Chick embryo extract induces several changes in cultured chick chondroblasts, including a shift in morphology from a distinctive chondroblast to that of a fibroblast, a change from an exclusive synthesis of chondroitin sulfate to that of chondroitin sulfate and hyaluronic acid and a switch from the synthesis of type II collagen to type I collagen. The overall objective of this research is to study the cellular and biochemical mechanisms which underlies this transformation, with particular emphasis on the switch in collagen expression. The work will focus mainly on the role of the cell cycle in the switch, the nature of the chondroblast which responds to embryo extract and on the illucidation of the active components of the embryo extract. Studies will also be conducted with the regulation of collagen synthesis and type in certain normal and disease processes of human skin. This work will be done with cultured fibroblast from patients with epidermolysis bullosa dystrophica-recessive and scleroderma. BBLIOGRAPHIC REFERENCES: Schlitz, J., Rosenbloom, J. and Levenson, G. (1977). The effects of ascorbic acid deficiency on collagen synthesis by mouse molar tooth germs in organ culture. J. Exptl. Embry. & Morph. (In press). Schiltz, J. (1977). Collagen synthesis during the cell cycle of chick embryo chondroblasts; Evidence for two distinct chondroblast populations. (In review).