MLF is required for RUNX1-ETO activity. (A and B) The phenotypes induced on expression of RUNX1-ETO in the LZ+ blood cell lineage are suppressed in the absence of mlf. (A) Absolute number of circulating LZ-GFP+ cells in third instar larvae. (B) Ratio of circulating progenitors (GFP+, PO45−) to differentiated (GFP+, PO45+) LZ+ cells in third instar larvae. (C–E) MLF is required for RUNX1-ETO expression in Drosophila. (C and D) Fluorescent immunostaining against RUNX1-ETO in lz-Gal4,UAS-GFP;UAS-RUNX1-ETO (C, control) and lz-Gal4,UAS-GFP;mlfΔ5–3/Δ5–3;UAS-RUNX1-ETO (D, mlfΔ5–3/Δ5–3) circulating larval blood cells. Nuclei were stained with DAPI. (E) Western blot analysis shows that RUNX1-ETO levels decrease after depletion of MLF by dsRNA in Kc cells. (F and G) In Kasumi-1 cells, MLF1 depletion by siRNA does not affect RUNX1-ETO mRNA levels (F; real-time qPCR), but does reduce RUNX1-ETO protein levels (G; Western blot analysis). The asterisk indicates a nonspecific band that provides a loading control. (H) Knockdown of MLF1 expression inhibits Kasumi-1 cell growth.