The Cellular Basis for the Defect in Haemopoiesis in Flexed‐Tailed Mice

Abstract

Summary. Three assays for erythropoietic progenitor cells have been applied to mice of genotype f/f and to nearly congenic +/+ controls. When f/f mice were tested for their ability to generate transient endogenous erythroid spleen colonies 4–6 days after 800 rads and 10 units of erythropoietin, the numbers of such colonies detected were greatly reduced, although normal numbers of spleen colonies appeared at later times (9–12 days) postirradiation. In contrast, cells capable of erythropoietic colony formation in culture (CFU-E) were present within the normal range in both f/f spleen and marrow and their sensitivity to erythropoietin in culture was the same as that found previously for CFU-E in the marrow and spleen of +/+ mice. Transfusion-induced plethora reduced the number of CFU-E in marrow to a similar extent in both f/f and +/+ mice; likewise, subsequent administration of 10 units of erythropoietin induced a rapid return in the number of marrow CFU-E in both genotypes. In the spleen, CFU-E numbers were approximately three-fold lower in f/f mice in each group. These results support the view that the 5 day assay for transient endogenous spleen colonies detects cells (TE-CFU) that are different from both CFU-E and pluripotent stem cells (CFU-S), although possibly overlapping to some extent with the immediate progenitors of CFU-E. The results also indicate that the generation or maturation of TE-CFU represents a primary site of expression of the f/f defect.