In all multicellular animals, successful embryogenesis is dependent on the ability of cells to detect the status of the local environment and respond appropriately. The nature of the extracellular environment is communicated to the intracellular compartment by ligand/receptor interactions at the cell surface. The Wnt canonical and non-canonical signalling pathways are found in the most primitive metazoans, and they play an essential role in the most fundamental developmental processes in all multicellular organisms. Vertebrates have expanded the number of Wnts and Frizzled receptors and have additionally evolved novel Wnt receptor families (Ryk, Ror). The multiplicity of potential interactions between Wnts, their receptors and downstream effectors has exponentially increased the complexity of the signal transduction network. Signalling through each of the Wnt pathways, as well as crosstalk between them, plays a critical role in the establishment of the complex architecture of the vertebrate central nervous system. In this review, we explore the signalling networks triggered by non-canonical Wnt/receptor interactions, focussing on the emerging roles of the non-conventional Wnt receptors Ryk and Ror. We describe the role of these pathways in neural tube formation and axon guidance where Wnt signalling controls tissue polarity, coordinated cell migration and axon guidance via remodelling of the cytoskeleton.

Denudation of the ependyma due to loss of cell adhesion mediated by cadherin-based adherens junctions is a common feature of perinatal hydrocephalus. Junctional stability depends on the interaction between cadherins and the actin cytoskeleton. However, the molecular mechanism responsible for recruiting the actin nucleation machinery to the ependymal junction is unknown. Here, we reveal that loss of the netrin/RGM receptor, Neogenin, leads to severe hydrocephalus. We show that Neogenin plays a critical role in actin nucleation in the ependyma by anchoring the WAVE regulatory complex (WRC) and Arp2/3 to the cadherin complex. Blocking Neogenin binding to the Cyfip1/Abi WRC subunit results in actin depolymerization, junctional collapse, and denudation of the postnatal ventricular zone. In the embryonic cortex, this leads to loss of radial progenitor adhesion, aberrant neuronal migration, and neuronal heterotopias. Therefore, Neogenin-WRC interactions play a fundamental role in ensuring the fidelity of the embryonic ventricular zone and maturing ependyma.