Stage-specific cell-cycling of hematopoietic progenitor cells

We studied the growth of hematopoietic progenitors at different progressive stages of differentiation and focused especially on changes in cell-cycling. Hematopoietic progenitors from 5-fluorouracil (5-FU)-treated mice were separated into three groups on the basis of differentiation, Stages I, II, and III, and have studied their cell-cycling. Primary marrow cells collected from 5-FU-treated mice were categorized as Stage I progenitors. Stages II and III progenitors are early and late progenies of Stage I progenitors, respectively. The rate of growth of hematopoietic progenitors supported by interleukin-3 (IL-3) and steel factor (SF) was estimated by sequential analysis of colony formation and studying replating efficiency of individual colonies. The time required for hematopoietic progenitors to go through the cell-cycle shortened as their stage of differentiation progressed. Similar results were obtained with other growth factor combinations. The analysis of DNA content of cells suggests that shortening of cell-cycling is mainly due to a decrease in the time of G1 phase of the cell-cycle. Our results demonstrate that in early hematopoiesis, the cell-cycling of hematopoietic progenitors accelerates as they differentiate.