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Molecular dissection of the photoreceptor ribbon synapse: physical interaction of Bassoon and RIBEYE is essential for the assembly of the ribbon complex.

tom Dieck S, Altrock WD, Kessels MM, Qualmann B, Regus H, Brauner D, Fejtová A, Bracko O, Gundelfinger ED, Brandstätter JH - J. Cell Biol. (2005)

Bottom Line: Identifiable CAZ proteins segregate into two compartments at the ribbon: a ribbon-associated compartment including Piccolo, RIBEYE, CtBP1/BARS, RIM1, and the motor protein KIF3A, and an active zone compartment including RIM2, Munc13-1, a Ca2+ channel alpha1 subunit, and ERC2/CAST1.A direct interaction between the ribbon-specific protein RIBEYE and Bassoon seems to link the two compartments and is responsible for the physical integrity of the photoreceptor ribbon complex.Finally, we found the RIBEYE homologue CtBP1 at ribbon and conventional synapses, suggesting a novel role for the CtBP/BARS family in the molecular assembly and function of central nervous system synapses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroanatomy, Max Planck Institute for Brain Research, D-60528 Frankfurt/Main, Germany.

ABSTRACT
The ribbon complex of retinal photoreceptor synapses represents a specialization of the cytomatrix at the active zone (CAZ) present at conventional synapses. In mice deficient for the CAZ protein Bassoon, ribbons are not anchored to the presynaptic membrane but float freely in the cytoplasm. Exploiting this phenotype, we dissected the molecular structure of the photoreceptor ribbon complex. Identifiable CAZ proteins segregate into two compartments at the ribbon: a ribbon-associated compartment including Piccolo, RIBEYE, CtBP1/BARS, RIM1, and the motor protein KIF3A, and an active zone compartment including RIM2, Munc13-1, a Ca2+ channel alpha1 subunit, and ERC2/CAST1. A direct interaction between the ribbon-specific protein RIBEYE and Bassoon seems to link the two compartments and is responsible for the physical integrity of the photoreceptor ribbon complex. Finally, we found the RIBEYE homologue CtBP1 at ribbon and conventional synapses, suggesting a novel role for the CtBP/BARS family in the molecular assembly and function of central nervous system synapses.

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Screening the photoreceptor ribbon synaptic complex for ribbon-associated proteins in wild-type (+/+) and Bassoon mutant (−/−) retinae. (Left) Confocal laser-scanning micrographs of photoreceptor ribbons in the +/+ retina double labeled for RIBEYE combined with the following CAZ proteins: Piccolo, KIF3A, RIM1, RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. All CAZ proteins colocalize with RIBEYE as seen in the merge of the stainings. (Right) In the −/− retina, Piccolo, KIF3A, and RIM1 colocalize with RIBEYE, but not RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. Bars, 5 μm.
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fig2: Screening the photoreceptor ribbon synaptic complex for ribbon-associated proteins in wild-type (+/+) and Bassoon mutant (−/−) retinae. (Left) Confocal laser-scanning micrographs of photoreceptor ribbons in the +/+ retina double labeled for RIBEYE combined with the following CAZ proteins: Piccolo, KIF3A, RIM1, RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. All CAZ proteins colocalize with RIBEYE as seen in the merge of the stainings. (Right) In the −/− retina, Piccolo, KIF3A, and RIM1 colocalize with RIBEYE, but not RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. Bars, 5 μm.

Mentions: With immunocytochemistry and confocal laser-scanning microscopy, we screened in wild-type photoreceptor terminals a number of presynaptic proteins for their localization as compared with RIBEYE and thus for their potential to interact with the photoreceptor ribbon. The proteins synaptotagmin, VGLUT1 (vesicular glutamate transporter 1), SNAP-25 (synaptosomal-associated protein of 25 kD), syntaxin 3, and synaptophysin were present throughout the photoreceptor terminals; they did not specifically colocalize with RIBEYE, and thus were excluded from further analysis (unpublished data). Proteins that colocalized with RIBEYE in wild-type photoreceptor terminals were Piccolo, the kinesin motor protein KIF3A, RIM1, RIM2, Munc13-1, a Ca2+ channel α1 subunit, ERC2/CAST1 (Fig. 2), and Bassoon (see Fig. 6).


Molecular dissection of the photoreceptor ribbon synapse: physical interaction of Bassoon and RIBEYE is essential for the assembly of the ribbon complex.

tom Dieck S, Altrock WD, Kessels MM, Qualmann B, Regus H, Brauner D, Fejtová A, Bracko O, Gundelfinger ED, Brandstätter JH - J. Cell Biol. (2005)

Screening the photoreceptor ribbon synaptic complex for ribbon-associated proteins in wild-type (+/+) and Bassoon mutant (−/−) retinae. (Left) Confocal laser-scanning micrographs of photoreceptor ribbons in the +/+ retina double labeled for RIBEYE combined with the following CAZ proteins: Piccolo, KIF3A, RIM1, RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. All CAZ proteins colocalize with RIBEYE as seen in the merge of the stainings. (Right) In the −/− retina, Piccolo, KIF3A, and RIM1 colocalize with RIBEYE, but not RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. Bars, 5 μm.
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Related In: Results  -  Collection

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fig2: Screening the photoreceptor ribbon synaptic complex for ribbon-associated proteins in wild-type (+/+) and Bassoon mutant (−/−) retinae. (Left) Confocal laser-scanning micrographs of photoreceptor ribbons in the +/+ retina double labeled for RIBEYE combined with the following CAZ proteins: Piccolo, KIF3A, RIM1, RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. All CAZ proteins colocalize with RIBEYE as seen in the merge of the stainings. (Right) In the −/− retina, Piccolo, KIF3A, and RIM1 colocalize with RIBEYE, but not RIM2, Munc13-1, Ca2+ channel α1 subunit, and ERC2/CAST1. Bars, 5 μm.
Mentions: With immunocytochemistry and confocal laser-scanning microscopy, we screened in wild-type photoreceptor terminals a number of presynaptic proteins for their localization as compared with RIBEYE and thus for their potential to interact with the photoreceptor ribbon. The proteins synaptotagmin, VGLUT1 (vesicular glutamate transporter 1), SNAP-25 (synaptosomal-associated protein of 25 kD), syntaxin 3, and synaptophysin were present throughout the photoreceptor terminals; they did not specifically colocalize with RIBEYE, and thus were excluded from further analysis (unpublished data). Proteins that colocalized with RIBEYE in wild-type photoreceptor terminals were Piccolo, the kinesin motor protein KIF3A, RIM1, RIM2, Munc13-1, a Ca2+ channel α1 subunit, ERC2/CAST1 (Fig. 2), and Bassoon (see Fig. 6).

Bottom Line: Identifiable CAZ proteins segregate into two compartments at the ribbon: a ribbon-associated compartment including Piccolo, RIBEYE, CtBP1/BARS, RIM1, and the motor protein KIF3A, and an active zone compartment including RIM2, Munc13-1, a Ca2+ channel alpha1 subunit, and ERC2/CAST1.A direct interaction between the ribbon-specific protein RIBEYE and Bassoon seems to link the two compartments and is responsible for the physical integrity of the photoreceptor ribbon complex.Finally, we found the RIBEYE homologue CtBP1 at ribbon and conventional synapses, suggesting a novel role for the CtBP/BARS family in the molecular assembly and function of central nervous system synapses.

View Article: PubMed Central - PubMed

Affiliation: Department of Neuroanatomy, Max Planck Institute for Brain Research, D-60528 Frankfurt/Main, Germany.

ABSTRACT
The ribbon complex of retinal photoreceptor synapses represents a specialization of the cytomatrix at the active zone (CAZ) present at conventional synapses. In mice deficient for the CAZ protein Bassoon, ribbons are not anchored to the presynaptic membrane but float freely in the cytoplasm. Exploiting this phenotype, we dissected the molecular structure of the photoreceptor ribbon complex. Identifiable CAZ proteins segregate into two compartments at the ribbon: a ribbon-associated compartment including Piccolo, RIBEYE, CtBP1/BARS, RIM1, and the motor protein KIF3A, and an active zone compartment including RIM2, Munc13-1, a Ca2+ channel alpha1 subunit, and ERC2/CAST1. A direct interaction between the ribbon-specific protein RIBEYE and Bassoon seems to link the two compartments and is responsible for the physical integrity of the photoreceptor ribbon complex. Finally, we found the RIBEYE homologue CtBP1 at ribbon and conventional synapses, suggesting a novel role for the CtBP/BARS family in the molecular assembly and function of central nervous system synapses.

Show MeSH