Characterization of two populations of CFU-S fractionated from mouse fetal liver by fluorescence-activated cell...

The properties of spleen colony forming units (CFU-S) contained in two murine fetal liver cell populations (pre-colony-forming cell (CFC) and CFC fractions) obtained after fluorescence-activated cell sorting fractionation on the basis of pokeweed mitogen binding have been analyzed. Individual spleen colonies generated by both populations were examined to determine cellularity, differential cell morphology, as well as CFU-S and in vitro CFC content. Spleen colonies from both populations contained approximately equal numbers of cells 7 days after transplantation; at 12 days, however, CFU-S from the pre-CFC fraction produced four times as many cells per colony than colonies from the CFC fraction. Although the frequency of spleen colonies containing CFU-S was similar, in comparison to the CFC fraction, spleen colonies obtained from the pre-CFC fraction contained higher absolute numbers of CFU-S. This was most evident with CFU-S assayed 12 days after transplantation of 12-day spleen colony cells (pre-CFC fraction, 84% of colonies contained CFU-S, mean of 527 per colony; CFC fraction, 77% of colonies contained CFU-S, mean of 41 per colony). Similarly, the in vitro CFC content of 7- or 12-day spleen colonies was higher in colonies produced by pre-CFC fraction CFU-S. No significant differences were observed in either the proportion of CFU-S in S-phase or the morphology of spleen colonies produced by either cell population.