Pu.1 initiates the expression of runx1, whereas Runx1 suppresses late-phase expression of pu.1. (A-B) WISH of pu.1 expression in 17.5 hpf sib (A) and runx1^w84x (B) embryos. Arrows indicate WISH signal of pu.1. (C-D) Whole-mount antibody staining of Pu.1 protein in 17.5 hpf sib (C) and runx1^w84x (D) embryos. Arrows indicate fluorescent antibody staining signal for Pu.1 protein. (E-F) WISH of runx1 expression in 17 hpf control (E) and pu.1 morphants (F, n = 47 of 48). The arrow indicates WISH signal of runx1 in control morphants (E), which is absent in pu.1 morphants (F). (G-H) WISH of runx1 expression in 17 hpf sib (G) and pu.1^G242D mutants (H). Arrows indicate WISH signal of runx1, which is markedly reduced in pu.1^G242D mutants (H) compared with sib (G). (A-H) Embryos are viewed dorsally with the anterior to the left.