Expression of an activated erythropoietin or a colony-stimulating factor 1 receptor by pluripotent progenitors enhances colony formation but does not induce differentiation.

Whether the presence of specific receptors on the surface of developing cells is the cause or consequence of lineage restriction is not known. If activation of specific receptors is the driving event in differentiation, the premature expression of specific receptors would promote differentiation along that pathway. In this study pluripotent progenitors, obtained from blast cell colonies (pooled or individual) of 5-fluorouracil-treated mice, were infected with retroviral vectors containing either an activated receptor for erythropoietin (EPO), an erythroid progenitor growth factor, or the receptor for colony-stimulating factor 1 (CSF-1), a macrophage growth factor. These receptors exhibit expression patterns restricted to committed progenitors. The developmental potential of infected pluripotent progenitors was not changed, although they expressed the exogenous genes, suggesting that in these cells activation of lineage-specific receptors does not induce differentiation. Acquisition of a constitutively activated EPO receptor allowed erythroid development in mixed colonies in the absence of EPO, as expected. Infection of progenitors with a virus containing the CSF-1 receptor promoted the development of granulocyte/macrophage (GM) colonies but did not alter the differentiation potential of either colony-forming unit (CFU)-GM or CFU-mix.