Green fluorescent protein (GFP) expression in Tg ( myf 5(80K):GFP) transgenic embryos recapitulates endogenous myf5 expression in muscle precursors. GFP fluorescence is detected in the presomitic mesoderm of embryos by 10.5 hours postfertilization (hpf) (A), in the somites and the presomitic mesoderm in 16 hpf embryos (B). Endogenous myf5 transcripts (C,D,E) and GFP mRNA (F,G) were detectable at 7.5, 10.5, and 16 hpf. (A,D,G) Dorsal views, rostral to the left; (B,C,E,F) side views, rostral to the left, dorsal to the top. Scale bars: 100 μm in all panels.