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Wang FF, Wang MH, Zhang MK, Qin P, Cuthbertson AGS, Lei CL, Qiu BL, Yu L, Sang W. Blue light stimulates light stress and phototactic behavior when received in the brain of Diaphorina citri. ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 2023; 251:114519. [PMID: 36634478 DOI: 10.1016/j.ecoenv.2023.114519] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/15/2022] [Revised: 12/31/2022] [Accepted: 01/05/2023] [Indexed: 06/17/2023]
Abstract
Blue light with a wavelength of 400-470 nm is the composition of the visible light. However, in recent years, blue light contributed the most significance to light pollution due to the artificial light at night. Previously, we have demonstrated that the Asian citrus psyllid (ACP), Diaphorina citri, an important pest in citrus production, has significant positive phototaxis with a light-emitting diode light of 400 nm. In this study, ACP with positive phototactic behavior to 400 nm light (PH) and non-phototactic behavior to 400 nm light (NP) were collected, individually. Transcriptome dynamics of head tissues of PH and NP groups were captured by using RNA-sequencing technology, respectively. Forty-three to 46 million clean reads with high-quality values were obtained, and 1773 differential expressed genes (DEGs) were detected. Compared with the NP group, there were 841 up-regulated DEGs and 932 down-regulated DEGs in the PH group. Eight pathways were significantly enriched in the PH group in the KEGG database, while 43 up-regulated pathways and 25 down-regulated pathways were significantly enriched in the PH group in the GO database. The DGE approach was reliable validated by real time quantitative PCR. Results indicated that the blue light acted as an abiotic stress causing physiological and biochemical responses such as oxidative stress, protein denaturation, inflammation and tumor development in ACPs. Additionally, the light was absorbed by photoreceptors of ACPs, and converted into electrical signal to regulate neuromodulation. This study provides basic information for understanding the molecular mechanisms of ACP in response to blue light and provides a reference for further studies to elucidate phototactic behavior.
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Affiliation(s)
- Fei-Feng Wang
- South China Agricultural University, Guangzhou 510640, China
| | - Ming-Hui Wang
- South China Agricultural University, Guangzhou 510640, China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510640, China
| | - Meng-Ke Zhang
- South China Agricultural University, Guangzhou 510640, China
| | - Peng Qin
- South China Agricultural University, Guangzhou 510640, China
| | | | - Chao-Liang Lei
- Hubei Insect Resources Utilization and Sustainable Pest Management Key Laboratory, Huazhong Agricultural University, Wuhan 430070, China
| | - Bao-Li Qiu
- South China Agricultural University, Guangzhou 510640, China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510640, China
| | - Lin Yu
- Institute of Plant Protection, Guangdong Academy of Agricultural Sciences, Key Laboratory of Green Prevention and Control on Fruits and Vegetables in South China Ministry of Agriculture and Rural Affairs, Guangdong Provincial Key Laboratory of High Technology for Plant Protection, Guangzhou 510640, China.
| | - Wen Sang
- South China Agricultural University, Guangzhou 510640, China; Guangdong Laboratory for Lingnan Modern Agriculture, Guangzhou 510640, China.
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Smylla TK, Wagner K, Huber A. The Role of Reversible Phosphorylation of Drosophila Rhodopsin. Int J Mol Sci 2022; 23:ijms232314674. [PMID: 36499010 PMCID: PMC9740569 DOI: 10.3390/ijms232314674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2022] [Revised: 11/18/2022] [Accepted: 11/21/2022] [Indexed: 11/27/2022] Open
Abstract
Vertebrate and fly rhodopsins are prototypical GPCRs that have served for a long time as model systems for understanding GPCR signaling. Although all rhodopsins seem to become phosphorylated at their C-terminal region following activation by light, the role of this phosphorylation is not uniform. Two major functions of rhodopsin phosphorylation have been described: (1) inactivation of the activated rhodopsin either directly or by facilitating binding of arrestins in order to shut down the visual signaling cascade and thus eventually enabling a high-temporal resolution of the visual system. (2) Facilitating endocytosis of activated receptors via arrestin binding that in turn recruits clathrin to the membrane for clathrin-mediated endocytosis. In vertebrate rhodopsins the shutdown of the signaling cascade may be the main function of rhodopsin phosphorylation, as phosphorylation alone already quenches transducin activation and, in addition, strongly enhances arrestin binding. In the Drosophila visual system rhodopsin phosphorylation is not needed for receptor inactivation. Its role here may rather lie in the recruitment of arrestin 1 and subsequent endocytosis of the activated receptor. In this review, we summarize investigations of fly rhodopsin phosphorylation spanning four decades and contextualize them with regard to the most recent insights from vertebrate phosphorylation barcode theory.
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Ishii K, Cortese M, Leng X, Shokhirev MN, Asahina K. A neurogenetic mechanism of experience-dependent suppression of aggression. SCIENCE ADVANCES 2022; 8:eabg3203. [PMID: 36070378 PMCID: PMC9451153 DOI: 10.1126/sciadv.abg3203] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/24/2020] [Accepted: 07/21/2022] [Indexed: 06/15/2023]
Abstract
Aggression is an ethologically important social behavior, but excessive aggression can be detrimental to fitness. Social experiences among conspecific individuals reduce aggression in many species, the mechanism of which is largely unknown. We found that loss-of-function mutation of nervy (nvy), a Drosophila homolog of vertebrate myeloid translocation genes (MTGs), increased aggressiveness only in socially experienced flies and that this could be reversed by neuronal expression of human MTGs. A subpopulation of octopaminergic/tyraminergic neurons labeled by nvy was specifically required for such social experience-dependent suppression of aggression, in both males and females. Cell type-specific transcriptomic analysis of these neurons revealed aggression-controlling genes that are likely downstream of nvy. Our results illustrate both genetic and neuronal mechanisms by which the nervous system suppresses aggression in a social experience-dependent manner, a poorly understood process that is considered important for maintaining the fitness of animals.
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Affiliation(s)
- Kenichi Ishii
- Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Matteo Cortese
- Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Xubo Leng
- Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA, USA
- Department of Electrical and Computer Engineering, University of California, San Diego, La Jolla, CA, USA
| | - Maxim N. Shokhirev
- Razavi Newman Integrative Genomics and Bioinformatics Core, Salk Institute for Biological Studies, La Jolla, CA, USA
| | - Kenta Asahina
- Molecular Neurobiology Laboratory, Salk Institute for Biological Studies, La Jolla, CA, USA
- School of Biological Sciences, University of California, San Diego, La Jolla, CA, USA
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Ca2+ Signaling in Drosophila Photoreceptor Cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2020; 1131:857-879. [DOI: 10.1007/978-3-030-12457-1_34] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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Böhm M, Boness D, Fantisch E, Erhard H, Frauenholz J, Kowalzyk Z, Marcinkowski N, Kateriya S, Hegemann P, Kreimer G. Channelrhodopsin-1 Phosphorylation Changes with Phototactic Behavior and Responds to Physiological Stimuli in Chlamydomonas. THE PLANT CELL 2019; 31:886-910. [PMID: 30862615 PMCID: PMC6501600 DOI: 10.1105/tpc.18.00936] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/10/2018] [Revised: 02/25/2019] [Accepted: 03/11/2019] [Indexed: 05/26/2023]
Abstract
The unicellular alga Chlamydomonas (Chlamydomonas reinhardtii) exhibits oriented movement responses (phototaxis) to light over more than three log units of intensity. Phototaxis thus depends on the cell's ability to adjust the sensitivity of its photoreceptors to ambient light conditions. In Chlamydomonas, the photoreceptors for phototaxis are the channelrhodopsins (ChR)1 and ChR2; these light-gated cation channels are located in the plasma membrane. Although ChRs are widely used in optogenetic studies, little is known about ChR signaling in algae. We characterized the in vivo phosphorylation of ChR1. Its reversible phosphorylation occurred within seconds as a graded response to changes in the light intensity and ionic composition of the medium and depended on an elevated cytosolic Ca2+ concentration. Changes in the phototactic sign were accompanied by alterations in the phosphorylation status of ChR1. Furthermore, compared with the wild type, a permanently negative phototactic mutant required higher light intensities to evoke ChR1 phosphorylation. C-terminal truncation of ChR1 disturbed its reversible phosphorylation, whereas it was normal in ChR2-knockout and eyespot-assembly mutants. The identification of phosphosites in regions important for ChR1 function points to their potential regulatory role(s). We propose that multiple ChR1 phosphorylation, regulated via a Ca2+-based feedback loop, is an important component in the adaptation of phototactic sensitivity in Chlamydomonas.
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Affiliation(s)
- Michaela Böhm
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - David Boness
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Elisabeth Fantisch
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Hanna Erhard
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Julia Frauenholz
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Zarah Kowalzyk
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Nadin Marcinkowski
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
| | - Suneel Kateriya
- School of Biotechnology, Jawaharlal Nehru University, 110067 New Delhi, India
| | - Peter Hegemann
- Institute for Experimental Biophysics, Humboldt University, 10115 Berlin, Germany
| | - Georg Kreimer
- Department of Biology, Friedrich-Alexander University, 91058 Erlangen, Germany
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6
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Uveitis and Multiple Sclerosis: Potential Common Causal Mutations. Mol Neurobiol 2019; 56:8008-8017. [PMID: 31161422 PMCID: PMC6834745 DOI: 10.1007/s12035-019-1630-2] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2019] [Accepted: 04/26/2019] [Indexed: 12/19/2022]
Abstract
Uveitis, defined as inflammation of the uveal tract of the eye, is a leading cause of blindness and visual impairment throughout the world. The etiology of uveitis is complex, and autoimmunity plays a major role in its pathogenesis. Intermediate uveitis (IU), a subtype of ocular inflammation, has been associated with systemic autoimmune disorders, specifically with multiple sclerosis (MS). This article reports a rare three-generation family with several members affected by IU (four siblings) and comorbid MS (two siblings fulfilling MS diagnostic criteria and a third sibling presenting some neurological symptoms). Based on the clinical findings, we captured and sequenced whole exomes of seven pedigree members (affected and unaffected). Using a recessive model of transmission with full penetrance, we applied genetic linkage analysis to define minimal critical regions (MCRs) in suggestive or nominal regions of linkage. In these MCRs, we defined functional (some pathogenic), novel, and rare mutations that segregated as homozygous in affected and heterozygous in unaffected family members. The genes harboring these mutations, including DGKI, TNFRSF10A, GNGT1, CPAMD8, and BAFF, which are expressed in both eye and brain tissues and/or are related to autoimmune diseases, provide new avenues to evaluate the inherited causes of these devastating autoimmune conditions.
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Katz B, Minke B. The Drosophila light-activated TRP and TRPL channels - Targets of the phosphoinositide signaling cascade. Prog Retin Eye Res 2018; 66:200-219. [DOI: 10.1016/j.preteyeres.2018.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2018] [Revised: 04/29/2018] [Accepted: 05/02/2018] [Indexed: 01/28/2023]
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8
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Schopf K, Huber A. Membrane protein trafficking in Drosophila photoreceptor cells. Eur J Cell Biol 2016; 96:391-401. [PMID: 27964885 DOI: 10.1016/j.ejcb.2016.11.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 11/21/2016] [Accepted: 11/28/2016] [Indexed: 10/20/2022] Open
Abstract
Membrane protein trafficking occurs throughout the lifetime of neurons and includes the initial protein synthesis and anterograde transport to the plasma membrane as well as internalization, degradation, and recycling of plasma membrane proteins. Defects in protein trafficking can result in neuronal degeneration and underlie blinding diseases such as retinitis pigmentosa as well as other neuronal disorders. Drosophila photoreceptor cells have emerged as a model system for identifying the components and mechanisms involved in membrane protein trafficking in neurons. Here we summarize the current knowledge about trafficking of three Drosophila phototransduction proteins, the visual pigment rhodopsin and the two light-activated ion channels TRP (transient receptor potential) and TRPL (TRP-like). Despite some common requirements shared by rhodopsin and TRP, details in the trafficking of these proteins differ considerably, suggesting the existence of several trafficking pathways for these photoreceptor proteins.
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Affiliation(s)
- Krystina Schopf
- University of Hohenheim, Institute of Physiology, Department of Biosensorics, Stuttgart, Germany
| | - Armin Huber
- University of Hohenheim, Institute of Physiology, Department of Biosensorics, Stuttgart, Germany.
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9
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Robinson KA, Ou WL, Guan X, Sugamori KS, Bandyopadhyay A, Ernst OP, Mitchell J. The effect of phosphorylation on arrestin-rhodopsin interaction in the squid visual system. J Neurochem 2015; 135:1129-39. [PMID: 26375013 DOI: 10.1111/jnc.13366] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 08/07/2015] [Accepted: 09/02/2015] [Indexed: 11/30/2022]
Abstract
Invertebrate visual opsins are G protein-coupled receptors coupled to retinoid chromophores that isomerize reversibly between inactive rhodopsin and active metarhodopsin upon absorption of photons of light. The squid visual system has an arrestin protein that binds to metarhodopsin to block signaling to Gq and activation of phospholipase C. Squid rhodopsin kinase (SQRK) can phosphorylate both metarhodopsin and arrestin, a dual role that is unique among the G protein-coupled receptor kinases. The sites and role of arrestin phosphorylation by SQRK were investigated here using recombinant proteins. Arrestin was phosphorylated on serine 392 and serine 397 in the C-terminus. Unphosphorylated arrestin bound to metarhodopsin and phosphorylated metarhodopsin with similar high affinities (Kd 33 and 21 nM respectively), while phosphorylation of arrestin reduced the affinity 3- to 5-fold (Kd 104 nM). Phosphorylation of metarhodopsin slightly increased the dissociation of arrestin observed during a 1 hour incubation. Together these studies suggest a unique role for SQRK in phosphorylating both receptor and arrestin and inhibiting the binding of these two proteins in the squid visual system. Invertebrate visual systems are inactivated by arrestin binding to metarhodopsin that does not require receptor phosphorylation. Here we show that squid rhodopsin kinase phosphorylates arrestin on two serines (S392,S397) in the C-terminus and phosphorylation decreases the affinity of arrestin for squid metarhodopsin. Metarhodopsin phosphorylation has very little effect on arrestin binding but does increase arrestin dissociation.
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Affiliation(s)
- Kelly A Robinson
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - Wei-Lin Ou
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada
| | - Xinyu Guan
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - Kim S Sugamori
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | | | - Oliver P Ernst
- Department of Biochemistry, University of Toronto, Toronto, Ontario, Canada.,Department of Molecular Genetics, University of Toronto, Toronto, Ontario, Canada
| | - Jane Mitchell
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
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10
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Diacylglycerol activates the light-dependent channel TRP in the photosensitive microvilli of Drosophila melanogaster photoreceptors. J Neurosci 2014; 34:6679-86. [PMID: 24806693 DOI: 10.1523/jneurosci.0513-14.2014] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Drosophila light-dependent channels, TRP and TRPL, reside in the light-sensitive microvilli of the photoreceptor's rhabdomere. Phospholipase C mediates TRP/TRPL opening, but the gating process remains unknown. Controversial evidence has suggested diacylglycerol (DAG), polyunsaturated fatty acids (PUFAs, a DAG metabolite), phosphatidylinositol bisphosphate (PIP2), and H(+) as possible channel activators. We tested each of them directly in inside-out TRP-expressing patches excised from the rhabdomere, making use of mutants and pharmacology. When patches were excised in darkness TRP remained closed, while when excised under illumination it stayed constitutively active. TRP was opened by DAG and silenced by ATP, suggesting DAG-kinase (DGK) involvement. The ATP effect was abolished by inhibiting DGK and in the rdgA mutant, lacking functional DGK, implicating DGK. DAG activated TRP even in the presence of a DAG-lipase inhibitor, inconsistent with a requirement of PUFAs in opening TRP. PIP2 had no effect and acidification, pH 6.4, activated TRP irreversibly, unlike the endogenous activator. Complementary liquid-chromatography/mass-spectrometry determinations of DAG and PUFAs in membranes enriched in rhabdomere obtained from light- and dark-adapted eyes showed light-dependent increment in six DAG species and no changes in PUFAs. The results strongly support DAG as the endogenous TRP agonist, as some of its vertebrate TRPC homologs of the same channel family.
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11
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Shieh BH, Kristaponyte I, Hong Y. Distinct roles of arrestin 1 protein in photoreceptors during Drosophila development. J Biol Chem 2014; 289:18526-34. [PMID: 24838243 DOI: 10.1074/jbc.m114.571224] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Arrestin regulates many facets of G-protein coupled receptor signaling. In Drosophila, Arrestin 1 (Arr1) is expressed at a lower level than Arrestin 2 (Arr2), and the role of Arr1 in visual physiology is less understood. Here we generated transgenic flies expressing enhanced green fluorescent protein tagged Arr1 (Arr1-eGFP) and explored its trafficking in live photoreceptors. We show that Arr1-eGFP is localized in the cytoplasm and displays light-dependent translocation to the rhabdomere possibly by interacting with photoactivated rhodopsin 1 (Rh1*). In the adult, translocation of Arr1-eGFP occurs with slower kinetics when compared with that of Arr2-eGFP. This slower kinetic activity may be attributable to a reduced level of phosphorylated Rh1*. Indeed, a reduced level of phosphorylated Rh1* recruits a lower level of Arr1-eGFP to rhabdomeres. To investigate whether Arr1 is required for the deactivation of phosphorylated Rh1*, we show that in flies with reduced Arr1 prolonged depolarizing afterpotential can be triggered with fewer light pulses, indicating that inactivation of phosphorylated Rh1* is compromised when the Arr1 level is reduced. Consistently, Arr1 is no longer required for deactivation of Rh1 in flies expressing phosphorylation-deficient Rh1. Previously it was reported that Arr1 displays light-dependent internalization. Unexpectedly, in adult photoreceptors we failed to observe endocytosis of Arr1-eGFP. In contrast, we show that in pupal photoreceptors Arr1-eGFP becomes internalized and sequestered in vesicles within the cytoplasm. Taken together, we propose that Arr1 plays distinct roles during development and adulthood. Arr1 orchestrates the recycling of phosphorylated Rh1* in pupae whereas it regulates the deactivation in adult.
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Affiliation(s)
- Bih-Hwa Shieh
- From the Department of Pharmacology and the Center for Molecular Neuroscience and the Vision Research Center, Vanderbilt University, Nashville, Tennessee 37232
| | - Inga Kristaponyte
- From the Department of Pharmacology and the Center for Molecular Neuroscience and the Vision Research Center, Vanderbilt University, Nashville, Tennessee 37232
| | - Yuan Hong
- From the Department of Pharmacology and the Center for Molecular Neuroscience and the Vision Research Center, Vanderbilt University, Nashville, Tennessee 37232
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12
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Fuse N, Yu F, Hirose S. Gprk2 adjusts Fog signaling to organize cell movements in Drosophila gastrulation. Development 2013; 140:4246-55. [PMID: 24026125 DOI: 10.1242/dev.093625] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Gastrulation of Drosophila melanogaster proceeds through sequential cell movements: ventral mesodermal (VM) cells are induced by secreted Fog protein to constrict their apical surfaces to form the ventral furrow, and subsequently lateral mesodermal (LM) cells involute toward the furrow. How these cell movements are organized remains elusive. Here, we observed that LM cells extended apical protrusions and then underwent accelerated involution movement, confirming that VM and LM cells display distinct cell morphologies and movements. In a mutant for the GPCR kinase Gprk2, apical constriction was expanded to all mesodermal cells and the involution movement was abolished. In addition, the mesodermal cells halted apical constriction prematurely in accordance with the aberrant accumulation of Myosin II. Epistasis analyses revealed that the Gprk2 mutant phenotypes were dependent on the fog gene. Overexpression of Gprk2 suppressed the effects of excess Cta, a downstream component of Fog signaling. Based on these findings, we propose that Gprk2 attenuates and tunes Fog-Cta signaling to prevent apical constriction in LM cells and to support appropriate apical constriction in VM cells. Thus, the two distinct cell movements in mesoderm invagination are not predetermined, but rather are organized by the adjustment of cell signaling.
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Affiliation(s)
- Naoyuki Fuse
- Department of Developmental Genetics, National Institute of Genetics, Yata 1111, Mishima 411-8540, Japan
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Xiong B, Bellen HJ. Rhodopsin homeostasis and retinal degeneration: lessons from the fly. Trends Neurosci 2013; 36:652-60. [PMID: 24012059 DOI: 10.1016/j.tins.2013.08.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2013] [Revised: 08/02/2013] [Accepted: 08/12/2013] [Indexed: 11/16/2022]
Abstract
Rhodopsins (Rh) are G protein-coupled receptors that function as light-sensors in photoreceptors. In humans, Rh mutations cause retinitis pigmentosa (RP), a degenerative disease that ultimately results in blindness. Studies in Drosophila have provided many insights into basic Rh biology and have identified pathways that lead to retinal degeneration. It has been shown that, because Rh is very abundant in photoreceptors, its accumulation in numerous organelles induces severe stress and results in degeneration of these cells. Moreover, genetic lesions that affect proper activation of membrane-bound Rh lead to disruption in Ca(2+) homeostasis which also causes photoreceptor degeneration. We review here the molecular signals involved in Rh homeostasis and the mechanisms underlying retinal degeneration in flies, and discuss possible links to human diseases.
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Affiliation(s)
- Bo Xiong
- Program in Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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14
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Passamaneck YJ, Martindale MQ. Evidence for a phototransduction cascade in an early brachiopod embryo. Integr Comp Biol 2013; 53:17-26. [PMID: 23630970 DOI: 10.1093/icb/ict037] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
Bilaterian photoreceptor cells are characterized by the expression of opsins, signal transduction genes, and ion channels, which together facilitate behavioral responses to light. We have previously identified a ciliary opsin gene from the brachiopod Terebratalia transversa, whose expression in gastrula stage embryos coincides with a photoresponse behavior, suggesting the presence of a functional phototransduction system in these early embryos. To further evaluate the potential for light reception in these embryos, we surveyed transcriptome data to identify phototransduction genes and evaluated their expression. In addition to the previously described ciliary opsin gene, we have identified two Go-class opsins that are also expressed in gastrula stage embryos. Representative members from all classes of Gα-protein genes were also expressed, with a Gα12-class gene being localized in the same anterior ectodermal domain as the opsin transcripts. Both CNG-class and TRP-class ion channels were expressed in the gastrula stage embryos, as were GRK and arrestin genes, which are associated with inhibition of rhodopsin activity. Taken together, these data support the presence of a functional phototransduction system in the early brachiopod embryo.
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Affiliation(s)
- Yale J Passamaneck
- Whitney Laboratory for Marine Bioscience, University of Florida, St. Augustine, FL 32080, USA.
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15
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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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16
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Soibam B, Goldfeder RL, Manson-Bishop C, Gamblin R, Pletcher SD, Shah S, Gunaratne GH, Roman GW. Modeling Drosophila positional preferences in open field arenas with directional persistence and wall attraction. PLoS One 2012; 7:e46570. [PMID: 23071591 PMCID: PMC3468593 DOI: 10.1371/journal.pone.0046570] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2012] [Accepted: 08/31/2012] [Indexed: 12/02/2022] Open
Abstract
In open field arenas, Drosophila adults exhibit a preference for arena boundaries over internal walls and open regions. Herein, we investigate the nature of this preference using phenomenological modeling of locomotion to determine whether local arena features and constraints on movement alone are sufficient to drive positional preferences within open field arenas of different shapes and with different internal features. Our model has two components: directional persistence and local wall force. In regions far away from walls, the trajectory is entirely characterized by a directional persistence probability, , for each movement defined by the step size, , and the turn angle, . In close proximity to walls, motion is computed from and a local attractive force which depends on the distance between the fly and points on the walls. The directional persistence probability was obtained experimentally from trajectories of wild type Drosophila in a circular open field arena and the wall force was computed to minimize the difference between the radial distributions from the model and Drosophila in the same circular arena. The two-component model for fly movement was challenged by comparing the positional preferences from the two-component model to wild type Drosophila in a variety of open field arenas. In most arenas there was a strong concordance between the two-component model and Drosophila. In more complex arenas, the model exhibits similar trends, but some significant differences were found. These differences suggest that there are emergent features within these complex arenas that have significance for the fly, such as potential shelter. Hence, the two-component model is an important step in defining how Drosophila interact with their environment.
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Affiliation(s)
- Benjamin Soibam
- Department of Computer Science, University of Houston, Houston, Texas, United States of America
| | - Rachel L. Goldfeder
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Claire Manson-Bishop
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Rachel Gamblin
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
| | - Scott D. Pletcher
- University of Michigan Geriatrics Center, Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan, United States of America
| | - Shishir Shah
- Department of Computer Science, University of Houston, Houston, Texas, United States of America
| | - Gemunu H. Gunaratne
- Department of Physics, University of Houston, Houston, Texas, United States of America
| | - Gregg W. Roman
- Department of Biology and Biochemistry, University of Houston, Houston, Texas, United States of America
- Biology of Behavior Institute, University of Houston, Texas, United States of America
- * E-mail:
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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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18
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Blasic JR, Brown RL, Robinson PR. Light-dependent phosphorylation of the carboxy tail of mouse melanopsin. Cell Mol Life Sci 2012; 69:1551-62. [PMID: 22159583 PMCID: PMC4045631 DOI: 10.1007/s00018-011-0891-3] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2011] [Revised: 10/29/2011] [Accepted: 11/16/2011] [Indexed: 12/22/2022]
Abstract
Melanopsin-based phototransduction is involved in non-image forming light responses including circadian entrainment, pupil constriction, suppression of pineal melatonin synthesis, and direct photic regulation of sleep in vertebrates. Given that the functions of melanopsin involve the measurement and summation of total environmental luminance, there would appear to be no need for the rapid deactivation typical of other G-protein coupled receptors. In this study, however, we demonstrate that heterologously expressed mouse melanopsin is phosphorylated in a light-dependent manner, and that this phosphorylation is involved in regulating the rate of G-protein activation and the lifetime of melanopsin's active state. Furthermore, we provide evidence for light-dependent phosphorylation of melanopsin in the mouse retina using an in situ proximity ligation assay. Finally, we demonstrate that melanopsin preferentially interacts with the GRK2/3 family of G-protein coupled receptor kinases through co-immunoprecipitation assays. Based on the complement of G-protein receptor kinases present in the melanopsin-expressing retinal ganglion cells, GRK2 emerges as the best candidate for melanopsin's cognate GRK.
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Affiliation(s)
- Joseph R. Blasic
- Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, Maryland 21250
| | - R. Lane Brown
- Department of Veterinary & Comparative Anatomy, Pharmacology, and Physiology, Washington State University, Pullman, WA 99164
| | - Phyllis R. Robinson
- Department of Biological Sciences, University of Maryland, Baltimore County, Baltimore, Maryland 21250
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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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20
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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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21
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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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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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23
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Gurevich EV, Tesmer JJG, Mushegian A, Gurevich VV. G protein-coupled receptor kinases: more than just kinases and not only for GPCRs. Pharmacol Ther 2011; 133:40-69. [PMID: 21903131 DOI: 10.1016/j.pharmthera.2011.08.001] [Citation(s) in RCA: 319] [Impact Index Per Article: 24.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2011] [Accepted: 08/01/2011] [Indexed: 12/24/2022]
Abstract
G protein-coupled receptor (GPCR) kinases (GRKs) are best known for their role in homologous desensitization of GPCRs. GRKs phosphorylate activated receptors and promote high affinity binding of arrestins, which precludes G protein coupling. GRKs have a multidomain structure, with the kinase domain inserted into a loop of a regulator of G protein signaling homology domain. Unlike many other kinases, GRKs do not need to be phosphorylated in their activation loop to achieve an activated state. Instead, they are directly activated by docking with active GPCRs. In this manner they are able to selectively phosphorylate Ser/Thr residues on only the activated form of the receptor, unlike related kinases such as protein kinase A. GRKs also phosphorylate a variety of non-GPCR substrates and regulate several signaling pathways via direct interactions with other proteins in a phosphorylation-independent manner. Multiple GRK subtypes are present in virtually every animal cell, with the highest expression levels found in neurons, with their extensive and complex signal regulation. Insufficient or excessive GRK activity was implicated in a variety of human disorders, ranging from heart failure to depression to Parkinson's disease. As key regulators of GPCR-dependent and -independent signaling pathways, GRKs are emerging drug targets and promising molecular tools for therapy. Targeted modulation of expression and/or of activity of several GRK isoforms for therapeutic purposes was recently validated in cardiac disorders and Parkinson's disease.
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Affiliation(s)
- Eugenia V Gurevich
- Department of Pharmacology, Vanderbilt University, 2200 Pierce Avenue, Preston Research Building, Rm. 454, Nashville, TN 37232, United States.
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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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Arrestin in ciliary invertebrate photoreceptors: molecular identification and functional analysis in vivo. J Neurosci 2011; 31:1811-9. [PMID: 21289191 DOI: 10.1523/jneurosci.3320-10.2011] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Arrestin was identified in ciliary photoreceptors of Pecten irradians, and its role in terminating the light response was established electrophysiologically. Downstream effectors in these unusual visual cells diverge from both microvillar photoreceptors and rods and cones; the finding that key regulatory mechanisms of the early steps of visual excitation are conserved across such distant lineages of photoreceptors underscores that a common blueprint for phototransduction exists across metazoa. Arrestin was detected by Western blot analysis of retinal lysates, and localized in ciliary photoreceptors by immunostaining of whole-eye cryosections and dissociated cells. Two arrestin isoforms were molecularly identified by PCR; these present the canonical N- and C-arrestin domains, and are identical at the nucleotide level over much of their sequence. A high degree of homology to various β-arrestins (up to 70% amino acid identity) was found. In situ hybridization localized the two transcripts within the retina, but failed to reveal finer spatial segregation, possibly because of insufficient differences between the riboprobes. Intracellular dialysis of anti arrestin antibodies into voltage-clamped ciliary photoreceptors produced a gradual slow-down of the photocurrent falling phase, leaving a tail that decayed over many seconds after light termination. The antibodies also caused spectrally neutral flashes to elicit prolonged aftercurrents in the absence of large metarhodopsin accumulation; such aftercurrents could be quenched by chromatic illumination that photoconverts metarhodopsin back to rhodopsin. These observations indicate that the antibodies depleted functionally available arrestin, and implicate this molecule in the deactivation of the photoresponse at the rhodopsin level.
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Chatterjee A, Hardin PE. Time to taste: circadian clock function in the Drosophila gustatory system. Fly (Austin) 2010; 4:283-7. [PMID: 20798595 DOI: 10.4161/fly.4.4.13010] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Circadian clocks keep time in the digestive, circulatory, reproductive, excretory and nervous systems even in absence of external cues. Central oscillators in the brain control locomotor activity of organisms ranging from fruit flies to man, but the functions of the clocks in peripheral nervous system are not well understood. The presence of autonomous peripheral oscillators in the major taste organ of Drosophila, the proboscis, prompted us to test whether gustatory responses are under control of the circadian clock. We find that synchronous rhythms in physiological and behavioral responses to attractive and aversive tastants are driven by oscillators in gustatory receptor neurons (GRNs); primary sensory neurons that carry taste information from the proboscis to the brain. During the middle of the night, high levels of G protein-coupled receptor kinase 2 (GPRK2) in the GRNs suppresses tastant-evoked responses. Flies with disrupted gustatory clocks are hyperphagic and hyperactive, recapitulating behaviors typically seen under the stress of starvation. Temporal plasticity in innate behaviors should offer adaptive advantages to flies. In this Extra View article we discuss how oscillators inside GRNs regulate responsiveness to tastants and influence feeding, metabolism and general activity.
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Affiliation(s)
- Abhishek Chatterjee
- Department of Biology and Center for Biological Clocks Research, Texas A&M University, College Station, TX, USA
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27
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Regulation of smoothened by Drosophila G-protein-coupled receptor kinases. Dev Biol 2009; 337:99-109. [PMID: 19850026 DOI: 10.1016/j.ydbio.2009.10.014] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2009] [Revised: 10/09/2009] [Accepted: 10/12/2009] [Indexed: 11/20/2022]
Abstract
The Hedgehog (Hh) signaling pathway plays a conserved and essential role in regulating development and homeostasis of numerous tissues. Cytoplasmic signaling is initiated by Smoothened (Smo), a G-protein-coupled receptor (GPCR) family member, whose levels and activity are regulated by the Hh receptor Patched (Ptc). In response to Hh binding to Ptc, Ptc-mediated repression of Smo is relieved, leading to Smo activation, surface accumulation, and downstream signaling. We find that downregulation of Drosophila Smo protein in Hh-responding imaginal disc cells is dependent on the activity of G-protein-coupled receptor kinase 2 (Gprk2). By analyzing gain- and null loss-of-function phenotypes, we provide evidence that Gprk2 promotes Smo internalization subsequent to its activation, most likely by direct phosphorylation. Ptc-dependent regulation of Smo accumulation is normal in gprk2 mutants, indicating that Gprk2 and Ptc downregulate Smo by different mechanisms. Finally, we show that both Drosophila G-protein-coupled receptor kinase orthologues, Gprk1 and Gprk2, act in a partially redundant manner to promote Hh signaling. Our results suggest that Smo is regulated by distinct Ptc-dependent and Gprk2-dependent trafficking mechanisms in vivo, analogous to constitutive and activity-dependent regulation of GPCRs. G-protein-coupled receptor kinase activity is also important for efficient downstream signaling.
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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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29
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G protein-coupled receptor kinase 2 is required for rhythmic olfactory responses in Drosophila. Curr Biol 2008; 18:787-94. [PMID: 18499458 DOI: 10.1016/j.cub.2008.04.062] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2007] [Revised: 04/21/2008] [Accepted: 04/23/2008] [Indexed: 11/23/2022]
Abstract
BACKGROUND The Drosophila circadian clock controls rhythms in the amplitude of odor-induced electrophysiological responses that peak during the middle of night. These rhythms are dependent on clocks in olfactory sensory neurons (OSNs), suggesting that odorant receptors (ORs) or OR-dependent processes are under clock control. Because responses to odors are initiated by heteromeric OR complexes that form odor-gated and cyclic-nucleotide-activated cation channels, we tested whether regulators of ORs were under circadian-clock control. RESULTS The levels of G protein-coupled receptor kinase 2 (Gprk2) messenger RNA and protein cycle in a circadian-clock-dependent manner with a peak around the middle of the night in antennae. Gprk2 overexpression in OSNs from wild-type or cyc(01) flies elicits constant high-amplitude electroantennogram (EAG) responses to ethyl acetate, whereas Gprk2 mutants produce constant low-amplitude EAG responses. ORs accumulate to high levels in the dendrites of OSNs around the middle of the night, and this dendritic localization of ORs is enhanced by GPRK2 overexpression at times when ORs are primarily localized in the cell body. CONCLUSIONS These results support a model in which circadian-clock-dependent rhythms in GPRK2 abundance control the rhythmic accumulation of ORs in OSN dendrites, which in turn control rhythms in olfactory responses. The enhancement of OR function by GPRK2 contrasts with the traditional role of GPRKs in desensitizing activated receptors and suggests that GPRK2 functions through a fundamentally different mechanism to modulate OR activity.
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30
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Lee S, Leung HT, Kim E, Jang J, Lee E, Baek K, Pak WL, Yoon J. Effects of a mutation in the Drosophila porin gene encoding mitochondrial voltage-dependent anion channel protein on phototransduction. Dev Neurobiol 2007; 67:1533-45. [PMID: 17525991 DOI: 10.1002/dneu.20526] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Mitochondrial porins, also know as VDACs (voltage-dependent anion channels), play an important role in regulating energy metabolism, apoptosis, and the transport of metabolites across the mitochondrial outer membrane. So far three distinct isoforms of VDAC (VDAC1-3) have been reported in vertebrates, but their functions remain unknown. The annotation database of the Drosophila melanogaster genome sequence has identified four genes (porin, CG17137, CG17139, and CG17140) encoding different isoforms of VDACs. We identified post-translational modifications of PORIN that are specific to D. melanogaster eyes. We also identified the P-element insertion in the porin gene, porin(G2294), that is homozygous viable whereas all the porin mutants previously reported are homozygous lethal at the pupal stage. The mutant does not show any defects in fly morphology, survival, and photoreceptor structure. The mutant, however, produces <10% of the normal level of wild-type (WT) porin transcripts and 16.5% of WT level of the PORIN protein. The P-element insertion affects only the expression of Class I transcript but not Class II transcript of the porin gene. Unlike in WT, the mutant displays an ERG (electroretinogram) that is not maintained during a prolonged light stimulus. The revertant obtained from remobilization of the P-element in the mutant produces the WT level of porin transcripts and PORIN protein, and shows a normal ERG response. Our data suggest that the PORIN protein is important in maintaining a photoreceptor response during prolonged stimulation.
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Affiliation(s)
- Sunji Lee
- Graduate School of Biotechnology, KyungHee University, Yongin-si, Gyeonggi-do, Korea
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31
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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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32
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Ruiz-Gómez A, Molnar C, Holguín H, Mayor F, de Celis JF. The cell biology of Smo signalling and its relationships with GPCRs. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1768:901-12. [PMID: 17094938 DOI: 10.1016/j.bbamem.2006.09.020] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/13/2006] [Revised: 09/20/2006] [Accepted: 09/25/2006] [Indexed: 12/11/2022]
Abstract
The Smoothened (Smo) signalling pathway participates in many developmental processes, contributing to the regulation of gene expression by controlling the activity of transcription factors belonging to the Gli family. The key elements of the pathway were identified by means of genetic screens carried out in Drosophila, and subsequent analysis in other model organisms revealed a high degree of conservation in both the proteins involved and in their molecular interactions. Recent analysis of the pathway, using a combination of biochemical and cell biological approaches, is uncovering the intricacies of Smo signalling, placing its elements in particular cellular compartments and qualifying the molecular processes involved. These include the synthesis, secretion and diffusion of the ligand, the activation of the receptor and the modifications in the activity of nuclear effectors. In this review we discuss recent advances in understanding biochemical and cellular aspects of Smo signalling, with particular focus in the similarities in the mechanism of signal transduction between Smo and other transmembrane proteins belonging to the G-Protein coupled receptors superfamily (GPCR).
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Affiliation(s)
- Ana Ruiz-Gómez
- Departamento de Biología Molecular, Universidad Autónoma de Madrid, Cantoblanco, Madrid, Spain.
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Satoh AK, Ready DF. Arrestin1 mediates light-dependent rhodopsin endocytosis and cell survival. Curr Biol 2006; 15:1722-33. [PMID: 16213818 DOI: 10.1016/j.cub.2005.08.064] [Citation(s) in RCA: 107] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2005] [Revised: 08/29/2005] [Accepted: 08/31/2005] [Indexed: 11/23/2022]
Abstract
BACKGROUND Arrestins are pivotal, multifunctional organizers of cell responses to GPCR stimulation, including cell survival and cell death. In Drosophila norpA and rdgC mutants, endocytosis of abnormally stable complexes of rhodopsin (Rh1) and fly photoreceptor Arrestin2 (Arr2) triggers cell death, implicating Rh1/Arr2-bearing endosomes in pro-cell death signaling, potentially via arrestin-mediated GPCR activation of effector kinase pathways. In order to further investigate arrestin function in photoreceptor physiology and survival, we studied Arr2's partner photoreceptor arrestin, Arr1, in developing and adult Drosophila compound eyes. RESULTS We report that Arr1, but not Arr2, is essential for normal, light-induced rhodopsin endocytosis. Also distinct from Arr2, Arr1 is essential for light-independent photoreceptor survival. Photoreceptor cell death caused by loss of Arr1 is strongly suppressed by coordinate loss of Arr2. We further find that Rh1 C-terminal phosphorylation is essential for light-induced endocytosis and also for translocation of Arr1, but not Arr2, from dark-adapted photoreceptor cytoplasm to photosensory membrane rhabdomeres. In contrast to a previous report, we do not find a requirement for photoreceptor myosin kinase NINAC in Arr1 or Arr2 translocation. CONCLUSIONS The two Drosophila photoreceptor arrestins mediate distinct and essential cell pathways downstream of rhodopsin activation. We propose that Arr1 mediates an endocytotic cell-survival activity, scavenging phosphorylated rhodopsin and thereby countering toxic Arr2/Rh1 accumulation; elimination of toxic Arr2/Rh1 in double mutants could thus rescue arr1 mutant photoreceptor degeneration.
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Affiliation(s)
- Akiko K Satoh
- Department of Biological Sciences, Purdue University, West Lafayette, IN 47907, USA
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del Pilar Gomez M, Nasi E. A direct signaling role for phosphatidylinositol 4,5-bisphosphate (PIP2) in the visual excitation process of microvillar receptors. J Biol Chem 2005; 280:16784-9. [PMID: 15741162 DOI: 10.1074/jbc.m414538200] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In microvillar photoreceptors the pivotal role of phospholipase C in light transduction is undisputed, but previous attempts to account for the photoresponse solely in terms of downstream products of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis have proved wanting. In other systems PIP2 has been shown to possess signaling functions of its own, rather than simply serving as a precursor molecule. Because illumination of microvillar photoreceptors cells leads to PIP2 break-down, a potential role for this phospholipid in phototransduction would be to help maintain some element(s) of the transduction cascade in the inactive state. We tested the effect of intracellular dialysis of PIP2 on voltage-clamped molluscan photoreceptors and found a marked reduction in the amplitude of the photocurrent; by contrast, depolarization-activated calcium and potassium currents were unaffected, thus supporting the notion of a specific effect on light signaling. In the dark, PIP2 caused a gradual outward shift of the holding current; this change was due to a decrease in membrane conductance and may reflect the suppression of basal openings of the light-sensitive conductance. The consequences of depleting PIP2 were examined in patches of light-sensitive microvillar membrane screened for the exclusive presence of light-activated ion channels. After excision, superfusion with anti-PIP2 antibodies induced the appearance of single-channel currents. Replenishment of PIP2 by exogenous application reverted the effect. These data support the notion that PIP2, in addition to being the source of inositol trisphosphate and diacylglycerol, two messengers of visual excitation, may also participate in a direct fashion in the control of the light-sensitive conductance.
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Affiliation(s)
- Maria del Pilar Gomez
- Department of Physiology and Biophysics, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
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