Neuropilin 1 (NRP1) conveys SEMA3A signals to restrict physiological angiogenesis

The class 3 semaphorin SEMA3A is a secreted glycoprotein that serves as an evolutionary conserved axon repellent with proposed vascular functions. In mice, SEMA3A promotes vascular permeability in adults, but is dispensable for developmental brain, limb or trunk blood vessel patterning. By contrast, Sema3a restricts vessel branching in zebrafish embryo trunks. Whereas neuropilin 1 (NRP1) is thought to be the SEMA3A receptor in the mouse, prior reports identified Plxnd1 as the Sema3a receptor for zebrafish trunk vessel patterning, with no reported role for the zebrafish NRP1 orthologues, Nrp1a and Nrp1b, in this process. However, knockdown and knockout studies have yielded contradictory results on Nrp1 requirement for vessel patterning in zebrafish. To resolve conflicting prior information, we have refined the prior knockdown strategy to limit off target effects and generated mutant zebrafish embryos lacking both Nrp1a and Nrp1b to show that Nrp1 restricts trunk vessel patterning in a Sema3a-dependent manner. Moreover, we show that Nrp1 and Sema3a action does not involve the splicing regulation of Flt1, previously proposed to act downstream of Plxnd1, to restrict pro-angiogenic signals from the vascular endothelial growth factor VEGFA. In agreement, NRP1 is required in human endothelial cells for SEMA3A-induced repulsion. Together, these findings demonstrate that NRP1 mediates repulsive SEMA3A cues in endothelial cells to shape physiological vascular morphogenesis, in analogy to its role in axon guidance.