Integrin α6 (green) is returned to the cell surface from recycling endosomes (red).

On page 545, Strachan and Condic show that neural crest cells (NCCs) can be speedy if they remember to recycle receptors. The speed gained from their conservation efforts may expose them to differentiation pathways that other NCCs miss out on.

Populations of NCCs differ in their speed on various matrices. Cranial NCCs, for instance, pick up speed on higher concentrations on laminin, whereas trunk NCCs keep a slow pace. The new results show that the cranial population is able to move quickly because they both recycle and reduce the numbers of their laminin-binding integrin receptors.

More laminin might actually slow cells by promoting strong adhesions. But cranial NCCs avoided this slowdown by removing laminin receptors (integrin α6) from the cell surface. The removed α6 receptors were internalized into recycling endosomes and sent back to the surface. Through this recycling pathway, receptors that are freed from adhesions at the trailing edge may be quickly moved to the leading edge, where new adhesions are needed. Indeed, inhibition of α6 receptor recycling slowed NCC migration on high concentrations of laminin, but had no affect on low laminin levels.

On fibronectin, which binds to integrin α5, the surface levels of integrins α5 and α6 were unchanged, and α5 recycling was not increased. The lack of α5 recycling may explain why the speed of cranial NCCs does not vary based on fibronectin concentrations.

Integrin recycling may explain in part how some sets of NCCs acquire their fate. Upon emerging from the neural tube, NCCs migrate throughout the body and differentiate into cell types as varied as bone, nerves, and pigment cells. NCCs that move quickly on laminin may receive one set of differentiation instructions at their destination. By the time latecomers arrive, the environment may have changed such that these NCCs are told to adopt a different fate.