Common mechanisms of nerve and blood vessel wiring : Nature:
Blood vessels and nerve fibres course throughout the body in an orderly pattern, often alongside one another. Although superficially distinct, the mechanisms involved in wiring neural and vascular networks seem to share some deep similarities. The discovery of key axon guidance molecules over the past decade has shown that axons are guided to their targets by finely tuned codes of attractive and repulsive cues, and recent studies reveal that these cues also help blood vessels to navigate to their targets. Parallels have also emerged between the actions of growth factors that direct angiogenic sprouting and those that regulate axon terminal arborization.
During evolution, organisms have come to perform more specialized tasks, requiring an increased degree of information processing by neurons and supply of nutrients by blood vessels. Wiring of neuronal axons and blood vessels into functional circuits is therefore of utmost importance. The complexity of this task is underscored by the high degree of orderly patterning of the neural and vascular networks. The choreographed morphogenesis of both networks suggests that they are directed by genetically programmed mechanisms. Five centuries ago, Andreas Vesalius illustrated the parallels in the stereotyped branching patterns of vessels and nerves (Fig. 1a, b). Today, evidence is emerging that blood vessels, which arose later in evolution than nerves, co-opted several of the organizational principles and molecular mechanisms that evolved to wire up the nervous system. In this review, we highlight these common morphogenetic signals and mechanisms, and illustrate how intricately the navigational mechanisms for both systems are intertwined.
Co-opting of existing pathways is a common occurrence in evolution. This is all about testing evolutionary hypotheses.