The relationship of G0 to the cell cycle of haemopoietic spleen colony-forming cells.

Normal haemopoietic stem cells, defined here as spleen colony-forming units (CFUs), are slowly proliferating and are generally considered to spend most of their time in the non-proliferative G0-state. A series of experiments using various combinations of the stem cell proliferation inhibitor (NBME-IV) and stimulator (RBME-III) together with vinblastine as a mitotic blocking agent was designed to determine the location of the G0-state relative to the cell cycle of the CFUs. From a knowledge of the effects of these agents, the expected results from three different G0-cell cycle models were charted and compared with the observed proliferative behaviour of the CFUs following these treatments. It was concluded that the out-of-style G0-state is located at the end of the G1-phase of the cycle, so that on receiving a stimulatory signal, the CFUs can rapidly enter the DNA-synthesis phase.