Figure 1.

Schematic representation of the neuronal cytoskeleton. The role of the membrane periodic cytoskeleton and of myosin-II in the control of the axonal circumferential contractility is emphasized. In mature neurons, a 1D membrane periodic skeleton is present not only in axons but also in a fraction of dendrites. In contrast, in the somatodendritic compartment, an actin-spectrin based 2D polygonal lattice is formed, resembling the expanded erythrocyte membrane skeleton. Phosphorylated myosin light chain is highly enriched at the axon initial segment, where it may participate in the regulation of axon diameter during action potential firing. In the axon shaft, circumferential and longitudinal axon tension may also result from the regulation of an actomyosin network that remains to be solved at the structural level. Adducin, and additional actin-binding proteins that might be associated to axonal actin rings, may further contribute to fine-tune axon diameter.