Given the similar anatomies of vertebrate nerves, blood vessels and lymphatics, it is not surprising that guidance cues such as the netrins, which were discovered as molecules involved in axon pathfinding, also guide vessels. But do nerves and vessels share patterning mechanisms or do axons provide guidance for vessels? The laboratories of Dean Li, Chi-Bin Chien and Brant Weinstein now report that zebrafish motoneurons are essential for vascular pathfinding (see ). Netrin 1a is required for the development of the parachordal chain (PAC), a string of endothelial cells that are precursors of the main zebrafish lymphatic vessel. Here, the researchers identify muscle pioneers at the horizontal myoseptum (HMS) as the source of Netrin 1a for PAC formation. netrin 1a and dcc (which encodes the Netrin receptor) are required for the sprouting of the rostral primary axons and neighbouring axons along the HMS, they report, and genetic removal or laser ablation of these motoneurons prevents PAC formation. Together, these results reveal a direct requirement for axons in vascular guidance.
