Downloaded from http://cshperspectives.cshlp.org/ on September 23, 2021 - Published by Cold Spring Harbor Laboratory Press Perineurial Glia Sarah Kucenas Department of Biology, University of Virginia, Charlottesville, Virginia 22904 Correspondence:
[email protected] Although the ultrastructure of peripheral nerves has been known for nearly 200 years, the developmental origins and functional roles of all five main components of these specialized nervous system conduits are still poorly understood. One of these understudied nerve ele- ments, the perineurium, is a component of the blood–nerve barrier and is essential for protecting axons and their associated Schwann cells from ionic flux, toxins, and infection. However, until recently, it was thought that this vital nerve tissue was derived from the mesoderm and simply served a structural/barrier function with no other influence on the development, maintenance, or regeneration of peripheral nerves. Recent work in zebrafish using in vivo time-lapse imaging, genetic manipulation, and laser axotomy is shedding light on the origin and roles of this previously ignored glial nerve component and is changing how we view development of the nervous system. ll nerves of the peripheral nervous system linated, whereas smaller diameter axons are of- A(PNS) are structurally identical, consist- ten associated within nonmyelinating Schwann ing of five main components (Fig. 1) (Gamble cells known as Remak bundles (Fig. 1). These and Eames 1964; Cravioto 1965; Shantha and axon–Schwann cell complexes reside within Bourne 1968; Akert et al. 1976; Nordlander et the endoneurium, a neural crest–derived tissue, al.1981). Centralto all sensoryand motor nerves which synthesizes and secrets extracellular ma- are axons.