Sustained c-Myc expression is associated with survival of retinoic acid–treated PLZF-RARα–transformed murine progenitors. (A) Murine lin⁻ hematopoietic progenitors were infected with MPG or MPG-PLZF-RARα retrovirus and plated in methylcellulose under myeloid-promoting conditions for 7 days. Granulocytic differentiation was assessed by flow cytometry using CD11b-Pe-Cy7 and Gr-1-APC antibodies and gene expression was assessed by qRT-PCR. (B) Day-7 colonies were disaggregated and replated in the presence of 1μM ATRA (or dimethyl sulfoxide control). After 24 or 48 hours, several colonies were picked and disaggregated and differentiation was measured by flow cytometry as in panel A and changes in gene expression were measured by qRT-PCR. (C) Replated colonies treated with ATRA or control were harvested after 9 days of ATRA treatment, and differentiation was measured by flow cytometry as in panel A. Changes in gene expression were measured by qRT-PCR. Data are expressed as mean; error bars represent the maximum deviation of duplicate experiments. (D) PLZF-RARα blocks differentiation and activates proliferation by directly affecting genes involved in granulocyte differentiation and cell-cycle control. RA induces differentiation and transient growth arrest. The persistence of c-Myc expression and down-regulation of Dusp6 is associated with the continued survival of RA-treated PLZF-RARα–expressing cells.