Somite chondrogenesis in vitro. Stimulation by exogenous extracellular matrix components

Glycosaminoglycans and proteoglycans were assayed during induced and noninduced in vitro somite chondrogenesis. Proteoglycan aggregates and monomers can be detected during the first day of culture, with the monomeric form being the predominant molecule. Stimulation with notochordal tissue, exogenous collagens, proteoglycans, or matrices composed of collagen bound to proteoglycans resulted in qualitative and quantitative changes in proteoglycan synthesis. There was a quantitative increase in the amount of proteoglycan synthesized by the induced somites. The somites responded only to embryonic chick proteoglycans, whereas collagens from a variety of sources were effective. The process of chondrogenic differentiation in embryonic somites can be described as an increase in the size of the proteoglycan monomers synthesized and a progressive increase in the synthesis of proteoglycan aggregates. Of the exogenous agents used, collagen Type II (the type of collagen synthesized by the in vivo inducer, the notochord) was the most effective inducer of chondrogenesis.