Fig. 7. Barx1 effects on the spleen are not mediated through either Wnt signaling or a group of homeodomain transcription factors implicated in control of spleen development. (A-C) Lack of ß-gal activity in the pancreas or spleen of Barx1^-/-;TOPGAL E18.5 mouse embryos, shown in situ (A) to contrast with residual activity in the stomach (St) and native signal in duodenum (Du). The dotted line in A marks the fused spleen-pancreas (Pa), where absence of ß-gal activity is further revealed in B and confirmed by microscopic analysis in C. (D) In contrast to Barx1, homeobox genes previously implicated in spleen development are mostly expressed in prospective spleen mesenchyme (Sp) and excluded from the mesothelium. The left column shows low-magnification images from each in situ hybridization, and the boxed area of each image is shown at higher magnification in the middle column, where the splenic capsule is demarcated by dotted lines. Images in the right-hand column reveal that expression of each of these homeobox genes is maintained in Barx1^-/- spleen, which is recognized in part by juxtaposition to Pdx1⁺ pancreatic tissue (red box).