Ang1 promotes EC differentiation via Tie2 signaling. Flk-1⁺ MPCs were purified on E4.5 and cultured on OP9 cells. Control buffer (Control), Ang1 (200 ng/mL), sTie2-Fc (sT2, 25μg/mL), RGD peptide (GRGDSP, 25μg/mL), and control peptide (GRADSP, 25μg/mL) were administered alone or together on days 0 and 2, and analyses were performed on day 3. (A) Treatment scheme of Ang1 or inhibitor. (B) Comparison of cell number of each EC colony on day 3 (n = 4). *P < .05 compared with control. (C) Images showing CD144⁺ EC colonies on day 3. Nuclei were stained with Hoechst. Scale bar represents 200 μm. (D) Dose dependency of Ang1 on the percentage of CD31⁺/CD144⁺ ECs from purified Flk-1⁺ cells on day 3 (n = 3). *P < .05 compared with control. (E,G) Representative FACS analyses of the population of CD31⁺/CD144⁺ ECs. Numbers indicate the percentage of CD31⁺/CD144⁺ ECs. (F,H) Comparison percentages of CD31⁺/CD144⁺ ECs (n = 4). *P < .05 compared with control, GRGDSP, or GRADSP; ^#P < .01 compared with Ang1.