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Synbindin, A novel syndecan-2-binding protein in neuronal dendritic spines.

Ethell IM, Hagihara K, Miura Y, Irie F, Yamaguchi Y - J. Cell Biol. (2000)

Bottom Line: This effect requires the COOH-terminal EFYA sequence of syndecan-2, suggesting that cytoplasmic molecules interacting with this sequence play a critical role in spine morphogenesis.Our results show that synbindin is a physiological syndecan-2 ligand on dendritic spines.We suggest that syndecan-2 induces spine formation by recruiting intracellular vesicles toward postsynaptic sites through the interaction with synbindin.

View Article: PubMed Central - PubMed

Affiliation: The Burnham Institute, La Jolla, California 92037, USA.

ABSTRACT
Dendritic spines are small protrusions on the surface of dendrites that receive the vast majority of excitatory synapses. We previously showed that the cell-surface heparan sulfate proteoglycan syndecan-2 induces spine formation upon transfection into hippocampal neurons. This effect requires the COOH-terminal EFYA sequence of syndecan-2, suggesting that cytoplasmic molecules interacting with this sequence play a critical role in spine morphogenesis. Here, we report a novel protein that binds to the EFYA motif of syndecan-2. This protein, named synbindin, is expressed by neurons in a pattern similar to that of syndecan-2, and colocalizes with syndecan-2 in the spines of cultured hippocampal neurons. In transfected hippocampal neurons, synbindin undergoes syndecan-2-dependent clustering. Synbindin is structurally related to yeast proteins known to be involved in vesicle transport. Immunoelectron microscopy localized synbindin on postsynaptic membranes and intracellular vesicles within dendrites, suggesting a role in postsynaptic membrane trafficking. Synbindin coimmunoprecipitates with syndecan-2 from synaptic membrane fractions. Our results show that synbindin is a physiological syndecan-2 ligand on dendritic spines. We suggest that syndecan-2 induces spine formation by recruiting intracellular vesicles toward postsynaptic sites through the interaction with synbindin.

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Syndecan-2–mediated clustering of synbindin requires the COOH-terminal EFYA motif. (A–D) Hippocampal neurons cotransfected with synbindin-GFP and intact syndecan-2 were immunostained with anti–synapsin I antibody. Cells were examined at 8 DIV for the distribution of synbindin (visualized with GFP fluorescence) and synapsin I (visualized with RITC-labeled secondary antibody) on a confocal microscopy. (A, red) Synapsin I; (B, green) synbindin-GFP; and (C and D) superimposed views. Note that synbindin-GFP exhibits a partial overlapping with synapsin I puncta along dendrites. (E–H) Hippocampal neurons were cotransfected with synbindin-GFP and the syndecan-2ΔEFYA deletion mutant, and were examined as described above. (E, red) Synapsin I; (F, green) synbindin-GFP; (G and H) superimposed views. Note that synbindin-GFP is distributed diffusely in dendritic shafts and the cell body without clustering. No overlapping with synapsin I puncta are observed. Bars: (A–C and E–G) 20 μm; (D and H) 10 μm.
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Figure 4: Syndecan-2–mediated clustering of synbindin requires the COOH-terminal EFYA motif. (A–D) Hippocampal neurons cotransfected with synbindin-GFP and intact syndecan-2 were immunostained with anti–synapsin I antibody. Cells were examined at 8 DIV for the distribution of synbindin (visualized with GFP fluorescence) and synapsin I (visualized with RITC-labeled secondary antibody) on a confocal microscopy. (A, red) Synapsin I; (B, green) synbindin-GFP; and (C and D) superimposed views. Note that synbindin-GFP exhibits a partial overlapping with synapsin I puncta along dendrites. (E–H) Hippocampal neurons were cotransfected with synbindin-GFP and the syndecan-2ΔEFYA deletion mutant, and were examined as described above. (E, red) Synapsin I; (F, green) synbindin-GFP; (G and H) superimposed views. Note that synbindin-GFP is distributed diffusely in dendritic shafts and the cell body without clustering. No overlapping with synapsin I puncta are observed. Bars: (A–C and E–G) 20 μm; (D and H) 10 μm.

Mentions: To determine the localization of the synbindin clusters, we performed a series of double labeling experiments. These experiments demonstrated that the synbindin clusters observed in synbindin/syndecan-2 double-transfected neurons are localized in dendritic spines. As shown in Fig. 3, double staining with anti-MAP2 antibody demonstrated that the clusters of synbindin-GFP are localized in small protrusions along dendrites (Fig. 3, G–J). Double staining with the anti–synapsin I antibody revealed that synbindin clusters exhibit partial overlap with synapsin I immunoreactivities (Fig. 4, A–D), a pattern typically seen for postsynaptic proteins (Niethammer et al. 1998; Ethell and Yamaguchi 1999).


Synbindin, A novel syndecan-2-binding protein in neuronal dendritic spines.

Ethell IM, Hagihara K, Miura Y, Irie F, Yamaguchi Y - J. Cell Biol. (2000)

Syndecan-2–mediated clustering of synbindin requires the COOH-terminal EFYA motif. (A–D) Hippocampal neurons cotransfected with synbindin-GFP and intact syndecan-2 were immunostained with anti–synapsin I antibody. Cells were examined at 8 DIV for the distribution of synbindin (visualized with GFP fluorescence) and synapsin I (visualized with RITC-labeled secondary antibody) on a confocal microscopy. (A, red) Synapsin I; (B, green) synbindin-GFP; and (C and D) superimposed views. Note that synbindin-GFP exhibits a partial overlapping with synapsin I puncta along dendrites. (E–H) Hippocampal neurons were cotransfected with synbindin-GFP and the syndecan-2ΔEFYA deletion mutant, and were examined as described above. (E, red) Synapsin I; (F, green) synbindin-GFP; (G and H) superimposed views. Note that synbindin-GFP is distributed diffusely in dendritic shafts and the cell body without clustering. No overlapping with synapsin I puncta are observed. Bars: (A–C and E–G) 20 μm; (D and H) 10 μm.
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Figure 4: Syndecan-2–mediated clustering of synbindin requires the COOH-terminal EFYA motif. (A–D) Hippocampal neurons cotransfected with synbindin-GFP and intact syndecan-2 were immunostained with anti–synapsin I antibody. Cells were examined at 8 DIV for the distribution of synbindin (visualized with GFP fluorescence) and synapsin I (visualized with RITC-labeled secondary antibody) on a confocal microscopy. (A, red) Synapsin I; (B, green) synbindin-GFP; and (C and D) superimposed views. Note that synbindin-GFP exhibits a partial overlapping with synapsin I puncta along dendrites. (E–H) Hippocampal neurons were cotransfected with synbindin-GFP and the syndecan-2ΔEFYA deletion mutant, and were examined as described above. (E, red) Synapsin I; (F, green) synbindin-GFP; (G and H) superimposed views. Note that synbindin-GFP is distributed diffusely in dendritic shafts and the cell body without clustering. No overlapping with synapsin I puncta are observed. Bars: (A–C and E–G) 20 μm; (D and H) 10 μm.
Mentions: To determine the localization of the synbindin clusters, we performed a series of double labeling experiments. These experiments demonstrated that the synbindin clusters observed in synbindin/syndecan-2 double-transfected neurons are localized in dendritic spines. As shown in Fig. 3, double staining with anti-MAP2 antibody demonstrated that the clusters of synbindin-GFP are localized in small protrusions along dendrites (Fig. 3, G–J). Double staining with the anti–synapsin I antibody revealed that synbindin clusters exhibit partial overlap with synapsin I immunoreactivities (Fig. 4, A–D), a pattern typically seen for postsynaptic proteins (Niethammer et al. 1998; Ethell and Yamaguchi 1999).

Bottom Line: This effect requires the COOH-terminal EFYA sequence of syndecan-2, suggesting that cytoplasmic molecules interacting with this sequence play a critical role in spine morphogenesis.Our results show that synbindin is a physiological syndecan-2 ligand on dendritic spines.We suggest that syndecan-2 induces spine formation by recruiting intracellular vesicles toward postsynaptic sites through the interaction with synbindin.

View Article: PubMed Central - PubMed

Affiliation: The Burnham Institute, La Jolla, California 92037, USA.

ABSTRACT
Dendritic spines are small protrusions on the surface of dendrites that receive the vast majority of excitatory synapses. We previously showed that the cell-surface heparan sulfate proteoglycan syndecan-2 induces spine formation upon transfection into hippocampal neurons. This effect requires the COOH-terminal EFYA sequence of syndecan-2, suggesting that cytoplasmic molecules interacting with this sequence play a critical role in spine morphogenesis. Here, we report a novel protein that binds to the EFYA motif of syndecan-2. This protein, named synbindin, is expressed by neurons in a pattern similar to that of syndecan-2, and colocalizes with syndecan-2 in the spines of cultured hippocampal neurons. In transfected hippocampal neurons, synbindin undergoes syndecan-2-dependent clustering. Synbindin is structurally related to yeast proteins known to be involved in vesicle transport. Immunoelectron microscopy localized synbindin on postsynaptic membranes and intracellular vesicles within dendrites, suggesting a role in postsynaptic membrane trafficking. Synbindin coimmunoprecipitates with syndecan-2 from synaptic membrane fractions. Our results show that synbindin is a physiological syndecan-2 ligand on dendritic spines. We suggest that syndecan-2 induces spine formation by recruiting intracellular vesicles toward postsynaptic sites through the interaction with synbindin.

Show MeSH
Related in: MedlinePlus