Vascular signals coordinate cerebellar circuitry development

Neural circuit assembly requires precise coordinated interactions between developing neurons and the vasculature, yet the instructive signals provided by endothelial cells remain largely unknown. Here, we identify a vascular-to-neural signaling axis that orchestrates postnatal cerebellar development. Endothelial-specific deletion of the adaptor protein Dab1 in mice disrupted vascular patterning and uncoupled the growth of major cerebellar neuronal populations. We show that endothelial Dab1 in the cerebellum drives secretion of the morphogen Wnt5a, which acts through Frizzled-2 to restrain granule-cell progenitor proliferation and promote Purkinje-cell dendritic maturation. Endothelial Wnt5a deletion phenocopied Dab1 endothelial mutant (Dab1i{Delta}EC) defects, whereas exogenous Wnt5a restored normal progenitor dynamics in Dab1i{Delta}EC cerebellar slices, demonstrating pathway sufficiency. Functionally, loss of this vascular signal impaired Purkinje-cell firing, diminished parallel-fiber input, reduced synapse formation from both parallel and climbing fibers, and disrupted long-term plasticity. These findings reveal a key instructive role for blood vessels in shaping cerebellar architecture and establishing functional circuit connectivity.