C8161 cells co-labeled with Mart-1:GFP//H2B-mCherry and cultured in chamber slides were initially exposed to either head or trunk tissues isolated at increasing embryonic stages (HHSt10, 15, 17, and 21; Hamburger and Hamilton, 1951) for 72 h, and Mart-1:GFP-positive melanoma cells were counted (Fig. 2A). The gene discussed is H2BC21; the disease is melanoma.