title: Pronephric tubule morphogenesis in zebrafish depends on Mnx mediated repression of irx1b within the intermediate mesoderm.
abstract: Mutations in the homeobox transcription factor MNX1 are the major cause of dominantly inherited sacral agenesis. Studies in model organisms revealed conserved mnx gene requirements in neuronal and pancreatic development while Mnx activities that could explain the caudal mesoderm specific agenesis phenotype remain elusive. Here we use the zebrafish pronephros as a simple yet genetically conserved model for kidney formation to uncover a novel role of Mnx factors in nephron morphogenesis. Pronephros formation can formally be divided in four stages, the specification of nephric mesoderm from the intermediate mesoderm (IM), growth and epithelialisation, segmentation and formation of the glomerular capillary tuft. Two of the three mnx genes in zebrafish are dynamically transcribed in caudal IM in a time window that proceeds segmentation. We show that expression of one mnx gene, mnx2b, is restricted to the pronephric lineage and that mnx2b knock-down causes proximal pronephric tubule dilation and impaired pronephric excretion. Using expression profiling of embryos transgenic for conditional activation and repression of Mnx regulated genes, we further identified irx1b as a direct target of Mnx factors. Consistent with a repression of irx1b by Mnx factors, the transcripts of irx1b and mnx genes are found in mutual exclusive regions in the IM, and blocking of Mnx functions results in a caudal expansion of the IM-specific irx1b expression. Finally, we find that knock-down of irx1b is sufficient to rescue proximal pronephric tubule dilation and impaired nephron function in mnx-morpholino injected embryos. Our data revealed a first caudal mesoderm specific requirement of Mnx factors in a non-human system and they demonstrate that Mnx-dependent restriction of IM-specific irx1b activation is required for the morphogenesis and function of the zebrafish pronephros.
authors.affiliation: Institute for Molecular Biology/CMBI, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria. Electronic address: elisabeth.ott@uniklinik-freiburg.de.
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Ott
authors.affiliation: Developmental Biology, Institute Biology 1, University of Freiburg, Hauptstrasse 1, 79104 Freiburg, Germany. Electronic address: bjoern.Wendik@PERKINELMER.COM.
authors.forename: Björn
authors.initials: B
authors.lastname: Wendik
authors.affiliation: Developmental Biology, Institute Biology 1, University of Freiburg, Hauptstrasse 1, 79104 Freiburg, Germany. Electronic address: monika.srivastava@anu.edu.au.
authors.forename: Monika
authors.initials: M
authors.lastname: Srivastava
authors.affiliation: Institute for Molecular Biology/CMBI, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria. Electronic address: frederic.pacho@uibk.ac.at.
authors.forename: Frederic
authors.initials: F
authors.lastname: Pacho
authors.affiliation: Institute for Molecular Biology/CMBI, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria.
authors.forename: Sonja
authors.initials: S
authors.lastname: Töchterle
authors.affiliation: Institute of Zoology/CMBI, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria. Electronic address: willi.salvenmoser@uibk.ac.at.
authors.forename: Willi
authors.initials: W
authors.lastname: Salvenmoser
authors.affiliation: Institute for Molecular Biology/CMBI, University of Innsbruck, Technikerstr. 25, 6020 Innsbruck, Austria. Electronic address: dirk.meyer@uibk.ac.at.
authors.forename: Dirk
authors.initials: D
authors.lastname: Meyer
mesh_terms: D000015:Abnormalities, Multiple / Q000235:genetics; D000818:Animals; D030801:Animals, Genetically Modified; D019521:Body Patterning / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D055785:Gene Knockdown Techniques; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*; D007684:Kidney Tubules / Q000196:embryology*; D008588:Meningocele / Q000235:genetics; D008648:Mesoderm / Q000196:embryology; D023421:Models, Animal; D060172:Morpholinos / Q000235:genetics; D038081:Organogenesis / Q000235:genetics* / Q000502:physiology; D060910:Pronephros / Q000196:embryology*; D012445:Sacrococcygeal Region / Q000002:abnormalities; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics*; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D018398:Homeodomain Proteins; C000609365:Mnx2b protein, zebrafish; D060172:Morpholinos; D014157:Transcription Factors; D029961:Zebrafish Proteins; C459599:irx1b protein, zebrafish
keywords: Currarino syndrome; Development; Intermediate mesoderm; Pronephros; Sacral agenesis; Zebrafish; irx1b; mnx1; mnx2b