Glycosaminoglycan synthesis in the chick gastrula

Explanted definitive primitive streak to four somite chick embryos were labeled with H³]glucosamine or S³⁵O₄ and the glycosaminoglycans were isolated and characterized. On the basis of susceptibility to Streptomyces hyaluronidase, which specifically degrades hyaluronic acid, hyaluronic acid is the major glycosaminoglycan produced by these embryos (at least 84%). On the basis of electrophoretic mobility, about 10% of the H³]glucosamine-labeled glycoaminoglycan is sulfated. At least 55% of the sulfate-labeled glycosaminoglycan is sensitive to testicular hyaluronidase, and 36–39% is resistant to testicular hyaluronidase, but sensitive to nitrous acid treatment. About 94% of the labeled glycosaminoglycans can be accounted for in ratios of 22:1:5:1 as hyaluronic acid:chondroitin sulfate:heparan sulfate. No stage-related changes were observed. It is suggested that hyaluronic acid synthesis at this time might be related to the appearance of extensive cell-free spaces.