NOGGIN, CARTILAGE MORPHOGENESIS, AND JOINT FORMATION IN THE MAMMALIANSKELETON

Noggin is a bone morphogenetic protein (BMP) antagonist expressed in S pemann's organizer. Murine Noggin is expressed in condensing cartilage and immature chondrocytes, as are many BMPs. In mice lacking Noggin, cartilage condensations initiated normally but developed hyperplasia, and initiation of joint development failed as measured by the expressi on of growth and differentiation factor-5. The maturation of cartilage and Herd expression were unaffected. Excess BMP activity in the absen ce of Noggin antagonism may enhance the recruitment of cells into cart ilage, resulting in oversized growth plates; chondrocytes are also ref ractory to joint-inducing positional cues.