Fig. 5. Fgfs and T-box genes interact during posterior mesoderm development. Expression of ntl (purple) and Spt (brown) in 10-somite stage wild-type (A), fgf8 mutant (B) and fgf8^-;fgf24^MO embryos (C) reveals that fgf8^-;fgf24^MO embryos no longer have mesodermal precursors that in wild-type (A) and fgf8 mutants (B) are located in the tail bud (white asterisks) and presomitic mesoderm (arrows). In addition, analysis of these markers reveals that, at this stage, the tail buds of fgf8 mutant embryos (B) contain significantly less presomitic mesoderm precursors (Spt-expressing cells) in comparison with wild-type embryos (A; see also supplemental Fig. S1 at http://dev.biologists.org/supplemental/), and in the posterior notochord have a gap in the ntl expression domain (arrowhead). Dorsal (upper) and vegetal (lower) views showing expression of ntl (D,E), spt (F,G), fgf8 (H-K) and fgf24 (L-O) in mid-gastrula-stage (75-80% epiboly; 8.5 hpf) wild-type and mutant embryos (asterisks and arrows indicate dorsal and ventral tissues, respectively). fgf8^-;fgf24^MO embryos (E,G) have reduced expression of ntl and spt in mesodermal precursors relative to wild-type embryos (D,F). Expression of fgf8 in dorsal mesoderm is reduced in ntl (I), spt (J) and spt;ntl (K) mutant embryos relative to wild-type embryos (H). fgf24 expression is reduced dorsally in ntl embryos (M) ventrally in spt embryos (N) and dorsally and ventrally, but not laterally in spt;ntl embryos (O), relative to wild-type embryos (L). Scale bars: in A, 50 µm for AC; in D, 100 µm for D-O.