Proteoglycans synthesized during the cartilage to bone transition in developing chick embryos.

Osteogenesis of the long bone involves a series of cellular and molecular events culminating in the fabrication of a mineralized matrix of the long bone. These studies focus upon the chemical identity and morphology of newly synthesized proteoglycans formed during the cartilage to bone transition in embryonic chick tibia development. As early as the onset of major ossification events (day 13; Hamburger-Hamilton Stage 39), synthesis of a small, highly 4-sulfated chondroitin sulfate proteoglycan was detected in the shaft of the tibia. The characterization of the chondroitin sulfate-rich proteoglycans from cartilage, hypertrophic cartilage, bone marrow, and new bone lead to the suggestion that these molecules can be used as distinctive markers for the cellular phenotypes involved in the cartilage to bone transition.