Chicken myeloid stem cells infected by retroviruses carrying the v-fps oncogene do not require exogenous growth factors to differentiate in vitro.

To determine the function of c-fps in chicken macrophages and granulocytic cells we have infected chicken bone marrow cells with retroviruses containing the v-fps oncogene. Normal chicken macrophage progenitors, M-CFCs, give rise to macrophage colonies in semisolid cultures when macrophage colony stimulating factor (M-CSF) is added into the culture medium. Upon infection with v-fps bearing retroviruses, we observed that M-CFCs were induced to develop macrophage colonies in vitro without exogenous M-CSF. This activation results from a direct effect of v-fps on the M-CFCs. No leukemic transformation was observed in the infected colonies. By comparing the effects of several retroviruses, we showed that the induction of M-CFC development is specific to v-fps containing viruses and mediated by the v-fps protein. These observations support the hypothesis that the c-fps gene is involved in the control of proliferation and/or differentiation of myeloid cells.