Use of 5-BrdUrd/313 nm light technique for identification of cells in initial S-phase within GM-CFCc compartment

Long-term, low-level, BrdUrd infusion identifies two subpopulations of GM-CFCc with quite dissimilar sensitivities to 313 nm light. The responses of these two GM-CFCc subpopulations to hydroxyurea indicate that both are rapidly proliferating at the time of the assay. However, the absolute UV-light sensitivity of the S-phase components and the effects of increasing BrdUrd concentration indicate that the two GM-CFCc subpopulations passed through the previous cell cycle at widely disparate rates. Further, those GM-CFCc originating from a parental cell with a slow turnover are associated with a lower buoyant density than those GM-CFCc that have been in rapid cycle for at least two generations. These results indicate that the resistance to 313 nm-light irradiation, shown by S-phase cells in the first cell cycle of the BrdUrd labeling, may provide evidence of the proliferative history of the cell being assayed.