Mandibular condylar cartilage is often classified as a secondary cartilage, differing from the primary cartilaginous skeleton in its rapid progress from progenitor cells to @entity1184 chondrocytes. In this study we used in situ hybridization and immunohistochemistry to investigate whether the formation of primary (tibial) and secondary (condylar) cartilage also differs with respect to the expression of two major non-collagenous glycoproteins of bone matrix, bone sialoprotein (BSP) and @entity1189 ( @entity1189 , osteopontin). The mRNAs for both molecules were never expressed until @entity1184 chondrocytes appeared. In the tibial cartilage, @entity1184 chondrocytes first appeared at E14 and the expression of BSP and @entity1189 mRNAs was detected in the lower @entity1184 cell zone, but the expression of BSP mRNA was very weak. In the condylar cartilage, @entity1184 chondrocytes appeared at E15 as soon as cartilage tissue appeared. The mRNAs for both molecules were expressed in the newly formed condylar cartilage, although the proteins were not detected by immunostaining; BSP mRNA in the condylar cartilage was more extensively expressed than that in the tibial cartilage at the corresponding stage (first appearance of @entity1184 cell zone). Endochondral bone formation started at E15 in the tibial cartilage and at E16 in the condylar cartilage. At this stage (first appearance of endochondral bone formation), BSP mRNA was also more extensively expressed in the condylar cartilage than in the tibial cartilage. The @entity1184 cell zone in the condylar cartilage rapidly extended during E15-16. These results indicate that the formation process of the mandibular condylar cartilage differs from that of limb bud cartilage with respect to the extensive expression of BSP mRNA and the rapid extension of the @entity1184 cell zone at early stages of cartilage formation. Furthermore, these results support the hypothesis that, in vivo, BSP promotes the initiation of mineralization.

In situ hybridization and immunohistochemistry of bone sialoprotein and XXXX (osteopontin) in the developing mouse mandibular condylar cartilage compared with limb bud cartilage.

@entity1184 :: ('MESH:D006984', 'Disease') :: ['hypertrophic'] @entity1189 :: ('20750(Tax:10090)', 'Gene') :: ['secreted phosphoprotein 1', 'Spp1']
@entity1189 :: (20750(Tax:10090),Gene) :: ['secreted phosphoprotein 1']
