title: Ptk7 promotes non-canonical Wnt/PCP-mediated morphogenesis and inhibits Wnt/β-catenin-dependent cell fate decisions during vertebrate development.
abstract: Using zebrafish, we have characterised the function of Protein tyrosine kinase 7 (Ptk7), a transmembrane pseudokinase implicated in Wnt signal transduction during embryonic development and in cancer. Ptk7 is a known regulator of mammalian neural tube closure and Xenopus convergent extension movement. However, conflicting reports have indicated both positive and negative roles for Ptk7 in canonical Wnt/β-catenin signalling. To clarify the function of Ptk7 in vertebrate embryonic patterning and morphogenesis, we generated maternal-zygotic (MZ) ptk7 mutant zebrafish using a zinc-finger nuclease (ZFN) gene targeting approach. Early loss of zebrafish Ptk7 leads to defects in axial convergence and extension, neural tube morphogenesis and loss of planar cell polarity (PCP). Furthermore, during late gastrula and segmentation stages, we observe significant upregulation of β-catenin target gene expression and demonstrate a clear role for Ptk7 in attenuating canonical Wnt/β-catenin activity in vivo. MZptk7 mutants display expanded differentiation of paraxial mesoderm within the tailbud, suggesting an important role for Ptk7 in regulating canonical Wnt-dependent fate specification within posterior stem cell pools post-gastrulation. Furthermore, we demonstrate that a plasma membrane-tethered Ptk7 extracellular fragment is sufficient to rescue both PCP morphogenesis and Wnt/β-catenin patterning defects in MZptk7 mutant embryos. Our results indicate that the extracellular domain of Ptk7 acts as an important regulator of both non-canonical Wnt/PCP and canonical Wnt/β-catenin signalling in multiple vertebrate developmental contexts, with important implications for the upregulated PTK7 expression observed in human cancers.
authors.affiliation: Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada.
authors.forename: Madeline
authors.initials: M
authors.lastname: Hayes
authors.forename: Mizue
authors.initials: M
authors.lastname: Naito
authors.forename: Avais
authors.initials: A
authors.lastname: Daulat
authors.forename: Stephane
authors.initials: S
authors.lastname: Angers
authors.forename: Brian
authors.initials: B
authors.lastname: Ciruna
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D016764:Cell Polarity / Q000502:physiology; D017931:DNA Primers / Q000235:genetics; D018507:Gene Expression Regulation, Developmental / Q000502:physiology; D018390:Gene Targeting; D057809:HEK293 Cells; D006801:Humans; D017403:In Situ Hybridization; D018613:Microscopy, Confocal; D009024:Morphogenesis / Q000502:physiology*; D016296:Mutagenesis; D054259:Neural Tube / Q000196:embryology; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D060449:Wnt Signaling Pathway / Q000502:physiology*; D015027:Zebrafish / Q000196:embryology*; D029961:Zebrafish Proteins; D051176:beta Catenin / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D029961:Zebrafish Proteins; D051176:beta Catenin; D011505:Protein-Tyrosine Kinases; D020794:Receptor Protein-Tyrosine Kinases; C581480:ptk7b protein, zebrafish