Fig. 8. Impact of the loss of Hoxa5 function on signaling pathways involved in stomach morphogenesis. The biological effect of FGF10-impregnated beads was tested on cultured embryonic stomach explants. Ihh expression was stimulated by FGF10 when the bead was implanted in the hindstomach (B), whereas the control bead had no effect (A). In contrast, FGF10-soaked beads were unable to induce Ihh expression when positioned in the forestomach (C), as shown after overexposure of the section. (D) Representation of the stomach mesenchyme (green) and endoderm (yellow) with the associated genes expressed during its ontogenesis. The gradient and domain of expression of Ihh, Shh, Fgf10 and Tgfb1 in the wt stomach as well as the changes in their expression pattern in Hoxa5^–/– mutants are schematized. The lower panel represents a model of presumptive interactions between these signaling molecules in the developing stomach. Hypothetical links are indicated by dashed arrows. Shh and Ihh delimitate functional domains in the gastric endoderm. Fgf10 contributes to establish Ihh expression in the hindstomach. In absence of Hoxa5 function, Fgf10 expression domain extends rostrally while Tgfb1 is no longer restricted. Consequently, Ihh expression domain expands toward the forestomach, while that of Shh regresses. b, bead; d, duodenum; e, esophagus; f, forestomach; h, hindstomach. Scale bar: 100 µm.