Analysis of perinotochordal materials. 2. Studies on the influence of proteoglycans in somite chondrogenesis

Notochodal proteoglycans influence somite chondrogenesis. In earlier work we learned that notochord cultured under improved conditions for 8 days contains three different classes of proteoglycans (Vasan, 1981). The question was whether these three different classes of perinotochordal proteoglycan molecules, are necessary for inducing somite chondrogenesis. When the notochords were exposed to substances causing metabolic alterations (BUdR, excess vitamin A, and hyaluronic acid), only small proteoglycans accumulated in the perinotochordal sheath. Such treated notochords or the proteoglycans extracted from them failed to support somite chondrogenesis, suggesting that the large aggregate in the perinotochordal matrix may be necessary for somite induction. Adding a crude proteoglycan prepared from embryonic sternal cartilage increased the induction of chondrogenesis in somites, but papain treatment of the proteoglycan diminished its inductive capacity. This result further suggests that large aggregate proteoglycan may be necessary for the tissue interactions that promote chondrogenesis.