Effect of BMP-4 on the differentiating ES cells. Undifferentiated E14 ES cells (day 0) were stained with anti-CD31-PE and anti-CD34-FITC monoclonal antibodies (A). The ES cells were also induced to differentiate for 7 days in the serum-free medium with or without 2 ng/mL BMP-4 or in the serum-containing medium, and they were analyzed with anti-CD45-PE, Ter119-PE, or CD31-PE, and anti-CD34-FITC monoclonal antibodies (B). The scatter patterns as well as the isotype control staining patterns (rIgG-FITC/rIgG-PE) for the undifferentiated ES cells and EB cells are shown in the top two panels of A, and in the two panels of the left most column of B, respectively. The region R7 represents the CD45⁺ cell population, and R3 represents the Ter119⁺ cell population. R5 corresponds to CD34⁺ CD31^hi cells, and R6 corresponds to CD34⁺ CD31^lo cells. (A) R5: 0.16%; R6: 0.03%. (B, left to right) R7: 0.0%, 1.2%, 3.1%; R3: 0.41%, 3.2%, 14.1%; R5: 0.30%, 3.4%, 2.0%; R6: 0.37%, 2.4%, 6.5%. R4 was used as a gate for sorting CD34⁺ CD45⁻ cells in Table 2.