Fig. 3. FoxF1 is required for smooth muscle differentiation in the gut. Immunostaining with antibodies against -smooth muscle actin on transverse sections through the hindgut of CoMo (A) and FoxF1 knockdown (C) embryos at stage 43/44. -smooth muscle actin is expressed in the smooth muscle layer surrounding the gut endoderm (A) but absent in the knockdown embryo (C). (B,D) Nuclear staining by Hoechst dye on the same sections shows a layer of smooth muscle cells with elongated nuclei (arrows) surrounding the gut of CoMo-injected embryos (B), but highly disorganized gut mesoderm in knockdown embryos (D). (E) Close-up view of the area boxed in (C), visualizing the endodermal yolk platelets (arrows) in the visceral cavity.