Fig. 4

Expression of sox4b in response to affected retinoic acid, Hedgehog and Delta/Notch signaling. Dorsal views of whole-mount in situ hybridization for sox4b expression. Anterior to the left; B and F scale bars = 100 μm in A–D panels and in panels E–G, respectively. Arrowheads and brackets indicate sox4b expression in pancreas and in neural crest, respectively. Panels A and B present yolk-free embryos. e: eye. Exogenous RA leads to an anterior shift of sox4b expression in pancreas, as described for pancreatic markers (A: control embryo, B: RA-treated embryos). In the nls mutant, defective in RA synthesis, sox4b expression is absent from the pancreatic region (C: wild-type sibling embryo, D: nls mutant embryo). Up-regulation of sox4b is observed in the mib mutant embryos (E: wild-type sibling, F: mib mutant embryo), defective in the Delta-Notch signaling pathway. Alterations of the Hedgehog signaling affect also sox4b expression in pancreas (G–J). In the smu mutant embryos, in which the endocrine part of pancreas fails to develop, sox4b is absent (G: wild-type sibling, H: smu mutant embryo). In addition, injection of shh mRNA induces the over-expression of sox4b (I: GFP mRNA-injected embryo, J: shh mRNA-injected embryo), as previously shown for endocrine pancreatic markers.