(A, B) Wild type expression of embryonic globin hbae3 (A), and mpx (B) is normal in 100% (n=23) and 61% (n=28) of control uninjected embryos, respectively, in the intermediate cell mass region at the 22-somite stage. (C, D) scl morpholino knockdown results in the loss of hbae3 (C) and mpx (D) expression in 100% (n=24) and 97% (n=32) of embryos, respectively. (E, F) Knockdown of pu.1 does not affect hbae3 expression (E, 100% of embryos, n=54), or mpx expression (F, 70% of embryos, n=37). (G, H) Wild type expression of embryonic globin hbae3 (G), and mpx (H) in the intermediate cell mass region at the 20-somite stage is normal in 100% (n=20) and 78% (n=60) of control uninjected embryos, respectively. (I, J) Knockdown of gata1 results in the loss of expression of both hbae3 (I) and mpx in 100% of embryos, n=28 and n=100, respectively (J). (K, L) mpx expression is strongly reduced or absent in the anterior of mpx morpholino knockdown embryos (L, 92% of embryos, n=25) compared to uninjected controls (K, 13% of embryos, n=8). (M, N) mpx expression is normal in the posterior of mpx morpholino knockdown embryos (N, 88% of embryos, n=25) compared to uninjected controls (M, 75% of embryos, n=8).