A non-programmatic approach to hemopoiesis.

The currently prevailing concept of hemopoietic differentiation is that the pathway starts at the multipotential stem cell and proceeds in a programmatic, relatively fixed fashion to the development of circulating blood cells. We have presented considerations supporting a more dynamic regulation. Self-renewal capacity within a compartment is seen as a measure of the cell's resistance to differentiation pressures. Mutable environmental factors, including feedback interactions, are proposed to regulate in each compartment the relative probabilities of renewal and maturation. We question the rigid distinction between multipotential and committed cells, generally believed to be separated by a discrete "determination" event. We prefer to see commitment as a manifestation of a gradually increasing bias for a given developmental fate. Such commitment might be modulated under different environmental conditions. Multipotency and stemness are two aspects of cellular resistance to maturation pressures.