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Abstract
Illumination of Drosophila photoreceptor cells induces multi-facet responses, which include generation of the photoreceptor potential, screening pigment migration and translocation of signaling proteins which is the focus of recent extensive research. Translocation of three signaling molecules is covered in this review: (1) Light-dependent translocation of arrestin from the cytosol to the signaling membrane, the rhabdomere, determines the lifetime of activated rhodopsin. Arrestin translocates in PIP3 and NINAC myosin III dependent manner, and specific mutations which disrupt the interaction between arrestin and PIP3 or NINAC also impair the light-dependent translocation of arrestin and the termination of the response to light. (2) Activation of Drosophila visual G protein, DGq, causes a massive and reversible, translocation of the alpha subunit from the signaling membrane to the cytosol, accompanied by activity-dependent architectural changes. Analysis of the translocation and the recovery kinetics of DGq(alpha) in wild-type flies and specific visual mutants indicated that DGq(alpha) is necessary but not sufficient for the architectural changes. (3) The TRP-like (TRPL) but not TRP channels translocate in a light-dependent manner between the rhabdomere and the cell body. As a physiological consequence of this light-dependent modulation of the TRP/TRPL ratio, the photoreceptors of dark-adapted flies operate at a wider dynamic range, which allows the photoreceptors enriched with TRPL to function better in darkness and dim background illumination. Altogether, signal-dependent movement of signaling proteins plays a major role in the maintenance and function of photoreceptor cells.
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Affiliation(s)
| | - Baruch Minke
- *Corresponding author. Tel.: +972 2 6758407; fax: +972 2 6439736. E-mail address: (B. Minke)
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52
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Abstract
Phosphoinositide phosphates (PIPs) correspond to phosphorylated derivatives of phosphatidylinositol (PI). Despite their relatively low abundance in the plasma membrane, PIPs play a crucial role as precursors of second messengers and are themselves important signaling and targeting molecules. Indeed, modulation of levels of PIPs affects, for example, cortical actin organization, membrane dynamics, and cell migration. The focus of this review is on selected interesting targets of PIPs. Those proteins that bind PIPs and are involved in regulation of actin assembly, actin membrane linkage, and actin contractility are discussed, as well as those that are involved in signaling, such as small GTPases, protein kinases, and phosphatases, or in regulation of membrane dynamics.
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Affiliation(s)
- Verena Niggli
- Department of Pathology, University of Bern, CH-3010 Bern, Switzerland.
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53
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Rajaram S, Scott RL, Nash HA. Retrograde signaling from the brain to the retina modulates the termination of the light response in Drosophila. Proc Natl Acad Sci U S A 2005; 102:17840-5. [PMID: 16314566 PMCID: PMC1308915 DOI: 10.1073/pnas.0508858102] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A critical factor in visual function is the speed with which photoreceptors (PRs) return to the resting state when light intensity dims. Several elements subserve this process, many of which promote the termination of the phototransduction cascade. Although the known elements are intrinsic to PRs, we have found that prompt restoration to the resting state of the Drosophila electroretinogram can require effective communication between the retina and the underlying brain. The requirement is seen more dramatically with long than with short light pulses, distinguishing the phenomenon from gross disruption of the termination machinery. The speed of recovery is affected by mutations (in the Hdc and ort genes) that prevent PRs from transmitting visual information to the brain. It is also affected by manipulation (using either drugs like neostigmine or genetic tools to inactivate neurotransmitter release) of cholinergic signals that arise in the brain. Intracellular recordings support the hypothesis that PRs are the target of this communication. We infer that signaling from the retina to the optic lobe prompts a feedback signal to retinal PRs. Although the mechanism of this retrograde signaling remains to be discerned, the phenomenon establishes a previously unappreciated mode of control of the temporal responsiveness of a primary sensory neuron.
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Affiliation(s)
- Shantadurga Rajaram
- Laboratory of Molecular Biology, National Institute of Mental Health, National Institutes of Health, Bethesda, MD 20892-3736, USA
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54
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Kassai H, Aiba A, Nakao K, Nakamura K, Katsuki M, Xiong WH, Yau KW, Imai H, Shichida Y, Satomi Y, Takao T, Okano T, Fukada Y. Farnesylation of retinal transducin underlies its translocation during light adaptation. Neuron 2005; 47:529-39. [PMID: 16102536 PMCID: PMC2885908 DOI: 10.1016/j.neuron.2005.07.025] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2005] [Revised: 05/18/2005] [Accepted: 07/28/2005] [Indexed: 11/26/2022]
Abstract
G proteins are posttranslationally modified by isoprenylation: either farnesylation or geranylgeranylation. The gamma subunit of retinal transducin (Talpha/Tbetagamma) is selectively farnesylated, and the farnesylation is required for light signaling mediated by transducin in rod cells. However, whether and how this selective isoprenylation regulates cellular functions remain poorly understood. Here we report that knockin mice expressing geranylgeranylated Tgamma showed normal rod responses to dim flashes under dark-adapted conditions but exhibited impaired properties in light adaptation. Of note, geranylgeranylation of Tgamma suppressed light-induced transition of Tbetagamma from membrane to cytosol, and also attenuated its light-dependent translocation from the outer segment to the inner region, an event contributing to retinal light adaptation. These results indicate that, while the farnesylation of transducin is interchangeable with the geranylgeranylation in terms of the light signaling, the selective farnesylation is important for visual sensitivity regulation by providing sufficient but not excessive membrane anchoring of Tbetagamma.
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Affiliation(s)
- Hidetoshi Kassai
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
| | - Atsu Aiba
- Division of Cell Biology, Department of Molecular and Cellular Biology, Kobe University Graduate School of Medicine, Kobe, Hyogo 650-0017, Japan
| | - Kazuki Nakao
- RIKEN Center for Developmental Biology, Kobe, Hyogo 650-0047, Japan
| | - Kenji Nakamura
- Mitsubishi Kagaku Institute of Life Sciences, Machida, Tokyo 194-8511, Japan
| | - Motoya Katsuki
- National Institute of Basic Biology, Okazaki National Research Institute, Okazaki, Aichi 444-8585, Japan
| | - Wei-Hong Xiong
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - King-Wai Yau
- Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205
| | - Hiroo Imai
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan
| | - Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
- CREST, Japan Science and Technology Agency (JST), Kawaguchi, Saitama 332-0012, Japan
| | - Yoshinori Satomi
- Laboratory of Protein Profiling and Functional Proteomics, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Toshifumi Takao
- Laboratory of Protein Profiling and Functional Proteomics, Institute for Protein Research, Osaka University, Suita, Osaka 565-0871, Japan
| | - Toshiyuki Okano
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- PRESTO, JST, Kawaguchi, Saitama 332-0012, Japan
| | - Yoshitaka Fukada
- Department of Biophysics and Biochemistry, Graduate School of Science, The University of Tokyo, Tokyo 113-0033, Japan
- Correspondence:
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55
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Abstract
The myosin family of actin filament-based molecular motors consists of at least 20 structurally and functionally distinct classes. The human genome contains nearly 40 myosin genes, encoding 12 of these classes. Myosins have been implicated in a variety of intracellular functions, including cell migration and adhesion; intracellular transport and localization of organelles and macromolecules; signal transduction; and tumor suppression. In this review, recent insights into the remarkable diversity in the mechanochemical and functional properties associated with this family of molecular motors are discussed.
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Affiliation(s)
- Mira Krendel
- Department of Molecular Biology, Yale University, New Haven, CN, USA.
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56
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Nair KS, Hanson SM, Mendez A, Gurevich EV, Kennedy MJ, Shestopalov VI, Vishnivetskiy SA, Chen J, Hurley JB, Gurevich VV, Slepak VZ. Light-dependent redistribution of arrestin in vertebrate rods is an energy-independent process governed by protein-protein interactions. Neuron 2005; 46:555-67. [PMID: 15944125 PMCID: PMC2752952 DOI: 10.1016/j.neuron.2005.03.023] [Citation(s) in RCA: 149] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Revised: 03/07/2005] [Accepted: 03/30/2005] [Indexed: 11/21/2022]
Abstract
In rod photoreceptors, arrestin localizes to the outer segment (OS) in the light and to the inner segment (IS) in the dark. Here, we demonstrate that redistribution of arrestin between these compartments can proceed in ATP-depleted photoreceptors. Translocation of transducin from the IS to the OS also does not require energy, but depletion of ATP or GTP inhibits its reverse movement. A sustained presence of activated rhodopsin is required for sequestering arrestin in the OS, and the rate of arrestin relocalization to the OS is determined by the amount and the phosphorylation status of photolyzed rhodopsin. Interaction of arrestin with microtubules is increased in the dark. Mutations that enhance arrestin-microtubule binding attenuate arrestin translocation to the OS. These results indicate that the distribution of arrestin in rods is controlled by its dynamic interactions with rhodopsin in the OS and microtubules in the IS and that its movement occurs by simple diffusion.
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Affiliation(s)
- K. Saidas Nair
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami, Miami, Florida 33136
| | - Susan M. Hanson
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232
| | - Ana Mendez
- Zilkha Neurogenetic Institute, University of Southern California, Keck School of Medicine, Los Angeles, California 90089
| | - Eugenia V. Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232
| | - Matthew J. Kennedy
- Department of Biochemistry, University of Washington, Seattle, Washington 98195
| | | | | | - Jeannie Chen
- Zilkha Neurogenetic Institute, University of Southern California, Keck School of Medicine, Los Angeles, California 90089
| | - James B. Hurley
- Department of Biochemistry, University of Washington, Seattle, Washington 98195
| | - Vsevolod V. Gurevich
- Department of Pharmacology, Vanderbilt University, Nashville, Tennessee 37232
- Correspondence: (V.Z.S.); (V.V.G.)
| | - Vladlen Z. Slepak
- Department of Molecular and Cellular Pharmacology and Neuroscience Program, University of Miami, Miami, Florida 33136
- Correspondence: (V.Z.S.); (V.V.G.)
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57
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Abstract
The transient receptor potential (TRP) superfamily comprises a large group of related cation channels that display surprising diversity in the specific modes of activation and cation selectivities. However, a unifying theme is that many TRP channels play important roles in sensory physiology. The superfamily includes 28 mammalian members, which are subdivided into multiple subfamilies. Each of these subfamilies is represented by at least one of the 13 members in Drosophila, suggesting common evolutionary relationships. In recent years it has become clear that TRP channels in flies and mammals participate in similar sensory modalities. These include, but are not limited to, hearing, thermosensation, and certain specialized types of vision. With the recent flurry of new studies, 9 out of the 13 TRPs have been addressed in various contexts. As a result, the repertoire of biological roles attributed to Drosophila TRPs has increased considerably and is likely to lead to many additional surprises over the next few years.
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Affiliation(s)
- Craig Montell
- Department of Biological Chemistry, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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58
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Balla T. Inositol-lipid binding motifs: signal integrators through protein-lipid and protein-protein interactions. J Cell Sci 2005; 118:2093-104. [PMID: 15890985 DOI: 10.1242/jcs.02387] [Citation(s) in RCA: 208] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Inositol lipids have emerged as universal lipid regulators of protein signaling complexes in defined membrane compartments. The number of protein modules that are known to recognise these membrane lipids is rapidly increasing. Pleckstrin homology domains, FYVE domains, PX domains, ENTH domains, CALM domains, PDZ domains, PTB domains and FERM domains are all inositide-recognition modules. The latest additions to this list are members of the clathrin adaptor protein and arrestin families. Initially, inositol lipids were believed to recruit signaling molecules to specific membrane compartments, but many of the domains clearly do not possess high enough affinity to act alone as localisation signals. Another important notion is that some (and probably most) of these protein modules also have protein binding partners, and their protein- and lipid-binding activities might influence one another through allosteric mechanisms. Comparison of the structural features of these domains not only reveals a high degree of conservation of their lipid interaction sites but also highlights their evolutionary link to protein modules known for protein-protein interactions. Protein-protein interactions involving lipid-binding domains could serve as the basis for phosphoinositide-induced conformational regulation of target proteins at biological membranes. Therefore, these modules function as crucially important signal integrators, which explains their involvement in a broad range of regulatory functions in eukaryotic cells.
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Affiliation(s)
- Tamas Balla
- Endocrinology and Reproduction Research Branch, NICHD, National Institutes of Health, Bethesda, MD 20892, USA.
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59
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Abstract
Recent studies have revealed that light adaptation of both vertebrate and invertebrate photoreceptors is accompanied by massive translocations of major signaling proteins in and out of the cellular compartments where visual signal transduction takes place. In this issue of Neuron, Lee and Montell report a breakthrough in understanding the mechanism of arrestin translocation in Drosophila. They show that arrestin is carried into the light-sensitive microvilli by phosphoinositide-enriched vesicles driven by a myosin motor.
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