Vdr signaling maintains cycling of cKit⁺CD71^lo/negcells. (A) Proliferation of cKit⁺CD71^lo/neg cells cultured under progenitor conditions (in PM) for 2 days (n = 3). (B) Representative flow cytometry analysis of cKit and Ter119 expression on cKit⁺CD71^lo/neg cells after 2 days of culture in PM. (C) Distribution of colonies formed from cKit⁺CD71^lo/neg cells after 2 days of culture in methylcellulose (250 cells in 250 μL, 24-well dish), with or without calcitriol (n = 3). The cells were plated at low density to ensure that the colonies would be well separated and that scoring would be accurate. (D) Proliferation of cKit⁺CD71^lo/neg cells cultured for 2 days in PM then transferred to MM with or without calcitriol (n = 5). (E) CD71^lo/neg cells on day 4 of culture in MM were labeled with carboxyfluorescein diacetate succinimidyl ester and fluorescence measured on the indicated days. Percentages are shown above each gate. (F) Flow cytometry analysis of EdU incorporation in CD71^lo/neg cells cultured in MM on the indicated days (n = 3). Data were analyzed using an unpaired Student t test (C) or a 2-way ANOVA (D-F; *P < .05, C,F; ***P < .001 D,F). Error bars, ± SEM.