Abstract
In mammals, urorectal development starts at early embryonic stage, defective urorectal development results in anorectal malformations, which are common congenital developmental defects of the anus and the urethra in newborns. The etiology and embryology of the defects are still largely unknown. Platelet-derived growth factor receptor alpha (Pdgfra) is a cell surface receptor tyrosine kinase, upon binding to its ligands (Pdgfa-d), mediates intracellular signaling and regulates embryonic development. The expression of Pdgfra is tightly regulated in the developing urorectal mesenchyme, and its dysregulation is associated with urorectal defects in animals with urorectal defects. Knockout of Pdgfra induces early embryo lethality which precludes investigation of Pdgfra in urorectal development. To address the temporal requirement of Pdgfra in urorectal development, we conditionally deleted Pdgfra in Pdgfra-expressing tissues using a tamoxifen inducible Cre-loxP approach in mice, examined the urorectal development in Pdgfra conditional knockout (Pdgfra-cKO) embryos. We showed that conditional deletion of Pdgfra in Pdgfra-expressing tissues at E10-E11 caused cloaca septation defect, anteriorly displaced anus, defective urogenital folds development and abnormal urethra tubularization in both male and female mice. Furthermore, we showed that Pdgfra was required for the survival of urorectal mesenchyme, deletion of Pdgfra caused apoptosis in the peri-cloacal, the peri-urethra and the urorectal septum mesenchyme of Pdgfra-cKO mutants, associated with an induction of p53, Ndrg1 and activation of caspase-3 in Pdgfra-cKO embryos. In conclusion, Pdgfra is required for the development and survival of the urorectal mesenchyme in embryo, dysregulated Pdgfra signaling induced urorectal defects in mice resembling human congenital diseases of anorectal malformations and hypospadias. Perturbation of PDGFRA signaling may contribute to anorectal malformations and hypospadias in human.