Axons glial role

Certain enzymes shown to be present in myelin could be involved in ion transport. Carbonic anhydrase has generally been considered a soluble enzyme and a glial marker but myelin accounts for a large part of the membrane-bound form in brain. This enzyme may play a role in removal of carbonic acid from metabolically active axons. The enzymes 5 -nucleotidase and Na+, K+-ATPase have long been considered specific markers for plasma membranes and are found in myelin at low levels. The 5 -nucleotidase activity may be related to a transport mechanism for adenosine, and Na+, K+-ATPase could well be involved in transport of monovalent cations. The presence of these enzymes suggests that myelin may have an active role in ion transport in and out of the axon. In connection with this hypothesis, it is of interest that the PLP gene family may have evolved from a pore-forming polypeptide [9],... 

Cell adhesion molecules (CAMs) play critical roles in all facets of nervous system development and maintenance. Important phenomena in which CAMs are involved include initial formation of the neural tube and the neural crest, migration of all neurons and glial cells, axonal outgrowth and guidance, target selection, synaptic stabilization and plasticity, myelination and nerve regeneration after injury (see Chs 4,24,28-30 and 53). Adhesion molecules interact with each other and with nonadhesive cell-surface and/or cytoplasmic molecules, and, in the two... 

Snow, D. M., Steindler, D. A., and Silver, J., Molecular and cellular characterisation of the glial roof plate of the spinal cord and optic tectum. A possible role for a proteoglycan in the development of an axonal barrier, Dev. Biol., 138, 359, 1990. 

Tomac, A., Widenfalk, J., Lin, L. F., Kohno, T., Ebendal, T., Hoffer, B. J., and Olson, L., Retrograde axonal transport of glial cell line-derived neurotrophic factor in the adult nigrostriatal system suggests a trophic role in the adult, I roc. Natl. Acad. Sci. U.S.A., 92, 8274, 1995. 

The cellular studies discussed in Section 3.4.3 provide evidence for a role for glia in guiding axons in insect embryos. To date, however, there are no well-documented examples of molecules that may subserve this function. The case of the DER protein in the Drosophila embryo has been discussed above. Some proteins, such as fasciclin in (see Section 5.1.1) and neuroglian (Section 5.3), are expressed on glia as well as on neurons, but their glial function has not been determined. Oth-... 

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