttothefifthsomitomeresappearalongthemidline,butdonotmigrate,creatingagapanteriortotheoticcrest.Bystage9,anarrowfinger-likesegmentoftheoticcrestmigratesfromaspecificneuromereintothegroovedinterfacebetweenthefifthandsixthsomitomeres,delimitingtherostralborderoftheoticplacodeintheectodermabove.Bytheendofstage9,crestcellsdelimitingthecaudalborderoftheplacodehavemigratedalongtheinterfaceoftheseventhandeighthsomitomeres.Thecrestcellsadjacenttothesixthandseventhsomitomeres,betweentherostralandcaudaloticpopulations,appearbutdonotmigrate,remainingcondensedalongthemidline.Thus,oticcrestcellsformaringwhichcircumscribestheinvaginatingoticplacode.Thisstudysuggeststhattheprecisedistributionofcranialneuralcrestcellsmayresultfromtheirintroductionatspecifictimes,asspecificpopulationsfromspecificbrainregions(neuromeres),ontoapatternedmesodermallayer.

[学科分类] 生物科学（综合）