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Cyclic hematopoiesis in dogs: studies of erythroid burst-forming cells confirm an early stem cell defect
J L Abkowitz1, R D Holly, W P Hammond
1Department of Medicine, University of Washington, Seattle 98195.
Studies of early erythropoiesis in dogs have been hampered by the lack of an efficient assay for canine erythroid burst-forming cells (BFU-E). We have developed a methyl-cellulose culture system for hematopoietic progenitors in dog marrow with a plating efficiency for BFU-E of 98 +/- 26 (SD) per 10(5) marrow mononuclear cells. We then applied this assay to the study of cyclic hematopoiesis in grey collie dogs, and regular fluctuations of colonies derived from erythroid colony-forming cells (CFU-E), BFU-E, and granulocyte-macrophage colony-forming cells (CFU-GM) were seen at 12- to 13-day intervals. Defining Cycle Day 1 as the first day that the granulocyte count falls below 1000/mm3, we found that the peak frequency of BFU-E (Cycle Day 10) always preceded the peak frequency of CFU-E (Cycle Day 12), which preceded that of the reticulocyte count (Cycle Day 3). The peak frequency of CFU-GM (Cycle Days 9-2) and neutrophil-containing colonies in agar culture (Cycle Days 1-2) preceded the peak of granulocytes (Cycle Day 6). The percentage of the various progenitors in the DNA synthetic phase of the cell cycle was similar in grey collies and normal dogs and showed no cyclic fluctuations. These data indicate that cyclic hematopoiesis results from a defect in a hematopoietic stem cell more primitive than BFU-E and CFU-GM. Cycling appears to be due to the commitment of this primitive cell to differentiation only at discrete intervals. The cell cycle kinetics and differentiation of subsequent cells appear normal.
Studies of early erythropoiesis in dogs have been hampered by the lack of an efficient assay for canine erythroid burst-forming cells (BFU-E). We have developed a methyl-cellulose culture system for hematopoietic progenitors in dog marrow with a plating efficiency for BFU-E of 98 +/- 26 (SD) per 10(5) marrow mononuclear cells. We then applied this assay to the study of cyclic hematopoiesis in grey collie dogs, and regular fluctuations of colonies derived from erythroid colony-forming cells (CFU-E), BFU-E, and granulocyte-macrophage colony-forming cells (CFU-GM) were seen at 12- to 13-day intervals. Defining Cycle Day 1 as the first day that the granulocyte count falls below 1000/mm3, we found that the peak frequency of BFU-E (Cycle Day 10) always preceded the peak frequency of CFU-E (Cycle Day 12), which preceded that of the reticulocyte count (Cycle Day 3). The peak frequency of CFU-GM (Cycle Days 9-2) and neutrophil-containing colonies in agar culture (Cycle Days 1-2) preceded the peak of granulocytes (Cycle Day 6). The percentage of the various progenitors in the DNA synthetic phase of the cell cycle was similar in grey collies and normal dogs and showed no cyclic fluctuations. These data indicate that cyclic hematopoiesis results from a defect in a hematopoietic stem cell more primitive than BFU-E and CFU-GM. Cycling appears to be due to the commitment of this primitive cell to differentiation only at discrete intervals. The cell cycle kinetics and differentiation of subsequent cells appear normal.