NmU stimulates proliferation in K562-MERT cells. K562-MERT cells were cultured in methylcellulose with GM-CSF and IL-3 (A). In addition, some of the cultures received either 35 mM NmU (B), or 1 mM 4-OHT (C), or both 35 mM NmU and 1 mM 4-OHT (D). Colonies consisting of 20 or more cells were manually counted on day 14 using an Olympus IX 70 microscope at 100 × magnification using a 10 ×/0.3 objective and 10 × ocular and a CoolSnap HQ camera (Photometrics, Tucson, AZ). Representative colonies from 8 independent experiments are shown for each treatment at the same magnification.