R-spondin2 regulates planar cell polarity in the vertebrate neural plate

Vertebrate neural tube closure requires planar cell polarity (PCP) signaling to coordinate cell behaviors in the neuroepithelium. In the Xenopus neural plate, PCP is marked by enrichment of the core PCP protein Vangl2 at the anterior edge of every cell, but the distribution of the extracellular factors modulating this asymmetry remains largely unknown. Here, we identify the secreted protein R-spondin2 (Rspo2) as a modulator of neural plate PCP. Rspo2 exhibits predominantly anterior localization in neuroepithelial cells. Morpholino-mediated knockdown of Rspo2 causes neural tube closure defects and disrupts the anterior enrichment of Vangl2. Rspo2 associates with Vangl2 and inhibits FGF receptor-dependent Vangl2 tyrosine phosphorylation in vivo, as shown by both depletion and overexpression experiments. Rspo2 domain analysis shows that the thrombospondin domain contributes to both anterior Rspo2 membrane enrichment and inhibition of Vangl2 phosphorylation. Together, these findings identify a role of Rspo2 in PCP signaling in the Xenopus neural plate and support a model in which anteriorly localized Rspo2 helps maintain Vangl2 asymmetry while limiting Vangl2 tyrosine phosphorylation during neural plate morphogenesis.