Fig. 6

Nodal and Fgf signaling are required for mesoderm induction

(A–E) WISH showing lateral (L) and dorsal views (D) of 8-hpf epiboly embryos stained for tbx16. Embryos underwent a time series of drug treatments with either 50 μM SB-505124 (left), 5 μM PD-0325901 (middle) or the combination of the two (right). Drug treatments were started at either 4 hpf, 5 hpf, 6 hpf, or 7 hpf, and embryos were fixed at 8 hpf epiboly (A). 8-hpf epiboly control (CTRL) embryos are shown for comparison (B). Note that for embryos treated from sphere stage with SB-505124 or the combination of SB-505124 and PD-0325901 the dorsal side cannot be unequivocally identified, as early Nodal inhibition prevents both tbx16 expression and the formation of the dorsal shield. Therefore, for these samples, side views of representative embryos are shown.

(F–J) As in (A–E), but embryos were fixed at 24 hpf and stained for myod. 24-hpf CTRL embryos shown for comparison (G). In this case, all views are lateral. In (H), the black arrow marks the most anterior position of the somites. In (I), the gray arrow indicates the jaw muscle (shown magnified, top right).

Numbers in the bottom right of the images refer to the number of embryos showing the phenotype out of the total number studied. Scale bars: 250 μm (B–G).