Transcription Factors that Control Schwann Cell Development and myelination

Abstract

Abstract It is now well established that the continuous dialog between neuron and Schwann cell underlies the development, maintenance and regeneration of peripheral nerves (see Chapters 1 and 15). Most of the Schwann cells within the developing nerve, as well as the other glial cell types in the peripheral nervous system (PNS), such as the satellite cells, the teloglia and enteric glial cells, derive from the neural crest (Le Douarin et al., 1991; Anderson, 1997). Immature Schwann cells proliferate, migrate, invade, bundle and sort the axonal fibers of the embryonic nerve. This process continues until the Schwann cells ensheath individual larger caliber axons or multiple lower caliber axons. Schwann cells then cease to proliferate and commence to myelinate the larger axons, while the non-myelin-forming Schwann cells further ensheath multiple smaller axons resulting in the mature Schwann cell phenotypes observed in the nerves of adult animals (Webster, 1993). The differentiation of the two types of Schwann cells takes place during the first weeks of postnatal life in rodents. A number of distinct steps in the generation of mature Schwann cells can be distinguished. (i) Pluripotent neural crest stem cells must acquire a glial cell fate during entry into, or within the embryonic nerve. (ii) This glial cell population expands and invades the nerve bundle. (iii) Immature cells will adopt a promyelin-forming or a pro-nonmyelin-forming configuration with axons and cease to proliferate.