Fig. 1. Human nestin intron-II-driven EGFP expression in undifferentiated ES cells and corresponding immunocytochemical expression pattern. (A) A single Neo^R clone after electroporation of h-Nestin-EGFP construct and G418 selection for 12 days shows heterogeneous EGFP expression. (B,C) The EGFP expression in ES cells (arrow) remains patchy during propagation on mitotically inactive feeders (arrow head) in clone-1. (D,E) Weak EGFP expression in one of the few (<15%) EGFP-positive ES-cell clones transfected with tkEGFP. (B,D) Combined transmission and fluorescent light; (C,E) fluorescence light alone. (G,H) A complete overlap between EGFP expression (G) and (H) nestin-immunoreactivity was observed in undifferentiated ES cells during feeder-free propagation. Bars, 100 µM (A), 75 µM (D,E), 50 µM (B,C,G,H).