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Gierke K, Lux UT, Regus-Leidig H, Brandstätter JH. The first synapse in vision in the aging mouse retina. Front Cell Neurosci 2023; 17:1291054. [PMID: 38026697 PMCID: PMC10654782 DOI: 10.3389/fncel.2023.1291054] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2023] [Accepted: 10/20/2023] [Indexed: 12/01/2023] Open
Abstract
Vision is our primary sense, and maintaining it throughout our lifespan is crucial for our well-being. However, the retina, which initiates vision, suffers from an age-related, irreversible functional decline. What causes this functional decline, and how it might be treated, is still unclear. Synapses are the functional hub for signal transmission between neurons, and studies have shown that aging is widely associated with synaptic dysfunction. In this study, we examined the first synapse of the visual system - the rod and cone photoreceptor ribbon synapse - in the mouse retina using light and electron microscopy at 2-3 months, ~1 year, and >2 years of age. We asked, whether age-related changes in key synaptic components might be a driver of synaptic dysfunction and ultimately age-related functional decline during normal aging. We found sprouting of horizontal and bipolar cells, formation of ectopic photoreceptor ribbon synapses, and a decrease in the number of rod photoreceptors and photoreceptor ribbon synapses in the aged retina. However, the majority of the photoreceptors did not show obvious changes in the structural components and protein composition of their ribbon synapses. Noteworthy is the increase in mitochondrial size in rod photoreceptor terminals in the aged retina.
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Affiliation(s)
| | | | | | - Johann Helmut Brandstätter
- Animal Physiology/Neurobiology, Department of Biology, Friedrich-Alexander-Universität Erlangen-Nürnberg, Erlangen, Germany
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Falk N, Kessler K, Schramm SF, Boldt K, Becirovic E, Michalakis S, Regus-Leidig H, Noegel AA, Ueffing M, Thiel CT, Roepman R, Brandstätter JH, Gießl A. Functional analyses of Pericentrin and Syne-2 interaction in ciliogenesis. J Cell Sci 2018; 131:jcs.218487. [PMID: 30054381 DOI: 10.1242/jcs.218487] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2018] [Accepted: 07/12/2018] [Indexed: 01/31/2023] Open
Abstract
Pericentrin (Pcnt) is a multifunctional scaffold protein and mutations in the human PCNT gene are associated with several diseases, including ciliopathies. Pcnt plays a crucial role in ciliary development in olfactory receptor neurons, but its function in the photoreceptor-connecting cilium is unknown. We downregulated Pcnt in the retina ex vivo and in vivo via a virus-based RNA interference approach to study Pcnt function in photoreceptors. ShRNA-mediated knockdown of Pcnt impaired the development of the connecting cilium and the outer segment of photoreceptors, and caused a nuclear migration defect. In protein interaction screens, we found that the outer nuclear membrane protein Syne-2 (also known as Nesprin-2) is an interaction partner of Pcnt in photoreceptors. Syne-2 is important for positioning murine photoreceptor cell nuclei and for centrosomal migration during early ciliogenesis. CRISPR/Cas9-mediated knockout of Syne-2 in cell culture led to an overexpression and mislocalization of Pcnt and to ciliogenesis defects. Our findings suggest that the Pcnt-Syne-2 complex is important for ciliogenesis and outer segment formation during retinal development and plays a role in nuclear migration.
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Affiliation(s)
- Nathalie Falk
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Kristin Kessler
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Sinja-Fee Schramm
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Karsten Boldt
- Division of Experimental Ophthalmology and Medical Proteome Center, Center of Ophthalmology, University of Tübingen, 72074 Tübingen, Germany
| | - Elvir Becirovic
- Center for Integrated Protein Science Munich (CIPSM) at the Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - Stylianos Michalakis
- Center for Integrated Protein Science Munich (CIPSM) at the Department of Pharmacy, Center for Drug Research, Ludwig-Maximilians-Universität München, 81377 Munich, Germany
| | - Hanna Regus-Leidig
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
| | - Angelika A Noegel
- Institute of Biochemistry I, Medical Faculty, University Hospital, University of Cologne, 50931 Cologne, Germany
| | - Marius Ueffing
- Division of Experimental Ophthalmology and Medical Proteome Center, Center of Ophthalmology, University of Tübingen, 72074 Tübingen, Germany
| | - Christian T Thiel
- Institute of Human Genetics, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91054 Erlangen, Germany
| | - Ronald Roepman
- Department of Human Genetics, Radboud University Medical Center, Nijmegen 6525 GA, The Netherlands
| | | | - Andreas Gießl
- Animal Physiology, Friedrich-Alexander-Universität Erlangen-Nürnberg, 91058 Erlangen, Germany
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Regus-Leidig H, Fuchs M, Löhner M, Leist SR, Leal-Ortiz S, Chiodo VA, Hauswirth WW, Garner CC, Brandstätter JH. In vivo knockdown of Piccolino disrupts presynaptic ribbon morphology in mouse photoreceptor synapses. Front Cell Neurosci 2014; 8:259. [PMID: 25232303 PMCID: PMC4153300 DOI: 10.3389/fncel.2014.00259] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2014] [Accepted: 08/13/2014] [Indexed: 01/08/2023] Open
Abstract
Piccolo is the largest known cytomatrix protein at active zones of chemical synapses. A growing number of studies on conventional chemical synapses assign Piccolo a role in the recruitment and integration of molecules relevant for both endo- and exocytosis of synaptic vesicles, the dynamic assembly of presynaptic F-actin, as well as the proteostasis of presynaptic proteins, yet a direct function in the structural organization of the active zone has not been uncovered in part due to the expression of multiple alternatively spliced isoforms. We recently identified Piccolino, a Piccolo splice variant specifically expressed in sensory ribbon synapses of the eye and ear. Here we down regulated Piccolino in vivo via an adeno-associated virus-based RNA interference approach and explored the impact on the presynaptic structure of mouse photoreceptor ribbon synapses. Detailed immunocytochemical light and electron microscopical analysis of Piccolino knockdown in photoreceptors revealed a hitherto undescribed photoreceptor ribbon synaptic phenotype with striking morphological changes of synaptic ribbon ultrastructure.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Michaela Fuchs
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Martina Löhner
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
| | - Sarah R Leist
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany ; Department of Infection Genetics, Helmholtz Centre for Infection Research Braunschweig, Germany
| | - Sergio Leal-Ortiz
- Department of Psychiatry and Behavioral Sciences, Stanford University Palo Alto, CA, USA
| | - Vince A Chiodo
- Department of Ophthalmology, College of Medicine, University of Florida Gainesville, FL, USA
| | - William W Hauswirth
- Department of Ophthalmology, College of Medicine, University of Florida Gainesville, FL, USA
| | - Craig C Garner
- Department of Psychiatry and Behavioral Sciences, Stanford University Palo Alto, CA, USA ; Deutsches Zentrum für Neurodegenerative Erkrankungen Charité, Berlin, Germany
| | - Johann H Brandstätter
- Department of Biology, Animal Physiology, Friedrich-Alexander-University of Erlangen-Nuremberg Erlangen, Germany
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Fuchs M, Brandstätter JH, Regus-Leidig H. Evidence for a Clathrin-independent mode of endocytosis at a continuously active sensory synapse. Front Cell Neurosci 2014; 8:60. [PMID: 24616664 PMCID: PMC3934443 DOI: 10.3389/fncel.2014.00060] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2013] [Accepted: 02/10/2014] [Indexed: 11/13/2022] Open
Abstract
Synaptic vesicle exocytosis at chemical synapses is followed by compensatory endocytosis. Multiple pathways including Clathrin-mediated retrieval of single vesicles, bulk retrieval of large cisternae, and kiss-and-run retrieval have been reported to contribute to vesicle recycling. Particularly at the continuously active ribbon synapses of retinal photoreceptor and bipolar cells, compensatory endocytosis plays an essential role to provide ongoing vesicle supply. Yet, little is known about the mechanisms that contribute to endocytosis at these highly complex synapses. To identify possible specializations in ribbon synaptic endocytosis during different states of activity, we exposed mice to controlled lighting conditions and compared the distribution of endocytotic proteins at rod and cone photoreceptor, and ON bipolar cell ribbon synapses with light and electron microscopy. In mouse ON bipolar cell terminals, Clathrin-mediated endocytosis seemed to be the dominant mode of endocytosis at all adaptation states analyzed. In contrast, in mouse photoreceptor terminals in addition to Clathrin-coated pits, clusters of membranously connected electron-dense vesicles appeared during prolonged darkness. These clusters labeled for Dynamin3, Endophilin1, and Synaptojanin1, but not for AP180, Clathrin LC, and hsc70. We hypothesize that rod and cone photoreceptors possess an additional Clathrin-independent mode of vesicle retrieval supporting the continuous synaptic vesicle supply during prolonged high activity.
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Affiliation(s)
- Michaela Fuchs
- Animal Physiology, Department of Biology, Friedrich-Alexander-University Erlangen-Nuremberg Erlangen, Germany
| | - Johann Helmut Brandstätter
- Animal Physiology, Department of Biology, Friedrich-Alexander-University Erlangen-Nuremberg Erlangen, Germany
| | - Hanna Regus-Leidig
- Animal Physiology, Department of Biology, Friedrich-Alexander-University Erlangen-Nuremberg Erlangen, Germany
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Regus-Leidig H, Atorf J, Feigenspan A, Kremers J, Maw MA, Brandstätter JH. Photoreceptor degeneration in two mouse models for congenital stationary night blindness type 2. PLoS One 2014; 9:e86769. [PMID: 24466230 PMCID: PMC3897778 DOI: 10.1371/journal.pone.0086769] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2013] [Accepted: 12/17/2013] [Indexed: 02/02/2023] Open
Abstract
Light-dependent conductance changes of voltage-gated Cav1.4 channels regulate neurotransmitter release at photoreceptor ribbon synapses. Mutations in the human CACNA1F gene encoding the α1F subunit of Cav1.4 channels cause an incomplete form of X-linked congenital stationary night blindness (CSNB2). Many CACNA1F mutations are loss-of-function mutations resulting in non-functional Cav1.4 channels, but some mutations alter the channels’ gating properties and, presumably, disturb Ca2+ influx at photoreceptor ribbon synapses. Notably, a CACNA1F mutation (I745T) was identified in a family with an uncommonly severe CSNB2-like phenotype, and, when expressed in a heterologous system, the mutation was shown to shift the voltage-dependence of channel activation, representing a gain-of-function. To gain insight into the pathomechanism that could explain the severity of this disorder, we generated a mouse model with the corresponding mutation in the murine Cacna1f gene (I756T) and compared it with a mouse model carrying a loss-of-function mutation (ΔEx14–17) in a longitudinal study up to eight months of age. In ΔEx14–17 mutants, the b-wave in the electroretinogram was absent, photoreceptor ribbon synapses were abnormal, and Ca2+ responses to depolarization of photoreceptor terminals were undetectable. In contrast, I756T mutants had a reduced scotopic b-wave, some intact rod ribbon synapses, and a strong, though abnormal, Ca2+ response to depolarization. Both mutants showed a progressive photoreceptor loss, but degeneration was more severe and significantly enhanced in the I756T mutants compared to the ΔEx14–17 mutants.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jenny Atorf
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Andreas Feigenspan
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Marion A. Maw
- Department of Biochemistry, University of Otago, Dunedin, New Zealand
- * E-mail: (MAM); (JHB)
| | - Johann Helmut Brandstätter
- Department of Biology, Animal Physiology, FAU Erlangen-Nuremberg, Erlangen, Germany
- * E-mail: (MAM); (JHB)
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Regus-Leidig H, Ott C, Löhner M, Atorf J, Fuchs M, Sedmak T, Kremers J, Fejtová A, Gundelfinger ED, Brandstätter JH. Identification and immunocytochemical characterization of Piccolino, a novel Piccolo splice variant selectively expressed at sensory ribbon synapses of the eye and ear. PLoS One 2013; 8:e70373. [PMID: 23936420 PMCID: PMC3735604 DOI: 10.1371/journal.pone.0070373] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2013] [Accepted: 06/17/2013] [Indexed: 02/03/2023] Open
Abstract
Piccolo is one of the largest cytomatrix proteins present at active zones of chemical synapses, where it is suggested to play a role in recruiting and integrating molecules relevant for both synaptic vesicle exo- and endocytosis. Here we examined the retina of a Piccolo-mutant mouse with a targeted deletion of exon 14 in the Pclo gene. Piccolo deficiency resulted in its profound loss at conventional chemical amacrine cell synapses but retinal ribbon synapses were structurally and functionally unaffected. This led to the identification of a shorter, ribbon-specific Piccolo variant, Piccolino, present in retinal photoreceptor cells, bipolar cells, as well as in inner hair cells of the inner ear. By RT-PCR analysis and the generation of a Piccolino-specific antibody we show that non-splicing of intron 5/6 leads to premature translation termination and generation of the C-terminally truncated protein specifically expressed at active zones of ribbon synapse containing cell types. With in situ proximity ligation assays we provide evidence that this truncation leads to the absence of interaction sites for Bassoon, Munc13, and presumably also ELKS/CAST, RIM2, and the L-type Ca2+ channel which exist in the full-length Piccolo at active zones of conventional chemical synapses. The putative lack of interactions with proteins of the active zone suggests a function of Piccolino at ribbon synapses of sensory neurons different from Piccolo’s function at conventional chemical synapses.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Corinna Ott
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Martina Löhner
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jenny Atorf
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Michaela Fuchs
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Tina Sedmak
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
| | - Jan Kremers
- Department of Ophthalmology, University Hospital Erlangen, Erlangen, Germany
| | - Anna Fejtová
- Leibniz Institute for Neurobiology, Magdeburg, Germany
- Center for Behavioral Brain Science, Magdeburg, Germany
| | - Eckart D. Gundelfinger
- Leibniz Institute for Neurobiology, Magdeburg, Germany
- Center for Behavioral Brain Science, Magdeburg, Germany
| | - Johann H. Brandstätter
- Department of Biology, Animal Physiology, Friedrich-Alexander-University Erlangen-Nuremberg, Erlangen, Germany
- * E-mail:
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Abstract
Vision is the most important of the senses for humans, and the retina is the first stage in the processing of light signals in the visual system. In the retina, highly specialized light-sensing neurons, the rod and cone photoreceptors, convert light into neural signals. These signals are extensively processed and filtered in the subsequent retinal network before transmitted to the higher visual centres in the brain, where the perception of viewed objects and scenes is finally constructed. A key feature of signal processing in the mammalian retina is parallel processing. Visual information is segregated in parallel pathways already at the rod and cone photoreceptor terminals, which provide multiple output synapses for the faithful encoding and transfer of the visual signals to the post-receptoral retinal network. This review aims at highlighting the current knowledge about the structural and functional pre- and post-synaptic specializations of rod and cone photoreceptor ribbon synapses, which belong to the most complex chemical synapses in the central nervous system.
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Affiliation(s)
- H Regus-Leidig
- Animal Physiology, Department of Biology, University of Erlangen-Nuremberg, Germany
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Clemen CS, Tangavelou K, Strucksberg KH, Just S, Gaertner L, Regus-Leidig H, Stumpf M, Reimann J, Coras R, Morgan RO, Fernandez MP, Hofmann A, Müller S, Schoser B, Hanisch FG, Rottbauer W, Blümcke I, von Hörsten S, Eichinger L, Schröder R. Strumpellin is a novel valosin-containing protein binding partner linking hereditary spastic paraplegia to protein aggregation diseases. ACTA ACUST UNITED AC 2010; 133:2920-41. [PMID: 20833645 DOI: 10.1093/brain/awq222] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Mutations of the human valosin-containing protein gene cause autosomal-dominant inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia. We identified strumpellin as a novel valosin-containing protein binding partner. Strumpellin mutations have been shown to cause hereditary spastic paraplegia. We demonstrate that strumpellin is a ubiquitously expressed protein present in cytosolic and endoplasmic reticulum cell fractions. Overexpression or ablation of wild-type strumpellin caused significantly reduced wound closure velocities in wound healing assays, whereas overexpression of the disease-causing strumpellin N471D mutant showed no functional effect. Strumpellin knockdown experiments in human neuroblastoma cells resulted in a dramatic reduction of axonal outgrowth. Knockdown studies in zebrafish revealed severe cardiac contractile dysfunction, tail curvature and impaired motility. The latter phenotype is due to a loss of central and peripheral motoneuron formation. These data imply a strumpellin loss-of-function pathogenesis in hereditary spastic paraplegia. In the human central nervous system strumpellin shows a presynaptic localization. We further identified strumpellin in pathological protein aggregates in inclusion body myopathy associated with Paget disease of bone and frontotemporal dementia, various myofibrillar myopathies and in cortical neurons of a Huntington's disease mouse model. Beyond hereditary spastic paraplegia, our findings imply that mutant forms of strumpellin and valosin-containing protein may have a concerted pathogenic role in various protein aggregate diseases.
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Affiliation(s)
- Christoph S Clemen
- Institute of Biochemistry I, University of Cologne, Joseph-Stelzmann-Street 52, Cologne, Germany.
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Reim K, Regus-Leidig H, Ammermüller J, El-Kordi A, Radyushkin K, Ehrenreich H, Brandstätter JH, Brose N. Aberrant function and structure of retinal ribbon synapses in the absence of complexin 3 and complexin 4. J Cell Sci 2009; 122:1352-61. [PMID: 19386896 DOI: 10.1242/jcs.045401] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Complexins regulate the speed and Ca(2+) sensitivity of SNARE-mediated synaptic vesicle fusion at conventional synapses. Two of the vertebrate complexins, Cplx3 and Cplx4, are specifically localized to retinal ribbon synapses. To test whether Cplx3 and Cplx4 contribute to the highly efficient transmitter release at ribbon synapses, we studied retina function and structure in Cplx3 and Cplx4 single- and double-knockout mice. Electroretinographic recordings from single and double mutants revealed a cooperative perturbing effect of Cplx3 and Cplx4 deletion on the b-wave amplitude, whereas most other detected effects in both plexiform synaptic layers were additive. Light and electron microscopic analyses uncovered a disorganized outer plexiform layer in the retinae of mice lacking Cplx3 and Cplx4, with a significant proportion of photoreceptor terminals containing spherical free-floating ribbons. These structural and functional aberrations were accompanied by behavioural deficits indicative of a vision deficit. Our results show that Cplx3 and Cplx4 are essential regulators of transmitter release at retinal ribbon synapses. Their loss leads to aberrant adjustment and fine-tuning of transmitter release at the photoreceptor ribbon synapse, alterations in transmission at bipolar cell terminals, changes in the temporal structure of synaptic processing in the inner plexiform layer of the retina and perturbed vision.
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Affiliation(s)
- Kerstin Reim
- Department of Molecular Neurobiology and Center for the Molecular Physiology of the Brain, Max Planck Institute of Experimental Medicine, D-37075 Göttingen, Germany
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Regus-Leidig H, Tom Dieck S, Specht D, Meyer L, Brandstätter JH. Early steps in the assembly of photoreceptor ribbon synapses in the mouse retina: the involvement of precursor spheres. J Comp Neurol 2009; 512:814-24. [PMID: 19067356 DOI: 10.1002/cne.21915] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The retinal photoreceptor ribbon synapse is a chemical synapse structurally and functionally specialized for the tonic release of neurotransmitter. It is characterized by the presynaptic ribbon, an electron-dense organelle at the active zone covered by hundreds of synaptic vesicles. In conventional synapses, dense-core transport vesicles carrying a set of active zone proteins are implicated in early steps of synapse formation. In photoreceptor ribbon synapses, synaptic spheres are suggested to be involved in ribbon synapse assembly, but nothing is known about the molecular composition of these organelles. With light, electron, and stimulated emission depletion microscopy and immunocytochemistry, we investigated a series of presynaptic proteins during photoreceptor synaptogenesis. The cytomatrix proteins Bassoon, Piccolo, RIBEYE, and RIM1 appear early in synaptogenesis. They are transported in nonmembranous, electron-dense, spherical transport units, which we called precursor spheres, to the future presynaptic site. Other presynaptic proteins, i.e., Munc13, CAST1, RIM2, and an L-type Ca(2+) channel alpha1 subunit are not associated with the precursor spheres. They cluster directly at the active zone some time after the first set of cytomatrix proteins has arrived. By quantitative electron microscopy, we found an inverse correlation between the numbers of spheres and synaptic ribbons in the postnatally developing photoreceptor synaptic terminals. From these results, we suggest that the precursor spheres are the transport units for proteins of the photoreceptor ribbon compartment and are involved in the assembly of mature synaptic ribbons.
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Affiliation(s)
- Hanna Regus-Leidig
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, Erlangen, Germany
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Specht D, Tom Dieck S, Ammermüller J, Regus-Leidig H, Gundelfinger ED, Brandstätter JH. Structural and functional remodeling in the retina of a mouse with a photoreceptor synaptopathy: plasticity in the rod and degeneration in the cone system. Eur J Neurosci 2007; 26:2506-15. [PMID: 17970721 DOI: 10.1111/j.1460-9568.2007.05886.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Knowledge about the plastic and regenerative capacity of the retina is of key importance for therapeutic approaches to restore vision in patients who suffer from degenerative retinal diseases. In the retinae of mice, mutant for the presynaptic scaffolding protein Bassoon, signal transfer at photoreceptor ribbon synapses is disturbed due to impaired ribbon attachment to the active zone. In a long-term study we observed, with light and electron microscopic immunocytochemistry and electroretinographic recordings, two overlapping events in the Bassoon mutant retina, i.e. loss of photoreceptor synapses in the outer plexiform layer, and structural remodeling and formation of ectopic photoreceptor synapses in the outer nuclear layer, a region usually devoid of synapses. Formation of ectopic synaptic sites starts around the time when photoreceptor synaptogenesis is completed in wild-type mice and progresses throughout life. The result is a dense plexus of ectopic photoreceptor synapses with significantly altered but considerable synaptic transmission. Ectopic synapse formation is led by the sprouting of horizontal cells followed by the extension of rod bipolar cell neurites that fasciculate with and grow along the horizontal cell processes. Although only the rod photoreceptors and their postsynaptic partners show structural and functional remodeling, our study demonstrates the potential of the retina for long-lasting plastic changes.
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Affiliation(s)
- Dana Specht
- Department of Biology, Animal Physiology, University of Erlangen-Nuremberg, Staudtstrasse 5, 91058 Erlangen, Germany
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Abstract
Cone photoreceptors have a continuous release of glutamate that is modulated by light. Vesicular glutamate transporters (vGluT) play an essential role for sustaining this release by loading synaptic vesicles in the cone synapse, the so-called cone pedicle. In the present study mouse retinas were immunostained for vGluT1 and vGluT2. vGluT1 was localized to all cone pedicles and rod spherules, whereas vGluT2 was found in only 10% of the cone pedicles. The vGluT2-expressing cones were characterized in more detail. They are distributed in a regular array, suggesting they are a distinct type. Their proportion does not differ between dorsal (L-cone-dominated) and ventral (S-cone-dominated) retina, and they are not the genuine blue cones of the mouse retina. During development, vGluT1 and vGluT2 expression in cones starts at around P0 and right from the beginning vGluT2 is only expressed in a subset of cones. Bipolar cells contact the vGluT2-expressing cones and other cones nonselectively. The possible functional role of vGluT2 expression in a small fraction of cones is discussed.
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Affiliation(s)
- Heinz Wässle
- Department of Neuroanatomy, Max-Planck-Institute for Brain Research, D-60528 Frankfurt/Main, Germany.
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