(A) Upon activation, Notch receptors on ependymal cell membranes are cleaved into NICD, an intracellular isoform, which is translocated into the nucleus. In the nucleus, Rnd3 controls NICD protein accessibility to MAML and CSL through physical interaction with NICD. In the absence of Rnd3, Notch signaling is significantly enhanced due to the extra amount of NICD available for MAML and CSL to form transcriptomes; which facilitates ependymal cell proliferation resulting in aqueductal stenosis and hydrocephalus. (B) Illustrations of aqueductal stenosis formation. Depletion of Rnd3 promotes ependymal cell proliferation through an enhanced Notch signaling mechanism. The overgrowth of ependymal cells leads to the formation of multiple ependymal cell layers, inward cellular folding, and eventually luminal stenosis or closure. This figure was published as Figure 7 in ref. (78) and republished with press authorization.