(A) Teratomas generated by clones 2K-1 (middle) and 2K-3 (right) were comparable in weight and appearance to those generated by control ES cells (left).
(B) Teratomas generated by both clones were similar to control ES cells (data not shown) and contained derivatives of all three germ layers, such as cartilage and gut epithelium (left panel) and neural tissue (right panel).
(C) High-contribution chimera resulting from the injection of clone 2K-1 into blastocysts. Similar results were obtained for clone 2K-3.
(D) Sections showing extensive contribution of injected cells to brain (m, midbrain), heart (v, ventricular myocardium), and gut endoderm (i, intestinal epithelium).

(A) Alkaline phosphatase staining of ES-like colonies induced in the absence of drug selection.
(B) Colonies induced in the presence of serum at 11 days postinfection. No GFP expression was detected.
(C) Clones were picked and expanded in serum-based medium. Patchy GFP expression is seen in some colonies.
(D) Colonies induced in serum-based medium, then replaced with KSR based medium at day 4. Representative colonies from 11 days postinfection are shown. Note that colonies induced in KSR are smaller and more compact than the ones induced in serum (compare to Figure 1B). Furthermore, the majority of ES-like colonies induced in KSR conditions are GFP positive, although some GFP negative colonies are still present (arrow). GFP negative colonies are less compact and have poorly defined edges.
(E) Clones were picked and expanded in KSR-based medium. Clones have excellent ES-cell colony morphology and maintain strong and uniform GFP expression.
(F) Cells of all three clones expanded in KSR-based medium were predominantly diploid. Images in (B), (C), and (D) were taken with a 20× objective, (E) with 10×, and (F) with 100×.