Ptk7 promotes non-canonical Wnt/PCP-mediated morphogenesis and inhibits Wnt/β-catenin-dependent cell fate decisions during vertebrate development

Author:

Hayes Madeline12,Naito Mizue1,Daulat Avais3,Angers Stephane3,Ciruna Brian12

Affiliation:

1. Program in Developmental & Stem Cell Biology, The Hospital for Sick Children, Toronto, ON, M5G 1X8, Canada.

2. Department of Molecular Genetics, The University of Toronto, ON, M5S 1A8, Canada.

3. Departments of Biochemistry and Pharmaceutical Sciences, The University of Toronto, ON, M5S 1A8, Canada.

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.

Publisher

The Company of Biologists

Subject

Developmental Biology,Molecular Biology

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