Eosinophils from Lineage-Ablated ΔdblGATA Bone Marrow Progenitors: The dblGATA Enhancer in the Promoter of GATA-1 Is Not Essential for Differentiation Ex Vivo

A critical role for eosinophils in remodeling of allergic airways was observed in vivo upon disruption of the dblGATA enhancer that regulates expression of GATA-1, which resulted in an eosinophil-deficient phenotype in the ΔdblGATA mouse. We demonstrate here that bone marrow progenitors isolated from ΔdblGATA mice can differentiate into mature eosinophils when subjected to cytokine stimulation ex vivo. Cultured ΔdblGATA eosinophils contain cytoplasmic granules with immunoreactive major basic protein and they express surface Siglec F and transcripts encoding major basic protein, eosinophil peroxidase, and GATA-1, -2, and -3 to an extent indistinguishable from cultured wild-type eosinophils. Fibroblast coculture and bone marrow cross-transplant experiments indicate that the in vivo eosinophil deficit is an intrinsic progenitor defect, and remains unaffected by interactions with stromal cells. Interestingly, and in contrast to those from the wild type, a majority of the GATA-1 transcripts from cultured ΔdblGATA progenitors express a variant GATA-1 transcript that includes a first exon (1EB), located ∼3700 bp downstream to the previously described first exon found in hemopoietic cells (1EA) and ∼42 bp upstream to another variant first exon, 1EC. These data suggest that cultured progenitors are able to circumvent the effects of the ΔdblGATA ablation by using a second, more proximal, promoter and use this mechanism to generate quantities of GATA-1 that will support eosinophil growth and differentiation.