Compound loss of TR2/TR4 impairs erythropoiesis. (A) WT and Tr2^−/−:Tr4^f/f Lin⁻ BM cells were mock infected (Cre⁻) or infected with Ad-Cre (Cre⁺) on days 0 and 2 of culture. An aliquot of cells was stained daily with anti-CD71 and anti-Ter119 antibodies prior to flow cytometric analyses. As erythroid differentiation progressed, CD71⁺Ter119⁻ immature erythroid cells (quadrant II) became CD71⁺Ter119⁺ (quadrant III) before becoming CD71⁻Ter119⁺ (quadrant IV). Numbers represent the fractional percentages of cells in each quadrant. Only Tr2^−/−:Tr4^f/f Lin⁻ BM cells, which had been exposed to Ad-Cre infection, had far fewer circulation mature CD71⁻Ter119⁺ cells and an increased number of immature CD71⁺Ter119⁺ cells. (B) Data from erythroid cells at each maturational state (quadrants I-IV) from 4 to 6 mice of either genotype are summarized in the histogram. WT, wild type.