Figure 1.

Schwann cells and Schwann cell precursors are endowed with significant plasticity. (a) Schwann cell precursors derive from the neural crest and maintain some of the neural crest’s multipotency. They can act as multipotent progenitors for several glia and nonglial cell types such as odontoblasts, melanocytes, autonomic neurons, chondrocytes, endoneurial fibroblasts, chromaffin cells, and enteric glia. Enteric glia are shown in detail in panel b. Schwann cell precursors’ main function is to develop into immature and then myelinating or nonmyelinating Schwann cells, which fulfill the canonical functions of axonal ensheathment and myelination. In a process known as axonal sorting, large axons that are destined to be myelinated, such as motor axons or sensory axons that transmit positional information, are segregated by immature Schwann cells from axon bundles into a 1:1 Schwann cell relationship (promyelinating Schwann cells) and finally wrapped by multiple layers of membrane to form the myelin sheath. Nonmyelinating Schwann cells form Remak bundles by ensheathing the small-caliber axons (e.g., sensory axons that transmit pain and temperature information) that remain after the large axons have been sorted out.