Enforced Pu.1 expression promotes the formation of embryonic macrophages at the expense of embryonic neutrophils. (A-B) WISH of irf8 expression at 21 hpf in heat-shocked Tg(hsp70:myc-pu.1)hkz03t (Tg+, panel B arrows) and nontransgenic sibling (Tg-, panel A arrows). (C-D) WISH of csf1ra expression at 25 hpf in heat-shocked Tg(hsp70:myc-pu.1)hkz03t (Tg+, panel D arrows) and nontransgenic sibling (Tg-, panel C arrows). Arrowheads indicate csf1ra expression in neural crest cells. (E-F) WISH of cebp1 expression at 21 hpf in heat-shocked Tg(hsp70:myc-pu.1)hkz03t (Tg+, panel F arrows) and nontransgenic sibling (Tg-, panel E arrows). (G-H) SB staining at 36 hpf in heat-shocked Tg(hsp70:myc-pu.1)hkz03t (Tg+, panel H arrows) and nontransgenic sibling (Tg-, panel G arrows). (I) Summary of effects of transient Pu.1 overexpression on the development of cebp1⁺, mpx⁺, SB⁺ neutrophils and irf8⁺, csf1ra⁺ macrophages. Embryos from Tg(hsp70:myc-pu.1)hkz03t^+/− crossed with AB WT are heat shocked at 11 hpf and fixed at 21 hpf, 33 hpf, 36 hpf, 21 hpf, 25 hpf for WISH detection of cebp1 (E-F), mpx, SB (G-H), irf8 (A-B), csf1ra (C-D), respectively. Number (No.) of cells positive for these markers were counted and compared between Tg(hsp70:myc-pu.1)hkz03t (Tg+) and nontransgenic sibling (Tg-) embryos having undergone the same heat-shock and staining protocol. The asterisks indicate statistical difference (t test, cebp1_Tg-(mean/SE/n) = 35.6/2.9/12, cebp1_Tg+ = 15.6/1.7/11; mpx_Tg- = 96.9/4.8/13; mpx_Tg+ = 74.4/5.8/10; SB_Tg- = 134.4/5.6/18, SB_Tg+ = 99.3/5.0/16; irf8_Tg- = 41.8/7.6/4; irf8_Tg+ = 66.3/5.2/12; csf1ra_Tg- = 46.4/6.6/12; csf1ra_Tg+ = 70.5/4.3/12; *P < .05, **P < .001). (A-B,E-F) Embryos are viewed dorsally with the anterior to the left.