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[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier.

Komada M, Soriano P - J. Cell Biol. (2002)

Bottom Line: In betaIV-spectrin- neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype.Conversely, in ankyrin-G- neurons, betaIV-spectrin is not localized to these sites.These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Biology and Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA. makomada@bio.titech.ac.jp

ABSTRACT
beta-Spectrin and ankyrin are major components of the membrane cytoskeleton. We have generated mice carrying a mutation in the betaIV-spectrin gene using gene trapping in embryonic stem cells. Mice homozygous for the mutation exhibit tremors and contraction of hindlimbs. betaIV-spectrin expression is mostly restricted to neurons, where it colocalizes with and binds to ankyrin-G at axon initial segments (AISs) and nodes of Ranvier (NR). In betaIV-spectrin- neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype. Conversely, in ankyrin-G- neurons, betaIV-spectrin is not localized to these sites. These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR.

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Localization of βIV-spectrin at AIS of ankyrin-G– neurons. Cerebellum (A, A′, B, and B′) and hippocampus (C and C′) of wild-type (A and A′) and cerebellum-specific ankyrin-G–  (B, B′, C, and C′) mice were stained with anti–ankyrin-G (A, B, and C) and anti–βIV-spectrin (A′, B′, and C′) antibodies. In D and E, Purkinje cells from wild-type (D) and ankyrin-G– (E) mice were double stained for bIV-spectrin (red) and calbindin D-28K (green), and are shown at higher magnification. The granular layer (G), Purkinje cell layer (P), and molecular layer (M) of the cerebellum are separated by dotted lines (A, A′, B, and B′). Purkinje cell bodies (Pu) are indicated in (D) and (E). Arrowheads indicate AIS of Purkinje cells (A, A′, and D). In B and B′, the contours of Purkinje cell bodies were observed in the absence of specific staining in the mutant due to background staining. Mice were killed at 5 wk of age. Bars, 50 μm.
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fig8: Localization of βIV-spectrin at AIS of ankyrin-G– neurons. Cerebellum (A, A′, B, and B′) and hippocampus (C and C′) of wild-type (A and A′) and cerebellum-specific ankyrin-G– (B, B′, C, and C′) mice were stained with anti–ankyrin-G (A, B, and C) and anti–βIV-spectrin (A′, B′, and C′) antibodies. In D and E, Purkinje cells from wild-type (D) and ankyrin-G– (E) mice were double stained for bIV-spectrin (red) and calbindin D-28K (green), and are shown at higher magnification. The granular layer (G), Purkinje cell layer (P), and molecular layer (M) of the cerebellum are separated by dotted lines (A, A′, B, and B′). Purkinje cell bodies (Pu) are indicated in (D) and (E). Arrowheads indicate AIS of Purkinje cells (A, A′, and D). In B and B′, the contours of Purkinje cell bodies were observed in the absence of specific staining in the mutant due to background staining. Mice were killed at 5 wk of age. Bars, 50 μm.

Mentions: Next, we examined whether localization of βIV-spectrin to AIS requires ankyrin-G. To test this, we examined the localization of βIV-spectrin in cerebellar neurons of mutant mice generated by Zhou et al. (1998) in which the cerebellum-specific form of ankyrin-G is knocked out. Compared with wild-type cerebellum where AIS of both Purkinje and granular neurons were positive for ankyrin-G and βIV-spectrin (Fig. 8, A , A′, and D), βIV-spectrin staining as well as ankyrin-G staining was mostly lost in the knockout mice (Fig. 8, B, B′, and E). βIV-spectrin localization was normal in the mutant in other regions than the cerebellum, such as the hippocampus, where ankyrin-G was expressed (Fig. 8, C and C′; unpublished data), indicating that ankyrin-G is a prerequisite for the correct βIV-spectrin localization in AIS.


[Beta]IV-spectrin regulates sodium channel clustering through ankyrin-G at axon initial segments and nodes of Ranvier.

Komada M, Soriano P - J. Cell Biol. (2002)

Localization of βIV-spectrin at AIS of ankyrin-G– neurons. Cerebellum (A, A′, B, and B′) and hippocampus (C and C′) of wild-type (A and A′) and cerebellum-specific ankyrin-G–  (B, B′, C, and C′) mice were stained with anti–ankyrin-G (A, B, and C) and anti–βIV-spectrin (A′, B′, and C′) antibodies. In D and E, Purkinje cells from wild-type (D) and ankyrin-G– (E) mice were double stained for bIV-spectrin (red) and calbindin D-28K (green), and are shown at higher magnification. The granular layer (G), Purkinje cell layer (P), and molecular layer (M) of the cerebellum are separated by dotted lines (A, A′, B, and B′). Purkinje cell bodies (Pu) are indicated in (D) and (E). Arrowheads indicate AIS of Purkinje cells (A, A′, and D). In B and B′, the contours of Purkinje cell bodies were observed in the absence of specific staining in the mutant due to background staining. Mice were killed at 5 wk of age. Bars, 50 μm.
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Related In: Results  -  Collection

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fig8: Localization of βIV-spectrin at AIS of ankyrin-G– neurons. Cerebellum (A, A′, B, and B′) and hippocampus (C and C′) of wild-type (A and A′) and cerebellum-specific ankyrin-G– (B, B′, C, and C′) mice were stained with anti–ankyrin-G (A, B, and C) and anti–βIV-spectrin (A′, B′, and C′) antibodies. In D and E, Purkinje cells from wild-type (D) and ankyrin-G– (E) mice were double stained for bIV-spectrin (red) and calbindin D-28K (green), and are shown at higher magnification. The granular layer (G), Purkinje cell layer (P), and molecular layer (M) of the cerebellum are separated by dotted lines (A, A′, B, and B′). Purkinje cell bodies (Pu) are indicated in (D) and (E). Arrowheads indicate AIS of Purkinje cells (A, A′, and D). In B and B′, the contours of Purkinje cell bodies were observed in the absence of specific staining in the mutant due to background staining. Mice were killed at 5 wk of age. Bars, 50 μm.
Mentions: Next, we examined whether localization of βIV-spectrin to AIS requires ankyrin-G. To test this, we examined the localization of βIV-spectrin in cerebellar neurons of mutant mice generated by Zhou et al. (1998) in which the cerebellum-specific form of ankyrin-G is knocked out. Compared with wild-type cerebellum where AIS of both Purkinje and granular neurons were positive for ankyrin-G and βIV-spectrin (Fig. 8, A , A′, and D), βIV-spectrin staining as well as ankyrin-G staining was mostly lost in the knockout mice (Fig. 8, B, B′, and E). βIV-spectrin localization was normal in the mutant in other regions than the cerebellum, such as the hippocampus, where ankyrin-G was expressed (Fig. 8, C and C′; unpublished data), indicating that ankyrin-G is a prerequisite for the correct βIV-spectrin localization in AIS.

Bottom Line: In betaIV-spectrin- neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype.Conversely, in ankyrin-G- neurons, betaIV-spectrin is not localized to these sites.These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR.

View Article: PubMed Central - PubMed

Affiliation: Program in Developmental Biology and Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA. makomada@bio.titech.ac.jp

ABSTRACT
beta-Spectrin and ankyrin are major components of the membrane cytoskeleton. We have generated mice carrying a mutation in the betaIV-spectrin gene using gene trapping in embryonic stem cells. Mice homozygous for the mutation exhibit tremors and contraction of hindlimbs. betaIV-spectrin expression is mostly restricted to neurons, where it colocalizes with and binds to ankyrin-G at axon initial segments (AISs) and nodes of Ranvier (NR). In betaIV-spectrin- neurons, neither ankyrin-G nor voltage-gated sodium channels (VGSC) are correctly clustered at these sites, suggesting that impaired action potential caused by mislocalization of VGSC leads to the phenotype. Conversely, in ankyrin-G- neurons, betaIV-spectrin is not localized to these sites. These results indicate that betaIV-spectrin and ankyrin-G mutually stabilize the membrane protein cluster and the linked membrane cytoskeleton at AIS and NR.

Show MeSH
Related in: MedlinePlus