A dual role for βII-spectrin in axons

Overview & Synopsis

Spectrins have been known for a long time as submembrane structural proteins, but a study from Lorenzo et al. (1) demonstrates an unexpected role for a neuronal spectrin in axonal transport. Actin and spectrins form specialized submembrane scaffolds important for the morphogenesis, compartmentation, and mechanical properties in a range of differentiated cell types (2, 3). Spectrin assembles the submembrane scaffold that shapes red blood cells—in fact, it was named from the membranous ghosts (specter) of erythrocytes where it was first discovered (4). In these cells, spectrins arrange in a hexagonal pattern, connecting short actin nodes (5⇓–7), generating the toroidal shape of erythrocytes. Spectrins are tetramers made of 2 α- and 2 β-spectrin subunits (αI and βI in erythrocytes) that can stretch between 60 and 200 nm in length (8). The actin/spectrin scaffold thus provides flexibility and mechanical resistance to the large deformations that erythrocytes undergo along small capillaries (9).