BM erythroid progenitors develop ex vivo sequentially as stage E1, E2, and E3 cohorts. (A) Outlined are ex vivo culture conditions for BM preparations and for the synchronous development of a murine BM erythroid series. (B) Time course and frequencies of stage E1 → E2 → E3 cell formation ex vivo. Here, stage E1 cell isolation (before return to culture) was via Lin⁺ depletion and subsequent MACS-based Kit⁺ selection. (C) Representative flow cytometric analyses of purified BM-derived stage E1, E2, and E3 cells. (D) Initial transcript profiling of select receptors (Kit, Tfrn, and Epor), transcription factors (Gata1, Lmo2, and Tal1), cytoskeletal components (Band 4.1, Ankyrin, and beta-adducin), and heme synthetic factors (Alas2, Urod, and Eraf) within purified stage E1, E2, and E3 cohorts. The potential occurrence of alternate splice forms is not accounted for via 430 2.0 array scanning.