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Interleukin-3 (IL-3) stimulates colony formation of multiple lineages of hematopoietic cells. Bone marrow cells of A/J mice are nonresponsive to IL-3, and this observation has recently been correlated with aberrant mRNA splicing and impaired expression of the IL-3 receptor alpha subunit (IL-3R alpha), a binding component of the high-affinity receptors. We examined the IL-3R alpha gene in 27 inbred mouse strains and found the identical mutation, a 5-bp deletion at the branch point of intron 7, in 10 of these mouse strains. Bone marrow cells isolated from these 10 mouse strains did not express IL-3R alpha on the cell surface and did not form colonies in response to IL-3. Because the defective IL-3R alpha gene was found in several distantly related mouse strains, it appears to be a recessive allele rather than a sporadic mutation. In contrast, only 1 of 21 wild-derived mouse strains carried the 5-bp deletion in the IL-3R alpha gene. This study suggests that IL-3 function is not required for normal hematopoiesis in mice, but the retention of the IL-3 and IL-3R system may be of some selective advantage in wild populations.
Hara et al. (Mon,) studied this question.