To build a node

Neurons rely on different structures to ignite nerve impulses and to propel them along the axon. Dzhashiashvili et al. show on page 857 that these structures develop in distinct ways. One structure depends on internal signals, whereas the other receives guidance from glial cells that wrap the axon in a myelin sheath.

The two types of structures, axon initial segments (AISs) and nodes of Ranvier, are molecularly similar, carrying current-producing sodium channels, the adhesion molecule neurofascin186 (NF186), and the actin–membrane linker ankyrin G. AISs touch off an action potential, whereas the nodes relay it along the axon. Evidence suggested that the two structures formed differently, but researchers didn't know the details.

To determine how NF186 gets into place, the researchers created composites that contained part of this protein and part of ICAM1, an...