ABSTRACT
The synthesis of glycosaminoglycans and acidic polysaccharides during embryonic and fetal development in mammals and molluscs is briefly reviewed. A sequential order of appearance of each of the acidic polysaccharides was observed, coinciding with the major processes of the ontogeny. In mammals, hyaluronic acid is the first glycosaminoglycan synthesized at the beginning of morphogenesis. This glycosaminoglycan is then replaced by chondroitin 6-sulfate during the migration of the mesenchymal cells. Heparan sulfate, dermatan sulfate and chondroitin 4-sulfate are synthesized only during cell differentiation. The synthesis of heparin, on the other hand, is confined to mast cells in a few tissues and is a late event in the differentiation process. The same general pattern is also observed in molluscs except that hyaluronic acid is replaced by an acidic galactan in the morphogenetic process. The activity of the degrading enzymes responsible for the disappearance of hyaluronic acid, chondroitin sulfate and the acidic galactan in each phase of embryonic development is also reviewed.