Epo-specific PODXL induction in developmentally staged marrow erythroblasts. (A) In MACS-purified Kit⁺CD71^high erythroblasts, time courses of EPO and SCF induction of PODXL expression (after cytokine withdrawal) were assessed by quantitative RT-PCR. (B) In SP34-EX expansion cultures, cell-surface PODXL expression among Kit⁺CD71^high, Kit⁻CD71^high, and Kit⁻CD71^highTer119⁺ erythroblasts was analyzed by flow cytometry. Frequencies of PODXL⁺ cells are indicated for bisected PODXL^low and PODXL^high subpopulations. (C) For the above stages of maturing erythroblasts, cytospin morphologies for MACS and/or FACS-purified populations also are shown. (Images were seen with a Zeiss (Oberkochen, Germany) model Axioskop 2 microscope with a 100 ×/1.3 oil lens, Immersol 518 (Zeiss) imaging solution, and Volu-sol (Volu-Sol Inc.) dip stain solution. Images were photographed with a Spotflex (Diagnostic Instruments Inc., Sterling Heights, MI) model 15.2 camera and processed with Spot advance (Diagnostic Instruments Inc.) version 4.6 and Photoshop (Adobe, San Jose, CA) version CS2 software.