Somite Chondrogenesis in vitro: Differential Induction by Modified Matrix- a Biochemical and Morphological Study*:...

The stimulation of somite chondrogenesis by extracellular matrix components was studied by monitering the synthesis of cartilage-specific large proteoglycan aggregates. Chick embryonic sternal proteoglycans were separated into various components: monomers, hyaluronic acid, link protein and glycosaminoglycan side chains. The effects of these components, either individually or in various combinations, on somite chondrogenesis was examined. Proteoglycan monomers, alone or in a mixture with other components, induced chondrogenesis. The other components did not have any stimulating effect of their own. The results of these induction studies were also observed on a Sepharose CL-2B column and correlated using electron microscopy. Stimulation of somites resulted in an increase in the amount of proteoglycan aggregation (material excluded from the column) and was in agreement with the morphological appearance of the matrix in that there was increased accumulation of large proteoglycan granules. A matrix mixture of collagen and proteoglycans showed significant stimulation. When the matrix environment of the somites was altered to be unfavorable to the explants (medium containing hyaluronic acid) there was altered synthesis of cartilage-specific molecules. The results presented in this report strongly suggest that the composition of the extracellular matrix material is critical for somite chondrogenesis.