Wnt/Frizzled-PCP signaling in development and disease

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Epithelial cells are polarized in two axes for their function, ubiquitous apical-basal polarity and a second axis within the epithelial plane, referred to as Planar Cell Polarity (PCP). Cell polarity and ordered cellular patterning during organ development and homeostasis depend on PCP mechanisms. Classical PCP examples include in Drosophila adult cuticular structures. Similarly, in mammals striking aspects of PCP are evident in the skin, the inner ear epithelium, or the respiratory system and most other internal organs. Moreover, convergent extension processes during gastrulation and neural tube closure requires PCP signaling, and the PCP pathway is linked to the regulation of asymmetric cell divisions in stem cells of many organs. Studies of PCP establishment in Drosophila serve as a paradigm to unravel this type of polarity in development and human disease. PCP is coordinated by long-range Wnt ligand signals, resulting in asymmetric localization of their receptors, the Frizzled (Fz) proteins, and associated signaling cascade. Core Fz/PCP factors are required to interpret polarity within the cell and relay this to neighboring cells. All core Fz/PCP members are evolutionarily conserved and regulate all PCP aspects. This Wnt-pathway is distinct from canonical Wnt-Fz/β-catenin signaling (and correct regulation of signaling specificity between the two Wnt-pathways, activated by the same receptor(s), is critical for development and disease). In Wnt-PCP-signaling Fz's act both, as receptors for Wnts and ligands for its intercellular binding partner(s) Van Gogh/Vang (Vangl1/2 in mammals). The cellular mechanism(s) affecting polarity downstream of either Fz or Vang upon polarized localization remain very poorly understood. The scope and focus of my lab's research and this application is to investigate the mechanistic interactions of long-range PCP signaling and the resulting cell biological read-outs and intracellular responses. Our recent focus has been/is on Vang/Vangl function, as a result of its intercellular interaction with Fz, and the associated cellular response. Our work is and will be also guided by patient derived data and the respective functional dissection of these mutations. Based on exciting ongoing experiments, we will address the physiological significance of Fz-induced Vang phosphorylation and associated kinase function, and how these affect Vang interactions with cytoplasmic effectors. These studies will be aided by including patient data with Vangl1/2 associated neural tube closure defects. In parallel, we are dissecting the intracellular cell biological responses to PCP signaling and how these affect positioning and the mechanistic interplay with cilia associated proteins, with the advantage of being able to do so in non-ciliated Drosophila cells. A combination of in vivo studies and cell culture biochemical experiments will be performed to achieve these goals. The processes of PCP establishment and Wnt/Fz signaling have been linked to several medical abnormalities, ranging from deafness to neural tube closure defects and cancer, or ciliopathies in general. Information acquired will advance our understanding of cellular polarization, and provide medical relevance in many disease contexts.