Induction of CD-RAP mRNA during periosteal chondrogenesis

Induction of chondrogenesis and maintenance of the chondrocyte phenotype are critical events for autologous periosteal transplantation, which is a viable approach for cartilage repair. Cartilage-derived retinoic acid-sensitive protein (CD-RAP) is a recently discovered protein that is mainly produced in cartilage. During development, CD-RAP expression starts at the beginning of chondrogenesis and continues throughout cartilage maturation. In order to investigate the involvement of CD-RAP during periosteal chondrogenesis we have determined the nucleotide sequence of the rabbit CD-RAP mRNA and utilized this information to evaluate the temporal and spatial expression pattern of CD-RAP at the mRNA level during chondrogenesis. When the periosteal explants were cultured under chondrogenic conditions, the expression of CD-RAP was induced, as shown by a 40-fold increase in CD-RAP mRNA between days 7 and 10. The temporal expression pattern of CD-RAP closely mimicked that of collagen type IIB mRNA. Also, the CD-RAP mRNA was localized to the matrix forming chondrocytes in the cambium layer of the periosteum by in situ hybridization as indicated by colocalization with collagen type II mRNA and positive safranin O staining. These data suggest a regulatory role of CD-RAP in periosteal chondrogenesis, which is potentially important for both cartilage repair and fracture healing via callus formation.