The present invention relates to an isolated protein or polypeptide selectively expressed in chondrocytes in lower proliferative or upper hypertrophic zones of long bone and embryonic vertebrae growth plates as well as to antibodies, fragments, and probes recognizing these proteins or polypeptides. The proteins or polypeptides can be used for treating non-union bone defects. The antibodies, binding portions thereof, and probes can be used to inhibit arthritic progression of articular chondrocytes. The antibodies, binding portions thereof, and probes can also be used to identify the occurrence of chondrocytes proliferation or hypertrophy. The encoding DNA molecule, either alone in isolated form or in an expression system or a host cell, is also disclosed.