Fig. 2. Fgfr2-IIIb^-/- and Fgf10^-/- mutants develop hypospadias. Scanning electron micrographs of the ventral aspect of male genital tubercles are shown in A-F and female genital tubercles are shown in I,J. Scale bar: 100 µm. Arrows indicate position of urethral epithelium. (A) Wild-type genital tubercle at E13.5. (B) Genital tubercle of Fgfr2-IIIb^-/- mutant at E13.5. Arrowhead indicates precocious, ectopic opening of urethral plate and white arrow indicates deep grove in urethral seam. (C) Wild-type genital tubercle at E15.5. Proximal (arrow) and definitive distal (arrowhead) opening of the urethral plate are indicated. (D) Genital tubercle of Fgfr2-IIIb^-/- mutant at E15.5 exhibits an open urethral plate along the proximal half of the penis and agenesis of the prepuce ventrally. (E) Penis of wild-type embryo at E17. The prepuce (pseudocolored green) has surrounded the glans (pseudocolored red) ventrally, and the original proximal urethral meatus (arrow in C) has closed. (F) Penis of Fgfr2-IIIb^-/- mutant at E17 exhibits a completely open urethra. Arrow indicates the dorsal midline (roof) of the urethral plate, and the walls of the urethra now line the ventral surface of the glans (red). Prepuce (green) is present laterally but not ventrally. (G,H) Transverse sections through phallus of E19.5 wild-type (G) and Fgfr2-IIIb^-/- mutant (H) embryos. u, urethral tube; p, prepuce; cc, corpus cavernosum. Arrows indicate the open urethra in the Fgfr2-IIIb^-/- mutant. (I,J) Hypospadias and agenesis of ventral prepuce in external genitalia of Fgf10^-/- mutants at E15.5 (I) and E17.5 (J). Arrows indicate ectopic opening of urethra.