Clonal analysis in vitro of osteogenic differentiation of marrow CFU-F

Fibroblastic colonies, each of which is derived from a single precursor cell (CFU-F), are formed when suspensions of marrow cells are cultured in vitro. The ability of marrow CFU-F to differentiate in vitro was investigated using the expression of alkaline phosphatase activity as a marker for osteogenic differentiation. In cultures of rabbit marrow cells the colonies formed varied in size, morphology and expression of enzyme activity, indicating that marrow stromal CFU-F are a heterogeneous population. Growth and differentiation of marrow CFU-F can be modified in vitro. Epidermal growth factor increased average colony size and reduced clonal expression of alkaline phosphatase activity to very low levels. Hydrocortisone activated the osteogenic differentiation programme within the cellular progeny of a wide spectrum of CFU-F. The results support the possible development of in vitro clonal methods for the study of differentiation and regulation of the osteogenic and other fibroblastic cell lines of the marrow stromal system.