Histogenesis of mandibular condylar cartilage in mice

P(論文)Mandibular condylar cartilage is a member of temporo-mandibular joint and function both as growth and articular cartilage. Developmentally, mandibular condylar cartilage is classified as being the secondary cartilage, differing from primary cartilage including limb bud cartilage, Meckel's cartilage etc. as follows : 1) It appears at later stages than primary cartilage. 2) It is derived from alkaline phosphatase-positive progenitor cells in the periosteum-like tissue adjacent to the mandibular bone. 3) Its progenitor cells rapidly differentiate into hypertrophic chondrocytes. The main function of secondary cartilage is considered to support the growth of mandibular bone. Additionally, three transcription factors related to bone and cartilage formation, Runx2, Osterix, and Sox9 are involved in the formation of condylar cartilage. Messenger RNAs for these molecules were simultaneously expressed in the anlagen of the condylar cartilage at embryonic day (E) 14. Reduced expression of osterix and continuous expression of Sox9 together with Sox5 expression are recognized in the newly formed condylar cartilage at E15. Therefore reduced expression of Osterix in combination with Sox9-Sox5 expression is important for the onset of condylar (secondary) cartilage formation. With futher development, the condylar cartilage extends in length, especially the hypertrophic cell zone at E16. This phenomenon indicates that rapid interstitial growth occurs at this stage, and supports the function of secondary cartilage described above.departmental bulletin pape