GSK3β is upregulated and exhibits high nuclear localization in mouse hematopoietic progenitor cells after MLL-AF9-mediated transformation. 5-Fluoruracil-mobilized mouse progenitor cells were transduced with vector control or MLL-AF9 and serially passaged in semisolid media for 3 passages or until colonies failed to form. Cells were analyzed by imaging cytometry following each passage for GSK3β intensity and nuclear localization score. Note: no colonies formed for vector control at the second serial passage.