title: A context-dependent combination of Wnt receptors controls axis elongation and leg development in a short germ insect.
abstract: Short germ embryos elongate their primary body axis by consecutively adding segments from a posteriorly located growth zone. Wnt signalling is required for axis elongation in short germ arthropods, including Tribolium castaneum, but the precise functions of the different Wnt receptors involved in this process are unclear. We analysed the individual and combinatorial functions of the three Wnt receptors, Frizzled-1 (Tc-Fz1), Frizzled-2 (Tc-Fz2) and Frizzled-4 (Tc-Fz4), and their co-receptor Arrow (Tc-Arr) in the beetle Tribolium. Knockdown of gene function and expression analyses revealed that Frizzled-dependent Wnt signalling occurs anteriorly in the growth zone in the presegmental region (PSR). We show that simultaneous functional knockdown of the Wnt receptors Tc-fz1 and Tc-fz2 via RNAi resulted in collapse of the growth zone and impairment of embryonic axis elongation. Although posterior cells of the growth zone were not completely abolished, Wnt signalling within the PSR controls axial elongation at the level of pair-rule patterning, Wnt5 signalling and FGF signalling. These results identify the PSR in Tribolium as an integral tissue required for the axial elongation process, reminiscent of the presomitic mesoderm in vertebrates. Knockdown of Tc-fz1 alone interfered with the formation of the proximo-distal and the dorso-ventral axes during leg development, whereas no effect was observed with single Tc-fz2 or Tc-fz4 RNAi knockdowns. We identify Tc-Arr as an obligatory Wnt co-receptor for axis elongation, leg distalisation and segmentation. We discuss how Wnt signalling is regulated at the receptor and co-receptor levels in a dose-dependent fashion.
authors.affiliation: Universität Rostock, Institut für Biowissenschaften/Abt. Genetik, D-18059 Rostock, Germany. beermann@uni-tuebingen.de
authors.forename: Anke
authors.initials: A
authors.lastname: Beermann
authors.forename: Romy
authors.initials: R
authors.lastname: Prühs
authors.forename: Rebekka
authors.initials: R
authors.lastname: Lutz
authors.forename: Reinhard
authors.initials: R
authors.lastname: Schröder
mesh_terms: D000818:Animals; D019521:Body Patterning / Q000235:genetics / Q000502:physiology*; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian / Q000378:metabolism; D051157:Frizzled Receptors / Q000235:genetics / Q000378:metabolism*; D018507:Gene Expression Regulation, Developmental / Q000235:genetics / Q000502:physiology*; D019476:Insect Proteins / Q000235:genetics / Q000378:metabolism*; D007814:Larva / Q000378:metabolism; D035002:Lower Extremity / Q000196:embryology*; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D034622:RNA Interference; D043562:Receptors, G-Protein-Coupled / Q000235:genetics / Q000378:metabolism*; D014231:Tribolium; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D029721:Drosophila Proteins; D051157:Frizzled Receptors; D019476:Insect Proteins; D011518:Proto-Oncogene Proteins; D043562:Receptors, G-Protein-Coupled; D051153:Wnt Proteins; C491438:Wnt5 protein, Drosophila; C432152:frizzled protein 4, Drosophila; C058784:fz protein, Drosophila; C101703:fz2 protein, Drosophila