Heterozygous Kit Mutants with Little or No Apparent Anemia Exhibit Large Defects in Overall Hematopoietic Stem Cell Function

Objective The evolutionarily conserved Kit receptor is vital for function of hematopoietic stem cells (HSC). KitW-41 (W-41) and KitW-42 (W-42) are single residue changes in the KIT intracellular phosphotransferase domain, while KitW-v (W-v) is a single residue change in the ATP binding domain. This study tests how each mutation affects HSC function. Methods Cells in mutant and C57BL/6J+/+ blood and marrow were compared. Overall HSC function was measured by competitive repopulation. Functions of specific progenitor populations were tested with stage-specific competitive repopulation and standard colony-forming unit assays. Results Bone marrow cells from these Kit mutants are severely defective at reconstituting peripheral blood lineages and bone marrow of irradiated recipients, when compared to +/+ control marrow. These defects increased with time. Marrow from W-41/+ and W-v/+ functions similarly but better than marrow from W-41/W-41 and W-42/+, to repopulate the erythroid and lymphoid lineages. Long-term (LT) and short-term (ST) HSC from W-v/+, W-41/W-41, and W-42/+ are more defective at reconstituting bone marrow than LT- and ST-HSC from W-41/+ and +/+. Common myeloid progenitor (CMP) cells from W-42/+ and W-41/W-41 are more defective at producing spleen colonies than CMP from W-v/+ and W-41/+. Conclusion Heterozygous Kit mutants with little or no apparent anemia exhibit surprisingly large defects in overall HSC function. Multiplying the fractional defects in LT-HSC, ST-HSC, and CMP can account for overall effects of W-v/+, but does not completely account for the defects observed with W-41/+, W-42/+, and W-41/W-41.