An Immunohistochemical Study of Matrix Components in Primary and Secondary Cartilages of Embryonic Chick Skull.

OBJECTIVES:This study aimed to compare the extracellular matrix of primary cartilage with the secondary cartilage of chicks using immunohistochemical analyses in order to understand the features of chick secondary chondrogenesis.METHODS:Immunohistochemical analysis was performed on the extracellular matrix of quadrate (primary), squamosal, surangular, and anterior pterygoid secondary cartilages using various antibodies targeting the extracellular matrix of cartilage and bone.RESULTS:The localization of collagen types I, II, and X, versican, aggrecan, hyaluronan, link protein, and tenascin-C was identified in the quadrate cartilage, with variations within and between the regions. Newly formed squamosal and surangular secondary cartilages showed simultaneous immunoreactivity for all molecules investigated. However, collagen type X immunoreactivity was not observed, and there was weak immunoreactivity for versican and aggrecan in the anterior pterygoid secondary cartilage.CONCLUSIONS:The immunohistochemical localization of extracellular matrix in the quadrate (primary) cartilage was comparable to that of long bone (primary) cartilage in mammals. The fibrocartilaginous nature and rapid differentiation into hypertrophic chondrocytes, which are known structural features of secondary cartilage, were confirmed in the extracellular matrix of squamosal and surangular secondary cartilages. Furthermore, these tissues appear to undergo developmental processes similar to those in mammals. However, the anterior pterygoid secondary cartilage exhibited unique features that differed from primary and other secondary cartilages, suggesting it is formed through a distinct developmental process.