The role of glial cell line-derived neurotrophic factor signalling pathway in mammalian organogenesis

Ret is a receptor tyrosine kinase which binds GDNF*, in partnership with GDNFRα**, a glycosylphosphatidyiinositol-linked cell surface receptor. Ret and GDNF have been implicated in branching morphogenesis of the metanephros. Ret is expressed by the ureteric bud and its derivatives, whilst GDNF is expressed by the mesenchyme. Null mutant mice for either gene exhibit severe dysgenesis or agenesis of the kidney and ureter. However, their role in branching morphogenesis of other organs is unclear. This study has further examined the expression pattern of ret, GDNFRα, and GDNF during mouse development, with particular reference to organs that develop through branching morphogenesis. The pathway was expressed in both the metanephros and lung, but in differing spatial and temporal patterns in the mesenchyme and epithelia, but only in presumed ganglia cells of the submandibular gland. Ureteric bud and nephron formation were accelerated in organ cultures containing exogenous GDNF, with the ectopic growth of supranumary ureteric buds; the opposite effect was observed in cultures containing neutralising antibodies. Development of the lungs and submandibular glands were unaffected under these conditions. Hence, GDNF is a mesenchymaly derived factor which causes outgrowth and development of the ureteric bud epithelia. The role of ret activation in monoclonal cell lines was also investigated. Renal cells lines were stabley transfected with ret and a ret oncogene, ret/PTC2. They were assayed for changes in proliferation, and growth morphology in three dimensional cultures. The activation of ret, and the presence of ret/PTC2, caused a significant reduction in cellular proliferation as well as causing MDCK cells to produce 'spikes' when grown in collagen gels. Together these results suggest a morphogenetic role for ret in development. Finally, a three dimensional culture system has been described. This may be used in future work to assay the effects of other factors on nephrogenesis. * Glial cell line-derived neurotrophic factor **Glial cell line-derived neruotrophic factor receptor