Glial-defined boundaries in Xenopus CNS.

Regional specificity, which arises early during central nervous system (CNS) development, reflects the generation of boundary regions that define the domains of distinct neural cell types and the guidance of axonal growth. The boundaries between discrete CNS domains often appear to be established by specialized glial cells. Boundary glia have been implicated in supporting neurite extension by providing mechanical and chemical barriers during development and regeneration. The present study demonstrates biochemical and morphological differences in boundary glial cells in the hindbrain and spinal cord of developing Xenopus laevis. DM gamma, a membrane protein of the proteolipid protein family, is localized to radial glial processes in hindbrain boundary regions. By contrast, DM beta, a neuronal protein that bears significant homology to DM gamma in primary sequence and that promotes neurite outgrowth, is expressed in hindbrain axonal pathways. In addition, the expression of two intermediate filament proteins, glial fibrillary acidic protein and vimentin, are progressively restricted to glial cells in the rhombomere center and boundary regions, respectively. Those two intermediate filament proteins show distinct expression domains in the spinal cord as well. The present study suggests that a glial surface protein, DM gamma, may act as a boundary molecule in developing Xenopus hindbrain and that a distinct subpopulation of glial cells may define functional domains within the CNS. Copyright 2001 S. Karger AG, Basel