Tbx18 LOF phenotype in P0 UGS.

(A-I) H&E stains of P0 urogenital sinuses. (A-C) Wild type histology shows high cell density in the mesenchyme surrounding the epithelial prostate buds (A, B), and urethral epithelium is composed of 4–6 cell layers with a smooth apical surface (C). (D-F) 12Gso/Tbx18^LacZ compound heterozygotes present an intermediate phenotype in the UGS mesenchyme and the urethral epithelium. (G-I) Tbx18^GFP/GFP mutants have very low mesenchymal cell density surrounding epithelial prostate buds. The urethral epithelium in these mutants is increased in thickness with larger cell volumes (compare arrows in C, F, and I). (J) Measurements of the epithelial thickness in the urethral epithelium. The epithelium on the dorsal side is significantly increased in thickness compared to wild type littermates.