BEHAVIOR OF MACROGLIAL CELLS, AS IDENTIFIED BY THEIR INTERMEDIATE FILAMENT COMPLEMENT, DURING OPTIC-NERVE REGENERATION OF XENOPUS TADPOLE

Assessment of glial cell behaviour during optic nerve (ON) regeneratio n in Xenopus tadpoles is hampered by the lack of classical cellular ma rkers that distinguish different glial cells in mammals. We thus have characterized the intermediate filament (IF) complement of tadpole gli al cells and used it to follow the fate of glial cell subsets during t he first 10 days after ON crush. Glial cells synthesize a restricted n umber of cytokeratin (CK) species and vimentin. This pattern remains e ssentially unchanged during metamorphosis and regeneration. However, v imentin turnover is specifically enhanced after injury. The expression of CKs and vimentin has been followed immunocytochemically in situ an d in isolated cells recovered from dissociated ON segments. In the nor mal nerve, 79% of ramified glial cells express both CK and vimentin, 1 % CK and 4% vimentin only, whereas 16% express neither IF protein. We tentatively classified CK expressing cells as mature astrocytes and th ose without IF proteins as oligodendrocytes. In the regenerating ON, t he relative number of oligodendrocytes is decreased, while the astrocy tic subset becomes accordingly larger but is decreased by day 10 alrea dy in favour of cells expressing vimentin only. Astrocytes invade the lesion site soon after crush, arrange into a central core within the d istal nerve segment and establish a peripheral scaffold that is readil y crossed by axons. Unlike mammalian astrocytes that remain absent fro m the lesion site but form a scar at some distance to it, amphibian as trocytes appear to provide active guidance to axons growing through th e lesion site. (C) 1995 Wiley-Liss, Inc.