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Singh S, Srivastava D, Boyd K, Artemyev NO. Reconstitution of the phosphodiesterase 6 maturation process important for photoreceptor cell function. J Biol Chem 2024; 300:105576. [PMID: 38110033 PMCID: PMC10819763 DOI: 10.1016/j.jbc.2023.105576] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2023] [Revised: 12/01/2023] [Accepted: 12/10/2023] [Indexed: 12/20/2023] Open
Abstract
The sixth family phosphodiesterases (PDE6) are principal effector enzymes of the phototransduction cascade in rods and cones. Maturation of nascent PDE6 protein into a functional enzyme relies on a coordinated action of ubiquitous chaperone HSP90, its specialized cochaperone aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1), and the regulatory Pγ-subunit of PDE6. Deficits in PDE6 maturation and function underlie severe visual disorders and blindness. Here, to elucidate the roles of HSP90, AIPL1, and Pγ in the maturation process, we developed the heterologous expression system of human cone PDE6C in insect cells allowing characterization of the purified enzyme. We demonstrate that in the absence of Pγ, HSP90, and AIPL1 convert the inactive and aggregating PDE6C species into dimeric PDE6C that is predominantly misassembled. Nonetheless, a small fraction of PDE6C is properly assembled and fully functional. From the analysis of mutant mice that lack both rod Pγ and PDE6C, we conclude that, in contrast to the cone enzyme, no maturation of rod PDE6AB occurs in the absence of Pγ. Co-expression of PDE6C with AIPL1 and Pγ in insect cells leads to a fully mature enzyme that is equivalent to retinal PDE6. Lastly, using immature PDE6C and purified chaperone components, we reconstituted the process of the client maturation in vitro. Based on this analysis we propose a scheme for the PDE6 maturation process.
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Affiliation(s)
- Sneha Singh
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - Dhiraj Srivastava
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - Kimberly Boyd
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - Nikolai O Artemyev
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA; Department of Ophthalmology and Visual Sciences, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
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2
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Bocchero U, Pahlberg J. Origin of Discrete and Continuous Dark Noise in Rod Photoreceptors. eNeuro 2023; 10:ENEURO.0390-23.2023. [PMID: 37973380 PMCID: PMC10687842 DOI: 10.1523/eneuro.0390-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2023] [Accepted: 11/02/2023] [Indexed: 11/19/2023] Open
Abstract
The detection of a single photon by a rod photoreceptor is limited by two sources of physiological noise, called discrete and continuous noise. Discrete noise occurs as intermittent current deflections with a waveform very similar to that of the single-photon response to real light and is thought to be produced by spontaneous activation of rhodopsin. Continuous noise occurs as random and continuous fluctuations in outer-segment current and is usually attributed to some intermediate in the phototransduction cascade. To confirm the origin of these noise sources, we have recorded from retinas of mouse lines with rods having reduced levels of rhodopsin, transducin, or phosphodiesterase. We show that the rate of discrete noise is diminished in proportion to the decrease in rhodopsin concentration, and that continuous noise is independent of transducin concentration but clearly elevated when the level of phosphodiesterase is reduced. Our experiments provide new molecular evidence that discrete noise is indeed produced by rhodopsin itself, and that continuous noise is generated by spontaneous activation of phosphodiesterase resulting in random fluctuations in outer-segment current.
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Affiliation(s)
- Ulisse Bocchero
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510
| | - Johan Pahlberg
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, Maryland 20892-2510
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3
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Fehlhaber KE, Majumder A, Boyd KK, Griffis KG, Artemyev NO, Fain GL, Sampath AP. A Novel Role for UNC119 as an Enhancer of Synaptic Transmission. Int J Mol Sci 2023; 24:8106. [PMID: 37175812 PMCID: PMC10178850 DOI: 10.3390/ijms24098106] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2023] [Revised: 04/22/2023] [Accepted: 04/25/2023] [Indexed: 05/15/2023] Open
Abstract
Mammalian UNC119 is a ciliary trafficking chaperone highly expressed in the inner segment of retinal photoreceptors. Previous research has shown that UNC119 can bind to transducin, the synaptic ribbon protein RIBEYE, and the calcium-binding protein CaBP4, suggesting that UNC119 may have a role in synaptic transmission. We made patch-clamp recordings from retinal slices in mice with the UNC119 gene deleted and showed that removal of even one gene of UNC119 has no effect on the rod outer segment photocurrent, but acted on bipolar cells much like background light: it depolarized membrane potential, decreased sensitivity, accelerated response decay, and decreased the Hill coefficient of the response-intensity relationship. Similar effects were seen on rod bipolar-cell current and voltage responses, and after exposure to bright light to translocate transducin into the rod inner segment. These findings indicate that UNC119 deletion reduces the steady-state glutamate release rate at rod synapses, though no change in the voltage dependence of the synaptic Ca current was detected. We conclude that UNC119, either by itself or together with transducin, can facilitate the release of glutamate at rod synapses, probably by some interaction with RIBEYE or other synaptic proteins rather than by binding to CaBP4 or calcium channels.
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Affiliation(s)
- Katherine E. Fehlhaber
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA 90095, USA (G.L.F.)
| | - Anurima Majumder
- Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA (N.O.A.)
| | - Kimberly K. Boyd
- Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA (N.O.A.)
| | - Khris G. Griffis
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA 90095, USA (G.L.F.)
| | - Nikolai O. Artemyev
- Molecular Physiology and Biophysics, University of Iowa, Iowa City, IA 52242, USA (N.O.A.)
- Ophthalmology and Visual Sciences, University of Iowa, Iowa City, IA 52242, USA
| | - Gordon L. Fain
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA 90095, USA (G.L.F.)
| | - Alapakkam P. Sampath
- Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA 90095, USA (G.L.F.)
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4
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Sirés A, Pazo-González M, López-Soriano J, Méndez A, de la Rosa EJ, de la Villa P, Comella JX, Hernández-Sánchez C, Solé M. The Absence of FAIM Leads to a Delay in Dark Adaptation and Hampers Arrestin-1 Translocation upon Light Reception in the Retina. Cells 2023; 12:cells12030487. [PMID: 36766830 PMCID: PMC9914070 DOI: 10.3390/cells12030487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2022] [Revised: 01/14/2023] [Accepted: 01/29/2023] [Indexed: 02/05/2023] Open
Abstract
The short and long isoforms of FAIM (FAIM-S and FAIM-L) hold important functions in the central nervous system, and their expression levels are specifically enriched in the retina. We previously described that Faim knockout (KO) mice present structural and molecular alterations in the retina compatible with a neurodegenerative phenotype. Here, we aimed to study Faim KO retinal functions and molecular mechanisms leading to its alterations. Electroretinographic recordings showed that aged Faim KO mice present functional loss of rod photoreceptor and ganglion cells. Additionally, we found a significant delay in dark adaptation from early adult ages. This functional deficit is exacerbated by luminic stress, which also caused histopathological alterations. Interestingly, Faim KO mice present abnormal Arrestin-1 redistribution upon light reception, and we show that Arrestin-1 is ubiquitinated, a process that is abrogated by either FAIM-S or FAIM-L in vitro. Our results suggest that FAIM assists Arrestin-1 light-dependent translocation by a process that likely involves ubiquitination. In the absence of FAIM, this impairment could be the cause of dark adaptation delay and increased light sensitivity. Multiple retinal diseases are linked to deficits in photoresponse termination, and hence, investigating the role of FAIM could shed light onto the underlying mechanisms of their pathophysiology.
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Affiliation(s)
- Anna Sirés
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Mateo Pazo-González
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Department of Systems Biology, Facultad de Medicina, Universidad de Alcalá, 28871 Alcalá de Henares, Spain
| | - Joaquín López-Soriano
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Ana Méndez
- Department of Physiological Sciences, School of Medicine, Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
- Institut de Neurociències, Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
- Institut d’Investigació Biomèdica de Bellvitge (IDIBELL), Campus Universitari de Bellvitge, University of Barcelona, 08907 Barcelona, Spain
| | - Enrique J. de la Rosa
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, 28029 Madrid, Spain
| | - Pedro de la Villa
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Department of Systems Biology, Facultad de Medicina, Universidad de Alcalá, 28871 Alcalá de Henares, Spain
| | - Joan X. Comella
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
| | - Catalina Hernández-Sánchez
- Department of Molecular Biomedicine, Centro de Investigaciones Biológicas Margarita Salas (CSIC), 28040 Madrid, Spain
- Centro de Investigación Biomédica en Red de Diabetes y Enfermedades Metabólicas Asociadas (CIBERDEM), ISCIII, 28029 Madrid, Spain
| | - Montse Solé
- Cell Signaling and Apoptosis Group, Vall d’Hebron Institute of Research (VHIR), 08035 Barcelona, Spain
- Centro de Investigación Biomédica en Red sobre Enfermedades Neurodegenerativas (CIBERNED), ISCIII, 28029 Madrid, Spain
- Departament de Bioquímica i Biologia Molecular, Institut de Neurociències, Facultat de Medicina, Universitat Autònoma de Barcelona (UAB), 08193 Bellaterra, Spain
- Correspondence:
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5
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Campla CK, Bocchero U, Strickland R, Nellissery J, Advani J, Ignatova I, Srivastava D, Aponte AM, Wang Y, Gumerson J, Martemyanov K, Artemyev NO, Pahlberg J, Swaroop A. Frmpd1 Facilitates Trafficking of G-Protein Transducin and Modulates Synaptic Function in Rod Photoreceptors of Mammalian Retina. eNeuro 2022; 9:ENEURO.0348-22.2022. [PMID: 36180221 PMCID: PMC9581579 DOI: 10.1523/eneuro.0348-22.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2022] [Accepted: 09/23/2022] [Indexed: 12/15/2022] Open
Abstract
Trafficking of transducin (Gαt) in rod photoreceptors is critical for adaptive and modulatory responses of the retina to varying light intensities. In addition to fine-tuning phototransduction gain in rod outer segments (OSs), light-induced translocation of Gαt to the rod synapse enhances rod to rod bipolar synaptic transmission. Here, we show that the rod-specific loss of Frmpd1 (FERM and PDZ domain containing 1), in the retina of both female and male mice, results in delayed return of Gαt from the synapse back to outer segments in the dark, compromising the capacity of rods to recover from light adaptation. Frmpd1 directly interacts with Gpsm2 (G-protein signaling modulator 2), and the two proteins are required for appropriate sensitization of rod-rod bipolar signaling under saturating light conditions. These studies provide insight into how the trafficking and function of Gαt is modulated to optimize the photoresponse and synaptic transmission of rod photoreceptors in a light-dependent manner.
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Affiliation(s)
- Christie K Campla
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Ulisse Bocchero
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Ryan Strickland
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Jacob Nellissery
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Jayshree Advani
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Irina Ignatova
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Dhiraj Srivastava
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Angel M Aponte
- Proteomics Core, National Heart Lung and Blood Institute, National Institutes of Health, Bethesda, MD 20892
| | - Yuchen Wang
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458
| | - Jessica Gumerson
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Kirill Martemyanov
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458
| | - Nikolai O Artemyev
- Department of Molecular Physiology and Biophysics, University of Iowa Carver College of Medicine, Iowa City, IA 52242
- Department of Ophthalmology and Visual Sciences, University of Iowa Carver College of Medicine, Iowa City, IA 52242
| | - Johan Pahlberg
- Photoreceptor Physiology Group, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
| | - Anand Swaroop
- Neurobiology, Neurodegeneration and Repair Laboratory, National Eye Institute, National Institutes of Health, Bethesda, MD 20892
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6
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Gurevich VV, Gurevich EV. Solo vs. Chorus: Monomers and Oligomers of Arrestin Proteins. Int J Mol Sci 2022; 23:ijms23137253. [PMID: 35806256 PMCID: PMC9266314 DOI: 10.3390/ijms23137253] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Revised: 06/28/2022] [Accepted: 06/29/2022] [Indexed: 02/05/2023] Open
Abstract
Three out of four subtypes of arrestin proteins expressed in mammals self-associate, each forming oligomers of a distinct kind. Monomers and oligomers have different subcellular localization and distinct biological functions. Here we summarize existing evidence regarding arrestin oligomerization and discuss specific functions of monomeric and oligomeric forms, although too few of the latter are known. The data on arrestins highlight biological importance of oligomerization of signaling proteins. Distinct modes of oligomerization might be an important contributing factor to the functional differences among highly homologous members of the arrestin protein family.
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7
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Yadav RP, Boyd K, Artemyev NO. Molecular insights into the maturation of phosphodiesterase 6 by the specialized chaperone complex of HSP90 with AIPL1. J Biol Chem 2022; 298:101620. [PMID: 35065964 PMCID: PMC8857470 DOI: 10.1016/j.jbc.2022.101620] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Revised: 01/10/2022] [Accepted: 01/11/2022] [Indexed: 12/18/2022] Open
Abstract
Phosphodiesterase 6 (PDE6) is a key effector enzyme in vertebrate phototransduction, and its maturation and function are known to critically depend on a specialized chaperone, aryl hydrocarbon receptor-interacting protein-like 1 (AIPL1). Defects in PDE6 and AIPL1 underlie several severe retinal diseases, including retinitis pigmentosa and Leber congenital amaurosis. Here, we characterize the complex of AIPL1 with HSP90 and demonstrate its essential role in promoting the functional conformation of nascent PDE6. Our analysis suggests that AIPL1 preferentially binds to HSP90 in the closed state with a stoichiometry of 1:2, with the tetratricopeptide repeat domain and the tetratricopeptide repeat helix 7 extension of AIPL1 being the main contributors to the AIPL1/HSP90 interface. We demonstrate that mutations of these determinants markedly diminished both the affinity of AIPL1 for HSP90 and the ability of AIPL1 to cochaperone the maturation of PDE6 in a heterologous expression system. In addition, the FK506-binding protein (FKBP) domain of AIPL1 encloses a unique prenyl-binding site that anchors AIPL1 to posttranslational lipid modifications of PDE6. A mouse model with rod PDE6 lacking farnesylation of its PDE6A subunit revealed normal expression, trafficking, and signaling of the enzyme. Furthermore, AIPL1 was unexpectedly capable of inducing the maturation of unprenylated cone PDE6C, whereas mutant AIPL1 deficient in prenyl binding competently cochaperoned prenylated PDE6C. Thus, we conclude neither sequestration of the prenyl modifications is required for PDE6 maturation to proceed, nor is the FKBP-lipid interaction involved in the conformational switch of the enzyme into the functional state.
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Affiliation(s)
- Ravi P Yadav
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - Kimberly Boyd
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA
| | - Nikolai O Artemyev
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA; Department of Ophthalmology and Visual Sciences, The University of Iowa Carver College of Medicine, Iowa City, Iowa, USA.
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8
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Fina ME, Wang J, Vedula P, Tang HY, Kashina A, Dong DW. Arginylation Regulates G-protein Signaling in the Retina. Front Cell Dev Biol 2022; 9:807345. [PMID: 35127722 PMCID: PMC8815403 DOI: 10.3389/fcell.2021.807345] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2021] [Accepted: 12/17/2021] [Indexed: 12/03/2022] Open
Abstract
Arginylation is a post-translational modification mediated by the arginyltransferase (Ate1). We recently showed that conditional deletion of Ate1 in the nervous system leads to increased light-evoked response sensitivities of ON-bipolar cells in the retina, indicating that arginylation regulates the G-protein signaling complexes of those neurons and/or photoreceptors. However, none of the key players in the signaling pathway were previously shown to be arginylated. Here we show that Gαt1, Gβ1, RGS6, and RGS7 are arginylated in the retina and RGS6 and RGS7 protein levels are elevated in Ate1 knockout, suggesting that arginylation plays a direct role in regulating their protein level and the G-protein-mediated responses in the retina.
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Affiliation(s)
- Marie E. Fina
- Department of Biomedical Sciences, School of Veterinary Medicines, University of Pennsylvania, Philadelphia, PA, United States
| | - Junling Wang
- Department of Biomedical Sciences, School of Veterinary Medicines, University of Pennsylvania, Philadelphia, PA, United States
| | - Pavan Vedula
- Department of Biomedical Sciences, School of Veterinary Medicines, University of Pennsylvania, Philadelphia, PA, United States
| | - Hsin-Yao Tang
- Proteomics and Metabolomics Facility, The Wistar Institute, Philadelphia, PA, United States
| | - Anna Kashina
- Department of Biomedical Sciences, School of Veterinary Medicines, University of Pennsylvania, Philadelphia, PA, United States
- *Correspondence: Anna Kashina, ; Dawei W. Dong,
| | - Dawei W. Dong
- Department of Biomedical Sciences, School of Veterinary Medicines, University of Pennsylvania, Philadelphia, PA, United States
- Institute for Biomedical Informatics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, United States
- *Correspondence: Anna Kashina, ; Dawei W. Dong,
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9
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Abtout A, Fain G, Reingruber J. Analysis of waveform and amplitude of mouse rod and cone flash responses. J Physiol 2021; 599:3295-3312. [PMID: 33977528 DOI: 10.1113/jp281225] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2020] [Accepted: 04/28/2021] [Indexed: 12/14/2022] Open
Abstract
KEY POINTS Most vertebrate eyes have rod and cone photoreceptors, which use a signal transduction pathway consisting of many biological processes to transform light into an electrical response. We dissect and quantify the contribution of each of these processes to the photoreceptor light response by using a novel method of analysis that provides an analytical solution for the entire time course of the dim-flash light response. We find that the shape of the light response is exclusively controlled by deactivation parameters. Activation parameters scale this shape and alter the response amplitude. We show that the rising phase of the response depends on Ca2+ feedback, and we identify the deactivation parameters that control the recovery phase of the response. We devise new methods to extract values for deactivation and activation parameters from a separate analysis of response shape and response amplitude. ABSTRACT Vertebrate eyes have rod and cone photoreceptors, which use a complex transduction pathway comprising many biological processes to transform the absorption of light into an electrical response. A fundamental question in sensory transduction is how these processes contribute to the response. To study this question, we use a well-accepted phototransduction model, which we analyse with a novel method based on the log transform of the current. We derive an analytical solution that describes the entire time course of the photoreceptor response to dim flashes of light. We use this solution to dissect and quantify the contribution of each process to the response. We find that the entire dim-flash response is proportional to the flash intensity. By normalizing responses to unit amplitude, we define a waveform that is independent of the light intensity and characterizes the invariant shape of dim-flash responses. We show that this waveform is exclusively determined by deactivation rates; activation rates only scale the waveform and affect the amplitude. This analysis corrects a previous assumption that the rising phase is determined entirely by activation rates. We further show that the rising phase depends on Ca2+ feedback to the cyclase, contrary to current belief. We identify the deactivation rates that control the recovery phase of the response, and we devise new methods to extract activation and deactivation rates from an analysis of response shape and response amplitude. In summary, we provide a comprehensive understanding of how the various transduction processes produce the cellular response.
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Affiliation(s)
- Annia Abtout
- Institut de Biologie de l'École Normale Supérieure, Paris, France
| | - Gordon Fain
- Department of Integrative Biology and Physiology, University of California, Los Angeles, California, USA.,Department of Ophthalmology and Stein Eye Institute, University of California, Los Angeles, California, USA
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10
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Rod Photoreceptors Avoid Saturation in Bright Light by the Movement of the G Protein Transducin. J Neurosci 2021; 41:3320-3330. [PMID: 33593858 DOI: 10.1523/jneurosci.2817-20.2021] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2020] [Revised: 01/21/2021] [Accepted: 01/26/2021] [Indexed: 11/21/2022] Open
Abstract
Rod photoreceptors can be saturated by exposure to bright background light, so that no flash superimposed on the background can elicit a detectable response. This phenomenon, called increment saturation, was first demonstrated psychophysically by Aguilar and Stiles and has since been shown in many studies to occur in single rods. Recent experiments indicate, however, that rods may be able to avoid saturation under some conditions of illumination. We now show in ex vivo electroretinogram and single-cell recordings that in continuous and prolonged exposure even to very bright light, the rods of mice from both sexes recover as much as 15% of their dark current and that responses can persist for hours. In parallel to recovery of outer segment current is an ∼10-fold increase in the sensitivity of rod photoresponses. This recovery is decreased in transgenic mice with reduced light-dependent translocation of the G protein transducin. The reduction in outer-segment transducin together with a novel mechanism of visual-pigment regeneration within the rod itself enable rods to remain responsive over the whole of the physiological range of vision. In this way, rods are able to avoid an extended period of transduction channel closure, which is known to cause photoreceptor degeneration.SIGNIFICANCE STATEMENT Rods are initially saturated in bright light so that no flash superimposed on the background can elicit a detectable response. Frederiksen and colleagues show in whole retina and single-cell recordings that, if the background light is prolonged, rods slowly recover and can continue to produce significant responses over the entire physiological range of vision. Response recovery occurs by translocation of the G protein transducin from the rod outer to the inner segment, together with a novel mechanism of visual-pigment regeneration within the rod itself. Avoidance of saturation in bright light may be one of the principal mechanisms the retina uses to keep rod outer-segment channels from ever closing for too long a time, which is known to produce photoreceptor degeneration.
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11
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Light responses of mammalian cones. Pflugers Arch 2021; 473:1555-1568. [PMID: 33742309 DOI: 10.1007/s00424-021-02551-0] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Revised: 02/28/2021] [Accepted: 03/03/2021] [Indexed: 12/24/2022]
Abstract
Cone photoreceptors provide the foundation of most of human visual experience, but because they are smaller and less numerous than rods in most mammalian retinas, much less is known about their physiology. We describe new techniques and approaches which are helping to provide a better understanding of cone function. We focus on several outstanding issues, including the identification of the features of the phototransduction cascade that are responsible for the more rapid kinetics and decreased sensitivity of the cone response, the roles of inner-segment voltage-gated and Ca2+-activated channels, the means by which cones remain responsive even in the brightest illumination, mechanisms of cone visual pigment regeneration in constant light, and energy consumption of cones in comparison to that of rods.
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12
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Diversity of the Gβγ complexes defines spatial and temporal bias of GPCR signaling. Cell Syst 2021; 12:324-337.e5. [PMID: 33667409 DOI: 10.1016/j.cels.2021.02.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2020] [Revised: 12/09/2020] [Accepted: 02/04/2021] [Indexed: 01/04/2023]
Abstract
The signal transduction by G-protein-coupled receptors (GPCRs) is mediated by heterotrimeric G proteins composed from one of the 16 Gα subunits and the inseparable Gβγ complex assembled from a repertoire of 5 Gβ and 12 Gγ subunits. However, the functional role of compositional diversity in Gβγ complexes has been elusive. Using optical biosensors, we examined the function of all Gβγ combinations in living cells and uncovered two major roles of Gβγ diversity. First, we demonstrate that the identity of Gβγ subunits greatly influences the kinetics and efficacy of GPCR responses at the plasma membrane. Second, we show that different Gβγ combinations are selectively dispatched from the plasma membrane to various cellular organelles on a timescale from milliseconds to minutes. We describe the mechanisms regulating these processes and document their implications for GPCR signaling via various Gα subunits, thereby illustrating a role for the compositional diversity of G protein heterotrimers.
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13
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Chaya T, Furukawa T. Post-translational modification enzymes as key regulators of ciliary protein trafficking. J Biochem 2021; 169:633-642. [PMID: 33681987 PMCID: PMC8423421 DOI: 10.1093/jb/mvab024] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2021] [Accepted: 02/24/2021] [Indexed: 12/14/2022] Open
Abstract
Primary cilia are evolutionarily conserved microtubule-based organelles that protrude from the surface of almost all cell types and decode a variety of extracellular stimuli. Ciliary dysfunction causes human diseases named ciliopathies, which span a wide range of symptoms, such as developmental and sensory abnormalities. The assembly, disassembly, maintenance and function of cilia rely on protein transport systems including intraflagellar transport (IFT) and lipidated protein intraflagellar targeting (LIFT). IFT is coordinated by three multisubunit protein complexes with molecular motors along the ciliary axoneme, while LIFT is mediated by specific chaperones that directly recognize lipid chains. Recently, it has become clear that several post-translational modification enzymes play crucial roles in the regulation of IFT and LIFT. Here, we review our current understanding of the roles of these post-translational modification enzymes in the regulation of ciliary protein trafficking as well as their regulatory mechanisms, physiological significance and involvement in human diseases.
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Affiliation(s)
- Taro Chaya
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, 565-0871, Japan
| | - Takahisa Furukawa
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, 565-0871, Japan
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14
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Lankford CK, Laird JG, Inamdar SM, Baker SA. A Comparison of the Primary Sensory Neurons Used in Olfaction and Vision. Front Cell Neurosci 2020; 14:595523. [PMID: 33250719 PMCID: PMC7676898 DOI: 10.3389/fncel.2020.595523] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2020] [Accepted: 10/06/2020] [Indexed: 12/18/2022] Open
Abstract
Vision, hearing, smell, taste, and touch are the tools used to perceive and navigate the world. They enable us to obtain essential resources such as food and highly desired resources such as mates. Thanks to the investments in biomedical research the molecular unpinning’s of human sensation are rivaled only by our knowledge of sensation in the laboratory mouse. Humans rely heavily on vision whereas mice use smell as their dominant sense. Both modalities have many features in common, starting with signal detection by highly specialized primary sensory neurons—rod and cone photoreceptors (PR) for vision, and olfactory sensory neurons (OSN) for the smell. In this chapter, we provide an overview of how these two types of primary sensory neurons operate while highlighting the similarities and distinctions.
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Affiliation(s)
- Colten K Lankford
- Department of Biochemistry, University of Iowa, Iowa City, IA, United States
| | - Joseph G Laird
- Department of Biochemistry, University of Iowa, Iowa City, IA, United States
| | - Shivangi M Inamdar
- Department of Biochemistry, University of Iowa, Iowa City, IA, United States
| | - Sheila A Baker
- Department of Biochemistry, University of Iowa, Iowa City, IA, United States.,Department of Ophthalmology and Visual Sciences, University of Iowa, Iowa City, IA, United States
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15
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Srivastava D, Yadav RP, Inamdar SM, Huang Z, Sokolov M, Boyd K, Artemyev NO. Transducin Partners Outside the Phototransduction Pathway. Front Cell Neurosci 2020; 14:589494. [PMID: 33173469 PMCID: PMC7591391 DOI: 10.3389/fncel.2020.589494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Accepted: 09/10/2020] [Indexed: 11/13/2022] Open
Abstract
Transducin mediates signal transduction in a classical G protein-coupled receptor (GPCR) phototransduction cascade. Interactions of transducin with the receptor and the effector molecules had been extensively investigated and are currently defined at the atomic level. However, partners and functions of rod transducin α (Gαt 1) and βγ (Gβ1γ1) outside the visual pathway are not well-understood. In particular, light-induced redistribution of rod transducin from the outer segment to the inner segment and synaptic terminal (IS/ST) allows Gαt1 and/or Gβ1γ1 to modulate synaptic transmission from rods to rod bipolar cells (RBCs). Protein-protein interactions underlying this modulation are largely unknown. We discuss known interactors of transducin in the rod IS/ST compartment and potential pathways leading to the synaptic effects of light-dispersed Gαt1 and Gβ1γ1. Furthermore, we show that a prominent non-GPCR guanine nucleotide exchange factor (GEF) and a chaperone of Gα subunits, resistance to inhibitors of cholinesterase 8A (Ric-8A) protein, is expressed throughout the retina including photoreceptor cells. Recent structures of Ric-8A alone and in complexes with Gα subunits have illuminated the structural underpinnings of the Ric-8A activities. We generated a mouse model with conditional knockout of Ric-8A in rods in order to begin defining the functional roles of the protein in rod photoreceptors and the retina. Our analysis suggests that Ric-8A is not an obligate chaperone of Gαt1. Further research is needed to investigate probable roles of Ric-8A as a GEF, trafficking chaperone, or a mediator of the synaptic effects of Gαt1.
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Affiliation(s)
- Dhiraj Srivastava
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
| | - Ravi P Yadav
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
| | - Shivangi M Inamdar
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
| | - Zhen Huang
- Department of Neurology and Neuroscience, University of Wisconsin-Madison, Madison, WI, United States
| | - Maxim Sokolov
- Department of Ophthalmology, Biochemistry and Neuroscience, West Virginia University, Morgantown, WV, United States
| | - Kimberly Boyd
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
| | - Nikolai O Artemyev
- Department of Molecular Physiology and Biophysics, The University of Iowa Carver College of Medicine, Iowa City, IA, United States.,Department of Ophthalmology and Visual Sciences, Ophthalmology and Visual Sciences, The University of Iowa Carver College of Medicine, Iowa City, IA, United States
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16
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Genc AM, Makia MS, Sinha T, Conley SM, Al-Ubaidi MR, Naash MI. Retbindin: A riboflavin Binding Protein, Is Critical for Photoreceptor Homeostasis and Survival in Models of Retinal Degeneration. Int J Mol Sci 2020; 21:ijms21218083. [PMID: 33138244 PMCID: PMC7662319 DOI: 10.3390/ijms21218083] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2020] [Revised: 10/19/2020] [Accepted: 10/23/2020] [Indexed: 12/12/2022] Open
Abstract
The large number of inherited retinal disease genes (IRD), including the photopigment rhodopsin and the photoreceptor outer segment (OS) structural component peripherin 2 (PRPH2), has prompted interest in identifying common cellular mechanisms involved in degeneration. Although metabolic dysregulation has been shown to play an important role in the progression of the disease etiology, identifying a common regulator that can preserve the metabolic ecosystem is needed for future development of neuroprotective treatments. Here, we investigated whether retbindin (RTBDN), a rod-specific protein with riboflavin binding capability, and a regulator of riboflavin-derived cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), is protective to the retina in different IRD models; one carrying the P23H mutation in rhodopsin (which causes retinitis pigmentosa) and one carrying the Y141C mutation in Prph2 (which causes a blended cone-rod dystrophy). RTBDN levels are significantly upregulated in both the rhodopsin (Rho)P23H/+ and Prph2Y141C/+ retinas. Rod and cone structural and functional degeneration worsened in models lacking RTBDN. In addition, removing Rtbdn worsened other phenotypes, such as fundus flecking. Retinal flavin levels were reduced in RhoP23H/+/Rtbdn−/− and Prph2Y141C/+/Rtbdn−/− retinas. Overall, these findings suggest that RTBDN may play a protective role during retinal degenerations that occur at varying rates and due to varying disease mechanisms.
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Affiliation(s)
- Ayse M. Genc
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA; (A.M.G.); (M.S.M.); (T.S.)
| | - Mustafa S. Makia
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA; (A.M.G.); (M.S.M.); (T.S.)
| | - Tirthankar Sinha
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA; (A.M.G.); (M.S.M.); (T.S.)
| | - Shannon M. Conley
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA;
- Oklahoma Center for Neurosciences, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | - Muayyad R. Al-Ubaidi
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA; (A.M.G.); (M.S.M.); (T.S.)
- College of Optometry, University of Houston, Houston, TX 77204, USA
- Department of Biology and Biochemistry, University of Houston, TX 77204, USA
- Correspondence: (M.R.A.-U.); (M.I.N.); Tel.: +1-713-743-1651 (M.R.A.-U. & M.I.N.); Fax: +1-713-743-0226 (M.R.A.-U. & M.I.N.)
| | - Muna I. Naash
- Department of Biomedical Engineering, University of Houston, Houston, TX 77204, USA; (A.M.G.); (M.S.M.); (T.S.)
- College of Optometry, University of Houston, Houston, TX 77204, USA
- Department of Biology and Biochemistry, University of Houston, TX 77204, USA
- Correspondence: (M.R.A.-U.); (M.I.N.); Tel.: +1-713-743-1651 (M.R.A.-U. & M.I.N.); Fax: +1-713-743-0226 (M.R.A.-U. & M.I.N.)
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17
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Rhodopsin-mediated light-off-induced protein kinase A activation in mouse rod photoreceptor cells. Proc Natl Acad Sci U S A 2020; 117:26996-27003. [PMID: 33046651 DOI: 10.1073/pnas.2009164117] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Light-induced extrasynaptic dopamine release in the retina reduces adenosine 3',5'-cyclic monophosphate (cAMP) in rod photoreceptor cells, which is thought to mediate light-dependent desensitization. However, the fine time course of the cAMP dynamics in rods remains elusive due to technical difficulty. Here, we visualized the spatiotemporal regulation of cAMP-dependent protein kinase (PKA) in mouse rods by two-photon live imaging of retinal explants of PKAchu mice, which express a fluorescent biosensor for PKA. Unexpectedly, in addition to the light-on-induced suppression, we observed prominent light-off-induced PKA activation. This activation required photopic light intensity and was confined to the illuminated rods. The estimated maximum spectral sensitivity of 489 nm and loss of the light-off-induced PKA activation in rod-transducin-knockout retinas strongly suggest the involvement of rhodopsin. In support of this notion, rhodopsin-deficient retinal explants showed only the light-on-induced PKA suppression. Taken together, these results suggest that, upon photopic light stimulation, rhodopsin and dopamine signals are integrated to shape the light-off-induced cAMP production and following PKA activation. This may support the dark adaptation of rods.
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18
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Abstract
Numerous rhodopsin mutations have been implicated in night blindness and retinal degeneration, often with unclear etiology. D190N-rhodopsin (D190N-Rho) is a well-known inherited human mutation causing retinitis pigmentosa. Both higher-than-normal spontaneous-isomerization activity and misfolding/mistargeting of the mutant protein have been proposed as causes of the disease, but neither explanation has been thoroughly examined. We replaced wild-type rhodopsin (WT-Rho) in RhoD190N/WT mouse rods with a largely "functionally silenced" rhodopsin mutant to isolate electrical responses triggered by D190N-Rho activity, and found that D190N-Rho at the single-molecule level indeed isomerizes more frequently than WT-Rho by over an order of magnitude. Importantly, however, this higher molecular dark activity does not translate into an overall higher cellular dark noise, owing to diminished D190N-Rho content in the rod outer segment. Separately, we found that much of the degeneration and shortened outer-segment length of RhoD190N/WT mouse rods was not averted by ablating rod transducin in phototransduction-also consistent with D190N-Rho's higher isomerization activity not being the primary cause of disease. Instead, the low pigment content, shortened outer-segment length, and a moderate unfolded protein response implicate protein misfolding as the major pathogenic problem. Finally, D190N-Rho also provided some insight into the mechanism of spontaneous pigment excitation.
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19
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Dembla E, Dembla M, Maxeiner S, Schmitz F. Synaptic ribbons foster active zone stability and illumination-dependent active zone enrichment of RIM2 and Cav1.4 in photoreceptor synapses. Sci Rep 2020; 10:5957. [PMID: 32249787 PMCID: PMC7136232 DOI: 10.1038/s41598-020-62734-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2019] [Accepted: 03/18/2020] [Indexed: 02/08/2023] Open
Abstract
Rod photoreceptor synapses use large, ribbon-type active zones for continuous synaptic transmission during light and dark. Since ribbons are physically connected to the active zones, we asked whether illumination-dependent changes of ribbons influence Cav1.4/RIM2 protein clusters at the active zone and whether these illumination-dependent effects at the active zone require the presence of the synaptic ribbon. We found that synaptic ribbon length and the length of presynaptic Cav1.4/RIM2 clusters are tightly correlated. Dark-adaptation did not change the number of ribbons and active zone puncta. However, mean ribbon length and length of presynaptic Cav1.4/RIM2 clusters increased significantly during dark-adaptation when tonic exocytosis is highest. In the present study, we identified by the analyses of synaptic ribbon-deficient RIBEYE knockout mice that synaptic ribbons are (1) needed to stabilize Cav1.4/RIM2 at rod photoreceptor active zones and (2) are required for the darkness-induced active zone enrichment of Cav1.4/RIM2. These data propose a role of the ribbon in active zone stabilization and suggest a homeostatic function of the ribbon in illumination-dependent active zone remodeling.
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Affiliation(s)
- Ekta Dembla
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany.
| | - Mayur Dembla
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany
| | - Stephan Maxeiner
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany
- Institute of Anatomy and Cell Biology, Saarland University, AG Krasteva-Christ, 66421, Homburg, Germany
| | - Frank Schmitz
- Institute of Anatomy and Cell Biology, Department of Neuroanatomy, Saarland University, Medical School, 66421, Homburg, Germany.
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20
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Chaya T, Tsutsumi R, Varner LR, Maeda Y, Yoshida S, Furukawa T. Cul3-Klhl18 ubiquitin ligase modulates rod transducin translocation during light-dark adaptation. EMBO J 2019; 38:e101409. [PMID: 31696965 DOI: 10.15252/embj.2018101409] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2018] [Revised: 09/30/2019] [Accepted: 10/08/2019] [Indexed: 01/02/2023] Open
Abstract
Adaptation is a general feature of sensory systems. In rod photoreceptors, light-dependent transducin translocation and Ca2+ homeostasis are involved in light/dark adaptation and prevention of cell damage by light. However, the underlying regulatory mechanisms remain unclear. Here, we identify mammalian Cul3-Klhl18 ubiquitin ligase as a transducin translocation modulator during light/dark adaptation. Under dark conditions, Klhl18-/- mice exhibited decreased rod light responses and subcellular localization of the transducin α-subunit (Tα), similar to that observed in light-adapted Klhl18+/+ mice. Cul3-Klhl18 promoted ubiquitination and degradation of Unc119, a rod Tα-interacting protein. Unc119 overexpression phenocopied Tα mislocalization observed in Klhl18-/- mice. Klhl18 weakly recognized casein kinase-2-phosphorylated Unc119 protein, which is dephosphorylated by Ca2+ -dependent phosphatase calcineurin. Calcineurin inhibition increased Unc119 expression and Tα mislocalization in rods. These results suggest that Cul3-Klhl18 modulates rod Tα translocation during light/dark adaptation through Unc119 ubiquitination, which is affected by phosphorylation. Notably, inactivation of the Cul3-Klhl18 ligase and calcineurin inhibitors FK506 and cyclosporine A that are known immunosuppressant drugs repressed light-induced photoreceptor damage, suggesting potential therapeutic targets.
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Affiliation(s)
- Taro Chaya
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
| | - Ryotaro Tsutsumi
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
| | - Leah Rie Varner
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
| | - Yamato Maeda
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
| | - Satoyo Yoshida
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
| | - Takahisa Furukawa
- Laboratory for Molecular and Developmental Biology, Institute for Protein Research, Osaka University, Osaka, Japan
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21
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Satir P, Satir BH. The conserved ancestral signaling pathway from cilium to nucleus. J Cell Sci 2019; 132:132/15/jcs230441. [PMID: 31375541 DOI: 10.1242/jcs.230441] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 07/02/2019] [Indexed: 12/13/2022] Open
Abstract
Many signaling molecules are localized to both the primary cilium and nucleus. Localization of specific transmembrane receptors and their signaling scaffold molecules in the cilium is necessary for correct physiological function. After a specific signaling event, signaling molecules leave the cilium, usually in the form of an endocytic vesicle scaffold, and move to the nucleus, where they dissociate from the scaffold and enter the nucleus to affect gene expression. This ancient pathway probably arose very early in eukaryotic evolution as the nucleus and cilium co-evolved. Because there are similarities in molecular composition of the nuclear and ciliary pores the entry and exit of proteins in both organelles rely on similar mechanisms. In this Hypothesis, we propose that the pathway is a dynamic universal cilia-based signaling pathway with some variations from protists to man. Everywhere the cilium functions as an important organelle for molecular storage of certain key receptors and selection and concentration of their associated signaling molecules that move from cilium to nucleus. This could also have important implications for human diseases such as Huntington disease.
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Affiliation(s)
- Peter Satir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, New York, NY 10461 .,B&P Nanobiology Consultants, 7 Byfield Lane, Greenwich, CT 06830, USA
| | - Birgit H Satir
- Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, New York, NY 10461.,B&P Nanobiology Consultants, 7 Byfield Lane, Greenwich, CT 06830, USA
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Restoration of vision after de novo genesis of rod photoreceptors in mammalian retinas. Nature 2018; 560:484-488. [PMID: 30111842 PMCID: PMC6107416 DOI: 10.1038/s41586-018-0425-3] [Citation(s) in RCA: 166] [Impact Index Per Article: 27.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Accepted: 07/03/2018] [Indexed: 02/07/2023]
Abstract
In zebrafish, Müller glial cells (MGs) are a source of retinal stem cells that can replenish damaged retinal neurons and restore vision1. In mammals, however, MGs lack regenerative capability as they do not spontaneously re-enter the cell cycle to generate a population of stem/progenitor cells that differentiate into retinal neurons. The regenerative machinery may exist in the mammalian retina, however, as retinal injury can stimulate MG proliferation followed by limited neurogenesis2–7. The fundamental question remains whether MG-derived regeneration can be exploited to restore vision in mammalian retinas. Previously, we showed that gene transfer of β-catenin stimulates MG proliferation in the absence of injury in mouse retinas8. Here, we report that following gene transfer of β-catenin, cell-cycle-reactivated MGs can be reprogrammed into rod photoreceptors via a subsequent gene transfer of transcription factors that are essential for rod cell fate specification and determination. MG-derived rods restored visual responses in Gnat1rd17:Gnat2cpfl3 double mutant mice, a model of congenital blindness9,10, throughout the visual pathway from the retina to the primary visual cortex. Together, our results provide evidence of vision restoration after de novo MG-derived genesis of rod photoreceptors in mammalian retinas.
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Ex Vivo Functional Evaluation of Synaptic Transmission from Rods to Rod Bipolar Cells in Mice. Methods Mol Biol 2018; 1753:203-216. [PMID: 29564791 DOI: 10.1007/978-1-4939-7720-8_14] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Abstract
Mice have been widely used as a model organism to study mechanisms of phototransduction and synaptic transmission in the retina. Genetic manipulations and electrophysiological techniques for analysis of photoreceptor and rod bipolar cell function in mice are uniquely advanced. Here, we describe a set of biochemical and electrophysiological techniques for evaluation of synaptic transmission at the rod-rod bipolar cell synapse, which represents the first and key step in the processing of dim-light visual information.
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Jean F, Pilgrim D. Coordinating the uncoordinated: UNC119 trafficking in cilia. Eur J Cell Biol 2017; 96:643-652. [PMID: 28935136 DOI: 10.1016/j.ejcb.2017.09.001] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2017] [Revised: 08/25/2017] [Accepted: 09/05/2017] [Indexed: 12/29/2022] Open
Abstract
Constructing the distinct subcellular environment of the cilium relies in a large part upon intraflagellar transport (IFT) proteins, which traffic cargo both to and within the cilium. However, evidence from the last 10 years suggests that IFT alone is not sufficient to generate the ciliary environment. One essential factor is UNC119, which interacts with known IFT molecular switches to transport ciliary cargos. Despite its apparent importance in ciliary trafficking though, human UNC119 mutations have only rarely been associated with diseases commonly linked with ciliopathies. This review will outline the trafficking pathways required for constructing the cilium by highlighting UNC119's role and the complexities involved in ciliary trafficking. Finally, despite important roles for UNC119 in cilia, UNC119 proteins also interact with non-ciliary proteins to affect other cellular processes.
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25
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Eich ML, Dembla E, Wahl S, Dembla M, Schwarz K, Schmitz F. The Calcineurin-Binding, Activity-Dependent Splice Variant Dynamin1xb Is Highly Enriched in Synapses in Various Regions of the Central Nervous System. Front Mol Neurosci 2017; 10:230. [PMID: 28790889 PMCID: PMC5524891 DOI: 10.3389/fnmol.2017.00230] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2017] [Accepted: 07/06/2017] [Indexed: 12/22/2022] Open
Abstract
In the present study, we generated and characterized a splice site-specific monoclonal antibody that selectively detects the calcineurin-binding dynamin1 splice variant dynamin1xb. Calcineurin is a Ca2+-regulated phosphatase that enhances dynamin1 activity and is an important Ca2+-sensing mediator of homeostatic synaptic plasticity in neurons. Using this dynamin1xb-specific antibody, we found dynamin1xb highly enriched in synapses of all analyzed brain regions. In photoreceptor ribbon synapses, dynamin1xb was enriched in close vicinity to the synaptic ribbon in a manner indicative of a peri-active zone immunolabeling. Interestingly, in dark-adapted mice we observed an enhanced and selective enrichment of dynamin1xb in both synaptic layers of the retina in comparison to light-adapted mice. This could be due to an illumination-dependent recruitment of dynamin1xb to retinal synapses and/or due to a darkness-induced increase of dynamin1xb biosynthesis. These latter findings indicate that dynamin1xb is part of a versatile and highly adjustable, activity-regulated endocytic synaptic machinery.
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Affiliation(s)
- Marie-Lisa Eich
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
| | - Ekta Dembla
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
| | - Silke Wahl
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
| | - Mayur Dembla
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
| | - Karin Schwarz
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
| | - Frank Schmitz
- Department of Neuroanatomy, Medical School Homburg/Saar, Institute for Anatomy and Cell Biology, Saarland UniversityHomburg/Saar, Germany
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26
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Rose K, Walston ST, Chen J. Separation of photoreceptor cell compartments in mouse retina for protein analysis. Mol Neurodegener 2017; 12:28. [PMID: 28399904 PMCID: PMC5387348 DOI: 10.1186/s13024-017-0171-2] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2016] [Accepted: 03/30/2017] [Indexed: 02/02/2023] Open
Abstract
BACKGROUND Light exposure triggers movement of certain signaling proteins within the cellular compartments of the highly polarized rod photoreceptor cell. This redistribution of proteins between the inner and outer segment compartments affects the performance and physiology of the rod cell. In addition, newly synthesized phototransduction proteins traverse from the site of their synthesis in the inner segment, through the thin connecting cilium, to reach their destination in the outer segment. Processes that impede normal trafficking of these abundant proteins lead to cell death. The study of movement and unique localization of biomolecules within the different compartments of the rod cell would be greatly facilitated by techniques that reliably separate these compartments. Ideally, these methods can be applied to the mouse retina due to the widespread usage of transgenic mouse models in the investigation of basic visual processes and disease mechanisms that affect vision. Although the retina is organized in distinct layers, the small and highly curved mouse retina makes physical separation of retinal layers a challenge. We introduce two peeling methods that efficiently and reliably isolate the rod outer segment and other cell compartments for Western blots to examine protein movement across these compartments. METHODS The first separation method employs Whatman® filter paper to successively remove the rod outer segments from isolated, live mouse retinas. The second method utilizes ScotchTM tape to peel the rod outer segment layer and the rod inner segment layer from lyophilized mouse retinas. Both procedures can be completed within one hour. RESULTS We utilize these two protocols on dark-adapted and light-exposed retinas of C57BL/6 mice and subject the isolated tissue layers to Western blots to demonstrate their effectiveness in detecting light-induced translocation of transducin (GNAT1) and rod arrestin (ARR1). Furthermore, we provide evidence that RGS9 does not undergo light-induced translocation. CONCLUSIONS These results demonstrate the effectiveness of the two different peeling protocols for the separation of the layered compartments of the mouse retina and their utility for investigations of protein compositions within these compartments.
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Affiliation(s)
- Kasey Rose
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA
| | - Steven T Walston
- Department of Biomedical Engineering, Viterbi School of Engineering, University of Southern California, Los Angeles, California, USA
| | - Jeannie Chen
- Zilkha Neurogenetic Institute, Keck School of Medicine, University of Southern California, Los Angeles, California, USA. .,Department of Cell & Neurobiology, Keck School of Medicine, University of Southern California, Los Angeles, California, USA.
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A Presynaptic Group III mGluR Recruits Gβγ/SNARE Interactions to Inhibit Synaptic Transmission by Cone Photoreceptors in the Vertebrate Retina. J Neurosci 2017; 37:4618-4634. [PMID: 28363980 DOI: 10.1523/jneurosci.2948-16.2017] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Revised: 03/27/2017] [Accepted: 03/28/2017] [Indexed: 11/21/2022] Open
Abstract
G-protein βγ subunits (Gβγ) interact with presynaptic proteins and regulate neurotransmitter release downstream of Ca2+ influx. To accomplish their roles in sensory signaling, photoreceptor synapses use specialized presynaptic proteins that support neurotransmission at active zone structures known as ribbons. While several G-protein coupled receptors (GPCRs) influence synaptic transmission at ribbon synapses of cones and other retinal neurons, it is unknown whether Gβγ contributes to these effects. We tested whether activation of one particular GPCR, a metabotropic glutamate receptor (mGluR), can reduce cone synaptic transmission via Gβγ in tiger salamander retinas. In recordings from horizontal cells, we found that an mGluR agonist (L-AP4) reduced cone-driven light responses and mEPSC frequency. In paired recordings of cones and horizontal cells, L-AP4 slightly reduced cone ICa (∼10%) and caused a larger reduction in cone-driven EPSCs (∼30%). Proximity ligation assay revealed direct interactions between SNAP-25 and Gβγ subunits in retinal synaptic layers. Pretreatment with the SNAP-25 cleaving protease BoNT/A inhibited L-AP4 effects on synaptic transmission, as did introduction of a peptide derived from the SNAP-25 C terminus. Introducing Gβγ subunits directly into cones reduced EPSC amplitude. This effect was inhibited by BoNT/A, supporting a role for Gβγ/SNAP-25 interactions. However, the mGluR-dependent reduction in ICa was not mimicked by Gβγ, indicating that this effect was independent of Gβγ. The finding that synaptic transmission at cone ribbon synapses is regulated by Gβγ/SNAP-25 interactions indicates that these mechanisms are shared by conventional and ribbon-type synapses. Gβγ liberated from other photoreceptor GPCRs is also likely to regulate synaptic transmission.SIGNIFICANCE STATEMENT Dynamic regulation of synaptic transmission by presynaptic G-protein coupled receptors shapes information flow through neural circuits. At the first synapse in the visual system, presynaptic metabotropic glutamate receptors (mGluRs) regulate cone photoreceptor synaptic transmission, although the mechanisms and functional impact of this are unclear. We show that mGluRs regulate light response encoding across the cone synapse, accomplished in part by triggering G-protein βγ subunits (Gβγ) interactions with SNAP-25, a core component of the synaptic vesicle fusion machinery. In addition to revealing a role in visual processing, this provides the first demonstration that Gβγ/SNAP-25 interactions regulate synaptic function at a ribbon-type synapse, contributing to an emerging picture of the ubiquity of Gβγ/SNARE interactions in regulating synaptic transmission throughout the nervous system.
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28
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Wang Y, Fehlhaber KE, Sarria I, Cao Y, Ingram NT, Guerrero-Given D, Throesch B, Baldwin K, Kamasawa N, Ohtsuka T, Sampath AP, Martemyanov KA. The Auxiliary Calcium Channel Subunit α2δ4 Is Required for Axonal Elaboration, Synaptic Transmission, and Wiring of Rod Photoreceptors. Neuron 2017; 93:1359-1374.e6. [PMID: 28262416 PMCID: PMC5364038 DOI: 10.1016/j.neuron.2017.02.021] [Citation(s) in RCA: 67] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2016] [Revised: 12/31/2016] [Accepted: 02/08/2017] [Indexed: 11/24/2022]
Abstract
Neural circuit wiring relies on selective synapse formation whereby a presynaptic release apparatus is matched with its cognate postsynaptic machinery. At metabotropic synapses, the molecular mechanisms underlying this process are poorly understood. In the mammalian retina, rod photoreceptors form selective contacts with rod ON-bipolar cells by aligning the presynaptic voltage-gated Ca2+ channel directing glutamate release (CaV1.4) with postsynaptic mGluR6 receptors. We show this coordination requires an extracellular protein, α2δ4, which complexes with CaV1.4 and the rod synaptogenic mediator, ELFN1, for trans-synaptic alignment with mGluR6. Eliminating α2δ4 in mice abolishes rod synaptogenesis and synaptic transmission to rod ON-bipolar cells, and disrupts postsynaptic mGluR6 clustering. We further find that in rods, α2δ4 is crucial for organizing synaptic ribbons and setting CaV1.4 voltage sensitivity. In cones, α2δ4 is essential for CaV1.4 function, but is not required for ribbon organization, synaptogenesis, or synaptic transmission. These findings offer insights into retinal pathologies associated with α2δ4 dysfunction.
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Affiliation(s)
- Yuchen Wang
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Katherine E Fehlhaber
- Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Ignacio Sarria
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Yan Cao
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA
| | - Norianne T Ingram
- Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Debbie Guerrero-Given
- Electron Microscopy Core Facility, Max Planck Florida Institute, 1 Max Planck Way, Jupiter, FL 33458, USA
| | - Ben Throesch
- Department of Molecular and Cellular Neuroscience, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92121, USA
| | - Kristin Baldwin
- Department of Molecular and Cellular Neuroscience, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92121, USA
| | - Naomi Kamasawa
- Electron Microscopy Core Facility, Max Planck Florida Institute, 1 Max Planck Way, Jupiter, FL 33458, USA
| | - Toshihisa Ohtsuka
- Department of Biochemistry, University of Yamanashi, Yamanashi 409-3898, Japan
| | - Alapakkam P Sampath
- Jules Stein Eye Institute, Department of Ophthalmology, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Kirill A Martemyanov
- Department of Neuroscience, The Scripps Research Institute, Jupiter, FL 33458, USA.
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29
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Pahlberg J, Frederiksen R, Pollock GE, Miyagishima KJ, Sampath AP, Cornwall MC. Voltage-sensitive conductances increase the sensitivity of rod photoresponses following pigment bleaching. J Physiol 2017; 595:3459-3469. [PMID: 28168711 DOI: 10.1113/jp273398] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Accepted: 01/29/2017] [Indexed: 01/16/2023] Open
Abstract
KEY POINTS Following substantial bleaching of the visual pigment, the desensitization of the rod photovoltage is not as substantial as the desensitization of the rod outer segment photocurrent. The block of cation conductances during the internal dialysis of Cs+ further desensitizes the photovoltage thereby eliminating its difference in desensitization with the rod outer segment photocurrent. Bleached visual pigment produced an acceleration of the rod photovoltage with respect to the outer segment photocurrent, which is eliminated upon internal dialysis of Cs+ . ABSTRACT A majority of our visual experience occurs during the day when a substantial fraction of the visual pigment in our photoreceptor cells is bleached. Under these conditions it is widely believed that rods are saturated and do not contribute substantially to downstream signalling. However, behavioural experiments on subjects with only rod function reveals that these individuals unexpectedly retain substantial vision in daylight. We sought to understand this discrepancy by characterizing the sensitivity of rod photoresponses following exposure to bright bleaching light. Measurements of the rod outer segment photocurrent in transgenic mice, which have only rod function, revealed the well-studied reduction in the sensitivity of rod photoresponses following pigment bleaching. However, membrane voltage measurements showed that the desensitization of the photovoltage was considerably less than that of the outer segment photocurrent following equivalent pigment bleaching. This discrepancy was largely eliminated during the blockade of cation channels due to the internal dialysis of Cs+ , which increased the bleach-induced desensitization of the photovoltage and slowed its temporal characteristics. Thus, sensitization of the photovoltage by rod inner segment conductances appears to extend the operating range of rod phototransduction following pigment bleaching.
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Affiliation(s)
- Johan Pahlberg
- Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, 90095, USA
| | - Rikard Frederiksen
- Physiology and Biophysics, Boston University School of Medicine, Boston, MA, 02118, USA
| | - Gabriel E Pollock
- Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, 90095, USA
| | - Kiyoharu J Miyagishima
- Unit on Retinal Neurophysiology, National Eye Institute Intramural Program, National Institutes of Health, Bethesda, MD, 20892, USA
| | - Alapakkam P Sampath
- Ophthalmology, Stein Eye Institute, University of California, Los Angeles, CA, 90095, USA
| | - M Carter Cornwall
- Physiology and Biophysics, Boston University School of Medicine, Boston, MA, 02118, USA
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30
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In vivo optophysiology reveals that G-protein activation triggers osmotic swelling and increased light scattering of rod photoreceptors. Proc Natl Acad Sci U S A 2017; 114:E2937-E2946. [PMID: 28320964 DOI: 10.1073/pnas.1620572114] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The light responses of rod and cone photoreceptors have been studied electrophysiologically for decades, largely with ex vivo approaches that disrupt the photoreceptors' subretinal microenvironment. Here we report the use of optical coherence tomography (OCT) to measure light-driven signals of rod photoreceptors in vivo. Visible light stimulation over a 200-fold intensity range caused correlated rod outer segment (OS) elongation and increased light scattering in wild-type mice, but not in mice lacking the rod G-protein alpha subunit, transducin (Gαt), revealing these responses to be triggered by phototransduction. For stimuli that photoactivated one rhodopsin per Gαt the rod OS swelling response reached a saturated elongation of 10.0 ± 2.1%, at a maximum rate of 0.11% s-1 Analyzing swelling as osmotically driven water influx, we find the H2O membrane permeability of the rod OS to be (2.6 ± 0.4) × 10-5 cm⋅s-1, comparable to that of other cells lacking aquaporin expression. Application of Van't Hoff's law reveals that complete activation of phototransduction generates a potentially harmful 20% increase in OS osmotic pressure. The increased backscattering from the base of the OS is explained by a model combining cytoplasmic swelling, translocation of dissociated G-protein subunits from the disc membranes into the cytoplasm, and a relatively higher H2O permeability of nascent discs in the basal rod OS. Translocation of phototransduction components out of the OS may protect rods from osmotic stress, which could be especially harmful in disease conditions that affect rod OS structural integrity.
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31
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Murphy J, Kolandaivelu S. Palmitoylation of Progressive Rod-Cone Degeneration (PRCD) Regulates Protein Stability and Localization. J Biol Chem 2016; 291:23036-23046. [PMID: 27613864 DOI: 10.1074/jbc.m116.742767] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2016] [Indexed: 11/06/2022] Open
Abstract
Progressive rod-cone degeneration (PRCD) is a photoreceptor outer segment (OS) disc-specific protein with unknown function that is associated with retinitis pigmentosa (RP). The most common mutation in PRCD linked with severe RP phenotype is substitution of the only cysteine to tyrosine (C2Y). In this study, we find that PRCD is post-translationally modified by a palmitoyl lipid group at the cysteine residue linked with RP. Disrupting PRCD palmitoylation either chemically or by genetically eliminating the modified cysteine dramatically affects the stability of PRCD. Furthermore, in vivo electroporation of PRCD C2Y mutant in the mouse retina demonstrates that the palmitoylation of PRCD is important for its proper localization in the photoreceptor OS. Mutant PRCD C2Y was found in the inner segment in contrast to normal localization of WT PRCD in the OS. Our results also suggest that zDHHC3, a palmitoyl acyltransferase (PAT), catalyzes the palmitoylation of PRCD in the Golgi compartment. In conclusion, we find that the palmitoylation of PRCD is crucial for its trafficking to the photoreceptor OS and mislocalization of this protein likely leads to RP-related phenotypes.
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Affiliation(s)
- Joseph Murphy
- From the Department of Ophthalmology, West Virginia University Eye institute, Morgantown, West Virginia 26506
| | - Saravanan Kolandaivelu
- From the Department of Ophthalmology, West Virginia University Eye institute, Morgantown, West Virginia 26506
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32
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Reingruber J, Holcman D, Fain GL. How rods respond to single photons: Key adaptations of a G-protein cascade that enable vision at the physical limit of perception. Bioessays 2015; 37:1243-52. [PMID: 26354340 DOI: 10.1002/bies.201500081] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Rod photoreceptors are among the most sensitive light detectors in nature. They achieve their remarkable sensitivity across a wide variety of species through a number of essential adaptations: a specialized cellular geometry, a G-protein cascade with an unusually stable receptor molecule, a low-noise transduction mechanism, a nearly perfect effector enzyme, and highly evolved mechanisms of feedback control and receptor deactivation. Practically any change in protein expression, enzyme activity, or feedback control can be shown to impair photon detection, either by decreasing sensitivity or signal-to-noise ratio, or by reducing temporal resolution. Comparison of mammals to amphibians suggests that rod outer-segment morphology and the molecules and mechanism of transduction may have evolved together to optimize light sensitivity in darkness, which culminates in the extraordinary ability of these cells to respond to single photons at the ultimate limit of visual perception.
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Affiliation(s)
- Jürgen Reingruber
- IBENS, Group of Computational Biology and Applied Mathematics, École Normale Supérieure, Paris, France.,INSERM U1024, Paris, France
| | - David Holcman
- IBENS, Group of Computational Biology and Applied Mathematics, École Normale Supérieure, Paris, France.,Department of Mathematics and Theoretical Physics, University of Cambridge, Cambridge, UK
| | - Gordon L Fain
- Department of Integrative Biology and Physiology, Terasaki Life Sciences, University of California, Los Angeles, CA, USA.,Department of Ophthalmology, Jules Stein Eye Institute, University of California, Los Angeles, CA, USA
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33
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Exchange of Cone for Rod Phosphodiesterase 6 Catalytic Subunits in Rod Photoreceptors Mimics in Part Features of Light Adaptation. J Neurosci 2015; 35:9225-35. [PMID: 26085644 DOI: 10.1523/jneurosci.3563-14.2015] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
UNLABELLED Despite the expression of homologous phototransduction components, the molecular basis for differences in light-evoked responses between rod and cone photoreceptors remains unclear. We examined the role of cGMP phosphodiesterase (PDE6) in this difference by expressing cone PDE6 (PDE6C) in rd1/rd1 rods lacking rod PDE6 (PDE6AB) using transgenic mice. The expression of PDE6C rescues retinal degeneration observed in rd1/rd1 rods. Double-transgenic rods (PDE6C++) were compared with rd1/+ rods based on similar PDE6 expression. PDE6C increased the basal PDE activity and speeded the rate-limiting step for phototransduction deactivation, causing rod photoresponses to appear light adapted, with reduced dark current and sensitivity and faster response kinetics. When PDE6C++ and rd1/+ rods were exposed to similar background light, rd1/+ rods displayed greater desensitization. These results indicate an increased spontaneous activity and faster deactivation of PDE6C compared with PDE6AB in darkness, but that background light increases steady PDE6C activity to a lesser extent. In addition to accelerating the recovery of the photoresponse, faster PDE6C deactivation may blunt the rise in background-induced steady PDE6C activity. Therefore, higher basal PDE6C activity and faster deactivation together partially account for faster and less sensitive cone photoresponses in darkness, whereas a reduced rise of steady PDE6C activity in background light may allow cones to avoid saturation. SIGNIFICANCE STATEMENT Cones are the primary photoreceptors responsible for most of our visual experience. Cone light responses are less sensitive and display speeded responses compared with rods. Despite the fact that rods and cones use a G-protein signaling cascade with similar organization, the mechanistic basis for these differences remains unclear. Here, we examined the role of distinct isoforms of PDE6, the effector enzyme in phototransduction, in these differences. We developed a transgenic mouse model that expresses cone PDE6 in rods and show that the cone PDE6 isoform is partially responsible for the difference in sensitivity and response kinetics between rods and cones.
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34
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Ramon E, Cordomí A, Aguilà M, Srinivasan S, Dong X, Moore AT, Webster AR, Cheetham ME, Garriga P. Differential light-induced responses in sectorial inherited retinal degeneration. J Biol Chem 2014; 289:35918-28. [PMID: 25359768 DOI: 10.1074/jbc.m114.609958] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Retinitis pigmentosa (RP) is a group of genetically and clinically heterogeneous inherited degenerative retinopathies caused by abnormalities of photoreceptors or retinal pigment epithelium in the retina leading to progressive sight loss. Rhodopsin is the prototypical G-protein-coupled receptor located in the vertebrate retina and is responsible for dim light vision. Here, novel M39R and N55K variants were identified as causing an intriguing sector phenotype of RP in affected patients, with selective degeneration in the inferior retina. To gain insights into the molecular aspects associated with this sector RP phenotype, whose molecular mechanism remains elusive, the mutations were constructed by site-directed mutagenesis, expressed in heterologous systems, and studied by biochemical, spectroscopic, and functional assays. M39R and N55K opsins had variable degrees of chromophore regeneration when compared with WT opsin but showed no gross structural misfolding or altered trafficking. M39R showed a faster rate for transducin activation than WT rhodopsin with a faster metarhodopsinII decay, whereas N55K presented a reduced activation rate and an altered photobleaching pattern. N55K also showed an altered retinal release from the opsin binding pocket upon light exposure, affecting its optimal functional response. Our data suggest that these sector RP mutations cause different protein phenotypes that may be related to their different clinical progression. Overall, these findings illuminate the molecular mechanisms of sector RP associated with rhodopsin mutations.
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Affiliation(s)
- Eva Ramon
- From the Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain
| | - Arnau Cordomí
- the Laboratori de Medicina Computacional, Unitat de Bioestadística, Facultat de Medicina, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Spain
| | - Mònica Aguilà
- the University College London Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, United Kingdom, and
| | - Sundaramoorthy Srinivasan
- From the Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain
| | - Xiaoyun Dong
- From the Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain
| | - Anthony T Moore
- the University College London Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, United Kingdom, and the Moorfields Eye Hospital, London EC1V 2PD, United Kingdom
| | - Andrew R Webster
- the University College London Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, United Kingdom, and the Moorfields Eye Hospital, London EC1V 2PD, United Kingdom
| | - Michael E Cheetham
- the University College London Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, United Kingdom, and
| | - Pere Garriga
- From the Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Rambla de Sant Nebridi 22, 08222 Terrassa, Spain,
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