The Journal of Neuroscience, August 15, 2002, 22(16):6972-6979
Protective Role of Phosphorylation in Turnover of Glial
Fibrillary Acidic Protein in Mice
Masaaki
Takemura1, 3,
Hiroshi
Gomi1,
Emma
Colucci-Guyon2, and
Shigeyoshi
Itohara1
1 Laboratory for Behavioral Genetics, RIKEN Brain
Science Institute, Wako 351-0198, Japan, 2 Unité de
Biologie du Développement, Institut Pasteur, Centre National de
la Recherche Scientifique Unité de Recherche Associée 1960, 75015 Paris, France, and 3 Institute for Virus Research,
Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
Glial fibrillary acidic protein (GFAP), the principal intermediate
filament (IF) protein of mature astrocytes in the CNS, plays
specific roles in astrocyte functions. GFAP has multiple phosphorylation sites at its N-terminal head domain. To examine the
role of phosphorylation at these sites, we generated a series of
substitution mutant mice in which phosphorylation sites (Ser/Thr) were replaced by Ala, in different combinations.
Gfaphm3/hm3 mice carrying
substitutions at all five phosphorylation sites showed extensive
decrease in both filament formation and amounts of GFAP.
Gfaphm1/hm1 and
Gfaphm2/hm2 mice, which carry
substitutions at three of five sites and in different combinations,
showed differential phenotypes. Although Gfaphm3/hm3 mice retained GFAP
filaments in Bergmann glia in the cerebellum, the
(Gfaphm3/hm3:Vim
/)
mice lacked GFAP filaments. Pulse-chase experiments of cultured astrocytes indicated that the Hm3-GFAP encoded by
Gfaphm3 was unstable particularly in
the absence of vimentin, another IF protein. These results revealed the
role of phosphorylation in turnover of GFAP and a synergistic role of
GFAP and vimentin in the dynamics of glial filaments. The data further
suggest that each of the phosphorylated sites has a distinct impact on
the dynamics of GFAP.
Key words:
glial fibrillary acidic protein; GFAP; vimentin; phosphorylation; intermediate filament; astrocyte; filament formation; degradation; knock-in mice; gene targeting
Copyright © 2002 Society for Neuroscience 0270-6474/02/22166972-08$05.00/0
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