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.