Compared to wild-type mice, mice lacking one or both alleles of miR-21 showed reduced numbers of HSPCs and increased sensitivity to an LD<sub>50/30</sub> dose of TBI with evidence of bone marrow failure.
Next, we tested the role of miR-21 in regulating TGF-β signaling in a TGF-β-overexpressing transgenic mouse model that develops progressive anemia and dysplasia and thus serves as a model of human bone marrow failure.