Characteristics of the rat C-6 glioma maintained in organ culture systems. Production of glial fibrillary acidic protein in the absence of gliofibrillogenesis

Cells from a cloned rat C-6 glioma cell line were cultured on collagen-coated coverslips for up to 30 days and on organ culture systems using sponge foam matrices or Millipore filter platforms up to 44 days. The light microscopic features throughout the period of observation were those of a relatively poorly differentiated small-cell glioma that did not form glial fibrils. Electron microscopy of the cell line originally obtained and of the same cells maintained in organ culture systems demonstrated only infrequent and sparse microfilaments and no glycogen rosettes. Immunofluorescence staining for glial fibrillary acidic (GFA) protein, a specific marker for fibrillary astrocytes, was positive in only an occasional cell in monolayer or suspension cell cultures, but was markedly positive in most cells maintained for 12–14 days on sponge foam matrices. These findings suggest that the production of GFA protein can occur in the absence of gliofibrillogenesis in an in vitro system that has been shown to favor differentiation, and that therefore the rat C-6 glioma cell line represents a still undifferentiated glial cell type with the potential to differentiate into fibrillary astrocytes.