Nervous chemokines

Guidance molecules from the immune and nervous systems are getting mixed up in each others business. Yan Zhu, Yi Rao (Washington University, St. Louis, MO), and colleagues have found that a leukocyte attractant called stromal-derived factor 1 (SDF-1) is the main factor that entices embryonic cerebellar neurons to their correct location.

SDF-1 is a chemokine—a peptide that attracts leukocytes by activating a G protein signaling cascade. In contrast, neuronal guidance molecules such as the netrins, ephrins, and Slit are proteins that bind single transmembrane receptors linked to a variety of downstream signaling pathways. The two worlds were bridged last year when Rao found that the neuronal repellant Slit could also inhibit leukocyte chemotaxis. Now, he has completed the loop by confirming SDF-1's function in the brain.

This function was suspected when immunologists made mice lacking SDF-1 and...