Time-lapse characterization of erythrocytic colony-forming cells in plasma cultures

The development of erythrocytic colonies in plasma cultures of C3H/Bi mouse fetal liver cells stimulated with erythropoietin was recorded by time-lapse cinemicrography, in order to investigate the nature of the colony-forming unit (CFU-E) from which they arose. Each colony was found to develop from a single cell, which in most cases underwent two divisions before acquiring hemoglobin, as detected by absorption in the Soret band. Less frequently, there were one or three divisions before hemoglobin appeared at 11.7 to 29.2 h. The diameter of the colony-forming cells in G2 was 16.0+/-1.3 mum (mean+/-SD). Daughter cells in each colony had similar generation times, with a TG of 11.0+/-2.2 h (mean+/-SD) for the first generation of colony cells. Evidence is presented that while some of the colony-forming cells were triggered into division by the erythropoietin added at plating, others had already been stimulated by endogenous erythropoietin in the fetus.