Dicer is critical for the earliest stages of the erythroid progenitor compartment. (A-C) Mean (± SEM) CFU-GM (A), CFU-Mk (B), and BFU-E (C) colonies at 8 to 9 days of culture from unfractionated BM cells isolated 12 days after intraperitoneal injections of 200 μg polyI:C every second day, 3 injections in total, of 11-day-old Dicer^fl/fl (n = 4) and Dicer ^fl/fl;Mx1Cre mice (n = 8). Each mouse was analyzed in quadruplicate. (D) Representative FACS profiles of myelo/erythroid progenitor cells from lethally irradiated CD45.1 wild-type mice transplanted noncompetitively with Dicer^fl/fl and Dicer^Δ/Δ (CD45.2) BM cells, analyzed 12 days after polyI:C treatment. Numbers indicate percentage within indicated gate, of total BM cells. (E-F) Mean (± SEM) frequencies of test cell-derived myelo/erythroid progenitors in transplanted mice. n = 10 or 11 mice/group, analyzed individually. (G) Mean (± SEM) numbers of test cell-derived myelo/erythroid progenitors in transplanted mice. n = 4 or 5 mice/group, analyzed individually. (H) Dicer deletion efficiency in pre-GMs, GMPs, pre-MegEs, and MkPs isolated from mice transplanted with Dicer^Δ/Δ BM cells and injected with polyI:C 12 days prior to analysis. Data are mean (± SEM) values from cells purified from 2 different pools of mice/genotype, 2 or 3 replicate wells/pool. (I) Megakaryocyte/erythroid gene expression in 100-200 pre-MegEs isolated from Dicer^fl/fl and Dicer^Δ/Δ mice. Mean (± SEM) expression in Dicer^Δ/Δ relative to control Dicer^fl/fl pre-MegEs, calculated using the 2^−ΔΔCT method.¹⁷  Data generated from sorts performed on 6 cohorts of mice/genotype (2 or 3 mice/cohort), 13 or 14 technical replicates, 3 experiments in total. *P < .05. **P < .01. ***P < .001. ns indicates not significant. Statistics refer to comparison between Dicer^Δ/Δ mice and Dicer^fl/fl control mice.