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Castillo García M, Urdapilleta E. A dynamical adaptation model of visual spatiotemporal processing in cones and horizontal cells. Math Biosci 2023; 366:109104. [PMID: 37918478 DOI: 10.1016/j.mbs.2023.109104] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 10/26/2023] [Accepted: 10/29/2023] [Indexed: 11/04/2023]
Abstract
In this work, we introduce a phenomenological model for the cone-horizontal cell assembly, including spatial integration and formation of receptive field-like structures. The model extends our previous dynamical adaptation description with gain control accounting for processes in single cones, valid in severe nonlinear regimes. Here, a spatially extended feedback mechanism is introduced from horizontal cells to cones to account for experimental evidence, contributing thus to the development of a center-surround receptive field in cones and downstream bipolar cells. Feedback gain is defined on different spatial scales by weighting spatial filters: a short scale accounting for cone input to the feedback mechanism and a large scale driven by the syncytium characteristics of horizontal cells. A third spatial scale improves the description, mimicking neighboring cone-cone coupling. This overall spatial integration couples to temporal signal processing, thus obtaining a spatiotemporal model of outer retina responses capable of reproducing nonlinear features in both dimensions (space and time). The model was tested and validated using measurements on horizontal cells from different studies, with excellent performance. By its phenomenological nature, signal processing properties are inferred from model parameters. The model can be used in arrays of processing units with more complex incoming patterns of visual stimuli.
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Affiliation(s)
- Miguel Castillo García
- Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica (CNEA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo, Av. E. Bustillo 9500, R8402AGP San Carlos de Bariloche, Río Negro, Argentina
| | - Eugenio Urdapilleta
- Centro Atómico Bariloche and Instituto Balseiro, Comisión Nacional de Energía Atómica (CNEA), Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET), Universidad Nacional de Cuyo, Av. E. Bustillo 9500, R8402AGP San Carlos de Bariloche, Río Negro, Argentina.
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2
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Abtout A, Reingruber J. Analysis of dim-light responses in rod and cone photoreceptors with altered calcium kinetics. J Math Biol 2023; 87:69. [PMID: 37823947 PMCID: PMC10570263 DOI: 10.1007/s00285-023-02005-4] [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: 12/07/2022] [Revised: 09/12/2023] [Accepted: 09/25/2023] [Indexed: 10/13/2023]
Abstract
Rod and cone photoreceptors in the retina of vertebrates are the primary sensory neurons underlying vision. They convert light into an electrical current using a signal transduction pathway that depends on Ca[Formula: see text] feedback. It is known that manipulating the Ca[Formula: see text] kinetics affects the response shape and the photoreceptor sensitivity, but a precise quantification of these effects remains unclear. We have approached this task in mouse retina by combining numerical simulations with mathematical analysis. We consider a parsimonious phototransduction model that incorporates negative Ca[Formula: see text] feedback onto the synthesis of cyclic GMP, and fast buffering reactions to alter the Ca[Formula: see text] kinetics. We derive analytic results for the photoreceptor functioning in sufficiently dim light conditions depending on the photoreceptor type. We exploit these results to obtain conceptual and quantitative insight into how response waveform and amplitude depend on the underlying biophysical processes and the Ca[Formula: see text] feedback. With a low amount of buffering, the Ca[Formula: see text] concentration changes in proportion to the current, and responses to flashes of light are monophasic. With more buffering, the change in the Ca[Formula: see text] concentration becomes delayed with respect to the current, which gives rise to a damped oscillation and a biphasic waveform. This shows that biphasic responses are not necessarily a manifestation of slow buffering reactions. We obtain analytic approximations for the peak flash amplitude as a function of the light intensity, which shows how the photoreceptor sensitivity depends on the biophysical parameters. Finally, we study how changing the extracellular Ca[Formula: see text] concentration affects the response.
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Affiliation(s)
- Annia Abtout
- Institute of Biology, Ecole Normale Supérieure, Paris, France
| | - Jürgen Reingruber
- Institute of Biology, Ecole Normale Supérieure, Paris, France.
- INSERM, U1024, Paris, France.
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3
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Muangkram Y, Himeno Y, Amano A. Clarifying the composition of the ATP consumption factors required for maintaining ion homeostasis in mouse rod photoreceptors. Sci Rep 2023; 13:14161. [PMID: 37644037 PMCID: PMC10465610 DOI: 10.1038/s41598-023-40663-y] [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: 04/11/2023] [Accepted: 08/16/2023] [Indexed: 08/31/2023] Open
Abstract
To date, no effective treatment has been established for photoreceptor loss due to energy imbalances, but numerous therapeutic approaches have reported some success in slowing photoreceptor degeneration by downregulating energy demand. However, the detailed mechanisms remain unclear. This study aimed to clarify the composition of ATP consumption factors in photoreceptors in darkness and in light. We introduced mathematical formulas for ionic current activities combined with a phototransduction model to form a new mathematical model for estimating the energy expenditure of each ionic current. The proposed model included various ionic currents identified in mouse rods using a gene expression database incorporating an available electrophysiological recording of each specific gene. ATP was mainly consumed by Na+/K+-ATPase and plasma membrane Ca2+-ATPase pumps to remove excess Na+ and Ca2+. The rod consumed 7 [Formula: see text] 107 molecules of ATP s-1, where 65% was used to remove ions from the cyclic nucleotide-gated channel and 20% from the hyperpolarization-activated current in darkness. Increased light intensity raised the energy requirements of the complex phototransduction cascade mechanisms. Nevertheless, the overall energy consumption was less than that in darkness due to the significant reduction in ATPase activities, where the hyperpolarization-activated current proportion increased to 83%. A better understanding of energy demand/supply may provide an effective tool for investigating retinal pathophysiological changes and analyzing novel therapeutic treatments related to the energy consumption of photoreceptors.
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Affiliation(s)
- Yuttamol Muangkram
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan.
| | - Yukiko Himeno
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan
| | - Akira Amano
- Department of Bioinformatics, College of Life Sciences, Ritsumeikan University, Shiga, Japan
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Yee C, Görtemaker K, Wellpott R, Koch KW. Kinetics of cone specific G-protein signaling in avian photoreceptor cells. Front Mol Neurosci 2023; 16:1107025. [PMID: 36733826 PMCID: PMC9887155 DOI: 10.3389/fnmol.2023.1107025] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2022] [Accepted: 01/03/2023] [Indexed: 01/19/2023] Open
Abstract
Cone photoreceptor cells of night-migratory songbirds seem to process the primary steps of two different senses, vision and magnetoreception. The molecular basis of phototransduction is a prototypical G protein-coupled receptor pathway starting with the photoexcitation of rhodopsin or cone opsin thereby activating a heterotrimeric G protein named transducin. This interaction is well understood in vertebrate rod cells, but parameter describing protein-protein interactions of cone specific proteins are rare and not available for migratory birds. European robin is a model organism for studying the orientation of birds in the earth magnetic field. Recent findings showed a link between the putative magnetoreceptor cryptochrome 4a and the cone specific G-protein of European robin. In the present work, we investigated the interaction of European robin cone specific G protein and cytoplasmic regions of long wavelength opsin. We identified the second loop in opsin connecting transmembrane regions three and four as a critical binding interface. Surface plasmon resonance studies using a synthetic peptide representing the second cytoplasmic loop and purified G protein α-subunit showed a high affinity interaction with a K D value of 21 nM. Truncation of the G protein α-subunit at the C-terminus by six amino acids slightly decreased the affinity. Our results suggest that binding of the G protein to cryptochrome can compete with the interaction of G protein and non-photoexcited long wavelength opsin. Thus, the parallel presence of two different sensory pathways in bird cone photoreceptors is reasonable under dark-adapted conditions or during illumination with short wavelengths.
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Affiliation(s)
- Chad Yee
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, Oldenburg, Germany
| | - Katharina Görtemaker
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, Oldenburg, Germany
| | - Rieke Wellpott
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, Oldenburg, Germany
| | - Karl-Wilhelm Koch
- Division of Biochemistry, Department of Neuroscience, University of Oldenburg, Oldenburg, Germany,Research Center Neurosensory Sciences, University of Oldenburg, Oldenburg, Germany,*Correspondence: Karl-Wilhelm Koch, ✉
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Caruso G, Klaus C, Hamm HE, Gurevich VV, Bisegna P, Andreucci D, DiBenedetto E, Makino CL. Pepperberg plot: Modeling flash response saturation in retinal rods of mouse. Front Mol Neurosci 2023; 15:1054449. [PMID: 36710929 PMCID: PMC9880052 DOI: 10.3389/fnmol.2022.1054449] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Accepted: 11/09/2022] [Indexed: 01/15/2023] Open
Abstract
Retinal rods evolved to be able to detect single photons. Despite their exquisite sensitivity, rods operate over many log units of light intensity. Several processes inside photoreceptor cells make this incredible light adaptation possible. Here, we added to our previously developed, fully space resolved biophysical model of rod phototransduction, some of the mechanisms that play significant roles in shaping the rod response under high illumination levels: the function of RGS9 in shutting off G protein transducin, and calcium dependences of the phosphorylation rates of activated rhodopsin, of the binding of cGMP to the light-regulated ion channel, and of two membrane guanylate cyclase activities. A well stirred version of this model captured the responses to bright, saturating flashes in WT and mutant mouse rods and was used to explain "Pepperberg plots," that graph the time during which the response is saturated against the natural logarithm of flash strength for bright flashes. At the lower end of the range, saturation time increases linearly with the natural logarithm of flash strength. The slope of the relation (τD) is dictated by the time constant of the rate-limiting (slowest) step in the shutoff of the phototransduction cascade, which is the hydrolysis of GTP by transducin. We characterized mathematically the X-intercept ( Φ o ) which is the number of photoisomerizations that just saturates the rod response. It has been observed that for flash strengths exceeding a few thousand photoisomerizations, the curves depart from linearity. Modeling showed that the "upward bend" for very bright flash intensities could be explained by the dynamics of RGS9 complex and further predicted that there would be a plateau at flash strengths giving rise to more than ~107 photoisomerizations due to activation of all available PDE. The model accurately described alterations in saturation behavior of mutant murine rods resulting from transgenic perturbations of the cascade targeting membrane guanylate cyclase activity, and expression levels of GRK, RGS9, and PDE. Experimental results from rods expressing a mutant light-regulated channel purported to lack calmodulin regulation deviated from model predictions, suggesting that there were other factors at play.
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Affiliation(s)
- Giovanni Caruso
- Italian National Research Council, Istituto di Scienze del Patrimonio Culturale, Rome, Italy
| | - Colin Klaus
- The College of Public Health Division of Biostatistics and The Mathematical Biosciences Institute, The Ohio State University, Columbus, OH, United States
| | - Heidi E. Hamm
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Vsevolod V. Gurevich
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States
| | - Paolo Bisegna
- Department of Civil Engineering and Computer Science, University of Rome Tor Vergata, Rome, Italy
| | - Daniele Andreucci
- Department of Basic and Applied Sciences for Engineering, Sapienza University of Rome, Rome, Italy
| | | | - Clint L. Makino
- Department of Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, MA, United States,*Correspondence: Clint L. Makino,
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Klaus C, Caruso G, Gurevich VV, Hamm HE, Makino CL, DiBenedetto E. Phototransduction in retinal cones: Analysis of parameter importance. PLoS One 2021; 16:e0258721. [PMID: 34710119 PMCID: PMC8553137 DOI: 10.1371/journal.pone.0258721] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Accepted: 10/05/2021] [Indexed: 12/26/2022] Open
Abstract
In daylight, cone photoreceptors in the retina are responsible for the bulk of visual perception, yet compared to rods, far less is known quantitatively about their biochemistry. This is partly because it is hard to isolate and purify cone proteins. The issue is also complicated by the synergistic interaction of these parameters in producing systems biology outputs, such as photoresponse. Using a 3-D resolved, finite element model of cone outer segments, here we conducted a study of parameter significance using global sensitivity analysis, by Sobol indices, which was contextualized within the uncertainty surrounding these parameters in the available literature. The analysis showed that a subset of the parameters influencing the circulating dark current, such as the turnover rate of cGMP in the dark, may be most influential for variance with experimental flash response, while the shut-off rates of photoexcited rhodopsin and phosphodiesterase also exerted sizable effect. The activation rate of transducin by rhodopsin and the light-induced hydrolysis rate of cGMP exerted measurable effects as well but were estimated as relatively less significant. The results of this study depend on experimental ranges currently described in the literature and should be revised as these become better established. To that end, these findings may be used to prioritize parameters for measurement in future investigations.
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Affiliation(s)
- Colin Klaus
- The Mathematical Biosciences Institute, The Ohio State University, Columbus, Ohio, United States of America
| | - Giovanni Caruso
- CNR, Ist. Tecnologie Applicate ai Beni Culturali, Rome, Italy
| | - Vsevolod V. Gurevich
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States of America
| | - Heidi E. Hamm
- Department of Pharmacology, Vanderbilt University Medical Center, Nashville, TN, United States of America
| | - Clint L. Makino
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, MA, United States of America
| | - Emmanuele DiBenedetto
- Department of Mathematics, Vanderbilt University, Nashville, TN, United States of America
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Zang J, Gesemann M, Keim J, Samardzija M, Grimm C, Neuhauss SCF. Circadian regulation of vertebrate cone photoreceptor function. eLife 2021; 10:e68903. [PMID: 34550876 PMCID: PMC8494479 DOI: 10.7554/elife.68903] [Citation(s) in RCA: 6] [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: 03/30/2021] [Accepted: 09/20/2021] [Indexed: 12/16/2022] Open
Abstract
Eukaryotes generally display a circadian rhythm as an adaption to the reoccurring day/night cycle. This is particularly true for visual physiology that is directly affected by changing light conditions. Here we investigate the influence of the circadian rhythm on the expression and function of visual transduction cascade regulators in diurnal zebrafish and nocturnal mice. We focused on regulators of shut-off kinetics such as Recoverins, Arrestins, Opsin kinases, and Regulator of G-protein signaling that have direct effects on temporal vision. Transcript as well as protein levels of most analyzed genes show a robust circadian rhythm-dependent regulation, which correlates with changes in photoresponse kinetics. Electroretinography demonstrates that photoresponse recovery in zebrafish is delayed in the evening and accelerated in the morning. Functional rhythmicity persists in continuous darkness, and it is reversed by an inverted light cycle and disrupted by constant light. This is in line with our finding that orthologous gene transcripts from diurnal zebrafish and nocturnal mice are often expressed in an anti-phasic daily rhythm.
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Affiliation(s)
- Jingjing Zang
- University of Zurich, Department of Molecular Life SciencesZurichSwitzerland
| | - Matthias Gesemann
- University of Zurich, Department of Molecular Life SciencesZurichSwitzerland
| | - Jennifer Keim
- University of Zurich, Department of Molecular Life SciencesZurichSwitzerland
| | - Marijana Samardzija
- Lab for Retinal Cell Biology, Department of Ophthalmology, University Hospital Zurich, University of ZurichZurichSwitzerland
| | - Christian Grimm
- Lab for Retinal Cell Biology, Department of Ophthalmology, University Hospital Zurich, University of ZurichZurichSwitzerland
| | - Stephan CF Neuhauss
- University of Zurich, Department of Molecular Life SciencesZurichSwitzerland
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A hybrid stochastic/deterministic model of single photon response and light adaptation in mouse rods. Comput Struct Biotechnol J 2021; 19:3720-3734. [PMID: 34285774 PMCID: PMC8258797 DOI: 10.1016/j.csbj.2021.06.033] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2021] [Revised: 06/19/2021] [Accepted: 06/21/2021] [Indexed: 12/02/2022] Open
Abstract
A hybrid stochastic/deterministic model of mouse rod phototransduction is presented. Rod photocurrent to photovoltage conversion in darkness is accurately characterized. Photoresponses to dim and bright stimuli and in various mutants are well reproduced. Recently debated molecular mechanisms of the phototransduction cascade are examined.
The phototransduction cascade is paradigmatic for signaling pathways initiated by G protein-coupled receptors and is characterized by a fine regulation of photoreceptor sensitivity and electrical response to a broad range of light stimuli. Here, we present a biochemically comprehensive model of phototransduction in mouse rods based on a hybrid stochastic and deterministic mathematical framework, and a quantitatively accurate description of the rod impedance in the dark. The latter, combined with novel patch clamp recordings from rod outer segments, enables the interconversion of dim flash responses between photovoltage and photocurrent and thus direct comparison with the simulations. The model reproduces the salient features of the experimental photoresponses at very dim and bright stimuli, for both normal photoreceptors and those with genetically modified cascade components. Our modelling approach recapitulates a number of recent findings in vertebrate phototransduction. First, our results are in line with the recently established requirement of dimeric activation of PDE6 by transducin and further show that such conditions can be fulfilled at the expense of a significant excess of G protein activated by rhodopsin. Secondly, simulations suggest a crucial role of the recoverin-mediated Ca2+-feedback on rhodopsin kinase in accelerating the shutoff, when light flashes are delivered in the presence of a light background. Finally, stochastic simulations suggest that transient complexes between dark rhodopsin and transducin formed prior to light stimulation increase the reproducibility of single photon responses. Current limitations of the model are likely associated with the yet unknown mechanisms governing the shutoff of the cascade.
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Key Words
- ADP, adenosine diphosphate
- ATP, adenosine-5′-triphosphate
- Arr, arrestin
- BG, background illumination
- CNG, cyclic nucleotide-gated (channel)
- CSM, completely substituted mutant of rhodopsin
- CV, coefficient of variation
- DM, deterministic model
- Dynamic modeling
- E, effector of the phototransduction cascade, activated PDE
- FFT, fast Fourier-transform
- GC, guanylate cyclase
- GCAPs, guanylate cyclase-activating proteins
- GDP, guanosine-5′-diphosphate
- GPCR, G protein-coupled receptor
- GTP, guanosine-5′-triphosphate
- Gt, G protein/transducin
- Gα, α-subunit of the G protein
- Gβγ, β- and γ-subunit of the G protein
- HSDM, hybrid stochastic/deterministic model
- Light adaptation
- MPR, multiple photon response
- PDE, phosphodiesterase 6
- Ph, photons
- Phototransduction
- R, rhodopsin
- RGS, regulator of G protein signaling
- RK, rhodopsin kinase
- ROS, rod outer segment
- Rec, recoverin
- Rn, activated rhodopsin that has been phosphorylated n times
- SD, standard deviation
- SPR, single photon response
- Stochastic simulation
- Systems biology
- TTP, time to peak
- cGMP, cyclic guanosine monophosphate
- ΔJ, photocurrent
- ΔU, photovoltage
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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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Avesani A, Marino V, Zanzoni S, Koch KW, Dell'Orco D. Molecular properties of human guanylate cyclase-activating protein 2 (GCAP2) and its retinal dystrophy-associated variant G157R. J Biol Chem 2021; 296:100619. [PMID: 33812995 PMCID: PMC8113879 DOI: 10.1016/j.jbc.2021.100619] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2021] [Revised: 03/25/2021] [Accepted: 03/30/2021] [Indexed: 12/31/2022] Open
Abstract
In murine and bovine photoreceptors, guanylate cyclase-activating protein 2 (GCAP2) activates retinal guanylate cyclases (GCs) at low Ca2+ levels, thus contributing to the Ca2+/cGMP negative feedback on the cyclase together with its paralog guanylate cyclase-activating protein 1, which has the same function but different Ca2+ sensitivity. In humans, a GCAP2 missense mutation (G157R) has been associated with inherited retinal degeneration (IRD) via an unknown molecular mechanism. Here, we characterized the biochemical properties of human GCAP2 and the G157R variant, focusing on its dimerization and the Ca2+/Mg2+-binding processes in the presence or absence of N-terminal myristoylation. We found that human GCAP2 and its bovine/murine orthologs significantly differ in terms of oligomeric properties, cation binding, and GC regulation. Myristoylated GCAP2 endothermically binds up to 3 Mg2+ with high affinity and forms a compact dimer that may reversibly dissociate in the presence of Ca2+. Conversely, nonmyristoylated GCAP2 does not bind Mg2+ over the physiological range and remains as a monomer in the absence of Ca2+. Both myristoylated and nonmyristoylated GCAP2 bind Ca2+ with high affinity. At odds with guanylate cyclase-activating protein 1 and independently of myristoylation, human GCAP2 does not significantly activate retinal GC1 in a Ca2+-dependent fashion. The IRD-associated G157R variant is characterized by a partly misfolded, molten globule-like conformation with reduced affinity for cations and prone to form aggregates, likely mediated by hydrophobic interactions. Our findings suggest that GCAP2 might be mostly implicated in processes other than phototransduction in human photoreceptors and suggest a possible molecular mechanism for G157R-associated IRD.
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Affiliation(s)
- Anna Avesani
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Valerio Marino
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy
| | - Serena Zanzoni
- Centro Piattaforme Tecnologiche, University of Verona, Verona, Italy
| | - Karl-Wilhelm Koch
- Department of Neuroscience, Division of Biochemistry, University of Oldenburg, Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurosciences, Biomedicine and Movement Sciences, Biological Chemistry Section, University of Verona, Verona, Italy.
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Yoshimatsu T, Schröder C, Nevala NE, Berens P, Baden T. Fovea-like Photoreceptor Specializations Underlie Single UV Cone Driven Prey-Capture Behavior in Zebrafish. Neuron 2020; 107:320-337.e6. [PMID: 32473094 PMCID: PMC7383236 DOI: 10.1016/j.neuron.2020.04.021] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2019] [Revised: 02/13/2020] [Accepted: 04/21/2020] [Indexed: 01/04/2023]
Abstract
In the eye, the function of same-type photoreceptors must be regionally adjusted to process a highly asymmetrical natural visual world. Here, we show that UV cones in the larval zebrafish area temporalis are specifically tuned for UV-bright prey capture in their upper frontal visual field, which may use the signal from a single cone at a time. For this, UV-photon detection probability is regionally boosted more than 10-fold. Next, in vivo two-photon imaging, transcriptomics, and computational modeling reveal that these cones use an elevated baseline of synaptic calcium to facilitate the encoding of bright objects, which in turn results from expressional tuning of phototransduction genes. Moreover, the light-driven synaptic calcium signal is regionally slowed by interactions with horizontal cells and later accentuated at the level of glutamate release driving retinal networks. These regional differences tally with variations between peripheral and foveal cones in primates and hint at a common mechanistic origin.
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Affiliation(s)
| | - Cornelius Schröder
- Institute of Ophthalmic Research, University of Tübingen, Tübingen 72076, Germany; Center for Integrative Neuroscience, University of Tübingen, Tübingen 72076, Germany
| | - Noora E Nevala
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK
| | - Philipp Berens
- Institute of Ophthalmic Research, University of Tübingen, Tübingen 72076, Germany; Center for Integrative Neuroscience, University of Tübingen, Tübingen 72076, Germany; Institute for Bioinformatics and Medical Informatics, University of Tübingen, Tübingen 72076, Germany
| | - Tom Baden
- School of Life Sciences, University of Sussex, Brighton BN1 9QG, UK; Institute of Ophthalmic Research, University of Tübingen, Tübingen 72076, Germany.
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Normal GCAPs partly compensate for altered cGMP signaling in retinal dystrophies associated with mutations in GUCA1A. Sci Rep 2019; 9:20105. [PMID: 31882816 PMCID: PMC6934868 DOI: 10.1038/s41598-019-56606-5] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2019] [Accepted: 12/12/2019] [Indexed: 01/20/2023] Open
Abstract
Missense mutations in the GUCA1A gene encoding guanylate cyclase-activating protein 1 (GCAP1) are associated with autosomal dominant cone/cone-rod (CORD) dystrophies. The nature of the inheritance pattern implies that a pool of normal GCAP proteins is present in photoreceptors together with the mutated variant. To assess whether human GCAP1 and GCAP2 may similarly regulate the activity of the retinal membrane guanylate cyclase GC-1 (GC-E) in the presence of the recently discovered E111V-GCAP1 CORD-variant, we combined biochemical and in silico assays. Surprisingly, human GCAP2 does not activate GC1 over the physiological range of Ca2+ whereas wild-type GCAP1 significantly attenuates the dysregulation of GC1 induced by E111V-GCAP1. Simulation of the phototransduction cascade in a well-characterized murine system, where GCAP2 is able to activate the GC1, suggests that both GCAPs can act in a synergic manner to mitigate the effects of the CORD-mutation. We propose the existence of a species-dependent compensatory mechanism. In murine photoreceptors, slight increases of wild-type GCAPs levels may significantly attenuate the increase in intracellular Ca2+ and cGMP induced by E111V-GCAP1 in heterozygous conditions. In humans, however, the excess of wild-type GCAP1 may only partly attenuate the mutant-induced dysregulation of cGMP signaling due to the lack of GC1-regulation by GCAP2.
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13
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Determination of basal phosphodiesterase activity in mouse rod photoreceptors with cGMP clamp. Sci Rep 2019; 9:1183. [PMID: 30718640 PMCID: PMC6362171 DOI: 10.1038/s41598-018-37661-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Accepted: 12/11/2018] [Indexed: 12/26/2022] Open
Abstract
Light regulates cGMP concentration in the photoreceptor cytoplasm by activating phosphodiesterase (PDE) molecules through a G-protein signalling cascade. Spontaneous PDE activity is present in rod outer segments even in darkness. This basal PDE activity (βdark) has not been determined in wild type mammalian photoreceptor cells although it plays a key role in setting the sensitivity and recovery kinetics of rod responses. We present a novel method for determination of βdark using local electroretinography (LERG) from isolated mouse retinas. The method is based on the ability of PDE inhibitors to decrease βdark, which can be counterbalanced by increasing PDE activity with light. This procedure clamps cytoplasmic cGMP to its dark value. βdark can be calculated based on the amount of light needed for the "cGMP clamp" and information extracted from the registered rod photoresponses. Here we apply this method to determine βdark values for the first time in the mammalian rods and obtain the following estimates for different mouse models: 3.9 s-1 for wild type, 4.5 s-1 for guanylate cyclase activating proteins (GCAPs) knockout, and 4.4 s-1 for GCAPs and recoverin double knockout mice. Our results suggest that depletion of GCAPs or recoverin do not affect βdark.
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14
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Tikidji-Hamburyan A, Reinhard K, Storchi R, Dietter J, Seitter H, Davis KE, Idrees S, Mutter M, Walmsley L, Bedford RA, Ueffing M, Ala-Laurila P, Brown TM, Lucas RJ, Münch TA. Rods progressively escape saturation to drive visual responses in daylight conditions. Nat Commun 2017; 8:1813. [PMID: 29180667 PMCID: PMC5703729 DOI: 10.1038/s41467-017-01816-6] [Citation(s) in RCA: 68] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2017] [Accepted: 10/18/2017] [Indexed: 12/21/2022] Open
Abstract
Rod and cone photoreceptors support vision across large light intensity ranges. Rods, active under dim illumination, are thought to saturate at higher (photopic) irradiances. The extent of rod saturation is not well defined; some studies report rod activity well into the photopic range. Using electrophysiological recordings from retina and dorsal lateral geniculate nucleus of cone-deficient and visually intact mice, we describe stimulus and physiological factors that influence photopic rod-driven responses. We find that rod contrast sensitivity is initially strongly reduced at high irradiances, but progressively recovers to allow responses to moderate contrast stimuli. Surprisingly, rods recover faster at higher light levels. A model of rod phototransduction suggests that phototransduction gain adjustments and bleaching adaptation underlie rod recovery. Consistently, exogenous chromophore reduces rod responses at bright background. Thus, bleaching adaptation renders mouse rods responsive to modest contrast at any irradiance. Paradoxically, raising irradiance across the photopic range increases the robustness of rod responses. Rod photoreceptors are thought to be saturated under bright light. Here, the authors describe the physiological parameters that mediate response saturation of rod photoreceptors in mouse retina, and show that rods can drive visual responses in photopic conditions.
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Affiliation(s)
- Alexandra Tikidji-Hamburyan
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,International Max Planck Research School, University of Tübingen, 72074, Tübingen, Germany.,Department of Neurosurgery and Hansen Experimental Physics Laboratory, Stanford University, Stanford, California, 94305-4085, USA
| | - Katja Reinhard
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,International Max Planck Research School, University of Tübingen, 72074, Tübingen, Germany.,Visual Circuits Laboratory, Neuro-Electronics Research Flanders, IMEC, KU Leuven and VIB, 3001, Leuven, Belgium
| | - Riccardo Storchi
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Johannes Dietter
- Institute for Ophthalmic Research, Department of Ophthalmology, University of Tübingen, 72076, Tübingen, Germany
| | - Hartwig Seitter
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,International Max Planck Research School, University of Tübingen, 72074, Tübingen, Germany.,Institute of Pharmacy, Department of Pharmacology and Toxicology, University of Innsbruck, A-6020, Innsbruck, Austria
| | - Katherine E Davis
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Saad Idrees
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,International Max Planck Research School, University of Tübingen, 72074, Tübingen, Germany
| | - Marion Mutter
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany.,International Max Planck Research School, University of Tübingen, 72074, Tübingen, Germany
| | - Lauren Walmsley
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Robert A Bedford
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK.,Stryker Imorphics, Worthington House, Towers Business Park, Wilmslow Road, Manchester, M20 2HJ, UK
| | - Marius Ueffing
- Institute for Ophthalmic Research, Department of Ophthalmology, University of Tübingen, 72076, Tübingen, Germany
| | - Petri Ala-Laurila
- Department of Biosciences, University of Helsinki, 00014, Helsinki, Finland.,Department of Neuroscience and Biomedical Engineering (NBE), Aalto University School of Science and Technology, 00076, Espoo, Finland
| | - Timothy M Brown
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK
| | - Robert J Lucas
- Faculty of Biology Medicine and Health, University of Manchester, Manchester, M13 9PT, UK.
| | - Thomas A Münch
- Retinal Circuits and Optogenetics, Centre for Integrative Neuroscience and Bernstein Center for Computational Neuroscience, University of Tübingen, 72076, Tübingen, Germany. .,Institute for Ophthalmic Research, Department of Ophthalmology, University of Tübingen, 72076, Tübingen, Germany.
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15
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Invergo BM, Montanucci L, Bertranpetit J. Dynamic sensitivity and nonlinear interactions influence the system-level evolutionary patterns of phototransduction proteins. Proc Biol Sci 2017; 282:20152215. [PMID: 26631565 DOI: 10.1098/rspb.2015.2215] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Determining the influence of complex, molecular-system dynamics on the evolution of proteins is hindered by the significant challenge of quantifying the control exerted by the proteins on system output. We have employed a combination of systems biology and molecular evolution analyses in a first attempt to unravel this relationship. We employed a comprehensive mathematical model of mammalian phototransduction to predict the degree of influence that each protein in the system exerts on the high-level dynamic behaviour. We found that the genes encoding the most dynamically sensitive proteins exhibit relatively relaxed evolutionary constraint. We also investigated the evolutionary and epistatic influences of the many nonlinear interactions between proteins in the system and found several pairs to have coevolved, including those whose interactions are purely dynamical with respect to system output. This evidence points to a key role played by nonlinear system dynamics in influencing patterns of molecular evolution.
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Affiliation(s)
- Brandon M Invergo
- IBE-Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia 08003, Spain
| | - Ludovica Montanucci
- IBE-Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia 08003, Spain
| | - Jaume Bertranpetit
- IBE-Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia 08003, Spain
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16
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Phototransduction early steps model based on Beer-Lambert optical law. Vision Res 2017; 131:75-81. [PMID: 28062154 DOI: 10.1016/j.visres.2016.12.012] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2016] [Revised: 10/27/2016] [Accepted: 12/07/2016] [Indexed: 01/24/2023]
Abstract
The amount of available rhodopsin on the photoreceptor outer segment and its change over time is not considered in classic models of phototransduction. Thus, those models do not take into account the absorptance variation of the outer segment under different brightness conditions. The relationship between the light absorbed by a medium and its absorptance is well described by the Beer-Lambert law. This newly proposed model implements the absorptance variation phenomenon in a set of equations that admit photons per second as input and results in active rhodopsins per second as output. This study compares the classic model of phototransduction developed by Forti et al. (1989) to this new model by using different light stimuli to measure active rhodopsin and photocurrent. The results show a linear relationship between light stimulus and active rhodopsin in the Forti model and an exponential saturation in the new model. Further, photocurrent values have shown that the new model behaves equivalently to the experimental and theoretical data as published by Forti in dark-adapted rods, but fits significantly better under light-adapted conditions. The new model successfully introduced a physics optical law to the standard model of phototransduction adding a new processing layer that had not been mathematically implemented before. In addition, it describes the physiological concept of saturation and delivers outputs in concordance to input magnitudes.
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17
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Periole X. Interplay of G Protein-Coupled Receptors with the Membrane: Insights from Supra-Atomic Coarse Grain Molecular Dynamics Simulations. Chem Rev 2016; 117:156-185. [PMID: 28073248 DOI: 10.1021/acs.chemrev.6b00344] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
G protein-coupled receptors (GPCRs) are central to many fundamental cellular signaling pathways. They transduce signals from the outside to the inside of cells in physiological processes ranging from vision to immune response. It is extremely challenging to look at them individually using conventional experimental techniques. Recently, a pseudo atomistic molecular model has emerged as a valuable tool to access information on GPCRs, more specifically on their interactions with their environment in their native cell membrane and the consequences on their supramolecular organization. This approach uses the Martini coarse grain (CG) model to describe the receptors, lipids, and solvent in molecular dynamics (MD) simulations and in enough detail to allow conserving the chemical specificity of the different molecules. The elimination of unnecessary degrees of freedom has opened up large-scale simulations of the lipid-mediated supramolecular organization of GPCRs. Here, after introducing the Martini CGMD method, we review these studies carried out on various members of the GPCR family, including rhodopsin (visual receptor), opioid receptors, adrenergic receptors, adenosine receptors, dopamine receptor, and sphingosine 1-phosphate receptor. These studies have brought to light an interesting set of novel biophysical principles. The insights range from revealing localized and heterogeneous deformations of the membrane bilayer at the surface of the protein, specific interactions of lipid molecules with individual GPCRs, to the effect of the membrane matrix on global GPCR self-assembly. The review ends with an overview of the lessons learned from the use of the CGMD method, the biophysical-chemical findings on lipid-protein interplay.
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Affiliation(s)
- Xavier Periole
- Biomolecular Sciences and Biotechnology Institute and Zernike Institute for Advanced Materials, University of Groningen , Nijenborgh 7, 9747AG Groningen, The Netherlands
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18
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Fernández-Sampedro MA, Invergo BM, Ramon E, Bertranpetit J, Garriga P. Functional role of positively selected amino acid substitutions in mammalian rhodopsin evolution. Sci Rep 2016; 6:21570. [PMID: 26865329 PMCID: PMC4749998 DOI: 10.1038/srep21570] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2015] [Accepted: 01/27/2016] [Indexed: 12/22/2022] Open
Abstract
Visual rhodopsins are membrane proteins that function as light photoreceptors in the vertebrate retina. Specific amino acids have been positively selected in visual pigments during mammal evolution, which, as products of adaptive selection, would be at the base of important functional innovations. We have analyzed the top candidates for positive selection at the specific amino acids and the corresponding reverse changes (F13M, Q225R and A346S) in order to unravel the structural and functional consequences of these important sites in rhodopsin evolution. We have constructed, expressed and immunopurified the corresponding mutated pigments and analyzed their molecular phenotypes. We find that position 13 is very important for the folding of the receptor and also for proper protein glycosylation. Position 225 appears to be important for the function of the protein affecting the G-protein activation process, and position 346 would also regulate functionality of the receptor by enhancing G-protein activation and presumably affecting protein phosphorylation by rhodopsin kinase. Our results represent a link between the evolutionary analysis, which pinpoints the specific amino acid positions in the adaptive process, and the structural and functional analysis, closer to the phenotype, making biochemical sense of specific selected genetic sequences in rhodopsin evolution.
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Affiliation(s)
- Miguel A Fernández-Sampedro
- Grup de Biotecnologia Molecular i Industrial, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Edifici Gaia, Rambla de Sant Nebridi 22, 08222 Terrassa, Catalonia, Spain
| | - Brandon M Invergo
- IBE - Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia, Spain
| | - Eva Ramon
- Grup de Biotecnologia Molecular i Industrial, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Edifici Gaia, Rambla de Sant Nebridi 22, 08222 Terrassa, Catalonia, Spain
| | - Jaume Bertranpetit
- IBE - Institute of Evolutionary Biology (CSIC-Universitat Pompeu Fabra), CEXS-UPF-PRBB, Barcelona, Catalonia, Spain
| | - Pere Garriga
- Grup de Biotecnologia Molecular i Industrial, Centre de Biotecnologia Molecular, Departament d'Enginyeria Química, Universitat Politècnica de Catalunya, Edifici Gaia, Rambla de Sant Nebridi 22, 08222 Terrassa, Catalonia, Spain
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19
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Koch KW, Dell'Orco D. Protein and Signaling Networks in Vertebrate Photoreceptor Cells. Front Mol Neurosci 2015; 8:67. [PMID: 26635520 PMCID: PMC4646965 DOI: 10.3389/fnmol.2015.00067] [Citation(s) in RCA: 74] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 10/26/2015] [Indexed: 01/10/2023] Open
Abstract
Vertebrate photoreceptor cells are exquisite light detectors operating under very dim and bright illumination. The photoexcitation and adaptation machinery in photoreceptor cells consists of protein complexes that can form highly ordered supramolecular structures and control the homeostasis and mutual dependence of the secondary messengers cyclic guanosine monophosphate (cGMP) and Ca2+. The visual pigment in rod photoreceptors, the G protein-coupled receptor rhodopsin is organized in tracks of dimers thereby providing a signaling platform for the dynamic scaffolding of the G protein transducin. Illuminated rhodopsin is turned off by phosphorylation catalyzed by rhodopsin kinase (GRK1) under control of Ca2+-recoverin. The GRK1 protein complex partly assembles in lipid raft structures, where shutting off rhodopsin seems to be more effective. Re-synthesis of cGMP is another crucial step in the recovery of the photoresponse after illumination. It is catalyzed by membrane bound sensory guanylate cyclases (GCs) and is regulated by specific neuronal Ca2+-sensor proteins called guanylate cyclase-activating proteins (GCAPs). At least one GC (ROS-GC1) was shown to be part of a multiprotein complex having strong interactions with the cytoskeleton and being controlled in a multimodal Ca2+-dependent fashion. The final target of the cGMP signaling cascade is a cyclic nucleotide-gated (CNG) channel that is a hetero-oligomeric protein located in the plasma membrane and interacting with accessory proteins in highly organized microdomains. We summarize results and interpretations of findings related to the inhomogeneous organization of signaling units in photoreceptor outer segments.
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Affiliation(s)
- Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg Oldenburg, Germany
| | - Daniele Dell'Orco
- Department of Neurological, Biomedical and Movement Sciences, Section of Biological Chemistry and Center for BioMedical Computing (CBMC), University of Verona Verona, Italy
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20
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Aquila M, Benedusi M, Fasoli A, Rispoli G. Characterization of Zebrafish Green Cone Photoresponse Recorded with Pressure-Polished Patch Pipettes, Yielding Efficient Intracellular Dialysis. PLoS One 2015; 10:e0141727. [PMID: 26513584 PMCID: PMC4626105 DOI: 10.1371/journal.pone.0141727] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2015] [Accepted: 10/12/2015] [Indexed: 11/18/2022] Open
Abstract
The phototransduction enzymatic cascade in cones is less understood than in rods, and the zebrafish is an ideal model with which to investigate vertebrate and human vision. Therefore, here, for the first time, the zebrafish green cone photoresponse is characterized also to obtain a firm basis for evaluating how it is modulated by exogenous molecules. To this aim, a powerful method was developed to obtain long-lasting recordings with low access resistance, employing pressure-polished patch pipettes. This method also enabled fast, efficient delivery of molecules via a perfusion system coupled with pulled quartz or plastic perfusion tubes, inserted very close to the enlarged pipette tip. Sub-saturating flashes elicited responses in different cells with similar rising phase kinetics but with very different recovery kinetics, suggesting the existence of physiologically distinct cones having different Ca2+ dynamics. Theoretical considerations demonstrate that the different recovery kinetics can be modelled by simulating changes in the Ca2+-buffering capacity of the outer segment. Importantly, the Ca2+-buffer action preserves the fast response rising phase, when the Ca2+-dependent negative feedback is activated by the light-induced decline in intracellular Ca2+.
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Affiliation(s)
- Marco Aquila
- Department of Life Science and Biotechnology, University of Ferrara, Ferrara, Italy
| | - Mascia Benedusi
- Department of Life Science and Biotechnology, University of Ferrara, Ferrara, Italy
| | - Anna Fasoli
- Department of Life Science and Biotechnology, University of Ferrara, Ferrara, Italy
| | - Giorgio Rispoli
- Department of Life Science and Biotechnology, University of Ferrara, Ferrara, Italy
- * E-mail:
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21
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Melanopsin-driven increases in maintained activity enhance thalamic visual response reliability across a simulated dawn. Proc Natl Acad Sci U S A 2015; 112:E5734-43. [PMID: 26438865 DOI: 10.1073/pnas.1505274112] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Twice a day, at dawn and dusk, we experience gradual but very high amplitude changes in background light intensity (irradiance). Although we perceive the associated change in environmental brightness, the representation of such very slow alterations in irradiance by the early visual system has been little studied. Here, we addressed this deficit by recording electrophysiological activity in the mouse dorsal lateral geniculate nucleus under exposure to a simulated dawn. As irradiance increased we found a widespread enhancement in baseline firing that extended to units with ON as well as OFF responses to fast luminance increments. This change in baseline firing was equally apparent when the slow irradiance ramp appeared alone or when a variety of higher-frequency artificial or natural visual stimuli were superimposed upon it. Using a combination of conventional knockout, chemogenetic, and receptor-silent substitution manipulations, we continued to show that, over higher irradiances, this increase in firing originates with inner-retinal melanopsin photoreception. At the single-unit level, irradiance-dependent increases in baseline firing were strongly correlated with improvements in the amplitude of responses to higher-frequency visual stimuli. This in turn results in an up to threefold increase in single-trial reliability of fast visual responses. In this way, our data indicate that melanopsin drives a generalized increase in dorsal lateral geniculate nucleus excitability as dawn progresses that both conveys information about changing background light intensity and increases the signal:noise for fast visual responses.
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22
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Dell'Orco D, Koch KW. Transient complexes between dark rhodopsin and transducin: circumstantial evidence or physiological necessity? Biophys J 2015; 108:775-7. [PMID: 25650944 DOI: 10.1016/j.bpj.2014.12.031] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2014] [Revised: 12/01/2014] [Accepted: 12/05/2014] [Indexed: 01/08/2023] Open
Affiliation(s)
- Daniele Dell'Orco
- Department of Life Sciences and Reproduction, Section of Biological Chemistry and Centre for BioMedical Computing, University of Verona, Verona, Italy.
| | - Karl-Wilhelm Koch
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Oldenburg, Germany.
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23
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Schöneberg J, Heck M, Hofmann KP, Noé F. Explicit spatiotemporal simulation of receptor-G protein coupling in rod cell disk membranes. Biophys J 2015; 107:1042-1053. [PMID: 25185540 DOI: 10.1016/j.bpj.2014.05.050] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2014] [Revised: 05/13/2014] [Accepted: 05/19/2014] [Indexed: 12/11/2022] Open
Abstract
Dim-light vision is mediated by retinal rod cells. Rhodopsin (R), a G-protein-coupled receptor, switches to its active form (R(∗)) in response to absorbing a single photon and activates multiple copies of the G-protein transducin (G) that trigger further downstream reactions of the phototransduction cascade. The classical assumption is that R and G are uniformly distributed and freely diffusing on disk membranes. Recent experimental findings have challenged this view by showing specific R architectures, including RG precomplexes, nonuniform R density, specific R arrangements, and immobile fractions of R. Here, we derive a physical model that describes the first steps of the photoactivation cascade in spatiotemporal detail and single-molecule resolution. The model was implemented in the ReaDDy software for particle-based reaction-diffusion simulations. Detailed kinetic in vitro experiments are used to parametrize the reaction rates and diffusion constants of R and G. Particle diffusion and G activation are then studied under different conditions of R-R interaction. It is found that the classical free-diffusion model is consistent with the available kinetic data. The existence of precomplexes between inactive R and G is only consistent with the data if these precomplexes are weak, with much larger dissociation rates than suggested elsewhere. Microarchitectures of R, such as dimer racks, would effectively immobilize R but have little impact on the diffusivity of G and on the overall amplification of the cascade at the level of the G protein.
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Affiliation(s)
- Johannes Schöneberg
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany
| | - Martin Heck
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Berlin, Germany.
| | - Klaus Peter Hofmann
- Institut für Medizinische Physik und Biophysik, Charité, Universitätsmedizin Berlin, Berlin, Germany
| | - Frank Noé
- Department of Mathematics, Computer Science and Bioinformatics, Freie Universität Berlin, Berlin, Germany.
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24
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Asteriti S, Dal Cortivo G, Pontelli V, Cangiano L, Buffelli M, Dell'Orco D. Effective delivery of recombinant proteins to rod photoreceptors via lipid nanovesicles. Biochem Biophys Res Commun 2015; 461:665-70. [PMID: 25918020 DOI: 10.1016/j.bbrc.2015.04.088] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2015] [Accepted: 04/17/2015] [Indexed: 10/23/2022]
Abstract
The potential of liposomes to deliver functional proteins in retinal photoreceptors and modulate their physiological response was investigated by two experimental approaches. First, we treated isolated mouse retinas with liposomes encapsulating either recoverin, an important endogenous protein operating in visual phototransduction, or antibodies against recoverin. We then intravitrally injected in vivo liposomes encapsulating either rhodamin B or recoverin and we investigated the distribution in retina sections by confocal microscopy. The content of liposomes was found to be released in higher amount in the photoreceptor layer than in the other regions of the retina and the functional effects of the release were in line with the current model of phototransduction. Our study sets the basis for quantitative investigations aimed at assessing the potential of intraocular protein delivery via biocompatible nanovesicles, with promising implications for the treatment of retinal diseases affecting the photoreceptor layer.
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Affiliation(s)
- Sabrina Asteriti
- Dept. of Translational Research, University of Pisa, Pisa, Italy
| | - Giuditta Dal Cortivo
- Dept. of Life Sciences and Reproduction, University of Verona, Strada Le Grazie 8, Verona, Italy
| | - Valeria Pontelli
- Dept. of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, Verona, Italy
| | - Lorenzo Cangiano
- Dept. of Translational Research, University of Pisa, Pisa, Italy
| | - Mario Buffelli
- Dept. of Neurological and Movement Sciences, University of Verona, Strada Le Grazie 8, Verona, Italy; Center for Biomedical Computing, University of Verona, Strada le Grazie 8, 37134 Verona, Italy.
| | - Daniele Dell'Orco
- Dept. of Life Sciences and Reproduction, University of Verona, Strada Le Grazie 8, Verona, Italy; Center for Biomedical Computing, University of Verona, Strada le Grazie 8, 37134 Verona, Italy.
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25
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Köster M, Dell'Orco D, Koch KW. The interaction network of rhodopsin involving the heterotrimeric G-protein transducin and the monomeric GTPase Rac1 is determined by distinct binding processes. FEBS J 2014; 281:5175-85. [PMID: 25243418 DOI: 10.1111/febs.13064] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2014] [Revised: 09/12/2014] [Accepted: 09/18/2014] [Indexed: 12/01/2022]
Abstract
The monomeric G-protein Rac1, a member of the family of Rho/Rac/Cdc42 GTPases, is involved in light-induced photoreceptor degeneration, but its specific role remains elusive. In particular, reports on Rac1 interacting with the visual pigment rhodopsin are puzzling and need a more quantitative examination. We probed the presence of Rac1 in rod outer segments by immunohistochemical staining of bovine retinae and western blot analysis of isolated rod outer segments. Rac1 was present throughout the whole retina except in the outer and inner nuclear layers, but was strongly expressed in photoreceptor cells. Rac1 was distributed in three different fractions of rod outer segments: one fraction was soluble in detergents, a second fraction cosegregated with lipid rafts, and a third fraction was associated with lipid bilayer free axonemal/cytoskeletal structures. We also investigated the interaction between rhodopsin and Rac1 by using surface plasmon resonance spectroscopy under dark and light conditions. Biophysical interaction studies revealed that Rac1 could interact with rhodopsin, but in a light-independent manner, and kinetic analysis indicated that binding of Rac1 occurred with lower affinity and speed than the association of transducin and rhodopsin. Thus, in dark-adapted rod cells, Rac1 cannot compete with transducin for binding to rhodopsin, and signalling can proceed normally. Instead, the concentration of transducin has to drop significantly so that Rac1 can bind to rhodopsin; in the outer segment, this occurs only under intense illumination, when transducin is translocated to the inner segment.
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Affiliation(s)
- Maike Köster
- Department of Neurosciences, Biochemistry Group, University of Oldenburg, Germany
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