In vitro colony-forming assays reveal a cell-autonomous defect in erythropoiesis and enhanced myeloid potential in Rcor1-deficient erythropoietic progenitors. (A-B) Numbers of colonies generated from (A) FACS-sorted R2 fetal liver cells or (B) R1 fetal liver cells in methylcellulose culture. Results from 4 experiments for R2 and 5 experiments for R1 are shown (mean ± SD). Equal numbers of control and mutant cells were plated in each experiment. (C) Representative myeloid colonies generated from methylcellulose cultures of mutant R2 cells. Scale bar: 200 μm. (D) Representative cells from cytospin preparations of mutant myeloid colonies stained with May-Grunwald Giemsa. (i) Macrophage, (ii-iii) mast cells, and (iv-vii) granulocytes. Scale bar: 10 μm. (E) Schematic diagram for generating inducible Rcor1 deletions in R1 fetal liver (FL) cells. (F) Numbers of colonies generated from FACS-sorted R1 Mx1-Cre; Rcor1^flox/– fetal liver cells cultured in methylcellulose with or without IFN-α. Results from 6 experiments are shown (mean ± SD). All images were acquired by using a Zeiss Axiovert S-100 and AxioCam HRc cameras. A Zeiss Fluar ×10/0.5 objective was used for the images in (C) and a Zeiss plan-neofluar ×100/1.30 oil objective was used for the images in (D). *P < .05; **P < .01; ***P < .001. Myeloid colonies, colonies containing mast cells, granulocytes, and/or macrophages; N.S., nonsignificant.