A PTK7/Ror2 Co-Receptor Complex Affects Xenopus Neural Crest Migration

Abstract

Neural crest cells are a highly migratory pluripotent cell population that generates a wide array of different cell types and failure in their migration can result in severe birth defects and malformation syndromes. Neural crest migration is controlled by various means including chemotaxis, repellent guidance cues and cell-cell interaction. Non-canonical Wnt PCP (planar cell polarity) signaling has previously been shown to control cell-contact mediated neural crest cell guidance. PTK7 (protein tyrosine kinase 7) is a transmembrane pseudokinase and a known regulator of Wnt/PCP signaling, which is expressed in Xenopus neural crest cells and required for their migration. PTK7 functions as a Wnt co-receptor; however, it remains unclear by which means PTK7 affects neural crest migration. Expressing fluorescently labeled proteins in Xenopus neural crest cells we find that PTK7 co-localizes with the Ror2 Wnt-receptor. Further, co-immunoprecipitation experiments demonstrate that PTK7 interacts with Ror2. The PTK7/Ror2 interaction is likely relevant for neural crest migration, because Ror2 expression can rescue the PTK7 loss of function migration defect. Live cell imaging of explanted neural crest cells shows that PTK7 loss of function affects the formation of cell protrusions as well as cell motility. Co-expression of Ror2 can rescue these defects. In vivo analysis demonstrates that a kinase dead Ror2 mutant cannot rescue PTK7 loss of function. Thus, our data suggest that Ror2 can substitute for PTK7 and that the signaling function of its kinase domain is required for this effect.

PTK7 localization and protein stability is affected by canonical Wnt ligands

“…PTK7 is an acknowledged regulator of vertebrate PCP and, as such, is involved in various morphogenetic processes (Hayes et al, 2013;Podleschny et al, 2015;Shnitsar and Borchers, 2008;Williams et al, 2014;Xu et al, 2016;Yen et al, 2009). Concerning the functional relevance of the canonical Wnt-mediated endocytosis of PTK7, this could be a mechanism by which a Wnt gradient affects PTK7 localization.…”

“…PTK7 internalization requires the Fz7 but not the Ror2 co-receptor PTK7 is a Wnt co-receptor that interacts with other known Wnt receptors (Bin-Nun et al, 2014;Martinez et al, 2015;Peradziryi et al, 2011;Podleschny et al, 2015). As the Fz7 receptor is required for the interaction of PTK7 with canonical Wnt ligands (Peradziryi et al, 2011), we analyzed whether the Wnt-mediated translocation of PTK7 is dependent on Fz7.…”

“…This suggests that Fz7 is required for the Wnt2b-mediated internalization of PTK7. As PTK7 can also interact with the non-canonical Wnt receptor Ror2 (Martinez et al, 2015;Podleschny et al, 2015), we also tested whether Ror2 is required. However, Ror2 loss of function did not affect the Wnt2b-mediated translocation of PTK7 (Fig.…”

“…In vertebrates, PTK7 plays a role in the regulation of PCP, and its loss of function results in classical PCP phenotypes, including convergent extension defects, disruption of stereociliary bundle orientation and inhibition of neural crest cell migration (Hayes et al, 2013;Lu et al, 2004;Paudyal et al, 2010;Shnitsar and Borchers, 2008;Yen et al, 2009). Consistent with a role in activation of PCP signaling, PTK7 has been shown to interact with Wnt ligands as well as the Frizzled 7 (Fz7; also known as Fzd7) and Ror2 receptors (Linnemannstöns et al, 2014;Martinez et al, 2015;Peradziryi et al, 2012;Podleschny et al, 2015;Shnitsar and Borchers, 2008). Furthermore, PTK7 has been reported to recruit Dishevelled (Dsh) proteins to the plasma membrane and to activate JNK and ATF2-dependent signaling (Martinez et al, 2015;Peradziryi et al, 2011;Shnitsar and Borchers, 2008).…”

Ptk7-Deficient Mice Have Decreased Hematopoietic Stem Cell Pools as a Result of Deregulated Proliferation and Migration

“…Such a function of PTK7 in the Wnt5a-mediated noncanonical pathway would fit with the PCP function of PTK7 and with the altered homing and migrating properties of Ptk7-deficient cells that likely depend on small Rho GTPase activation. Some studies showed that PTK7 regulates the balance between the Wnt canonical and noncanonical pathways by interacting with Dishevelled (26,46), ROR2 (42,47), b-catenin (25), and LRP6 (39). We unsuccessfully tried to identify downstream pathways that could be regulated by Ptk7 in HSCPs using a candidate gene/ protein approach.…”