Deciphering Wnt-Ror signaling in cytoskeletal regulation and tissue shape control

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A long-standing question in biology concerns how tissues and organs acquire their stereotyped shape during development. The Wnt5a-Ror signaling pathway is a master regulator of embryonic tissue morphogenesis, and deregulation of the pathway has been found to cause a broad range of human pathological conditions, including the congenital disorders Robinow syndrome and Brachydactyly Type B, as well as cancer metastasis. In contrast to most well characterized developmental signaling pathways that function via gene transcription, the Wnt5a-Ror pathway functions through cytoskeletal regulation to control key morphogenetic cell behaviors, such as cell migration, polarization and adhesion. However, the molecular mechanisms that underlie Wnt5a- Ror function remain enigmatic. Our research program aims to fill three major gaps in the field: (1) What are the biochemical interactions that mediate Wnt5a-Ror signal processing and propagation within cells? (2) How does Wnt5a-Ror signaling engage the cytoskeleton to control morphogenetic cell behaviors? (3) How do these Wnt5a/Ror-driven processes ultimately control tissue morphogenesis in vivo? To this end, we have integrated mouse genetics and comparative proteomics to construct the first extended inventory of Wnt5a-Ror pathway components. This work not only provided crucial insights into the molecular mechanism of Wnt5a-Ror signal transduction, but also identified Kif26b (a member of the kinesin microtubule motor family) as a critical cytoskeletal effector of the pathway. Through gain- and loss-of-function studies, we demonstrated that Kif26b mediates the ability of the Wnt5a-Ror pathway to control cell migration, and that this function of Kif26b is conserved from C. elegans to humans. Mechanistically, we have established the key finding that Wnt5a-Ror signaling controls the cellular steady-state concentration of Kif26b via a mechanism involving the ubiquitin- proteasome system. Using this novel Wnt5a-Ror-Kif26b signaling paradigm, we have successfully developed a reporter assay that for the first time, allows for quantitative measurement of Wnt5a-Ror signaling activity in live cells. In this application, we propose to use a combination of protein biochemistry, microscopy and genetics to elucidate the molecular mechanism linking Ror receptor activation to Kif26b degradation, the cell biological mechanism underlying Kif26b regulation of cytoskeletal dynamics and cell migration, and the in vivo role of the Wnt5a-Ror-Kif26b signaling cassette in embryonic tissue morphogenesis. Moreover, we will pair our Wnt5a- Ror signaling reporter with large-scale CRISPR/Cas9-based genetic screens to identify additional constituents of the pathway. The successful completion of the project will (1) provide the first detailed molecular portrait of the Wnt5a-Ror signaling network, (2) reveal the cell biological mechanisms by which Wnt5a-Ror signaling regulates cytoskeletal dynamics and tissue morphogenesis, and (3) suggest novel biomarkers and therapeutic targets for Wnt5a-Ror driven diseases.