shRNA lentivirus-mediated Meis1 knockdown inhibits cell growth and promotes differentiation in murine Mll-AF9 leukemia. The 4166 cells were transduced for 5 days with the various lentivirus constructs and cultured in the presence of puromycin as described. (A) RT-PCR for Meis1 and Gapdh (housekeeping gene). (B) Bar graph depicting cell growth after Meis1 shRNA transduction compared with vector control, the latter being 100%. (C) By light microscopy, Meis1 knockdown resulted in monocytic differentiation. Staining for the monocyte-specific marker F4/80 showed increased uptake with Meis1 knockdown. Slides were viewed with a Nikon Eclipse 80i microscope (Nikon, Melville, NY) at a 10×/0.3 NA, WD 16.0 mm objective with fixed cells imaging medium. Images were acquired using a Nikon Digital Sight DS-5M-L1 camera and were processed using Nikon DS-L1 image acquisition software. Image adjustment was performed using Adobe Photoshop CS2 (Adobe Systems, San Jose, CA).