Specific localization of phosphointermediate filament protein in the constricted area of dividing cells.

We developed antibodies pG1 and pG2 which recognize glial fibrillary acidic protein (GFAP) in its phosphorylated state. Antibodies pG1 and pG2 were produced against two synthetic peptides, Arg-Arg-Arg-Val-Thr-phosphoSer-Ala-Ala-Arg-Arg-phosphoSer (residues 3-13) and Pro-Gly-Pro-Arg-Leu-phosphoSer-Leu-Ala-Arg-Met-Pro (residues 29-39), respectively. The phosphorylation of these serine residues on the intact GFAP induces disassembly of glial filaments in vitro (Inagaki, M., Gonda, Y., Nishizawa, K., Kitamura, S., Sato, C., Ando, S., Tanabe, K., Kikuchi, K., Tsuiki, S., and Nishi, Y. (1990) J. Biol. Chem. 265, 4722-4729). Immunofluorescence and immunoblotting studies demonstrate that both antibodies react specifically with mitotic astroglial cells, thereby supporting the notion that increased phosphorylation during mitosis may directly influence intracellular organization of the glial filaments. The specific distribution pattern of the phosphoGFAP in the mitotic cells reveals that site-specific phosphorylation events may make way for the locally controlled breakdown of glial filaments in the constricted area, before the final separation of daughter cells.