Biochemical sequences in the transformation of normal fibroblasts in adolescent rats.

Coarse powders of acid-insoluble matrix of diaphysis and calvarial parietal bone rapidly and consistently transformed fibroblasts into masses of cartilage and bone containing hemopoietic marrow. The transformant was encapsulated by fibroblasts within 24 hr to form a plaque. Transformation was restricted to the central thicknesses of the plaque. Under the stated conditions the alteration of the phenotype, fibroblast to chondroblast, was an unstable transformation, whereas the phenotype change, fibroblast to osteoblast, was stable. The transformation occurred on a rigid timetable of sequences. Measurements of alkaline phosphatase activity and incorporation of radioactive sulfate, phosphate, and calcium were sensitive and quantitative assays for the appearance of the transformed products, cartilage and bone.