Expression of c-kit and c-mpl in CD34⁺ BM cells and cultured mast cells grown by SCF + TPO. The expression of c-kit and c-mpl in CD34⁺ BM cells and 15-week-old cultured cells grown by SCF + TPO were examined using (a) flow cytometric analysis and (b) RT-PCR analysis. Day 10 megakaryocytic cells generated by TPO alone from CD34⁺ cord blood cells were used as positive controls. (a) Flow cytometric analysis: (A), CD34⁺ BM cells; (B), 15-week-old cultured cells grown by SCF + TPO; (C), Day 10 cultured CD41⁺ cells grown by TPO. (—), labeled with PE-conjugated anti–c-kit MoAb or anti–c-mpl MoAb followed by FITC-conjugated GAM. (---), labeled with PE-conjugated mouse IgG1 or control mouse IgG1 followed by FITC-conjugated GAM. The abscissa shows the fluorescence intensity of each surface marker, and the ordinate shows the number of cells. (b) RT-PCR analysis: lane 1, no RNA; lane 2, CD34⁺ BM cells; lane 3, cultured c-kit⁺ cells grown by SCF + TPO; lane 4, cultured CD41⁺ cells grown by TPO.