Vdr signaling maintains erythroid progenitor potential. (A) Colony-forming potential of ckit⁺CD71^lo/neg or ckit⁺ CD71^hi cells cultured under maturation conditions (in MM) with or without calcitriol and then transferred to methylcellulose (250 cells in 250 μL, 24-well dish) on the indicated days (n = 3). (B) Representative flow cytometry analysis of the expression of cKit or CD71 vs Ter119 for ckit⁺CD71^lo/neg cells after 1 day in culture, with or without calcitriol (n = 3). (C) Distribution of colonies formed from ckit⁺CD71^lo/neg cells (125 cells in 250 μL, 24-well dish) cultured in methylcellulose with or without calcipotriol (100 nM), a low calcemic synthetic derivative of calcitriol that is <0.5% to 1% as active as calcitriol in regulating calcium metabolism, because of pharmacokinetic differences³⁸  (n = 3). (D) Proliferation of cKit⁺CD71^lo/neg cells in MM with or without calcipotriol (n = 3). (E) Colony-forming potential of ckit⁺CD71^lo/neg cells cultured in MM with or without dexamethasone (dex), calcitriol, or both ligands (100 nM) for 1 day and then transferred to methylcellulose (125 cells in 250 μL, 24-well dish) (n = 3). BFU-E and mCFU-E numbers were maintained in the presence of either ligand alone but the numbers increased if the 2 ligands were present together. (F) Proliferation of ckit⁺CD71^lo/neg, CD71^med, or CD71^hi cells cultured in MM with or without calcitriol, dex, or both ligands (100 nM) (n = 3). Data were analyzed using an unpaired Student t test (C,E) or 2-way ANOVA (A,D,F; (*P < .05, C,E; **P < .01, A,D,F). Error bars, ± SEM.