Meis1 and Meis2 induce CD41^int hematopoietic progenitors through Ptger3 signaling pathway. (A) A2lox.Meis1 or Meis2 ES cells were differentiated as described in Figure 3A in the presence of the indicated concentration of SC-51322 added on day 6 and replenished daily. On day 9, cells were harvested and analyzed by FACS for expression of CD42d and CD41. Cells are gated as GFP-negative to exclude OP9 cells. Numbers indicate the percentage of CD41⁺ CD42d⁻ cells developing in the indicated conditions from 3 independent experiments. Bars represent the SD. *P < .05 (paired Student t test). **P < .01 (paired Student t test). (B) A2lox.Meis1 ES cells were differentiated as in Figure 3A with the indicated concentration of SC-51322 added on day 6 and replenished each day until day 12. On day 12, cells were analyzed by FACS for expression of CD42d and CD41. Shown are data for GFP-negative cells to exclude analysis of OP9 cells. Numbers indicate the percentage of cells in the indicated gates. (C) A2lox.Meis2 ES cells were differentiated and analyzed as in panel A.