The epiphyseal organ contains two kinds of cartilage, articular and growth plate. Both enlarge during the growth phase of life. However, mitosis is not apparent in these tissues. In the current study, a search to trace the reservoirs of stem cells needed for the growth of these cartilages is done. A disorder in which the stem cells responsible for bone growth are mutated is achondroplasia; the mutation resides in the fibroblast growth factor receptor-3. Epiphyses stained with antifibroblast growth factor 3 antibodies reveal clusters of positively stained cells residing in the perichondrial mesenchyme, known as the ring of La Croix. Removal of the ring of La Croix causes a drastic growth arrest in the limbs of rat neonates. Cell cultures derived of the ring of La Croix biopsy specimens show high rates of cell proliferation and cell migration in vitro, in contrast to articular or growth plate derived chondrocytes. These cells stain intensely by antifibroblast growth factor receptor-3 antibodies and antiproliferative cells nuclear antigen, in contrast with articular and epiphyseal chondrocytes. Transfection of cells from the ring La Croix by an adenovirus vector containing the gene encoding for Escherichia coli beta-galactosidase (lacZ), allows tracing of these cells in tissues. Local injections were performed either to the ring of La Croix or to the joint cavity in a guinea pig model. A characteristic distribution was seen after injection. The transfected cells migrated to areas of bone and cartilage formation in the subchondral bone plate and on either side of the growth plate. This labeling and distribution is maintained for as many as 3 months after injection. The cells from the ring of La Croix appear to be responsible for bone growth. Furthermore, perichondrial cells and other precartilaginous cells expressing fibroblast growth factor-3 have been shown to be good cells for implantation to correct defects of articular cartilage.

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