Fig. 5. Modulation of the BMP signaling pathway in the stomach affects Sox9 expression. Whole-mount in situ hybridization using antisense Sox9 riboprobe on GFP- (A), Bmp4- (B), Nkx2.5- (C) and Noggin- (D,E) misexpressing E8 stomachs. The morphological change of Bmp4-misexpressing stomach is characterized by a reduced musculature of the gizzard (compare B with A). Noggin misexpression in the stomach gives rise to a range of phenotypes (D,E). Moderate phenotype present proventriculus fate change with gland formation inhibition and size increase (D). Severe Noggin phenotype is mainly characterized by stomach/duodenum connection defect and gizzard-like phenotype found in the whole stomach (E). Neither GFP (A) as control nor Nkx2.5 (C) misexpression affects stomach morphology. Sox9 expression is upregulated in Bmp4-misexpressing stomach (B), strongly downregulated in Noggin-misexpressing stomachs (D,E) and not affected in Nkx2.5- (C) or GFP- (A) misexpressing stomachs. Red and black arrows indicate pyloric sphincter area. (F) Bmp4-misexpressing stomach was sectioned and probed with anti-SOX9 antibodies and revealed SOX9 ectopic expression in the gizzard (red arrowheads, F).