Endothelial nature of cells expressing GFP driven by theFlk-1 promoter/enhancer.

(A) Sorted Flk-1⁺ cells derived from ES cells were cultured on OP9 stromal cells and analyzed for the expression of GFP and Flk-1 on wild-type cells (top row) or analyzed for the expressions of GFP and VE cadherin on Flk-1⁺ cells (bottom row) from day 1 to day 3. (B) After a 3-day culturing of the sorted Flk-1⁺ cells, Tie-2 and PECAM-1 expression in GFP⁺ cells were analyzed by flow cytometry. All the GFP⁺ cells express Tie-2 and PECAM-1. (C) Incorporation of DiI-labeled acetylated LDL (red) by GFP⁺ cells (green) was examined by fluorescent microscopy on day 3 of Flk-1⁺ cell culture on OP9 cells. Original magnification ×200. The results shown are representative of 3 independent experiments.