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ABSTRACT Our experiments were designed to identify the source of the increased number of cells forming colonies in culture (CFU‐C) detected after short‐term culture of mouse marrow cells over ‘feeders’ of renal tubules. Accordingly, marrow cell suspensions were fractionated by velocity sedimentation and aliquots of each fraction cultured for 2 days over tubule ‘feeders’. We found a greater increase of CFU‐C in suspensions of slowly sedimenting cells as compared to rapidly sedimenting cells. Colcemid and vinblastine were used to alter the peak sedimentation velocity of marrow suspensions by changing the distribution of cells in the cell cycle. After such manipulations, the peak increase in CFU‐C continued to be associated with fractions containing slowly sedimenting cells. Such fractions also contained most of the pluripotent stem cells identified by the spleen colony technique.
Sutherland et al. (Wed,) studied this question.