title: Angioblast-mesenchyme induction of early kidney development is mediated by Wt1 and Vegfa.
abstract: Most studies on kidney development have considered the interaction of the metanephric mesenchyme and the ureteric bud to be the major inductive event that maintains tubular differentiation and branching morphogenesis. The mesenchyme produces Gdnf, which stimulates branching, and the ureteric bud stimulates continued growth of the mesenchyme and differentiation of nephrons from the induced mesenchyme. Null mutation of the Wt1 gene eliminates outgrowth of the ureteric bud, but Gdnf has been identified as a target of Pax2, but not of Wt1. Using a novel system for microinjecting and electroporating plasmid expression constructs into murine organ cultures, it has been demonstrated that Vegfa expression in the mesenchyme is regulated by Wt1. Previous studies had identified a population of Flk1-expressing cells in the periphery of the induced mesenchyme, and adjacent to the stalk of the ureteric bud, and that Vegfa was able to stimulate growth of kidneys in organ culture. Here it is demonstrated that signaling through Flk1 is required to maintain expression of Pax2 in the mesenchyme of the early kidney, and for Pax2 to stimulate expression of Gdnf. However, once Gdnf stimulates branching of the ureteric bud, the Flk1-dependent angioblast signal is no longer required to maintain branching morphogenesis and induction of nephrons. Thus, this work demonstrates the presence of a second set of inductive events, involving the mesenchymal and angioblast populations, whereby Wt1-stimulated expression of Vegfa elicits an as-yet-unidentified signal from the angioblasts, which is required to stimulate the expression of Pax2 and Gdnf, which in turn elicits an inductive signal from the ureteric bud.
authors.affiliation: Department of Medicine, Children's Hospital, and Department of Pediatrics, Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Xiaobo
authors.initials: X
authors.lastname: Gao
authors.forename: Xing
authors.initials: X
authors.lastname: Chen
authors.forename: Mary
authors.initials: M
authors.lastname: Taglienti
authors.forename: Bree
authors.initials: B
authors.lastname: Rumballe
authors.forename: Melissa H
authors.initials: MH
authors.lastname: Little
authors.forename: Jordan A
authors.initials: JA
authors.lastname: Kreidberg
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D018274:Electroporation; D018507:Gene Expression Regulation, Developmental; D051100:Glial Cell Line-Derived Neurotrophic Factor / Q000378:metabolism; D007668:Kidney / Q000166:cytology / Q000196:embryology* / Q000378:metabolism; D008648:Mesoderm / Q000166:cytology / Q000502:physiology; D051379:Mice; D008845:Microinjections; D009024:Morphogenesis; D009399:Nephrons / Q000196:embryology / Q000502:physiology; D009924:Organ Culture Techniques; D051762:PAX2 Transcription Factor / Q000235:genetics / Q000378:metabolism; D051381:Rats; D015398:Signal Transduction; D014513:Ureter / Q000196:embryology; D042461:Vascular Endothelial Growth Factor A / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000378:metabolism; D025721:WT1 Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*
chemical_list: D051100:Glial Cell Line-Derived Neurotrophic Factor; D051762:PAX2 Transcription Factor; C497319:Pax2 protein, mouse; D042461:Vascular Endothelial Growth Factor A; D025721:WT1 Proteins; C467480:vascular endothelial growth factor A, mouse; D040301:Vascular Endothelial Growth Factor Receptor-2