Bmp7 expression and null phenotype in the urogenital system suggest a role in re-organization of the urethral epithelium

Signaling by Bone morphogenetic proteins (Bmps) has multiple and diverse roles in patterning and morphogenesis of the kidney, eye, limbs and the neural tube. Here, we employed the Bmp7lacZ strain to perform a detailed analysis of Bmp7 expression and the null phenotype during development of the mouse urogenital system. The urethral compartment originates in mid-embryogenesis from the ventral part of the cloaca, a transient cavity at the caudal end of the hindgut. At mid-gestation, Bmp7 expression was detected within several specific domains in the cloacal epithelium and mesenchyme. In late embryogenesis, Bmp7 expression was present in the urethra, rectum, the urethral glands, corpus cavernosum, and in the male and female genital ducts. Importantly, loss of Bmp7 resulted in arrest in cloacal septation, and severe defects in morphogenesis of the genital urethra and mesenchyme. Together, our analysis of Bmp7 expression and the null phenotype, indicates that Bmp7 may play an important role in re-organization of the epithelium during cloacal septation and morphogenesis of the genital tubercle.