Fig. 9. Androgen receptor (AR) expression in the developing glans and penile urethra of E15.5 Hoxa13^GFP male embryos. (A) AR expression is elevated in the UPE (arrow) as well as the surface ectoderm (arrowhead) of heterozygous controls. In these same embryos, the penian bone condensation (P) is readily detected. (B) AR expression in the distal glans of a homozygous mutant. Arrow denotes hypospadiac UPE. Arrowhead denotes reduced AR expression in the surface ectoderm. Note the poor condensation of the penian bone mesenchyme (P^*). (C) A more proximal cross-section through the glans. Arrowhead denotes high levels of Hoxa13^GFP/AR co-localization (yellow cells) in the mesenchyme immediately adjacent the UPE. Arrow denotes high levels of AR expression in the glans ectoderm. Note the extensive condensation of mesenchyme forming the penian bone (P). (D) Hoxa13^GFP/AR co-localization (yellow cells) is absent from the mesenchyme flanking the UPE in homozygous mutants and is relocated to the lateral glans mesenchyme (arrowhead). Arrow denotes reduced AR expression in the ectoderm covering the UPE. AR expression was also seen in the penian bone condensation (P), which was more disorganized than was the same site in the heterozygous control. Scale bar: 50 µm. (Below) Diagram to show planes of section through the developing glans and penile urethra (lines A,B and C,D).