Characteristics of fish glial cells in culture: possible implications as to their lineage

Regeneration of injured central nervous system axons is largely dependent on the response of the associated nonneuronal glial cells to injury. Glial cells of the mammalian central nervous system, unlike those of fish, are apparently not conducive to axonal regeneration. While the lineage of rat glial cells is well characterized and its role in the support or inhibition of regenerative growth is beginning to be understood, little is known about fish glial cells. Accordingly, glial cells in cultures of adult goldfish brain and of newly hatched goldfish larvae were studied in an attempt to establish their lineage. The cells were identified by means of indirect immunofluorescence, using antibodies against fish astrocytes and oligodendrocytes. The cell count in the cultures increased from a small number of cells at 24 h after plating to a large number of both astrocytes and oligodendrocytes after 1 week in culture. Both of these cell types had originated from proliferating cells, as shown by their uptake of tritiated thymidine and by the inhibition of cell proliferation by 5-fluoro-2'-deoxyuridine. Both astrocytes, i.e., glial fibrillary acidic protein-positive cells, and oligodendrocytes, i.e., 6D2-positive cells, were positively labeled also by A2B5 antibodies, which are known to label progenitors of type-2 astrocytes and oligodendrocytes in the rat optic nerve. The results suggest that A2B5 positive progenitor cells in the goldfish central nervous system, as in the rat optic nerve, might be a common progenitor of astrocytes and oligodendrocytes.