Fig. 2. GFP fluorescence of day 4 Mixl1^GFP/w EBs. Low-magnification bright-field (A) and epifluorescence (B) images showing that most EBs contain GFP-positive cells. (C) Confocal image showing that GFP-positive cells are present both on the surface and distributed throughout the EB. (D) High magnification of the EB in C, showing GFP-positive cells located on the surface of the EB have a flattened morphology reminiscent of endoderm (arrowhead).