The Experts below are selected from a list of 279 Experts worldwide ranked by ideXlab platform
Karl-wilhelm Koch - One of the best experts on this subject based on the ideXlab platform.
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Interaction of G protein-coupled receptor kinases and recoverin isoforms is determined by localization in zebrafish photoreceptors.
Biochimica et biophysica acta. Molecular cell research, 2020Co-Authors: Nicole Ahrens, Dana Elbers, Helena Greb, Ulrike Janssen-bienhold, Karl-wilhelm KochAbstract:The zebrafish retina expresses four recoverin genes (rcv1a, rcv1b, rcv2a and rcv2b) and four opsin kinase genes (grk1a, grk1b, grk7a and grk7b) coding for recoverin and G protein-coupled receptor kinase (opsin kinase) paralogs, respectively. Both protein groups are suggested to form regulatory complexes in Rod and cone outer segments, but at present, we lack information about co-localization of recoverin and opsin kinases in zebrafish retinae and which protein-protein interacting pairs form. We analyzed the distribution and co-localization of recoverin and opsin kinase expression in the zebrafish retina. For this purpose, we used custom-tailored monospecific antibodies revealing that the amount of recoverin paralogs in a zebrafish retina can differ by more than one order of magnitude with the highest amount for recoverin 1a and 2b. Further, immunohistochemical labelling showed presence of recoverin 1a in all Rod Cell compartments, but it only co-localized with opsin kinase 1a in Rod outer segments. In contrast, recoverin 2b was only detected in double cones and co-localized with opsin kinases 1b, 7a and 7b. Further, we investigated the interaction between recoverin and opsin kinase variants by surface plasmon resonance spectroscopy indicating interaction of recoverin 1a and recoverin 2b with all opsin kinases. However, binding kinetics for recoverin 1a differed from those observed with recoverin 2b that showed slower association and dissociation processes. Our results indicate diverse recoverin and opsin kinase properties due to differential expression and interaction profiles.
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molecular recognition of rhodopsin kinase grk1 and recoverin is tuned by switching intra and intermolecular electrostatic interactions
Biochemistry, 2019Co-Authors: Seher Abbas, Valerio Marino, Daniele Dellorco, Karl-wilhelm KochAbstract:G protein-coupled receptor kinase 1 (GRK1) or rhodopsin kinase is under specific control of the neuronal Ca2+-sensor protein recoverin, which is a critical feedback mechanism responsible for the modulation of the shape and sensitivity of the Rod Cell photoresponse. This process requires the precise matching of interacting protein surfaces and the dynamic changes in protein conformations. Here we study the molecular recognition process of recoverin and GRK1 by testing the hypothesis of a cation−π interaction pair in the recoverin–GRK1 complex. The critical role of residue K192 in recoverin was investigated by site-directed mutagenesis and subsequent structural and functional analysis. The following methods were used: isothermal titration calorimetry, fluorescence and circular dichroism spectroscopy, Ca2+-dependent membrane binding, and protein–protein interaction analysis by back scattering interferometry and surface plasmon resonance. While neutralizing the charge at K in the mutant K192L did not prevent ...
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recoverin and rhodopsin kinase activity in detergent resistant membrane rafts from Rod outer segments
Journal of Biological Chemistry, 2004Co-Authors: Ivan I Senin, Doris Hoppnerheitmann, Olga O Polkovnikova, Valeriya A Churumova, N K Tikhomirova, Pavel P Philippov, Karl-wilhelm KochAbstract:Abstract Cholesterol-rich membranes or detergent-resistant membranes (DRMs) have recently been isolated from bovine Rod outer segments and were shown to contain several signaling proteins such as, for example, transducin and its effector, cGMP-phosphodiesterase PDE6. Here we report the presence of rhodopsin kinase and recoverin in DRMs that were isolated in either light or dark conditions at high and low Ca2+ concentrations. Inhibition of rhodopsin kinase activity by recoverin was more effective in DRMs than in the initial Rod outer segment membranes. Furthermore, the Ca2+ sensitivity of rhodopsin kinase inhibition in DRMs was shifted to lower free Ca2+ concentration in comparison with the initial Rod outer segment membranes (IC50 = 0.76 μm in DRMs and 1.91 μm in Rod outer segments). We relate this effect to the high cholesterol content of DRMs because manipulating the cholesterol content of Rod outer segment membranes by methyl-β-cyclodextrin yielded a similar shift of the Ca2+-dependent dose-response curve of rhodopsin kinase inhibition. Furthermore, a high cholesterol content in the membranes also increased the ratio of the membrane-bound form of recoverin to its cytoplasmic free form. These data suggest that the Ca2+-dependent feedback loop that involves recoverin is spatially heterogeneous in the Rod Cell.
Anand Swaroop - One of the best experts on this subject based on the ideXlab platform.
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Cone-Rod homeobox CRX controls presynaptic active zone formation in photoreceptors of mammalian retina
Human Molecular Genetics, 2018Co-Authors: Juthaporn Assawachananont, Soo-young Kim, Koray Kaya, Jérôme E. Roger, Robert Fariss, Anand SwaroopAbstract:In the mammalian retina, Rod and cone photoreceptors transmit the visual information to bipolar neurons through highly specialized ribbon synapses. We have limited understanding of regulatory pathways that guide morphogenesis and organization of photoreceptor presynaptic architecture in the developing retina. While neural retina leucine zipper (NRL) transcription factor determines Rod Cell fate and function, cone-Rod homeobox (CRX) controls the expression of both Rod- and cone-specific genes and is critical for terminal differentiation of photoreceptors. A comprehensive immunohistochemical evaluation of Crx-/- (null), CrxRip/+ and CrxRip/Rip (models of dominant congenital blindness) mouse retinas revealed abnormal photoreceptor synapses, with atypical ribbon shape, number and length. Integrated analysis of retinal transcriptomes of Crx-mutants with CRX- and NRL-ChIP-Seq data identified a subset of differentially expressed CRX target genes that encode presynaptic proteins associated with the cytomatrix active zone (CAZ) and synaptic vesicles. Immunohistochemistry of Crx-mutant retina validated aberrant expression of REEP6, PSD95, MPP4, UNC119, UNC13, RGS7 and RGS11, with some reduction in Ribeye and no significant change in immunostaining of RIMS1, RIMS2, Bassoon and Pikachurin. Our studies demonstrate that CRX controls the establishment of CAZ and anchoring of ribbons, but not the formation of ribbon itself, in photoreceptor presynaptic terminals.
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nrl is required for Rod photoreceptor development
Nature Genetics, 2001Co-Authors: Alan J Mears, Paul A. Sieving, Ronald A. Bush, Mineo Kondo, Prabodha K Swain, Yuichiro Takada, Thomas L Saunders, Anand SwaroopAbstract:The protein neural retina leucine zipper (Nrl) is a basic motif-leucine zipper transcription factor that is preferentially expressed in Rod photoreceptors. It acts synergistically with Crx to regulate rhodopsin transcription. Missense mutations in human NRL have been associated with autosomal dominant retinitis pigmentosa. Here we report that deletion of Nrl in mice results in the complete loss of Rod function and super-normal cone function, mediated by S cones. The photoreceptors in the Nrl-/- retina have cone-like nuclear morphology and short, sparse outer segments with abnormal disks. Analysis of retinal gene expression confirms the apparent functional transformation of Rods into S cones in the Nrl-/- retina. On the basis of these findings, we postulate that Nrl acts as a 'molecular switch' during Rod-Cell development by directly modulating Rod-specific genes while simultaneously inhibiting the S-cone pathway through the activation of Nr2e3.
Martin Heck - One of the best experts on this subject based on the ideXlab platform.
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Response to Comment “Transient Complexes between Dark Rhodopsin and Transducin: Circumstantial Evidence or Physiological Necessity?” by D. Dell’Orco and K.-W. Koch
Biophysical journal, 2015Co-Authors: Johannes Schöneberg, Klaus Peter Hofmann, Martin Heck, Frank NoéAbstract:In retinal Rod Cells, absorption of a photon by the visual GPCR rhodopsin (R) initiates a cascade of biochemical reactions that amplifies the light signal and eventually generates an electrical response. Despite a vast number of experimental and simulation studies, the precise spatiotemporal mechanism by which Rod Cell phototransduction occurs on the supramolecular level is still elusive. As yet, the simultaneous observation of structure and dynamics in intact Rod Cells goes beyond experimental capabilities.
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Explicit Spatiotemporal Simulation of Receptor-G Protein Coupling in Rod Cell Disk Membranes
Biophysical journal, 2014Co-Authors: Johannes Schöneberg, Klaus Peter Hofmann, Martin Heck, Frank NoéAbstract: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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Not just signal shutoff: the protective role of arrestin-1 in Rod Cells.
Handbook of experimental pharmacology, 2013Co-Authors: Martha E. Sommer, Klaus Peter Hofmann, Martin HeckAbstract:The retinal Rod Cell is an exquisitely sensitive single-photon detector that primarily functions in dim light (e.g., moonlight). However, Rod Cells must routinely survive light intensities more than a billion times greater (e.g., bright daylight). One serious challenge to Rod Cell survival in daylight is the massive amount of all-trans-retinal that is released by Meta II, the light-activated form of the photoreceptor rhodopsin. All-trans-retinal is toxic, and its condensation pRoducts have been implicated in disease. Our recent work has developed the concept that Rod arrestin (arrestin-1), which terminates Meta II signaling, has an additional role in protecting Rod Cells from the consequences of bright light by limiting free all-trans-retinal. In this chapter we will elaborate upon the molecular mechanisms by which arrestin-1 serves as both a single-photon response quencher as well as an instrument of Rod Cell survival in bright light. This discussion will take place within the framework of three distinct functional modules of vision: signal transduction, the retinoid cycle, and protein translocation.
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Arrestin Allows All-Trans-Retinal to Enter the Ligand Binding Pocket of Phosphorylated Opsin
Biophysical Journal, 2012Co-Authors: Martha E. Sommer, Klaus Peter Hofmann, Martin HeckAbstract:Within the Rod Cell of the retina, absorption of light by the G-protein coupled receptor rhodopsin leads to the formation of the agonist all-trans-retinal directly within the ligand binding pocket of opsin and the eventual formation of the active species Metarhodopsin II (Meta II). Meta II signaling is terminated by phosphorylation and binding of arrestin, and Meta II eventually decays to opsin and free retinal via the spontaneous hydrolysis of the covalent retinal Schiff-base linkage. It has been known for some time that arrestin binds photo-decayed phosphorylated rhodopsin, as well as phosphorylated opsin (OpsP) supplied with exogenous all-trans-retinal. We find that all-trans-retinal can enter OpsP and form a Schiff-base in an arrestin-dependent fashion, thus forming a Meta II-like species. The agonist, arrestin, and the receptor exist in coupled equilibria, such that arrestin stabilizes an activated form of OpsP that allows all-trans-retinal to enter the binding pocket. This is the first direct observation of the reversible formation of a Meta II-like species from opsin and all-trans-retinal in the native membrane environment. As we recently reported for arrestin binding to Meta II (Sommer ME, Hofmann KP and Heck M (2011) JBC 286: 7359-69), we now find that one arrestin binds for every two OpsP receptors in the presence of excess all-trans-retinal. Furthermore, arrestin can induce the formation of the Meta II-like species in only half of the OpsP population. Likewise, regeneration of half the arrestin-bound OpsP population with 11-cis-retinal is blocked, supposedly because the binding pocket is already occupied. Regeneration of the remaining half of OpsP requires release of arrestin via the removal of all-trans-retinal by retinal dehydrogenase. Together these results suggest that arrestin serves to both terminate Meta II signaling and to regulate retinoid flow through opsin.
Robin Roberts - One of the best experts on this subject based on the ideXlab platform.
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Melanopsin Phototransduction Contributes to Light-Evoked Choroidal Expansion and Rod L-Type Calcium Channel Function In Vivo.
Investigative ophthalmology & visual science, 2016Co-Authors: Bruce A. Berkowitz, Tiffany M. Schmidt, Robert H. Podolsky, Robin RobertsAbstract:Purpose In humans, Rodents, and pigeons, the dark → light transition signals nonretinal brain tissue to increase choroidal thickness, a major control element of choroidal blood flow, and thus of photoreceptor and retinal pigment epithelium function. However, it is unclear which photopigments in the retina relay the light signal to the brain. Here, we test the hypothesis that melanopsin (Opn4)-regulated phototransduction modulates light-evoked choroidal thickness expansion in mice. Methods Two-month-old C57Bl/6 wild-type (B6), 4- to 5-month-old C57Bl/6/129S6 wild-type (B6 + S6), and 2-month-old melanopsin knockout (Opn4-/-) on a B6 + S6 background were studied. Retinal anatomy was evaluated in vivo by optical coherence tomography and MRI. Choroidal thickness in dark and light were measured by diffusion-weighted MRI. Rod Cell L-type calcium channel (LTCC) function in dark and light (manganese-enhanced MRI [MEMRI]) was also measured. Results Opn4-/- mice did not show the light-evoked expansion of choroidal thickness observed in B6 and B6 + S6 controls. Additionally, Opn4-/- mice had lower than normal Rod Cell and inner retinal LTCC function in the dark but not in the light. These deficits were not due to structural abnormalities because retinal laminar architecture and thickness, and choroidal thickness in the Opn4-/- mice were similar to controls. Conclusions First time evidence is provided that melanopsin phototransduction contributes to dark → light control of murine choroidal thickness. The data also highlight a contribution in vivo of melanopsin phototransduction to Rod Cell and inner retinal depolarization in the dark.
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Genetically heterogeneous mice show age-related vision deficits not related to increased Rod Cell L-type calcium channel function in vivo.
Neurobiology of aging, 2016Co-Authors: Bruce A. Berkowitz, Richard A. Miller, Robin RobertsAbstract:Visual performance declines over time in humans and 2-18 months outbred Long-Evans (LE) rats; vision is maintained in inbred 2-18 months C57BL/6 (B6) mice. Increased Rod L-type calcium channel (LTCC) function predicts visual decline in LE rats but does not occur in B6 mice. Genetic diversity may contribute to Rod LTCC function escalation time. To test this hypothesis, 4 and 18 months genetically heterogeneous UM-HET3 mice were studied. Rod LTCC function (manganese-enhanced magnetic resonance imaging [MRI]) and ocular anatomy (MRI, optical coherence tomography) were measured in vivo. Light-evoked subretinal space and choroid thickness changes were measured (diffusion-weighted MRI). Visual performance declined over time in the absence of (1) increased Rod LTCC function; (2) changes in light-dependent expansion of the subretinal space and choroidal thickness; and (3) retinal thinning. Aging changed anterior and vitreous chambers' axial length and decreased light-stimulated choroidal expansion. Species differences appear to contribute to the LTCC function differences. Aging-related declines in vision in the UM-HET3 mice deserve more attention than they have received so far.
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MRI of Rod Cell compartment-specific function in disease and treatment in vivo
Progress in retinal and eye research, 2015Co-Authors: Bruce A. Berkowitz, David Bissig, Robin RobertsAbstract:Rod Cell oxidative stress is a major pathogenic factor in retinal disease, such as diabetic retinopathy (DR) and retinitis pigmentosa (RP). Personalized, non-destructive, and targeted treatment for these diseases remains elusive since current imaging methods cannot analytically measure treatment efficacy against Rod Cell compartment-specific oxidative stress in vivo. Over the last decade, novel MRI-based approaches that address this technology gap have been developed. This review summarizes progress in the development of MRI since 2006 that enables earlier evaluation of the impact of disease on Rod Cell compartment-specific function and the efficacy of anti-oxidant treatment than is currently possible with other methods. Most of the new assays of Rod Cell compartment-specific function are based on endogenous contrast mechanisms, and this is expected to facilitate their translation into patients with DR and RP, and other oxidative stress-based retinal diseases.
Tanya T. Whitfield - One of the best experts on this subject based on the ideXlab platform.
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Olfactory Rod Cells: A Rare Cell Type in the Larval Zebrafish Olfactory Epithelium With a Large Actin-Rich Apical Projection
Frontiers in physiology, 2021Co-Authors: Yee Cheung, Suresh Jesuthasan, Sarah Baxendale, Nicholas J. Van Hateren, Mar Marzo, Christopher J. Hill, Tanya T. WhitfieldAbstract:We report the presence of a rare Cell type, the olfactory Rod Cell, in the developing zebrafish olfactory epithelium. These Cells each bear a single actin-rich Rod-like apical projection extending 5–10 µm from the epithelial surface. Live imaging with a ubiquitous Lifeact-RFP label indicates that the olfactory Rods can oscillate. Olfactory Rods arise within a few hours of the olfactory pit opening, increase in numbers and size during larval stages, and can develop in the absence of olfactory cilia. Olfactory Rod Cells differ in morphology from the known classes of olfactory sensory neuron, but express reporters driven by neuronal promoters. A sub-population of olfactory Rod Cells expresses a Lifeact-mRFPruby transgene driven by the sox10 promoter. Mosaic expression of this transgene reveals that olfactory Rod Cells have rounded Cell bodies located apically in the olfactory epithelium and have no detectable axon. We offer speculation on the possible function of these Cells in the Discussion.
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Olfactory Rod Cells: a rare Cell type in the larval zebrafish olfactory epithelium with an actin-rich apical projection
2020Co-Authors: Yee Cheung, Suresh Jesuthasan, Sarah Baxendale, Nicholas J. Van Hateren, Mar Marzo, Christopher J. Hill, Tanya T. WhitfieldAbstract:Abstract We report the presence of a rare Cell type, the olfactory Rod Cell, in the developing zebrafish olfactory epithelium. These Cells each bear a single actin-rich Rod-like apical projection extending about 10 μm from the epithelial surface. Live imaging with a ubiquitous Lifeact-RFP label indicates that the Rods can oscillate. Olfactory Rods arise within a few hours of the olfactory pit opening, increase in numbers and size during larval stages, and can develop in the absence of olfactory cilia. Olfactory Rod Cells differ in morphology from the known classes of olfactory sensory neuron, but express reporters driven by neuronal promoters. The Cells also differ from secondary sensory Cells such as hair Cells of the inner ear or lateral line, or sensory Cells in the taste bud, as they are not associated with established synaptic terminals. A sub-population of olfactory Rod Cells expresses a Lifeact-mRFPruby transgene driven by the sox10 promoter. Mosaic expression of this transgene reveals that olfactory Rod Cells have rounded Cell bodies located apically in the olfactory epithelium.
