ABSTRACT
Development of visceral left-right asymmetry in bilateria is based on initial symmetry breaking followed by subsequent asymmetric molecular patterning. An important step is the left-sided expression of transcription factor pitx2 which is mediated by asymmetric expression of the nodal morphogen in the left lateral plate mesoderm of vertebrates. Processes leading to emergence of the asymmetric nodal domain differ depending on the mode of symmetry breaking. In Xenopus laevis and mouse embryos, the leftward fluid flow on the ventral surface of the left-right organizer leads through intermediate steps to enhanced activity of the nodal protein on the left side of the organizer and subsequent asymmetric nodal induction in the lateral plate mesoderm. In the chick embryo, asymmetric morphogenesis of axial organs leads to paraxial nodal asymmetry during the late gastrulation stage. Although it was shown that hedgehog signaling is required for initiation of the nodal expression, the mechanism of its asymmetry remains to be clarified. In this study, we established the activation of hedgehog signaling in early chick embryos to further study its role in the initiation of asymmetric nodal expression. Our data reveal that hedgehog signaling is sufficient to induce the nodal expression in competent domains of the chick embryo, while treatment of Xenopus embryos led to moderate nodal inhibition. We discuss the role of symmetry breaking and competence in the initiation of asymmetric gene expression.
ABSTRACT
BACKGROUND: We reviewed our experience with ureteral complications and secondary ureteral implantation after kidney transplantation. METHODS: Between 1997 and 2005, 636 patients underwent kidney transplantation at our transplant center. Ureteral implantation was performed in the Lich-Gregoire technique. Thirty-one patients with ureteral complications after kidney transplantation and subsequent secondary ureteral implantation were analyzed for operative parameters and long-term transplant function. RESULTS: Twenty-seven patients had a ureteral stenosis and 4 patients a ureteral leakage. In 25 patients (81%), a resection of the distal transplant ureter followed by secondary ureteral implantation was performed. In 4 cases (13%), the native ureter was anastomosed to the transplant pelvis and in the remaining 2 cases (6%) to the transplant ureter. Three major complications occurred. At median follow-up of 5 years, 18/30 patients (60%) had a good transplant function and 12/30 patients (40%) had returned to dialysis. One patient with depression died from suicide. CONCLUSIONS: Secondary ureteral implantation can be performed with acceptable morbidity and good long-term transplant outcome.
