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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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Postembedding immunogold localization of CAZ proteins at wild-type photoreceptor ribbons. Electron micrographs showing different planes of section through photoreceptor ribbons that are postembedding immunogold labeled for RIM1 (A and B), KIF3A (C and D), and a Ca2+ channel α1 subunit (E and F). The gold particles for RIM1 and KIF3A are associated with the ribbon, the gold particles for the Ca2+ channel α1 subunit are associated with the active zone at the ribbon (arrowheads). Bars, 0.2 μm.
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fig3: Postembedding immunogold localization of CAZ proteins at wild-type photoreceptor ribbons. Electron micrographs showing different planes of section through photoreceptor ribbons that are postembedding immunogold labeled for RIM1 (A and B), KIF3A (C and D), and a Ca2+ channel α1 subunit (E and F). The gold particles for RIM1 and KIF3A are associated with the ribbon, the gold particles for the Ca2+ channel α1 subunit are associated with the active zone at the ribbon (arrowheads). Bars, 0.2 μm.

Mentions: To examine if the differential localization of CAZ proteins within the synaptic ribbon complex observed in Bassoon mutants reflects the wild-type situation, postembedding immunogold localization analyses were performed on wild-type retina. Gold particles for RIM1 are distributed in regularly spaced clusters along the whole length of the photoreceptor ribbon (Fig. 3, A and B) and the gold particles for KIF3A are evenly distributed along the photoreceptor ribbon (Fig. 3, C and D). For both proteins the arciform density is devoid of gold particles, which is also found for the distribution of Piccolo at the ribbon (Dick et al., 2001). In contrast, the Ca2+ channel α1 subunit is precisely localized to the plasma membrane at the active zone (Fig. 3, E and F, arrowheads), and the gold particles for Bassoon are located to the base of the ribbon (see Fig. 6; Brandstätter et al., 1999). These findings at wild-type photoreceptor ribbon synapses support our light microscopical findings of proteins associated with the ribbon, viz Bassoon, Piccolo, RIM1, and KIF3A, and of proteins associated with the presynaptic plasma membrane/arciform density, viz RIM2, Munc13-1, a Ca2+ channel α1 subunit, and ERC2/CAST1.


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)

Postembedding immunogold localization of CAZ proteins at wild-type photoreceptor ribbons. Electron micrographs showing different planes of section through photoreceptor ribbons that are postembedding immunogold labeled for RIM1 (A and B), KIF3A (C and D), and a Ca2+ channel α1 subunit (E and F). The gold particles for RIM1 and KIF3A are associated with the ribbon, the gold particles for the Ca2+ channel α1 subunit are associated with the active zone at the ribbon (arrowheads). Bars, 0.2 μm.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2171818&req=5

fig3: Postembedding immunogold localization of CAZ proteins at wild-type photoreceptor ribbons. Electron micrographs showing different planes of section through photoreceptor ribbons that are postembedding immunogold labeled for RIM1 (A and B), KIF3A (C and D), and a Ca2+ channel α1 subunit (E and F). The gold particles for RIM1 and KIF3A are associated with the ribbon, the gold particles for the Ca2+ channel α1 subunit are associated with the active zone at the ribbon (arrowheads). Bars, 0.2 μm.
Mentions: To examine if the differential localization of CAZ proteins within the synaptic ribbon complex observed in Bassoon mutants reflects the wild-type situation, postembedding immunogold localization analyses were performed on wild-type retina. Gold particles for RIM1 are distributed in regularly spaced clusters along the whole length of the photoreceptor ribbon (Fig. 3, A and B) and the gold particles for KIF3A are evenly distributed along the photoreceptor ribbon (Fig. 3, C and D). For both proteins the arciform density is devoid of gold particles, which is also found for the distribution of Piccolo at the ribbon (Dick et al., 2001). In contrast, the Ca2+ channel α1 subunit is precisely localized to the plasma membrane at the active zone (Fig. 3, E and F, arrowheads), and the gold particles for Bassoon are located to the base of the ribbon (see Fig. 6; Brandstätter et al., 1999). These findings at wild-type photoreceptor ribbon synapses support our light microscopical findings of proteins associated with the ribbon, viz Bassoon, Piccolo, RIM1, and KIF3A, and of proteins associated with the presynaptic plasma membrane/arciform density, viz RIM2, Munc13-1, a Ca2+ channel α1 subunit, and ERC2/CAST1.

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