Dicer regulates erythroid lineage transcriptional priming in HSCs. Lethally irradiated (9 Gy) wild-type CD45.1 mice were transplanted noncompetitively with 6 million BM cells from control (Dicer^fl/fl or Dicer^fl/+;Mx1Cre) or Dicer^Δ/Δ (Dicer^fl/fl;Mx1Cre) mice. At least 4 weeks after transplantation, Cre-mediated recombination was induced with polyriboinosinic acid/polyribocytidylic acid (polyI:C), by intraperitoneal injections of 200 μg polyI:C every second day, 3 injections in total. (A) Representative FACS profiles of HSCs (LSKCD105⁺CD150⁺) in Dicer^fl/fl and Dicer^Δ/Δ mice, respectively. Numbers in FACS profiles indicate percentage within indicated gate, relative to total BM cells. (B-C) Mean (± SEM) frequency relative to total BM cells (B; 10 or 11 mice/group, analyzed individually) and absolute number per 2 tibiae (C) of LSKCD105⁺CD150⁺ HSCs in Dicer^fl/fl and Dicer^Δ/Δ mice. n = 4 or 5 mice/group analyzed individually. (D) Deletion efficiency of Dicer from 100-200 sorted LSKCD150⁺ HSCs. n = 6 mice/group. *P < .05. (E) Sorting strategy for isolation of CD45.2⁺LSKFlt3⁻ cells from Dicer^Δ/+ and Dicer^Δ/Δ mice. FACS profiles are from kit-enriched samples. (F-I) Gene set enrichment analysis comparison of pre-B cell (preB-Sig; F), GM (GM-Sig; G), megakaryocyte (Mk-Sig; H), and erythroid (E-Sig; I) associated gene expression between Dicer^Δ/+ and Dicer^Δ/Δ LSKFlt3⁻ HSCs. NES indicates normalized enrichment score; FDR, false discovery rate q value; and P, nominal P value. Two biological replicates were analyzed/genotyped in 2 separate experiments, using Affymetrix Mouse Genome 430 Version 2.0 arrays.