Expression of ZMYM2/FGFR1, BCR/FGFR1, or BCR/ABL1 in human CD34⁺ CB cells leads to increased cellular proliferation and erythroid differentiation. (A) Cells transduced with ZMYM2/FGFR1 (●), BCR/FGFR1 (■), or BCR/ABL1 (▴) increase in numbers approximately 35-fold compared with MIG control cells (○) during 14 days of suspension culture. Cells were counted at days 7 and 14 after sorting and the mean values of 3 separate experiments are shown. (B) The immunophenotype of cultured cells was assessed after 14 days of culturing. At this stage, cells expressing ZMYM2/FGFR1, BCR/FGFR1, or BCR/ABL1 had become erythroid as shown by high levels of CD235a- and CD71-antigen expression. (C) Morphologic examination by May-Grünwald and Giemsa staining of cells on cytospin slides after 14 days of suspension culture shows that cells expressing either of the 3 fusion genes were at the pronormoblast stage of erythroid differentiation. (D) The proliferation rate of CD34⁺ CB cells expressing the kinase dead mutants BCR/FGFR1 653/654Y or ZMYM2/FGFR1 653/654Y (gray) was significantly reduced compared with cells expressing normal BCR/FGFR1 and ZMYM2/FGFR1 (black) after 2 weeks of suspension culture. The result shown is the mean value from 3 separate experiments with MIG control cell expansion (white) set to 100%. Error bars show SD.