[Visualization of phosphorylation events occurring in the intermediate filaments].

Glial fibrillary acidic protein (GFAP) is a component of glial filaments specific to astroglia. We now report the spatial and temporal distributions of four phosphorylated sites in the GFAP molecule during mitosis of astroglial cells, determined by antibodies which can distinguish phosphorylated-epitopes from non-phosphorylated-epitopes. Immunofluorescence microscopy showed that the Ser-8 residues in the entire cytoplasmic glial filament system are initially phosphorylated when the cells enter mitosis. In cytokinesis, the phospho Ser-8 residues become dephosphorylated, whereas Thr-7, Ser-13 and Ser-34 in glial filaments at the cleavage furrow become the preferred sites of phosphorylation. These results suggest that multiple glial filament kinases are activated with different time schedules in astroglial cells.