NORMAL LONG-BONE GROWTH AND DEVELOPMENT IN TYPE-X COLLAGEN NULL MICE

To investigate the role of type X collagen in skeletal development, we have generated type X collagen-null mice. Surprisingly, mice without type X collagen were viable and fertile and had no gross abnormalities in long bone growth or development. No differences were detected betw een the type X collagen-null mice and controls when growth plates of b oth newborn and 3-week old mice were examined by histology and by immu nostaining for extracellular matrix components of bone including osteo pontin, osteocalcin and type II collagen. Our results suggest that typ e X collagen is not required for long bone development. However, mice and humans with dominant acting type X collagen mutations have bone ab normalities, suggesting that only the presence of abnormal type X coll agen can modify bone growth and development.