INTERMEDIATE FILAMENTS REMINISCENT OF IMMATURE CELLS EXPRESSED BY GOLDFISH (CARASSIUS-AURATUS) ASTROCYTES AND OLIGODENDROCYTES IN-VITRO

The expression of intermediate filaments is developmentally regulated. In the mammalian embryo keratins are the first to appear, followed by vimentin, while the principal intermediate filament of the adult brai n is glial fibrillary acidic protein. The intermediate filaments expre ssed by a cell thus reflect its state of differentiation. The differen tiation state of cells, and especially of glial cells, in turn determi nes their ability to support axonal growth. In this study we used thre e new antibodies directed against three fish intermediate filaments (g lial fibrillary acidic protein, keratin 8 and vimentin), in order to d etermine the identity and level of expression of intermediate filament s present in fish glial cells in culture. We found that fish astrocyte s and oligodendrocytes are both able to express keratin 8 and vimentin . We further demonstrate that under proliferative conditions astrocyte s express high keratin 8 levels and most oligodendrocytes also express keratin 8, whereas under nonproliferative conditions the astrocytes e xpress only low keratin 8 levels and most oligodendrocytes do not expr ess keratin 8 at all. These results suggest that the fish glial cells retain characteristics of immature cells. The findings are also discus sed in relation to the fish glial lineage.