The first blood vessel formed in the embryo — the dorsal aorta — coordinates the formation of the sympathetic nervous system and the medulla of the adrenal gland, both of which marshal the body's fight-or-flight response.
The nervous system and the adrenal medulla are derived from progenitor neural-crest cells — some of which migrate towards the dorsal aorta during early development. Yoshiko Takahashi of Kyoto University in Japan and her colleagues studied developing chick and mouse embryos and found that the dorsal aorta secretes bone morphogenetic proteins. These stimulate the production of signalling molecules that, in turn, attract some of the neural-crest cells. Bone morphogenetic proteins are then involved in the formation of the separate lineages that give rise to the adrenal gland and the sympathetic nervous system.