Schwann cells don caps, touch nodes

In vertebrates, axons are covered with an insulating myelin sheath, punctuated by gaps called nodes of Ranvier where voltage-gated sodium channels cluster. The nodes are essential for propagating action potentials along the axon, but little is known about how they develop. Gatto et al. (page 489) imaged live cell cultures to watch Schwann cells myelinate explanted dorsal root ganglia and discovered a novel growth cone–like structure on the Schwann cells that appears to mediate node formation.

Previous studies have produced a controversy, since the development of nodes seems to require direct contact between Schwann cells and axons in some in vitro systems, but not in others. The authors used a new approach to transfect cultured Schwann cells with fluorescently labeled proteins and watch myelination using time-lapse videography. The Schwann cells initially migrate along axons...