The proto-oncogene c-myc is involved in cell differentiation as well as cell proliferation: studies on growth plate chondrocytes in situ.

A combination of immunocytochemistry and microdensitometry has been used to localize and quantify the expression of the proto-oncogene c-myc within chondrocytes of the proximal growth plates of rat and chick long bones. Although the c-myc protein was localized in all chondrocytes of the growth plate of both species the most intense staining was restricted to the proliferating and differentiating chondrocytes. These were identified by their ability to synthesize DNA (bromodeoxyuridine positive) and the presence of alkaline phosphatase activity, respectively. Species differences did exist with the c-myc concentration of the chick proliferating and differentiating chondrocytes being higher (128% and 240%, respectively) than the respective chondrocytes of the rat. The higher c-myc concentration in the chick proliferating chondrocytes paralleled the differences in the bromodeoxyuridine labelling index between the two species. In the rat, the concentration of c-myc protein present in the differentiating chondrocytes was 74% higher than in the respective proliferating chondrocytes, while in the chick it was 146% higher. The data not only provides further evidence for a role of the c-myc protein in cell proliferation but also suggests involvement of this protein in chondrocyte differentiation and/or hypertrophy.