The role of the extracellular matrix in skeletal development.

The extracellular matrix of cartilage and bone is composed mostly of collagen with lesser amounts of other constituents such as proteoglycans. The focus of this brief review will be on the dynamic expression of collagens and proteoglycans in the cartilage and bone extracellular matrices. Recent research has shown the presence of different collagen types and proteoglycans that are differentially expressed in cartilage, in the transition from cartilage to bone, and in the bone extracellular matrices. These findings suggest the complexity of the skeletal extracellular matrix as well as its dynamic expression. Although the composition of both the cartilage and bone extracellular matrices are largely known, the function of each of the macromolecules composing these matrices and their developmental regulation is not well understood. Defects that modify the extracellular matrix, like the chicken chondrodysplasia, nanomelia, and tibial dyschondroplasia, have profound affects on skeletal structure. The poultry industry is currently confronting a high percentage of skeletal deformities due to selection for increased growth rate and needs to consider the effect of extracellular matrix modifications and how to maintain extracellular matrix integrity.