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Negative regulation of the novel norpA(P24) suppressor, diehard4, in the endo-lysosomal trafficking underlies photoreceptor cell degeneration. PLoS Genet 2013; 9:e1003559. [PMID: 23754968 PMCID: PMC3674991 DOI: 10.1371/journal.pgen.1003559] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2012] [Accepted: 04/24/2013] [Indexed: 12/16/2022] Open
Abstract
Rhodopsin has been used as a prototype system to investigate G protein-coupled receptor (GPCR) internalization and endocytic sorting mechanisms. Failure of rhodopsin recycling upon light activation results in various degenerative retinal diseases. Accumulation of internalized rhodopsin in late endosomes and the impairment of its lysosomal degradation are associated with unregulated cell death that occurs in dystrophies. However, the molecular basis of rhodopsin accumulation remains elusive. We found that the novel norpAP24 suppressor, diehard4, is responsible for the inability of endo-lysosomal rhodopsin trafficking and retinal degeneration in Drosophila models of retinal dystrophies. We found that diehard4 encodes Osiris 21. Loss of its function suppresses retinal degeneration in norpAP24, rdgC306, and trp1, but not in rdgB2, suggesting a common cause of photoreceptor death. In addition, the loss of Osiris 21 function shifts the membrane balance between late endosomes and lysosomes as evidenced by smaller late endosomes and the proliferation of lysosomal compartments, thus facilitating the degradation of endocytosed rhodopsin. Our results demonstrate the existence of negative regulation in vesicular traffic between endosomes and lysosomes. We anticipate that the identification of additional components and an in-depth description of this specific molecular machinery will aid in therapeutic interventions of various retinal dystrophies and GPCR-related human diseases. Malfunctioning of phototransduction is the major cause of human blindness. Without functional phototransduction, rhodopsin-1, the major visual pigment, is rapidly endocytosed and accumulated in late endosomes. Impaired lysosomal delivery of endocytosed rhodopsin and its degradation has been reported to trigger progressive and light-dependent retinal degeneration in Drosophila models. It is intriguing why endocytosed rhodopsin accumulates in late endosomes instead of being delivered to lysosomes for degradation. Is this attributable to a saturation of rhodopsin endocytosis, which impedes the delivery capacity of the cell? To investigate the underlying mechanisms of rhodopsin accumulation in late endosomes, we used a suppressor of phototransduction mutants, which was identified previously from our unbiased genetic screen. This suppressor, called diehard4, shifts the membrane balance between late endosomes and lysosomes, resulting in the facilitated degradation of endocytosed rhodopsin. Our results clearly demonstrate that a previously unknown mechanism of negative regulation is actively engaged in vesicular traffic between endosomes and lysosomes in fly photoreceptors. We showed that eliminating such blockage alone was enough to rescue retinal degeneration in phototransduction mutants. From these results, we anticipate that the identification of additional components and an in-depth description of this molecular machinery will aid in therapeutic interventions of various retinal dystrophies and neurodegenerative disorders.
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Satoh T, Inagaki T, Liu Z, Watanabe R, Satoh AK. GPI biosynthesis is essential for rhodopsin sorting at the trans-Golgi network in Drosophila photoreceptors. Development 2013; 140:385-94. [PMID: 23250212 DOI: 10.1242/dev.083683] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
Sorting of integral membrane proteins plays crucial roles in establishing and maintaining the polarized structures of epithelial cells and neurons. However, little is known about the sorting mechanisms of newly synthesized membrane proteins at the trans-Golgi network (TGN). To identify which genes are essential for these sorting mechanisms, we screened mutants in which the transport of Rhodopsin 1 (Rh1), an apical integral membrane protein in Drosophila photoreceptors, was affected. We found that deficiencies in glycosylphosphatidylinositol (GPI) synthesis and attachment processes cause loss of the apical transport of Rh1 from the TGN and mis-sorting to the endolysosomal system. Moreover, Na(+)K(+)-ATPase, a basolateral membrane protein, and Crumbs (Crb), a stalk membrane protein, were mistransported to the apical rhabdomeric microvilli in GPI-deficient photoreceptors. These results indicate that polarized sorting of integral membrane proteins at the TGN requires the synthesis and anchoring of GPI-anchored proteins. Little is known about the cellular biological consequences of GPI deficiency in animals in vivo. Our results provide new insights into the importance of GPI synthesis and aid the understanding of pathologies involving GPI deficiency.
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Affiliation(s)
- Takunori Satoh
- Division of Life Science, Graduate School of Integral Arts and Science, Hiroshima University, 1-7-1 Kagamiyama, Higashi-hiroshima 739-8521, Japan
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Battelle BA, Kempler KE, Parker AK, Gaddie CD. Opsin1-2, G(q)α and arrestin levels at Limulus rhabdoms are controlled by diurnal light and a circadian clock. ACTA ACUST UNITED AC 2013; 216:1837-49. [PMID: 23393287 DOI: 10.1242/jeb.083519] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Dark and light adaptation in photoreceptors involve multiple processes including those that change protein concentrations at photosensitive membranes. Light- and dark-adaptive changes in protein levels at rhabdoms have been described in detail in white-eyed Drosophila maintained under artificial light. Here we tested whether protein levels at rhabdoms change significantly in the highly pigmented lateral eyes of wild-caught Limulus polyphemus maintained in natural diurnal illumination and whether these changes are under circadian control. We found that rhabdomeral levels of opsins (Ops1-2), the G protein activated by rhodopsin (G(q)α) and arrestin change significantly from day to night and that nighttime levels of each protein at rhabdoms are significantly influenced by signals from the animal's central circadian clock. Clock input at night increases Ops1-2 and G(q)α and decreases arrestin levels at rhabdoms. Clock input is also required for a rapid decrease in rhabdomeral Ops1-2 beginning at sunrise. We found further that dark adaptation during the day and the night are not equivalent. During daytime dark adaptation, when clock input is silent, the increase of Ops1-2 at rhabdoms is small and G(q)α levels do not increase. However, increases in Ops1-2 and G(q)α at rhabdoms are enhanced during daytime dark adaptation by treatments that elevate cAMP in photoreceptors, suggesting that the clock influences dark-adaptive increases in Ops1-2 and G(q)α at Limulus rhabdoms by activating cAMP-dependent processes. The circadian regulation of Ops1-2 and G(q)α levels at rhabdoms probably has a dual role: to increase retinal sensitivity at night and to protect photoreceptors from light damage during the day.
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Affiliation(s)
- Barbara-Anne Battelle
- The Whitney Laboratory for Marine Bioscience, 9505 Ocean Shore Blvd, St Augustine, FL 32080-8610, USA.
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Aubry L, Klein G. True arrestins and arrestin-fold proteins: a structure-based appraisal. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2013; 118:21-56. [PMID: 23764049 DOI: 10.1016/b978-0-12-394440-5.00002-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Arrestin-clan proteins are folded alike, a feature responsible for their recent grouping in a single clan. In human, it includes the well-characterized visual and β-arrestins, the arrestin domain-containing proteins (ARRDCs), isoforms of the retromer subunit VPS26, and DSCR3, a protein involved in Down syndrome. A new arrestin-fold-predicted protein, RGP1, described here may join the clan. Unicellular organisms like the yeast Saccharomyces cerevisiae or the amoeba Dictyostelium discoideum harbor VPS26, DSCR3, and RGP1 isoforms as well as arrestin-related trafficking adaptors or ADCs, but true arrestins are missing. Functionally, members of the arrestin clan have generally a scaffolding role in various membrane protein trafficking events. Despite their similar structure, the mechanism of cargo recognition and internalization and the nature of recruited partners differ for the different members. Based on the recent literature, true arrestins (visual and β-arrestins), ARRDCs, and yeast ARTS are the closest from a functional point of view.
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Affiliation(s)
- Laurence Aubry
- CEA, IRTSV, Laboratoire Biologie à Grande Echelle, F-38054, Grenoble, France
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Tian Y, Li T, Sun M, Wan D, Li Q, Li P, Zhang Z, Han J, Xie W. Neurexin Regulates Visual Function via Mediating Retinoid Transport to Promote Rhodopsin Maturation. Neuron 2013; 77:311-22. [DOI: 10.1016/j.neuron.2012.11.012] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/07/2012] [Indexed: 12/22/2022]
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Chen SF, Tsai YC, Fan SS. Drosophila king tubby (ktub) mediates light-induced rhodopsin endocytosis and retinal degeneration. J Biomed Sci 2012; 19:101. [PMID: 23228091 PMCID: PMC3541268 DOI: 10.1186/1423-0127-19-101] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2012] [Accepted: 12/04/2012] [Indexed: 11/10/2022] Open
Abstract
Background The tubby (tub) and tubby-like protein (tulp) genes encode a small family of proteins found in many organisms. Previous studies have shown that TUB and TULP genes in mammalian involve in obesity, neural development, and retinal degeneration. The purpose of this study was to investigate the role of Drosophila king tubby (ktub) in rhodopsin 1 (Rh1) endocytosis and retinal degeneration upon light stimulation. Results Drosophila ktub mutants were generated using imprecise excision. Wild type and mutant flies were raised in dark or constant light conditions. After a period of light stimulation, retinas were dissected, fixed and stained with anti-Rh1 antibody to reveal Rh1 endocytosis. Confocal and transmission electron microscope were used to examine the retinal degeneration. Immunocytochemical analysis shows that Ktub is expressed in the rhabdomere domain under dark conditions. When flies receive light stimulation, the Ktub translocates from the rhabdomere to the cytoplasm and the nucleus of the photoreceptor cells. Wild type photoreceptors form Rh1-immunopositive large vesicles (RLVs) shortly after light stimulation. In light-induced ktub mutants, the majority of Rh1 remains at the rhabdomere, and only a few RLVs appear in the cytoplasm of photoreceptor cells. Mutation of norpA allele causes massive Rh1 endocytosis in light stimulation. In ktub and norpA double mutants, however, Rh1 endocytosis is blocked under light stimulation. This study also shows that ktub and norpA double mutants rescue the light-induced norpA retinal degeneration. Deletion constructs further demonstrate that the Tubby domain of the Ktub protein participates in an important role in Rh1 endocytosis. Conclusions The results in this study delimit the novel function of Ktub in Rh1 endocytosis and retinal degeneration.
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Affiliation(s)
- Shu-Fen Chen
- Department of Life Science, Tunghai University, R,O,C 407, Taiwan
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Xiong B, Bayat V, Jaiswal M, Zhang K, Sandoval H, Charng WL, Li T, David G, Duraine L, Lin YQ, Neely GG, Yamamoto S, Bellen HJ. Crag is a GEF for Rab11 required for rhodopsin trafficking and maintenance of adult photoreceptor cells. PLoS Biol 2012; 10:e1001438. [PMID: 23226104 PMCID: PMC3514319 DOI: 10.1371/journal.pbio.1001438] [Citation(s) in RCA: 71] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2012] [Accepted: 10/22/2012] [Indexed: 11/29/2022] Open
Abstract
Transport of newly synthesized Rhodopsin upon light stimulation in adult Drosophila photoreceptors is mediated by a Crag/Rab11-dependent vesicular trafficking process. Rhodopsins (Rhs) are light sensors, and Rh1 is the major Rh in the Drosophila photoreceptor rhabdomere membrane. Upon photoactivation, a fraction of Rh1 is internalized and degraded, but it remains unclear how the rhabdomeric Rh1 pool is replenished and what molecular players are involved. Here, we show that Crag, a DENN protein, is a guanine nucleotide exchange factor for Rab11 that is required for the homeostasis of Rh1 upon light exposure. The absence of Crag causes a light-induced accumulation of cytoplasmic Rh1, and loss of Crag or Rab11 leads to a similar photoreceptor degeneration in adult flies. Furthermore, the defects associated with loss of Crag can be partially rescued with a constitutive active form of Rab11. We propose that upon light stimulation, Crag is required for trafficking of Rh from the trans-Golgi network to rhabdomere membranes via a Rab11-dependent vesicular transport. Animals sense light through receptors called Rhodopsins. These proteins are typically localized to stacked membranes in photoreceptors. In flies, upon light exposure, Rhodopsin undergoes conformational changes and becomes active as metarhodopsin. Metarhodopsin then initiates a signaling cascade that activates the photoreceptor cell. To deactivate the light response, metarhodopsin is converted back into Rhodopsin by absorption of another photon of light. Under certain conditions, metarhodopsin cannot be converted back to Rhodopsin, and it is then endocytosed and degraded. Rhodopsin then needs to be synthesized and delivered back to the membrane stacks. Here, we show that the Calmodulin-binding protein Crag is required for the delivery of newly made Rhodopsin to the membrane stacks. Loss of Crag leads to the accumulation of Rhodopsin in the cytosol, followed by shrinkage of membrane stack volume, and, eventually, photoreceptor cell degeneration. We also show that Crag activates a target protein, Rab11, which mediates the vesicular transport of Rhodospin to the membrane. Finally, we document that the human homolog of Crag, DENND4A, is able to rescue the loss of Crag in flies, suggesting that DENND4A functions in a similar process in vertebrates.
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Affiliation(s)
- Bo Xiong
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Vafa Bayat
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Medical Scientist Training Program, Baylor College of Medicine, Houston, Texas, United States of America
| | - Manish Jaiswal
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
| | - Ke Zhang
- Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Hector Sandoval
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Wu-Lin Charng
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Tongchao Li
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Gabriela David
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
| | - Lita Duraine
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
| | - Yong-Qi Lin
- Neuroscience Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - G. Gregory Neely
- Neuroscience Program, Garvan Institute of Medical Research, Sydney, New South Wales, Australia
| | - Shinya Yamamoto
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
| | - Hugo J. Bellen
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas, United States of America
- Howard Hughes Medical Institute, Baylor College of Medicine, Houston, Texas, United States of America
- Program in Structural and Computational Biology and Molecular Biophysics, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas, United States of America
- Neurological Research Institute, Baylor College of Medicine, Houston, Texas, United States of America
- * E-mail:
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Abstract
Arrestins belong to a family of multifunctional adaptor proteins that regulate internalization of diverse receptors including G-protein-coupled receptors (GPCRs). Defects associated with endocytosis of GPCRs have been linked to human diseases. We used enhanced green fluorescent protein-tagged arrestin 2 (Arr2) to monitor the turnover of the major rhodopsin (Rh1) in live Drosophila. We demonstrate that during degeneration of norpA(P24) photoreceptors the loss of Rh1 is parallel to the disappearance of rhabdomeres, the specialized visual organelle that houses Rh1. The cause of degeneration in norpA(P24) is the failure to activate CaMKII (Ca(2+)/calmodulin-dependent protein kinase II) and retinal degeneration C (RDGC) because of a loss of light-dependent Ca(2+) entry. A lack of activation in CaMKII, which phosphorylates Arr2, leads to hypophosphorylated Arr2, while a lack of activation of RDGC, which dephosphorylates Rh1, results in hyperphosphorylated Rh1. We investigated how reversible phosphorylation of Rh1 and Arr2 contributes to photoreceptor degeneration. To uncover the consequence underlying a lack of CaMKII activation, we characterized ala(1) flies in which CaMKII was suppressed by an inhibitory peptide, and showed that morphology of rhabdomeres was not affected. In contrast, we found that expression of phosphorylation-deficient Rh1s, which either lack the C terminus or contain Ala substitution in the phosphorylation sites, was able to prevent degeneration of norpA(P24) photoreceptors. This suppression is not due to a loss of Arr2 interaction. Importantly, co-expression of these modified Rh1s offered protective effects, which greatly delayed photoreceptor degeneration. Together, we conclude that phosphorylation of Rh1 is the major determinant that orchestrates its internalization leading to retinal degeneration.
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Regulation of arrestin translocation by Ca2+ and myosin III in Drosophila photoreceptors. J Neurosci 2012; 32:9205-16. [PMID: 22764229 DOI: 10.1523/jneurosci.0924-12.2012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Upon illumination several phototransduction proteins translocate between cell body and photosensory compartments. In Drosophila photoreceptors arrestin (Arr2) translocates from cell body to the microvillar rhabdomere down a diffusion gradient created by binding of Arr2 to photo-isomerized metarhodopsin. Translocation is profoundly slowed in mutants of key phototransduction proteins including phospholipase C (PLC) and the Ca(2+)-permeable transient receptor potential channel (TRP), but how the phototransduction cascade accelerates Arr2 translocation is unknown. Using real-time fluorescent imaging of Arr2-green fluorescent protein translocation in dissociated ommatidia, we show that translocation is profoundly slowed in Ca(2+)-free solutions. Conversely, in a blind PLC mutant with ∼100-fold slower translocation, rapid translocation was rescued by the Ca(2+) ionophore, ionomycin. In mutants lacking NINAC (calmodulin [CaM] binding myosin III) in the cell body, translocation remained rapid even in Ca(2+)-free solutions. Immunolabeling revealed that Arr2 in the cell body colocalized with NINAC in the dark. In intact eyes, the impaired translocation found in trp mutants was rescued in ninaC;trp double mutants. Nevertheless, translocation following prolonged dark adaptation was significantly slower in ninaC mutants, than in wild type: a difference that was reflected in the slow decay of the electroretinogram. The results suggest that cytosolic NINAC is a Ca(2+)-dependent binding target for Arr2, which protects Arr2 from immobilization by a second potential sink that sequesters and releases arrestin on a much slower timescale. We propose that rapid Ca(2+)/CaM-dependent release of Arr2 from NINAC upon Ca(2+) influx accounts for the acceleration of translocation by phototransduction.
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Dourlen P, Bertin B, Chatelain G, Robin M, Napoletano F, Roux MJ, Mollereau B. Drosophila fatty acid transport protein regulates rhodopsin-1 metabolism and is required for photoreceptor neuron survival. PLoS Genet 2012; 8:e1002833. [PMID: 22844251 PMCID: PMC3405995 DOI: 10.1371/journal.pgen.1002833] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2011] [Accepted: 06/05/2012] [Indexed: 01/16/2023] Open
Abstract
Tight regulation of the visual response is essential for photoreceptor function and survival. Visual response dysregulation often leads to photoreceptor cell degeneration, but the causes of such cell death are not well understood. In this study, we investigated a fatty acid transport protein (fatp) null mutation that caused adult-onset and progressive photoreceptor cell death. Consistent with fatp having a role in the retina, we showed that fatp is expressed in adult photoreceptors and accessory cells and that its re-expression in photoreceptors rescued photoreceptor viability in fatp mutants. The visual response in young fatp-mutant flies was abnormal with elevated electroretinogram amplitudes associated with high levels of Rhodopsin-1 (Rh1). Reducing Rh1 levels in rh1 mutants or depriving flies of vitamin A rescued photoreceptor cell death in fatp mutant flies. Our results indicate that fatp promotes photoreceptor survival by regulating Rh1 abundance.
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Affiliation(s)
- Pierre Dourlen
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
- * E-mail: (PD); (BM)
| | - Benjamin Bertin
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Gilles Chatelain
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Marion Robin
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Francesco Napoletano
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
| | - Michel J. Roux
- Translational Medicine and Neurogenetics, IGBMC, UMR7104 CNRS/Université de Strasbourg/Inserm U964, Strasbourg, France
| | - Bertrand Mollereau
- Laboratory of Molecular Biology of the Cell, UMR5239 CNRS/Ecole Normale Supérieure de Lyon, UMS 344 Biosciences Lyon Gerland, Université de Lyon, Lyon, France
- * E-mail: (PD); (BM)
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Kinser RD, Dolph PJ. Cathepsin proteases mediate photoreceptor cell degeneration in Drosophila. Neurobiol Dis 2012; 46:655-62. [PMID: 22426392 DOI: 10.1016/j.nbd.2012.03.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2011] [Revised: 02/14/2012] [Accepted: 03/01/2012] [Indexed: 11/23/2022] Open
Affiliation(s)
- Ronald D Kinser
- Department of Biology, Dartmouth College, 54 College St, Hanover, NH 03755, USA
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Montell C. Drosophila visual transduction. Trends Neurosci 2012; 35:356-63. [PMID: 22498302 DOI: 10.1016/j.tins.2012.03.004] [Citation(s) in RCA: 146] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2011] [Revised: 03/06/2012] [Accepted: 03/11/2012] [Indexed: 11/26/2022]
Abstract
Visual transduction in the Drosophila compound eye functions through a pathway that couples rhodopsin to phospholipase C (PLC) and the opening of transient receptor potential (TRP) channels. This cascade differs from phototransduction in mammalian rods and cones, but is remarkably similar to signaling in mammalian intrinsically photosensitive retinal ganglion cells (ipRGCs). In this review, I focus on recent advances in the fly visual system, including the discovery of a visual cycle and insights into the machinery and mechanisms involved in generating a light response in photoreceptor cells.
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Affiliation(s)
- Craig Montell
- Departments of Biological Chemistry and Neuroscience, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
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Raghu P, Yadav S, Mallampati NBN. Lipid signaling in Drosophila photoreceptors. Biochim Biophys Acta Mol Cell Biol Lipids 2012; 1821:1154-65. [PMID: 22487656 DOI: 10.1016/j.bbalip.2012.03.008] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2011] [Revised: 03/20/2012] [Accepted: 03/22/2012] [Indexed: 11/19/2022]
Abstract
Drosophila photoreceptors are sensory neurons whose primary function is the transduction of photons into an electrical signal for forward transmission to the brain. Photoreceptors are polarized cells whose apical domain is organized into finger like projections of plasma membrane, microvilli that contain the molecular machinery required for sensory transduction. The development of this apical domain requires intense polarized membrane transport during development and it is maintained by post developmental membrane turnover. Sensory transduction in these cells involves a high rate of G-protein coupled phosphatidylinositol 4,5 bisphosphate [PI(4,5)P(2)] hydrolysis ending with the activation of ion channels that are members of the TRP superfamily. Defects in this lipid-signaling cascade often result in retinal degeneration, which is a consequence of the loss of apical membrane homeostasis. In this review we discuss the various membrane transport challenges of photoreceptors and their regulation by ongoing lipid signaling cascades in these cells. This article is part of a Special Issue entitled Lipids and Vesicular Transport.
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Affiliation(s)
- Padinjat Raghu
- National Centre for Biological Sciences, TIFR, GKVK Campus, Bellary Road, Banglore 560065, India.
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Abstract
Drosophila photoreceptors (R cells) are an extreme instance of sensory membrane amplification via apical microvilli, a widely deployed and deeply conserved operation of polarized epithelial cells. Developmental rotation of R cell apices aligns rhabdomere microvilli across the optical axis and enables enormous membrane expansion in a new, proximal distal dimension. R cell ectoplasm, the specialized cortical cytoplasm abutting the rhabdomere is likewise enormously amplified. Ectoplasm is dominated by the actin-rich terminal web, a conserved operational domain of the ancient vesicle-transport motor, Myosin V. R cells harness Myosin V to move two distinct cargoes, the biosynthetic traffic that builds the rhabdomere during development, and the migration of pigment granules that mediates the adaptive "longitudinal pupil" in adults, using two distinct Rab proteins. Ectoplasm further shapes a distinct cortical endosome compartment, the subrhabdomeral cisterna (SRC), vital to normal cell function. Reticulon, a protein that promotes endomembrane curvature, marks the SRC. R cell visual arrestin 2 (Arr2) is predominantly cytoplasmic in dark-adapted photoreceptors but on illumination it translocates to the rhabdomere, where it quenches ongoing photosignaling by binding to activated metarhodopsin. Arr2 translocation is "powered" by diffusion; a motor is not required to move Arr2 and ectoplasm does not obstruct its rapid diffusion to the rhabdomere.
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Affiliation(s)
- Hongai Xia
- Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA
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Chan CC, Epstein D, Hiesinger PR. Intracellular trafficking in Drosophila visual system development: a basis for pattern formation through simple mechanisms. Dev Neurobiol 2012; 71:1227-45. [PMID: 21714102 DOI: 10.1002/dneu.20940] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Intracellular trafficking underlies cellular functions ranging from membrane remodeling to receptor activation. During multicellular organ development, these basic cell biological functions are required as both passive machinery and active signaling regulators. Exocytosis, endocytosis, and recycling of several key signaling receptors have long been known to actively regulate morphogenesis and pattern formation during Drosophila eye development. Hence, intracellular membrane trafficking not only sets the cell biological stage for receptor-mediated signaling but also actively controls signaling through spatiotemporally regulated receptor localization. In contrast to eye development, the role of intracellular trafficking for the establishment of the eye-to-brain connectivity map has only recently received more attention. It is still poorly understood how guidance receptors are spatiotemporally regulated to serve as meaningful synapse formation signals. Yet, the Drosophila visual system provides some of the most striking examples for the regulatory role of intracellular trafficking during multicellular organ development. In this review we will first highlight the experimental and conceptual advances that motivate the study of intracellular trafficking during Drosophila visual system development. We will then illuminate the development of the eye, the eye-to-brain connectivity map and the optic lobe from the perspective of cell biological dynamics. Finally, we provide a conceptual framework that seeks to explain how the interplay of simple genetically encoded intracellular trafficking events governs the seemingly complex cellular behaviors, which in turn determine the developmental product.
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Affiliation(s)
- Chih-Chiang Chan
- Department of Physiology and Green Center for Systems Biology, UT Southwestern Medical Center, Dallas, Texas, USA
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Hu W, Wan D, Yu X, Cao J, Guo P, Li HS, Han J. Protein Gq modulates termination of phototransduction and prevents retinal degeneration. J Biol Chem 2012; 287:13911-8. [PMID: 22389492 DOI: 10.1074/jbc.m112.339895] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Appropriate termination of the phototransduction cascade is critical for photoreceptors to achieve high temporal resolution and to prevent excessive Ca(2+)-induced cell toxicity. Using a genetic screen to identify defective photoresponse mutants in Drosophila, we isolated and identified a novel Gα(q) mutant allele, which has defects in both activation and deactivation. We revealed that G(q) modulates the termination of the light response and that metarhodopsin/G(q) interaction affects subsequent arrestin-rhodopsin (Arr2-Rh1) binding, which mediates the deactivation of metarhodopsin. We further showed that the Gα(q) mutant undergoes light-dependent retinal degeneration, which is due to the slow accumulation of stable Arr2-Rh1 complexes. Our study revealed the roles of G(q) in mediating photoresponse termination and in preventing retinal degeneration. This pathway may represent a general rapid feedback regulation of G protein-coupled receptor signaling.
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Affiliation(s)
- Wen Hu
- Institute of Life Science, the Key Laboratory of Developmental Genes and Human Disease, Southeast University, Nanjing 210096, China
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67
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Phototransduction in Drosophila. SCIENCE CHINA-LIFE SCIENCES 2012; 55:27-34. [PMID: 22314488 DOI: 10.1007/s11427-012-4272-4] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 09/12/2011] [Indexed: 10/14/2022]
Abstract
The Drosophila visual transduction is the fastest known G protein-coupled signaling cascade and has been served as a model for understanding the molecular mechanisms of other G protein-coupled signaling cascades. Numbers of components in visual transduction machinery have been identified. Based on the functional characterization of these genes, a model for Drosophila phototransduction has been outlined, including rhodopsin activation, phosphoinoside signaling, and the opening of TRP and TRPL channels. Recently, the characterization of mutants, showing slow termination, revealed the physiological significance and the mechanism of rapid termination of light response.
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68
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Pak WL, Shino S, Leung HT. PDA (prolonged depolarizing afterpotential)-defective mutants: the story of nina's and ina's--pinta and santa maria, too. J Neurogenet 2012; 26:216-37. [PMID: 22283778 PMCID: PMC3433705 DOI: 10.3109/01677063.2011.642430] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Our objective is to present a comprehensive view of the PDA (prolonged depolarizing afterpotential)-defective Drosophila mutants, nina's and ina's, from the discussion of the PDA and the PDA-based mutant screening strategy to summaries of the knowledge gained through the studies of mutants generated using the strategy. The PDA is a component of the light-evoked photoreceptor potential that is generated when a substantial fraction of rhodopsin is photoconverted to its active form, metarhodopsin. The PDA-based mutant screening strategy was adopted to enhance the efficiency and efficacy of ERG (electroretinogram)-based screening for identifying phototransduction-defective mutants. Using this strategy, two classes of PDA-defective mutants were identified and isolated, nina and ina, each comprising multiple complementation groups. The nina mutants are characterized by allele-dependent reduction in the major rhodopsin, Rh1, whereas the ina mutants display defects in some aspects of functions related to the transduction channel, TRP (transient receptor potential). The signaling proteins that have been identified and elucidated through the studies of nina mutants include the Drosophila opsin protein (NINAE), the chaperone protein for nascent opsin (NINAA), and the multifunctional protein, NINAC, required in multiple steps of the Drosophila phototransduction cascade. Also identified by the nina mutants are some of the key enzymes involved in the biogenesis of the rhodopsin chromophore. As for the ina mutants, they led to the discovery of the scaffold protein, INAD, responsible for the nucleation of the supramolecular signaling complex. Also identified by the ina mutants is one of the key members of the signaling complex, INAC (ePKC), and two other proteins that are likely to be important, though their roles in the signaling cascade have not yet been fully elucidated. In most of these cases, the protein identified is the first member of its class to be so recognized.
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Affiliation(s)
- William L Pak
- Department of Biological Sciences, Purdue University, 915 W. State Street, West Lafayette, IN 47907-2054, USA.
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69
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Pocha SM, Shevchenko A, Knust E. Crumbs regulates rhodopsin transport by interacting with and stabilizing myosin V. ACTA ACUST UNITED AC 2011; 195:827-38. [PMID: 22105348 PMCID: PMC3257572 DOI: 10.1083/jcb.201105144] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
In the absence of Crumbs, myosin V is degraded, resulting in defective rhodopsin 1 transport to the rhabdomere and subsequent photoreceptor degeneration. The evolutionarily conserved Crumbs (Crb) complex is crucial for photoreceptor morphogenesis and homeostasis. Loss of Crb results in light-dependent retinal degeneration, which is prevented by feeding mutant flies carotenoid-deficient medium. This suggests a defect in rhodopsin 1 (Rh1) processing, transport, and/or signaling, causing degeneration; however, the molecular mechanism of this remained elusive. In this paper, we show that myosin V (MyoV) coimmunoprecipitated with the Crb complex and that loss of crb led to severe reduction in MyoV levels, which could be rescued by proteasomal inhibition. Loss of MyoV in crb mutant photoreceptors was accompanied by defective transport of the MyoV cargo Rh1 to the light-sensing organelle, the rhabdomere. This resulted in an age-dependent accumulation of Rh1 in the photoreceptor cell (PRC) body, a well-documented trigger of degeneration. We conclude that Crb protects against degeneration by interacting with and stabilizing MyoV, thereby ensuring correct Rh1 trafficking. Our data provide, for the first time, a molecular mechanism for the light-dependent degeneration of PRCs observed in crb mutant retinas.
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Affiliation(s)
- Shirin Meher Pocha
- Max Planck Institute of Molecular Cell Biology and Genetics, 01307 Dresden, Germany.
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70
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Hardie RC. Phototransduction mechanisms in Drosophila microvillar photoreceptors. ACTA ACUST UNITED AC 2011. [DOI: 10.1002/wmts.20] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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71
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Abstract
Inherited retinal degeneration in Drosophila has been explored for insights into similar processes in humans. Based on the mechanisms, I divide these mutations in Drosophila into three classes. The first consists of genes that control the specialization of photoreceptor cells including the morphogenesis of visual organelles (rhabdomeres) that house the visual signaling proteins. The second class contains genes that regulate the activity or level of the major rhodopsin, Rh1, which is the light sensor and also provides a structural role for the maintenance of rhabdomeres. Some mutations in Rh1 (NinaE) are dominant due to constitutive activity or folding defects, like autosomal dominant retinitis pigmentosa (ADRP) in humans. The third class consists of genes that control the Ca ( 2+) influx directly or indirectly by promoting the turnover of the second messenger and regeneration of PIP 2, or mediate the Ca ( 2+) -dependent regulation of the visual response. These gene products are critical for the increase in cytosolic Ca ( 2+ ) following light stimulation to initiate negative regulatory events. Here I will focus on the signaling mechanisms underlying the degeneration in norpA, and in ADRP-type NinaE mutants that produce misfolded Rh1. Accumulation of misfolded Rh1 in the ER triggers the unfolded protein response (UPR), while endosomal accumulation of activated Rh1 may initiate autophagy in norpA. Both autophagy and the UPR are beneficial for relieving defective endosomal trafficking and the ER stress, respectively. However, when photoreceptors fail to cope with the persistence of these stresses, a cell death program is activated leading to retinal degeneration.
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Affiliation(s)
- Bih-Hwa Shieh
- Department of Pharmacology, Center for Molecular Neuroscience and Vision Research Center, Vanderbilt University, Nashville, TN USA.
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72
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Gurevich VV, Hanson SM, Song X, Vishnivetskiy SA, Gurevich EV. The functional cycle of visual arrestins in photoreceptor cells. Prog Retin Eye Res 2011; 30:405-30. [PMID: 21824527 DOI: 10.1016/j.preteyeres.2011.07.002] [Citation(s) in RCA: 94] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2011] [Revised: 07/20/2011] [Accepted: 07/21/2011] [Indexed: 01/14/2023]
Abstract
Visual arrestin-1 plays a key role in the rapid and reproducible shutoff of rhodopsin signaling. Its highly selective binding to light-activated phosphorylated rhodopsin is an integral part of the functional perfection of rod photoreceptors. Structure-function studies revealed key elements of the sophisticated molecular mechanism ensuring arrestin-1 selectivity and paved the way to the targeted manipulation of the arrestin-1 molecule to design mutants that can compensate for congenital defects in rhodopsin phosphorylation. Arrestin-1 self-association and light-dependent translocation in photoreceptor cells work together to keep a constant supply of active rhodopsin-binding arrestin-1 monomer in the outer segment. Recent discoveries of arrestin-1 interaction with other signaling proteins suggest that it is a much more versatile signaling regulator than previously thought, affecting the function of the synaptic terminals and rod survival. Elucidation of the fine molecular mechanisms of arrestin-1 interactions with rhodopsin and other binding partners is necessary for the comprehensive understanding of rod function and for devising novel molecular tools and therapeutic approaches to the treatment of visual disorders.
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Affiliation(s)
- Vsevolod V Gurevich
- Department of Pharmacology, Vanderbilt University, 2200 Pierce Ave, PRB, Rm 417D, Nashville, TN 37232, USA.
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73
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Aubry L, Guetta D, Klein G. The arrestin fold: variations on a theme. Curr Genomics 2011; 10:133-42. [PMID: 19794886 PMCID: PMC2699828 DOI: 10.2174/138920209787847014] [Citation(s) in RCA: 67] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Revised: 12/30/2008] [Accepted: 01/05/2009] [Indexed: 12/26/2022] Open
Abstract
Endocytosis of ligand-activated plasma membrane receptors has been shown to contribute to the regulation of their downstream signaling. β-arrestins interact with the phosphorylated tail of activated receptors and act as scaffolds for the recruitment of adaptor proteins and clathrin, that constitute the machinery used for receptor endocytosis. Visual- and β-arrestins have a two-lobe, immunoglobulin-like, β-strand sandwich structure. The recent resolution of the crystal structure of VPS26, one of the retromer subunits, unexpectedly evidences an arrestin fold in this protein, which is otherwise unrelated to arrestins. From a functional point of view, VPS26 is involved in the retrograde transport of the mannose 6-P receptor from the endosomes to the trans-Golgi network. In addition to the group of genuine arrestins and Vps26, mammalian cells harbor a vast repertoire of proteins that are related to arrestins on the basis of their PFAM Nter and Cter arrestin- domains, which are named Arrestin Domain- Containing proteins (ADCs). The biological role of ADC proteins is still poorly understood. The three subfamilies have been merged into an arrestin-related protein clan. This paper provides an overall analysis of arrestin clan proteins. The structures and functions of members of the subfamilies are reviewed in mammals and model organisms such as Drosophila, Caenorhabditis, Saccharomyces and Dictyostelium.
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Affiliation(s)
- Laurence Aubry
- CNRS, UMR 5092, 17 rue des Martyrs, Grenoble, 38054, France
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74
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Oberegelsbacher C, Schneidler C, Voolstra O, Cerny A, Huber A. The Drosophila TRPL ion channel shares a Rab-dependent translocation pathway with rhodopsin. Eur J Cell Biol 2011; 90:620-30. [PMID: 21507505 DOI: 10.1016/j.ejcb.2011.02.003] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2010] [Revised: 02/01/2011] [Accepted: 02/07/2011] [Indexed: 11/26/2022] Open
Abstract
The Drosophila visual transduction cascade is embedded in the rhabdomeres of photoreceptor cells and culminates in the opening of the two ion channels, TRP and TRPL. TRPL translocates from the rhabdomeres to the cell body upon illumination and vice versa when flies are kept in the dark. Here, we studied the mechanisms underlying the light-dependent internalization of TRPL. Co-localization of TRPL and rhodopsin in endocytic particles revealed that TRPL is internalized by a vesicular transport pathway that is also utilized, at least partially, for rhodopsin endocytosis. TRPL internalization is attenuated under light conditions that result in a high rate of rhodopsin internalization and is highest in orange light that result in very little rhodopsin internalization. In line with a canonical vesicular transport pathway, we found that rab proteins, Rab5 and RabX4, are required for the internalization of TRPL into the cell body. Our results provide insight into stimulus-dependent internalization of a prominent member of the TRP superfamily.
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Affiliation(s)
- Claudia Oberegelsbacher
- Department of Biosensorics, Institute of Physiology, University of Hohenheim, 70599 Stuttgart, Germany
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75
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Kawano-Yamashita E, Koyanagi M, Shichida Y, Oishi T, Tamotsu S, Terakita A. β-arrestin functionally regulates the non-bleaching pigment parapinopsin in lamprey pineal. PLoS One 2011; 6:e16402. [PMID: 21305016 PMCID: PMC3031554 DOI: 10.1371/journal.pone.0016402] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Accepted: 12/20/2010] [Indexed: 11/23/2022] Open
Abstract
The light response of vertebrate visual cells is achieved by light-sensing proteins such as opsin-based pigments as well as signal transduction proteins, including visual arrestin. Previous studies have indicated that the pineal pigment parapinopsin has evolutionally and physiologically important characteristics. Parapinopsin is phylogenetically related to vertebrate visual pigments. However, unlike the photoproduct of the visual pigment rhodopsin, which is unstable, dissociating from its chromophore and bleaching, the parapinopsin photoproduct is stable and does not release its chromophore. Here, we investigated arrestin, which regulates parapinopsin signaling, in the lamprey pineal organ, where parapinopsin and rhodopsin are localized to distinct photoreceptor cells. We found that beta-arrestin, which binds to stimulated G protein-coupled receptors (GPCRs) other than opsin-based pigments, was localized to parapinopsin-containing cells. This result stands in contrast to the localization of visual arrestin in rhodopsin-containing cells. Beta-arrestin bound to cultured cell membranes containing parapinopsin light-dependently and translocated to the outer segments of pineal parapinopsin-containing cells, suggesting that beta-arrestin binds to parapinopsin to arrest parapinopsin signaling. Interestingly, beta-arrestin colocalized with parapinopsin in the granules of the parapinopsin-expressing cell bodies under light illumination. Because beta-arrestin, which is a mediator of clathrin-mediated GPCR internalization, also served as a mediator of parapinopsin internalization in cultured cells, these results suggest that the granules were generated light-dependently by beta-arrestin-mediated internalization of parapinopsins from the outer segments. Therefore, our findings imply that beta-arrestin-mediated internalization is responsible for eliminating the stable photoproduct and restoring cell conditions to the original dark state. Taken together with a previous finding that the bleaching pigment evolved from a non-bleaching pigment, vertebrate visual arrestin may have evolved from a “beta-like” arrestin by losing its clathrin-binding domain and its function as an internalization mediator. Such changes would have followed the evolution of vertebrate visual pigments, which generate unstable photoproducts that independently decay by chromophore dissociation.
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Affiliation(s)
- Emi Kawano-Yamashita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Mitsumasa Koyanagi
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
| | - Yoshinori Shichida
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto, Japan
| | | | - Satoshi Tamotsu
- Graduate School of Humanities and Sciences, Nara Women's University, Nara, Japan
| | - Akihisa Terakita
- Department of Biology and Geosciences, Graduate School of Science, Osaka City University, Osaka, Japan
- * E-mail:
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76
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Cook T, Zelhof A, Mishra M, Nie J. 800 facets of retinal degeneration. PROGRESS IN MOLECULAR BIOLOGY AND TRANSLATIONAL SCIENCE 2011; 100:331-68. [PMID: 21377630 DOI: 10.1016/b978-0-12-384878-9.00008-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In today's world of genomics and large computational analyses, rapid progress has been made in identifying genes associated with human retinal diseases. Nevertheless, before significant advances toward effective therapeutic intervention is made, a clearer understanding of the molecular and cellular role of these gene products in normal and diseased photoreceptor cell biology is required. Given the complexity of the vertebrate retina, these advancements are unlikely to be revealed in isolated human cell lines, but instead, will require the use of numerous model systems. Here, we describe several parallels between vertebrate and invertebrate photoreceptor cell biology that are beginning to emerge and advocate the use of Drosophila melanogaster as a powerful genetic model system for uncovering molecular mechanisms of human retinal pathologies, in particular photoreceptor neurodegeneration.
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Affiliation(s)
- T Cook
- Department of Pediatric Ophthalmology, Division of Developmental Biology, Cincinnati Children's Hospital Medical Center, Cincinnati, Ohio, USA
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77
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Satoh AK, Xia H, Yan L, Liu CH, Hardie RC, Ready DF. Arrestin translocation is stoichiometric to rhodopsin isomerization and accelerated by phototransduction in Drosophila photoreceptors. Neuron 2010; 67:997-1008. [PMID: 20869596 PMCID: PMC2946946 DOI: 10.1016/j.neuron.2010.08.024] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/05/2010] [Indexed: 11/19/2022]
Abstract
Upon illumination, visual arrestin translocates from photoreceptor cell bodies to rhodopsin and membrane-rich photosensory compartments, vertebrate outer segments or invertebrate rhabdomeres, where it quenches activated rhodopsin. Both the mechanism and function of arrestin translocation are unresolved and controversial. In dark-adapted photoreceptors of the fruitfly Drosophila, confocal immunocytochemistry shows arrestin (Arr2) associated with distributed photoreceptor endomembranes. Immunocytochemistry and live imaging of GFP-tagged Arr2 demonstrate rapid reversible translocation to stimulated rhabdomeres in stoichiometric proportion to rhodopsin photoisomerization. Translocation is very rapid in normal photoreceptors (time constant <10 s) and can also be resolved in the time course of electroretinogram recordings. Genetic elimination of key phototransduction proteins, including phospholipase C (PLC), Gq, and the light-sensitive Ca2+-permeable TRP channels, slows translocation by 10- to 100-fold. Our results indicate that Arr2 translocation in Drosophila photoreceptors is driven by diffusion, but profoundly accelerated by phototransduction and Ca2+ influx.
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Affiliation(s)
- Akiko K. Satoh
- Department of Biological Sciences, Graduate School of Science, Nagoya University, Nagoya, 466-8601, Japan
| | - Hongai Xia
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
| | - Limin Yan
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, UK
| | - Che-Hsiung Liu
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, UK
| | - Roger C. Hardie
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB2 3DY, UK
| | - Donald F. Ready
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
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78
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Griciuc A, Aron L, Roux MJ, Klein R, Giangrande A, Ueffing M. Inactivation of VCP/ter94 suppresses retinal pathology caused by misfolded rhodopsin in Drosophila. PLoS Genet 2010; 6:e1001075. [PMID: 20865169 PMCID: PMC2928793 DOI: 10.1371/journal.pgen.1001075] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2010] [Accepted: 07/20/2010] [Indexed: 11/30/2022] Open
Abstract
The most common Rhodopsin (Rh) mutation associated with autosomal dominant retinitis pigmentosa (ADRP) in North America is the substitution of proline 23 by histidine (Rh(P23H)). Unlike the wild-type Rh, mutant Rh(P23H) exhibits folding defects and forms intracellular aggregates. The mechanisms responsible for the recognition and clearance of misfolded Rh(P23H) and their relevance to photoreceptor neuron (PN) degeneration are poorly understood. Folding-deficient membrane proteins are subjected to Endoplasmic Reticulum (ER) quality control, and we have recently shown that Rh(P23H) is a substrate of the ER-associated degradation (ERAD) effector VCP/ter94, a chaperone that extracts misfolded proteins from the ER (a process called retrotranslocation) and facilitates their proteasomal degradation. Here, we used Drosophila, in which Rh1(P37H) (the equivalent of mammalian Rh(P23H)) is expressed in PNs, and found that the endogenous Rh1 is required for Rh1(P37H) toxicity. Genetic inactivation of VCP increased the levels of misfolded Rh1(P37H) and further activated the Ire1/Xbp1 ER stress pathway in the Rh1(P37H) retina. Despite this, Rh1(P37H) flies with decreased VCP function displayed a potent suppression of retinal degeneration and blindness, indicating that VCP activity promotes neurodegeneration in the Rh1(P37H) retina. Pharmacological treatment of Rh1(P37H) flies with the VCP/ERAD inhibitor Eeyarestatin I or with the proteasome inhibitor MG132 also led to a strong suppression of retinal degeneration. Collectively, our findings raise the possibility that excessive retrotranslocation and/or degradation of visual pigment is a primary cause of PN degeneration.
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Affiliation(s)
- Ana Griciuc
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health, Neuherberg, Germany
| | - Liviu Aron
- Department of Molecular Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany
| | - Michel J. Roux
- Department of Neurobiology and Genetics, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch, France
| | - Rüdiger Klein
- Department of Molecular Neurobiology, Max-Planck-Institute of Neurobiology, Martinsried, Germany
| | - Angela Giangrande
- Department of Cell and Developmental Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire, CNRS/INSERM/ULP, Illkirch, France
| | - Marius Ueffing
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health, Neuherberg, Germany
- Institute for Ophthalmic Research, Center for Ophthalmology, University of Tuebingen, Tuebingen, Germany
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79
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Abstract
It was commonly accepted that the enzymatic pathway regenerating bleached visual pigments is present in vertebrate but not invertebrate animals. New studies indicate that this pathway is present in Drosophila and is vital for maintaining both the amount of visual pigment and photoreceptor health in light-exposed flies.
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80
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Elsaesser R, Kalra D, Li R, Montell C. Light-induced translocation of Drosophila visual Arrestin2 depends on Rac2. Proc Natl Acad Sci U S A 2010; 107:4740-5. [PMID: 20176938 PMCID: PMC2842041 DOI: 10.1073/pnas.0906386107] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Photoreceptor cells are remarkable in their ability to adjust their sensitivity to light over a wide range of intensities. Rapid termination of the photoresponse is achieved in part by shuttling proteins in and out of the light-transducing compartment of the photoreceptor cells. One protein that undergoes light-dependent translocation is the rhodopsin regulatory protein arrestin. However, the mechanisms coupling rhodopsin to arrestin movement are poorly understood. Here we show that light-dependent shuttling of the major arrestin in Drosophila photoreceptor cells, Arrestin2 (Arr2), occurs independently of known elements of the phototransduction cascade. Disruptions of the trimeric G protein, phospholipase Cbeta, the TRP channel, or the Na(+)/Ca(2+) exchanger did not influence Arr2 localization. Rather, we found that loss of the small GTPase Rac2 severely impaired Arr2 movement and prolonged the termination of the photoresponse. Our findings demonstrate that light-induced translocation of Arr2 occurs through a noncanonical rhodopsin/Rac2 pathway, which is distinct from the classical phototransduction cascade.
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Affiliation(s)
- Rebecca Elsaesser
- Center for Sensory Biology, Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Deepak Kalra
- Center for Sensory Biology, Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Ruoxia Li
- Center for Sensory Biology, Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Craig Montell
- Center for Sensory Biology, Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205
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81
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Griciuc A, Aron L, Piccoli G, Ueffing M. Clearance of Rhodopsin(P23H) aggregates requires the ERAD effector VCP. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2010; 1803:424-34. [PMID: 20097236 DOI: 10.1016/j.bbamcr.2010.01.008] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2009] [Revised: 12/29/2009] [Accepted: 01/15/2010] [Indexed: 11/15/2022]
Abstract
Dominant mutations in the visual pigment Rhodopsin (Rh) cause retinitis pigmentosa (RP) characterized by progressive blindness and retinal degeneration. The most common Rh mutation, Rh(P23H) forms aggregates in the endoplasmic reticulum (ER) and impairs the proteasome; however, the mechanisms linking Rh aggregate formation to proteasome dysfunction and photoreceptor cell loss remain unclear. Using mammalian cell cultures, we provide the first evidence that misfolded Rh(P23H) is a substrate of the ERAD effector VCP, an ATP-dependent chaperone that extracts misfolded proteins from the ER and escorts them for proteasomal degradation. VCP co-localizes with misfolded Rh(P23H) in retinal cells and requires functional N-terminal and D1 ATPase domains to form a complex with Rh(P23H) aggregates. Furthermore, VCP uses its D2 ATPase activity to promote Rh(P23H) aggregate retrotranslocation and proteasomal delivery. Our results raise the possibility that modulation of VCP and ERAD activity might have potential therapeutic significance for RP.
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Affiliation(s)
- Ana Griciuc
- Department of Protein Science, Helmholtz Zentrum Muenchen-German Research Center for Environmental Health (GmbH), 85764 Neuherberg, Germany
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82
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Wang X, Wang T, Jiao Y, von Lintig J, Montell C. Requirement for an enzymatic visual cycle in Drosophila. Curr Biol 2009; 20:93-102. [PMID: 20045325 DOI: 10.1016/j.cub.2009.12.022] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2009] [Accepted: 12/01/2009] [Indexed: 11/25/2022]
Abstract
BACKGROUND The visual cycle is an enzymatic pathway employed in the vertebrate retina to regenerate the chromophore after its release from light-activated rhodopsin. However, a visual cycle is thought to be absent in invertebrates such as the fruit fly Drosophila melanogaster. RESULTS We demonstrate that an enzymatic visual cycle exists in flies for chromophore regeneration and requires a retinol dehydrogenase, PDH, in retinal pigment cells. Absence of PDH resulted in progressive light-dependent loss of rhodopsin and retinal degeneration. These defects are suppressed by introduction of a mammalian dehydrogenase, RDH12, which is required in humans to prevent retinal degeneration. We demonstrate that a visual cycle is required in flies to sustain a visual response under nutrient deprivation conditions that preclude de novo production of the chromophore. CONCLUSIONS Our results demonstrate that an enzymatic visual cycle exists and is required in flies for maintaining rhodopsin levels. These findings establish Drosophila as an animal model for studying the visual cycle and retinal diseases associated with chromophore regeneration.
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Affiliation(s)
- Xiaoyue Wang
- Center for Sensory Biology, Departments of Biological Chemistry and Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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83
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Brown BM, Ramirez T, Rife L, Craft CM. Visual Arrestin 1 contributes to cone photoreceptor survival and light adaptation. Invest Ophthalmol Vis Sci 2009; 51:2372-80. [PMID: 20019357 DOI: 10.1167/iovs.09-4895] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE To evaluate morphologic and functional contributions of Arrestin 1 (Arr1) and Arrestin 4 (Arr4) in cone photoreceptors, the authors examined the phenotypes of visual arrestin knockout mice (Arr1(-/-), Arr4(-/-), Arr1(-/-)Arr4(-/-) [Arr-DKO]) reared in darkness. METHODS Retinal rods and cones were evaluated in wild-type (WT), Arr1(-/-), Arr4(-/-), and Arr-DKO mice using quantitative morphologic analysis, immunoblot, immunohistochemistry, TUNEL, and electroretinographic (ERG) techniques. RESULTS Compared with either Arr4(-/-) or WT, Arr1(-/-) and Arr-DKO mice had increased apoptotic nuclei in their retinal outer nuclear layer (ONL) at postnatal day (P) 22. By P60, cone density was significantly diminished, but the ONL appeared normal. After 1 minute of background illumination, cone ERG b-wave amplitudes were similar in WT and all Arr KO mice. However, by 3 minutes and continuing through 15 minutes of light adaptation, the cone b-wave amplitudes of WT and Arr4(-/-) mice increased significantly over those of the Arr1(-/-) and Arr-DKO mice, which demonstrated no cone b-wave amplitude increase. In contrast, ERG flicker analysis after the 15-minute light adaptation period demonstrated no loss in amplitude for either Arr1(-/-) or Arr4(-/-) mice, whereas Arr-DKO had significantly lower amplitudes. When Arr1 expression was restored in Arr1(-/-) mice (+p48(Arr1-/-)), normal cone density and light-adapted ERG b-wave amplitudes were observed. CONCLUSIONS In the adult dark-reared Arr1(-/-) and Arr-DKO mice, viable cones diminish over time. Arr1 expression is essential for cone photoreceptor survival and light adaptation, whereas either Arr1 or Arr4 is necessary for maintaining normal flicker responses.
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Affiliation(s)
- Bruce M Brown
- Department of Ophthalmology, Keck School of Medicine, University of Southern California, Los Angeles, CA 90033-9224, USA
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84
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Overexpressing temperature-sensitive dynamin decelerates phototransduction and bundles microtubules in Drosophila photoreceptors. J Neurosci 2009; 29:14199-210. [PMID: 19906968 DOI: 10.1523/jneurosci.2873-09.2009] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
shibire(ts1), a temperature-sensitive mutation of the Drosophila gene encoding a Dynamin orthologue, blocks vesicle endocytosis and thus synaptic transmission, at elevated, or restrictive temperatures. By targeted Gal4 expression, UAS-shibire(ts1) has been used to dissect neuronal circuits. We investigated the effects of UAS-shibire(ts1) overexpression in Drosophila photoreceptors at permissive (19 degrees C) and restrictive (31 degrees C) temperatures. At 19 degrees C, overexpression of UAS-shi(ts1) causes decelerated phototransduction and reduced neurotransmitter release. This phenotype is exacerbated with dark adaptation, age and in white mutants. Photoreceptors overexpressing UAS-shibire(ts1) contain terminals with widespread vacuolated mitochondria, reduced numbers of vesicles and bundled microtubules. Immuno-electron microscopy reveals that the latter are dynamin coated. Further, the microtubule phenotype is not restricted to photoreceptors, as UAS-shibire(ts1) overexpression in lamina cells also bundles microtubules. We conclude that dynamin has multiple functions that are interrupted by UAS-shibire(ts1) overexpression in Drosophila photoreceptors, destabilizing their neural communication irreversibly at previously reported permissive temperatures.
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85
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Belusic G, Pirih P, Stavenga DG. Photoreceptor responses of fruitflies with normal and reduced arrestin content studied by simultaneous measurements of visual pigment fluorescence and ERG. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2009; 196:23-35. [PMID: 19924417 PMCID: PMC2797847 DOI: 10.1007/s00359-009-0489-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2009] [Revised: 11/01/2009] [Accepted: 11/03/2009] [Indexed: 11/26/2022]
Abstract
We have simultaneously measured the electroretinogram (ERG) and the metarhodopsin content via fluorescence in white-eyed, wild-type Drosophila and the arrestin2 hypomorphic mutant (w(-);arr2 (3)) at a range of stimulus wavelengths and intensities. Photoreceptor response amplitude and termination (transition between full repolarization and prolonged depolarizing afterpotential, PDA) were related to visual pigment conversions and arrestin concentration. The data were implemented in a kinetic model of the rhodopsin-arrestin cycle, allowing us to estimate the active metarhodopsin concentration as a function of effective light intensity and arrestin concentration. Arrestin reduction in the mutant modestly increased the light sensitivity and decreased the photoreceptor dynamic range. Compared to the wild type, in the mutant the transition between full repolarization and PDA occurred at a lower metarhodopsin fraction and was more abrupt. We developed a steady-state stochastic model to interpret the dependence of the PDA on effective light intensity and arrestin content and to help deduce the arrestin to rhodopsin ratio from the sensitivity and PDA data. The feasibility of different experimental methods for the estimation of arrestin content from ERG and PDA is discussed.
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Affiliation(s)
- Gregor Belusic
- Department of Biology, Biotechnical Faculty, University of Ljubljana, 1000 Ljubljana, Slovenia.
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86
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Whitcomb T, Sakurai K, Brown BM, Young JE, Sheflin L, Dlugos C, Craft CM, Kefalov VJ, Khani SC. Effect of g protein-coupled receptor kinase 1 (Grk1) overexpression on rod photoreceptor cell viability. Invest Ophthalmol Vis Sci 2009; 51:1728-37. [PMID: 19834036 DOI: 10.1167/iovs.09-4499] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
PURPOSE Photoreceptor rhodopsin kinase (Rk, G protein-dependent receptor kinase 1 [Grk1]) phosphorylates light-activated opsins and channels them into an inactive complex with visual arrestins. Grk1 deficiency leads to human retinopathy and heightened susceptibility to light-induced photoreceptor cell death in the mouse. The goal of this study was to determine whether excess Grk1 activity is protective against photoreceptor cell death. METHODS Grk1-overexpressing transgenic mice (Grk1(+)) were generated by using a bacterial artificial chromosome (BAC) construct containing mouse Grk1, along with its flanking sequences. Quantitative reverse transcription-PCR, immunoblot analysis, immunostaining, and activity assays were combined with electrophysiology and morphometric analysis, to evaluate Grk1 overexpression and its effect on physiologic and morphologic retinal integrity. Morphometry and nucleosome release assays measured differences in resistance to photoreceptor cell loss between control and transgenic mice exposed to intense light. RESULTS Compared with control animals, the Grk1(+) transgenic line had approximately a threefold increase in Grk1 transcript and immunoreactive protein. Phosphorylated opsin immunochemical staining and in vitro phosphorylation assays confirmed proportionately higher Grk1 enzyme activity. Grk1(+) mice retained normal rod function, normal retinal appearance, and lacked evidence of spontaneous apoptosis when reared in cyclic light. In intense light, Grk1(+) mice showed photoreceptor damage, and their susceptibility was more pronounced than that of control mice with prolonged exposure times. CONCLUSIONS Enhancing visual pigment deactivation does not appear to protect against apoptosis; however, excess flow of opsin into the deactivation pathway may actually increase susceptibility to stress-induced cell death similar to some forms of retinal degeneration.
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Affiliation(s)
- Tiffany Whitcomb
- Ross Eye Institute, State University of New York at Buffalo, New York, USA
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87
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Kock I, Bulgakova NA, Knust E, Sinning I, Panneels V. Targeting of Drosophila rhodopsin requires helix 8 but not the distal C-terminus. PLoS One 2009; 4:e6101. [PMID: 19572012 PMCID: PMC2700256 DOI: 10.1371/journal.pone.0006101] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2009] [Accepted: 05/29/2009] [Indexed: 11/29/2022] Open
Abstract
Background The fundamental role of the light receptor rhodopsin in visual function and photoreceptor cell development has been widely studied. Proper trafficking of rhodopsin to the photoreceptor membrane is of great importance. In human, mutations in rhodopsin involving its intracellular mislocalization, are the most frequent cause of autosomal dominant Retinitis Pigmentosa, a degenerative retinal pathology characterized by progressive blindness. Drosophila is widely used as an animal model in visual and retinal degeneration research. So far, little is known about the requirements for proper rhodopsin targeting in Drosophila. Methodology/Principal Findings Different truncated fly-rhodopsin Rh1 variants were expressed in the eyes of Drosophila and their localization was analyzed in vivo or by immunofluorescence. A mutant lacking the last 23 amino acids was found to properly localize in the rhabdomeres, the light-sensing organelle of the photoreceptor cells. This constitutes a major difference to trafficking in vertebrates, which involves a conserved QVxPA motif at the very C-terminus. Further truncations of Rh1 indicated that proper localization requires the last amino acid residues of a region called helix 8 following directly the last transmembrane domain. Interestingly, the very C-terminus of invertebrate visual rhodopsins is extremely variable but helix 8 shows conserved amino acid residues that are not conserved in vertebrate homologs. Conclusions/Significance Despite impressive similarities in the folding and photoactivation of vertebrate and invertebrate visual rhodopsins, a striking difference exists between mammalian and fly rhodopsins in their requirements for proper targeting. Most importantly, the distal part of helix 8 plays a central role in invertebrates. Since the last amino acid residues of helix 8 are dispensable for rhodopsin folding and function, we propose that this domain participates in the recognition of targeting factors involved in transport to the rhabdomeres.
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Affiliation(s)
- Ines Kock
- Heidelberg University Biochemistry Center (BZH), INF328, Heidelberg, Germany
| | | | - Elisabeth Knust
- Max-Planck Institute for Molecular Cell Biology and Genetics, Dresden, Germany
| | - Irmgard Sinning
- Heidelberg University Biochemistry Center (BZH), INF328, Heidelberg, Germany
- * E-mail:
| | - Valérie Panneels
- Heidelberg University Biochemistry Center (BZH), INF328, Heidelberg, Germany
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88
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Lu H, Leung HT, Wang N, Pak WL, Shieh BH. Role of Ca2+/calmodulin-dependent protein kinase II in Drosophila photoreceptors. J Biol Chem 2009; 284:11100-9. [PMID: 19254957 DOI: 10.1074/jbc.m806956200] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ca(2+) modulates the visual response in both vertebrates and invertebrates. In Drosophila photoreceptors, an increase of cytoplasmic Ca(2+) mimics light adaptation. Little is known regarding the mechanism, however. We explored the role of the sole Drosophila Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) to mediate light adaptation. CaMKII has been implicated in the phosphorylation of arrestin 2 (Arr2). However, the functional significance of Arr2 phosphorylation remains debatable. We identified retinal CaMKII by anti-CaMKII antibodies and by its Ca(2+)-dependent autophosphorylation. Moreover, we show that phosphorylation of CaMKII is greatly enhanced by okadaic acid, and indeed, purified PP2A catalyzes the dephosphorylation of CaMKII. Significantly, we demonstrate that anti-CaMKII antibodies co-immunoprecipitate, and CaMKII fusion proteins pull down the catalytic subunit of PP2A from fly extracts, indicating that PP2A interacts with CaMKII to form a protein complex. To investigate the function of CaMKII in photoreceptors, we show that suppression of CaMKII in transgenic flies affects light adaptation and increases prolonged depolarizing afterpotential amplitude, whereas a reduced PP2A activity brings about reduced prolonged depolarizing afterpotential amplitude. Taken together, we conclude that CaMKII is involved in the negative regulation of the visual response affecting light adaptation, possibly by catalyzing phosphorylation of Arr2. Moreover, the CaMKII activity appears tightly regulated by the co-localized PP2A.
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Affiliation(s)
- Haiqin Lu
- Department of Pharmacology, Center for Molecular Neuroscience, and Vision Research Center, Vanderbilt University, Nashville, Tennessee 37232, USA
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89
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Accumulation of rhodopsin in late endosomes triggers photoreceptor cell degeneration. PLoS Genet 2009; 5:e1000377. [PMID: 19214218 PMCID: PMC2633617 DOI: 10.1371/journal.pgen.1000377] [Citation(s) in RCA: 86] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2008] [Accepted: 01/09/2009] [Indexed: 12/23/2022] Open
Abstract
Progressive retinal degeneration is the underlying feature of many human retinal dystrophies. Previous work using Drosophila as a model system and analysis of specific mutations in human rhodopsin have uncovered a connection between rhodopsin endocytosis and retinal degeneration. In these mutants, rhodopsin and its regulatory protein arrestin form stable complexes, and endocytosis of these complexes causes photoreceptor cell death. In this study we show that the internalized rhodopsin is not degraded in the lysosome but instead accumulates in the late endosomes. Using mutants that are defective in late endosome to lysosome trafficking, we were able to show that rhodopsin accumulates in endosomal compartments in these mutants and leads to light-dependent retinal degeneration. Moreover, we also show that in dying photoreceptors the internalized rhodopsin is not degraded but instead shows characteristics of insoluble proteins. Together these data implicate buildup of rhodopsin in the late endosomal system as a novel trigger of death of photoreceptor neurons.
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90
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Mutation of a TADR protein leads to rhodopsin and Gq-dependent retinal degeneration in Drosophila. J Neurosci 2009; 28:13478-87. [PMID: 19074021 DOI: 10.1523/jneurosci.2122-08.2008] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The Drosophila photoreceptor is a model system for genetic study of retinal degeneration. Many gene mutations cause fly photoreceptor degeneration, either because of excessive stimulation of the visual transduction (phototransduction) cascade, or through apoptotic pathways that in many cases involve a visual arrestin Arr2. Here we report a gene named tadr (for torn and diminished rhabdomeres), which, when mutated, leads to photoreceptor degeneration through a different mechanism. Degeneration in the tadr mutant is characterized by shrunk and disrupted rhabdomeres, the light sensory organelles of photoreceptor. The TADR protein interacted in vitro with the major light receptor Rh1 rhodopsin, and genetic reduction of the Rh1 level suppressed the tadr mutation-caused degeneration, suggesting the degeneration is Rh1-dependent. Nonetheless, removal of phospholipase C (PLC), a key enzyme in phototransduction, and that of Arr2 failed to inhibit rhabdomeral degeneration in the tadr mutant background. Biochemical analyses revealed that, in the tadr mutant, the G(q) protein of Rh1 is defective in dissociation from the membrane during light stimulation. Importantly, reduction of G(q) level by introducing a hypomorphic allele of G(alphaq) gene greatly inhibited the tadr degeneration phenotype. These results may suggest that loss of a potential TADR-Rh1 interaction leads to an abnormality in the G(q) signaling, which in turn triggers rhabdomeral degeneration independent of the PLC phototransduction cascade. We propose that TADR-like proteins may also protect photoreceptors from degeneration in mammals including humans.
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91
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Liu CH, Satoh AK, Postma M, Huang J, Ready DF, Hardie RC. Ca2+-dependent metarhodopsin inactivation mediated by calmodulin and NINAC myosin III. Neuron 2008; 59:778-89. [PMID: 18786361 DOI: 10.1016/j.neuron.2008.07.007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2008] [Revised: 06/03/2008] [Accepted: 07/09/2008] [Indexed: 10/21/2022]
Abstract
Phototransduction in flies is the fastest known G protein-coupled signaling cascade, but how this performance is achieved remains unclear. Here, we investigate the mechanism and role of rhodopsin inactivation. We determined the lifetime of activated rhodopsin (metarhodopsin = M( *)) in whole-cell recordings from Drosophila photoreceptors by measuring the time window within which inactivating M( *) by photoreisomerization to rhodopsin could suppress responses to prior illumination. M( *) was inactivated rapidly (tau approximately 20 ms) under control conditions, but approximately 10-fold more slowly in Ca2+-free solutions. This pronounced Ca2+ dependence of M( *) inactivation was unaffected by mutations affecting phosphorylation of rhodopsin or arrestin but was abolished in mutants of calmodulin (CaM) or the CaM-binding myosin III, NINAC. This suggests a mechanism whereby Ca2+ influx acting via CaM and NINAC accelerates the binding of arrestin to M( *). Our results indicate that this strategy promotes quantum efficiency, temporal resolution, and fidelity of visual signaling.
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Affiliation(s)
- Che-Hsiung Liu
- Department of Physiology, Development and Neuroscience, Cambridge University, Cambridge CB23DY, UK
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92
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Acharya JK, Dasgupta U, Rawat SS, Yuan C, Sanxaridis PD, Yonamine I, Karim P, Nagashima K, Brodsky MH, Tsunoda S, Acharya U. Cell-nonautonomous function of ceramidase in photoreceptor homeostasis. Neuron 2008; 57:69-79. [PMID: 18184565 DOI: 10.1016/j.neuron.2007.10.041] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2007] [Revised: 09/17/2007] [Accepted: 10/30/2007] [Indexed: 01/10/2023]
Abstract
Neutral ceramidase, a key enzyme of sphingolipid metabolism, hydrolyzes ceramide to sphingosine. These sphingolipids are critical structural components of cell membranes and act as second messengers in diverse signal transduction cascades. Here, we have isolated and characterized functional null mutants of Drosophila ceramidase. We show that secreted ceramidase functions in a cell-nonautonomous manner to maintain photoreceptor homeostasis. In the absence of ceramidase, photoreceptors degenerate in a light-dependent manner, are defective in normal endocytic turnover of rhodopsin, and do not respond to light stimulus. Consistent with a cell-nonautonomous function, overexpression of ceramidase in tissues distant from photoreceptors suppresses photoreceptor degeneration in an arrestin mutant and facilitates membrane turnover in a rhodopsin null mutant. Furthermore, our results show that secreted ceramidase is internalized and localizes to endosomes. Our findings establish a role for a secreted sphingolipid enzyme in the regulation of photoreceptor structure and function.
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Affiliation(s)
- Jairaj K Acharya
- Laboratory of Cell and Developmental Signaling, National Cancer Institute, Frederick, MD 21702, USA
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93
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New insights into Drosophila vision. Neuron 2008; 57:1-2. [PMID: 18184557 DOI: 10.1016/j.neuron.2007.12.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Studies of the Drosophila visual system have provided valuable insights into the function and regulation of phototransduction signaling pathways. Much of this work has stemmed from or relied upon the genetic tools offered by the Drosophila system. In this issue of Neuron, Wang and colleagues and Acharya and colleagues have further exploited the Drosophila genetic system to characterize two new phototransduction players.
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94
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Walker WB, Smith EM, Jan T, Zwiebel L. A functional role for Anopheles gambiae Arrestin1 in olfactory signal transduction. JOURNAL OF INSECT PHYSIOLOGY 2008; 54:680-690. [PMID: 18328499 PMCID: PMC2408752 DOI: 10.1016/j.jinsphys.2008.01.007] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2007] [Revised: 01/22/2008] [Accepted: 01/23/2008] [Indexed: 05/26/2023]
Abstract
Insect sensory arrestins act to desensitize visual and olfactory signal transduction pathways, as evidenced by the phenotypic effects of mutations in the genes encoding both Arr1 and Arr2 in Drosophila melanogaster. To assess whether such arrestins play similar roles in other, more medically relevant dipterans, we examined the ability of Anopheles gambiae sensory arrestin homologs AgArr1 and AgArr2 to rescue phenotypes associated with an olfactory deficit observed in D. melanogaster arrestin mutants. Of these, only AgArr1 facilitated significant phenotypic rescue of the corresponding Drosophila arr mutant olfactory phenotype, consistent with the view that functional orthology is shared by these Arr1 homologs. These results represent the first step in the functional characterization of AgArr1, which is highly expressed in olfactory appendages of An. gambiae in which it is likely to play an essential role in olfactory signal transduction. In addition to providing insight into the common elements of the peripheral olfactory system of dipterans, this work validates the importance of AgArr1 as a potential target for novel anti-malaria strategies that focus on olfactory-based behaviors in An. gambiae.
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Affiliation(s)
- William B. Walker
- Department of Biological Sciences, Centers for Molecular Neuroscience and Global Health and Programs in Development, Genetics Vanderbilt University, Nashville, Tennessee, 37232
- Neuroscience Graduate Program, Vanderbilt University, Nashville, Tennessee 37232
| | - Elaine M. Smith
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208
| | - Taha Jan
- Stanford University School of Medicine, Stanford, California, 94305
| | - L.J. Zwiebel
- Department of Biological Sciences, Centers for Molecular Neuroscience and Global Health and Programs in Development, Genetics Vanderbilt University, Nashville, Tennessee, 37232
- Neuroscience Graduate Program, Vanderbilt University, Nashville, Tennessee 37232
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95
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Han J, Reddig K, Li HS. Prolonged G(q) activity triggers fly rhodopsin endocytosis and degradation, and reduces photoreceptor sensitivity. EMBO J 2007; 26:4966-73. [PMID: 18034157 DOI: 10.1038/sj.emboj.7601929] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Accepted: 10/26/2007] [Indexed: 11/09/2022] Open
Abstract
Rapid deactivation of the Drosophila light receptor rhodopsin, through a visual arrestin Arr2 and a pathway that involves a transcription factor dCAMTA, is required for timely termination of light responses in the photoreceptor neuron. Here we report that this process is also critical for maintenance of the photoreceptor sensitivity. In both dCAMTA- and arr2-mutant flies, the endocytosis of the major rhodopsin Rh1 was dramatically increased, which was mediated by a G(q) protein that signals downstream of rhodopsin in the visual transduction pathway. Consequently, the Rh1 level was downregulated and the photoreceptor became less sensitive to light. Remarkably, the G(q)-stimulated Rh1 endocytosis does not require phospholipase C, a known effector of G(q), but depends on a tetraspanin protein. Our work has identified an arrestin-independent endocytic pathway of G protein-coupled receptor in the fly. This pathway may also function in mammals and mediate an early feedback regulation of receptor signaling.
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Affiliation(s)
- Junhai Han
- Department of Neurobiology, University of Massachusetts Medical School, Worcester, MA, USA
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96
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Walther RF, Pichaud F. Immunofluorescent staining and imaging of the pupal and adult Drosophila visual system. Nat Protoc 2007; 1:2635-42. [PMID: 17406519 DOI: 10.1038/nprot.2006.379] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
This immunofluorescence protocol can be used to assay cell morphology, cell positioning and subcellular localization of proteins in the fly eye at stages of development from early pupation to adult. The protocol includes the following procedures: collecting and developmentally staging Drosophila pupae, dissecting fly eyes at defined stages of development, immunostaining of retina and preparing visual system samples (i.e., retina and optic lobe) for confocal microscopy. It is supplemented with images of key dissection steps, guidelines for troubleshooting and examples of data obtained using these methods. Overall, this protocol takes up to 9 d to complete. The amount of hands-on time required on each day varies, ranging from 30 min to several hours depending on the number of stages and/or genotypes one wishes to study.
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Affiliation(s)
- Rhian F Walther
- MRC Laboratory for Molecular Cell Biology and Cell Biology Unit, Department of Anatomy and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
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97
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Abstract
The brain vesicle of the tadpole larva of ascidians, simple basal chordates, contains an eye-spot (ocellus), which is responsible for the photic swimming behavior. Ascidian adults also exhibit several types of light-responsive behaviors. Molecular phylogenetic studies have suggested that ascidians are the closest living relatives of vertebrates, and therefore, understanding the photoreceptive systems in ascidians is a key to uncover the origin and evolution of the vertebrate eyes. The ocellus of the ascidian larva has ciliary photoreceptors resembling those of the retina and pineal eye of vertebrates. Recent studies have indicated that the ascidian larva has phototransduction and visual cycle systems similar to those of vertebrate eyes. Comparative studies on photoreceptor systems between ascidians and vertebrates provide us clues to reconstructing the evolutionary pathway leading to the lateral and median eyes of vertebrates.
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Affiliation(s)
- Takehiro Kusakabe
- Department of Life Science, Graduate School of Life Science, University of Hyogo, Kouto, Kamigori, Ako-gun, Hyogo, Japan.
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98
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Frechter S, Elia N, Tzarfaty V, Selinger Z, Minke B. Translocation of Gq alpha mediates long-term adaptation in Drosophila photoreceptors. J Neurosci 2007; 27:5571-83. [PMID: 17522302 PMCID: PMC1934929 DOI: 10.1523/jneurosci.0310-07.2007] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Light adaptation is a process that enables photoreceptor cells to operate over a wide range of light intensities without saturation. In invertebrate photoreceptors, fast adaptation is mediated by a Ca2+-dependent negative-feedback mechanism, which mainly affects the terminal steps of the cascade. Therefore, the response to each photon is smaller as light intensity increases, accommodating both high sensitivity and a vast dynamic range. Here, we describe a novel type of adaptation, which is mediated by one of the first steps in the phototransduction cascade affecting the sensitivity to absorbed photons. Long exposure to light resulted in dramatic reduction in the probability of each absorbed photon to elicit a response, whereas the size and shape of each single photon response did not change. To dissect the molecular mechanism underlying this form of adaptation we used a series of Drosophila mutants. Genetic dissection showed a pivotal role for light-induced translocation of Gq alpha between the signaling membrane and the cytosol. Biochemical studies revealed that the sensitivity to light depends on membrane Gq alpha concentration, which was modulated either by light or by mutations that impaired its targeting to the membrane. We conclude that long-term adaptation is mediated by the movement of Gq alpha from the signaling membrane to the cytosol, thereby reducing the probability of each photon to elicit a response. The slow time scale of this adaptation fits well with day/night light intensity changes, because there is no need to maintain single photon sensitivity during daytime.
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Affiliation(s)
| | - Natalie Elia
- Biological Chemistry and Kühne Minerva Center for Studies of Visual Transduction, The Hebrew University of Jerusalem, Jerusalem 91120, Israel
| | | | - Zvi Selinger
- Biological Chemistry and Kühne Minerva Center for Studies of Visual Transduction, The Hebrew University of Jerusalem, Jerusalem 91120, Israel
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99
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Swardfager W, Mitchell J. Purification of visual arrestin from squid photoreceptors and characterization of arrestin interaction with rhodopsin and rhodopsin kinase. J Neurochem 2007; 101:223-31. [PMID: 17394465 DOI: 10.1111/j.1471-4159.2006.04364.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Invertebrate visual signal transduction involves photoisomerization of rhodopsin, activating a guanine nucleotide binding protein (G protein) of the G(q) class, iG(q), which stimulates a phospholipase C, increasing intracellular Ca2+. Arrestin binding to photoactivated rhodopsin is a key mechanism of desensitization. We have previously reported the cloning of a retina-specific arrestin cDNA from Loligo pealei displaying 56-64% sequence similarity to other reported arrestin sequences. Here, we report the purification of the 55-kDa squid visual arrestin. Purified squid visual arrestin is able to inhibit light-activated GTPase activity dose-dependently in arrestin-depleted rhabdomeric membranes and associate with the membrane in a light-dependent manner. Membrane association can be partially inhibited by inositol 1,2,3,4,5,6-hexakisphosphate (IP6), a soluble analog of the membrane lipid phosphatidylinositol 3,4,5-triphosphate. In reconstitution assays, we demonstrate arrestin phosphorylation by squid rhodopsin kinase, a novel function among the G protein-coupled receptor kinase family. Phosphorylation of purified arrestin requires squid rhodopsin kinase, membranes, light-activation, and the presence of Ca2+. This is the first large-scale purification of an invertebrate arrestin and biochemical demonstration of arrestin function in the invertebrate visual system.
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Affiliation(s)
- Walter Swardfager
- Department of Pharmacology, University of Toronto, Toronto, Ontario, Canada
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Wang T, Montell C. Phototransduction and retinal degeneration in Drosophila. Pflugers Arch 2007; 454:821-47. [PMID: 17487503 DOI: 10.1007/s00424-007-0251-1] [Citation(s) in RCA: 215] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2007] [Accepted: 03/05/2007] [Indexed: 01/05/2023]
Abstract
Drosophila visual transduction is the fastest known G-protein-coupled signaling cascade and has therefore served as a genetically tractable animal model for characterizing rapid responses to sensory stimulation. Mutations in over 30 genes have been identified, which affect activation, adaptation, or termination of the photoresponse. Based on analyses of these genes, a model for phototransduction has emerged, which involves phosphoinoside signaling and culminates with opening of the TRP and TRPL cation channels. Many of the proteins that function in phototransduction are coupled to the PDZ containing scaffold protein INAD and form a supramolecular signaling complex, the signalplex. Arrestin, TRPL, and G alpha(q) undergo dynamic light-dependent trafficking, and these movements function in long-term adaptation. Other proteins play important roles either in the formation or maturation of rhodopsin, or in regeneration of phosphatidylinositol 4,5-bisphosphate (PIP2), which is required for the photoresponse. Mutation of nearly any gene that functions in the photoresponse results in retinal degeneration. The underlying bases of photoreceptor cell death are diverse and involve mechanisms such as excessive endocytosis of rhodopsin due to stable rhodopsin/arrestin complexes and abnormally low or high levels of Ca2+. Drosophila visual transduction appears to have particular relevance to the cascade in the intrinsically photosensitive retinal ganglion cells in mammals, as the photoresponse in these latter cells appears to operate through a remarkably similar mechanism.
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Affiliation(s)
- Tao Wang
- Department of Biological Chemistry, Center for Sensory Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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