Mutually exclusive expression of fibronectin and glial fibrillary acidic protein in cultured brain cells

The reported expression of the cell surface-associated, mainly mesenchymal glycoprotein fibronectin by cultured glial cells is in discrepancy with recent work on brain tissue failing to demonstrate any glial or neuronal fibronectin. We have investigated the expression of fibronectin in relation to glial fibrillary acidic protein in cultured human glial and glioma cell lines as well as in cultures derived from newborn rat brain. Using double immunofluorescence technique we found that cells containing glial fibrillary acidic protein do not express fibronectin, and vice versa. The only exception to this rule was the occasional finding of fibronectin at points of cell-to-cell adhesion also in relation to cells containing glial fibrillary acidic protein. The results were also tested by polyacrylamide gel electrophoresis of the culture media of the human cell lines, and by subcultures from the brain of newborn rat, cultures stimulated with dibutyryl cyclic AMP (db-cAMP), and by vinblastine treatment of the cells. The lack of expression of fibronectin in cells containing glial fibrillary acidic protein, a gliospecific cytoskeletal protein, is discussed with reference to glio-mesenchymal interactions and glial markers in vitro.