Venous endothelin guides sympathetic innervation of the developing mouse heart.

The mechanisms responsible for establishing correct target innervation during organ development are largely unknown. Sympathetic nerves follow blood vessels--typically arteries--to reach their endorgans, suggesting the existence of vascular guidance cues that direct axonal extension. The sinoatrial node and the ventricle of the heart receive sympathetic innervation from the stellate ganglia (STG). Here we show that STG axons follow veins, specifically the superior vena cavae and sinus venosus, to reach these targets. We find that election of these routes is determined by venous endothelium-derived endothelin-1, acting through its specific receptor Ednra expressed within a subpopulation of STG neurons. Furthermore, we demonstrate that Edn1-Ednra signalling is essential for functional regulation of the heart by sympathetic nerves. Our findings present venous Edn1 as a sympathetic guidance cue, and show how axon guidance mechanisms are coordinated with endorgan morphogenesis.