HSC specification and proliferation are compromised in spt5^m806 mutants. (A) WISH for runx1 at 25 hpf in sibling control and spt5^m806 embryos. (B) Fluorescent microscopy imaging of Tg(cd41:GFP; kdrl:dsRed) embryos at 36 hpf. Arrowheads indicate nascent HSCs that are double positive for GFP and dsRed. Scale bar, 50 μM. (C) Double immunofluorescent staining for GFP and phosphorylated histone H3 (pH3) in Tg(cd41:GFP) embryos. GFP is in green and pH3 is in red. Arrowheads indicate cells that are GFP⁺pH3⁺. Scale bar, 50 μM. (D) TUNEL staining for apoptosis in CHT. (E-G) Quantification of the results from panels B, C, and D, respectively. Each dot represents an individual embryo. Values represent mean ± SEM. **P < .01. n.s., not significant; sib, sibling.