Regional mitotic activity in the precardiac mesoderm and differentiating heart tube in the chick embryo☆

[摘要] Aseriesofchickembryosrangingfromtheprimitivestreakstagetothe22-somitestageweretreatedwithColcemidfor2.5hours.Bymicro-dissection,theheart-formingmesodermoneachsidewasdividedintoarostrocaudalseriesofsevenfragments.Asquashpreparationwasmadefromeachfragment,andthepercentageofcellstrappedinmetaphasewasdetermined.Duringstages5–10,wavesofmitoticactivitytravelthroughtheheart-formingmesodermfromitsrostraltoitscaudalend,atarateofprogressionsimilartothatofsomiteformation.Intheventricularmesoderm,mitoticactivityfallsdramaticallyduringstages8–10tonearzerovalues,andremainslowthroughstages10+–12.Itrisesagainsuddenlyatstage12+–13.ItissuggestedthatthistemporarymitoticarrestresultsfromaG1blockinthemitoticcycle.Intheatrialmesoderm,mitoticactivityalsodecreasedduringstages10–11.However,thisreductionwasonlytoaboutone-thirdofthepreviouslevel,andwasnotfollowedbyapostdepressionalincrease.Themajordeclineinmitoticactivityprecedesbyafewhoursthestagesatwhichstriatedmyofibrilshavebeenobservedintheheartmesodermbyothers.Atnostagewasanyconsistentlateralasymmetryincellmultiplicationratesobserved,eitherregionallyorbetweentherightandleftsidesasawhole.Itisconcludedthatd-loopingandasymmetryofthehearttubemustresultfrommechanismsotherthandifferentiallateralmitoticactivity.Ahypothesisofheartasymmetryissuggested,basedmainlyupontheassumptionthatanincreaseincellularadhesivenessaccompaniesdifferentiationoftheheart-formingmesoderm,anduponevidenceforanearlieronsetofdifferentiationontherightside.

[学科分类] 生物科学（综合）