Fig. 3. Endodermal β-catenin is required to maintain GT outgrowth. (A-E) SEM analysis showing reduced distal growth and ectopic proximal opening in Shh^Cre/esr;β-Cat^c/c embryos (arrowheads in B-D), and excessive distal growth with no proximal opening in Shh^Cre/esr;β-Cat^loxEx3 GT (arrowheads, E). Dashed lines in A, C and E indicate the plane of transverse sections used for histological/immunostaining analysis in Fig. 4. (A'-E') Fgf8 in situ hybridization on E12.5 GTs. Note the graded decrease in Fgf8 in LOF GTs (B'-D'). Fgf8 is both elevated and ectopically activated in GOF GT (E'). (F-F'') ³⁵S Tcf-1 in situ hybridization revealed downregulation of Tcf1 in Shh^Cre/esr;β-cat^c/c dUE (F'), and upregulation and ectopic proximal UE expression in Shh^Cre/esr;β-Cat^loxEx3 GT (F''). (G-L'') Whole-mount in situ analysis using the probes indicated. Msx2 is expressed in the distal mesenchyme surrounding the dUE (H). Its expression domain is reduced in Shh^Cre/esr;β-Cat^c/c (H'), and is expanded proximally in Shh^Cre/esr;β-Cat^loxEx3 GT (H''). Lef1 and Wnt5a are strongly expressed in the distal mesenchyme, and this strong-expressing domain is also reduced in Shh^Cre/esr;β-Cat^c/c GT (I',J'), and expanded proximally in Shh^Cre/esr;β-Cat^loxEx3 GT (I'',J''). Hoxa13 and Hoxd13 expression remains unchanged in either mutant (K-K'' and L-L'', respectively). Scale bars: 100 µm in A-E; 100 µm in F-F''.