Reduced Sf3b1 expression is not sufficient to induce RARs. (A) Frequencies of sideroblastic erythroblasts in Sf3b1^+/− erythroblasts. CD71⁺ erythroblasts in BM of WT and Sf3b1^+/− mice and recipients repopulated with WT and Sf3b1^+/− BM cells at 11 months posttransplantation (WT BMT and Sf3b1^+/− BMT, respectively) were isolated by cell sorting. The cells were cytospun onto slide glasses, subjected to Prussian Blue staining, and then examined under a light microscope. Numbers of cells with siderotic granules per 1000 erythroblasts are shown in a table and a graph. Data are shown as mean ± SD. Counts of 1000 cells were independently performed 3 times. (B) Frequencies of sideroblastic erythroblasts in Sf3b1^+/− erythroblasts upon knockdown of Sf3b1. c-Kit⁺ progenitors transduced with shRNA against Sf3b1 were cultured in the presence of EPO to induce erythroblasts (bottom). GFP⁺CD71⁺-transduced erythroblasts were isolated by cell sorting, then evaluated for the presence of sideroblasts in a manner similar to (A). (C) Representative sideroblastic erythroblasts observed in (B). Arrows indicate siderotic granules.