Somite chondrogenesis in vitro: 1. Alterations in proteoglycan synthesis

During embryonic development, somites undergo chondrogenic differentiation when stimulated by notochord or spinal cord. The present study shows that, when cultured in suitable medium, explanted somites incorporated radioactive sulfate into cartilage-specific proteoglycans and the synthetic rate increased when notochord was included with somites. With increased culture time, explanted somites also synthesized proteoglycan monomers which were larger in size along with a larger proportion that were capable of interacting with exogenous hyaluronic acid. Interaction with notochord also resulted in increased synthesis of chondroitin 4-sulfate. Gel electrophoretic analysis showed that proteoglycans from unstimulated somites did not contain link protein (required for stable aggregate formation), even on day 9, while notochord-induced somites showed link protein as early as day 3, increasing 3-fold by day 9.