First bone formation in the developing chick limb☆

[摘要] Embryonicchicklimbmesenchymalcellsdifferentiateintofibrocytes,chondrocytes,myocytes,andbonecells.Previousstudiesofthesecellsinculturesuggestedthatosteoblastdifferentiationmaybecoincidentwithmuscleandcartilagecytodifferentiation.Characteristicfeaturesoftheosteoblastphenotypeseeninvivoincludetheexpressionofalkalinephosphataseactivityprecedingandassociatedwithcellselaboratingamineralized,collagenousmatrix.Thestudiesreportedheredemonstratethatosteoblastscanbedetectedasearlyasstage28inthedevelopingchicklimbbymonitoringthisactivity.Alkalinephosphatasehistochemistryandbiochemistryindicatethepresenceofenzymeactivityinthepresumptiveperiosteumbythisstage.Furthermore,thelocalizationofthisactivityprecedesthehypertrophyofcartilageandsubsequentmineralizationofthecartilagecore.Onthebasisoftheseobservations,aswellasstudiesoninorganicphosphateandcalciumaccumulationinthedevelopinglimb,wesuggestthattheosteoblastphenotypemaybecomecommittedtoitsphenotypicpathwayinthesametemporalsequenceasmuscleandcartilagecells.Inaddition,thefirstrecognizableexpressionoflimbosteoblastsisobservedlongbeforemajorcartilagecorehypertrophy,vascularinvasion,andsubsequentcoremineralization.Thus,thefirstboneformationisnotassociatedwithcartilage,butrepresentsaseparate,unique,andintrinsiclimbphenotype.

[学科分类] 生物科学（综合）