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Mishra S, Manohar V, Chandel S, Manoj T, Bhattacharya S, Hegde N, Nath VR, Krishnan H, Wendling C, Di Mattia T, Martinet A, Chimata P, Alpy F, Raghu P. A genetic screen to uncover mechanisms underlying lipid transfer protein function at membrane contact sites. Life Sci Alliance 2024; 7:e202302525. [PMID: 38499328 PMCID: PMC10948934 DOI: 10.26508/lsa.202302525] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2023] [Revised: 03/04/2024] [Accepted: 03/05/2024] [Indexed: 03/20/2024] Open
Abstract
Lipid transfer proteins mediate the transfer of lipids between organelle membranes, and the loss of function of these proteins has been linked to neurodegeneration. However, the mechanism by which loss of lipid transfer activity leads to neurodegeneration is not understood. In Drosophila photoreceptors, depletion of retinal degeneration B (RDGB), a phosphatidylinositol transfer protein, leads to defective phototransduction and retinal degeneration, but the mechanism by which loss of this activity leads to retinal degeneration is not understood. RDGB is localized to membrane contact sites through the interaction of its FFAT motif with the ER integral protein VAP. To identify regulators of RDGB function in vivo, we depleted more than 300 VAP-interacting proteins and identified a set of 52 suppressors of rdgB The molecular identity of these suppressors indicates a role of novel lipids in regulating RDGB function and of transcriptional and ubiquitination processes in mediating retinal degeneration in rdgB9 The human homologs of several of these molecules have been implicated in neurodevelopmental diseases underscoring the importance of VAP-mediated processes in these disorders.
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Affiliation(s)
- Shirish Mishra
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Vaishnavi Manohar
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Shabnam Chandel
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Tejaswini Manoj
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Subhodeep Bhattacharya
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Nidhi Hegde
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Vaisaly R Nath
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
- School of Biotechnology, Amrita Vishwa Vidyapeetham, Kollam, India
| | - Harini Krishnan
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Corinne Wendling
- Université de Strasbourg, CNRS, Inserm, IGBMC UMR 7104- UMR-S 1258, Illkirch, France
| | - Thomas Di Mattia
- Université de Strasbourg, CNRS, Inserm, IGBMC UMR 7104- UMR-S 1258, Illkirch, France
| | - Arthur Martinet
- Université de Strasbourg, CNRS, Inserm, IGBMC UMR 7104- UMR-S 1258, Illkirch, France
| | - Prasanth Chimata
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
| | - Fabien Alpy
- Université de Strasbourg, CNRS, Inserm, IGBMC UMR 7104- UMR-S 1258, Illkirch, France
| | - Padinjat Raghu
- https://ror.org/03gf8rp76 National Centre for Biological Sciences-TIFR, GKVK Campus, Bangalore, India
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2
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Cockcroft S. The expanding roles of PI4P and PI(4,5)P 2 at the plasma membrane: Role of phosphatidylinositol transfer proteins. Biochim Biophys Acta Mol Cell Biol Lipids 2024; 1869:159394. [PMID: 37714261 DOI: 10.1016/j.bbalip.2023.159394] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 08/31/2023] [Accepted: 09/05/2023] [Indexed: 09/17/2023]
Abstract
Phosphoinositides are phosphorylated derivatives of phosphatidylinositol, a phospholipid that is synthesised at the endoplasmic reticulum. The plasma membrane contains the enzymes to phosphorylate phosphatidylinositol and is therefore rich in the phosphorylated derivatives, PI4P and PI(4,5)P2. PI(4,5)P2 is a substrate for phospholipase C and during cell signaling, PI(4,5)P2 levels are reduced. Here I discuss a family of proteins, phosphatidylinositol transfer proteins (PITPs) that can restore PI(4,5)P2 levels.
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Affiliation(s)
- Shamshad Cockcroft
- Department of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, 21 University Street, London WC1E 6JJ, UK.
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3
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Hebbar S, Traikov S, Hälsig C, Knust E. Modulating the Kynurenine pathway or sequestering toxic 3-hydroxykynurenine protects the retina from light-induced damage in Drosophila. PLoS Genet 2023; 19:e1010644. [PMID: 36952572 PMCID: PMC10035932 DOI: 10.1371/journal.pgen.1010644] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2022] [Accepted: 01/30/2023] [Indexed: 03/25/2023] Open
Abstract
Tissue health is regulated by a myriad of exogenous or endogenous factors. Here we investigated the role of the conserved Kynurenine pathway (KP) in maintaining retinal homeostasis in the context of light stress in Drosophila melanogaster. cinnabar, cardinal and scarlet are fly genes that encode different steps in the KP. Along with white, these genes are known regulators of brown pigment (ommochrome) biosynthesis. Using white as a sensitized genetic background, we show that mutations in cinnabar, cardinal and scarlet differentially modulate light-induced retinal damage. Mass Spectrometric measurements of KP metabolites in flies with different genetic combinations support the notion that increased levels of 3-hydroxykynurenine (3OH-K) and Xanthurenic acid (XA) enhance retinal damage, whereas Kynurenic Acid (KYNA) and Kynurenine (K) are neuro-protective. This conclusion was corroborated by showing that feeding 3OH-K results in enhanced retinal damage, whereas feeding KYNA protects the retina in sensitized genetic backgrounds. Interestingly, the harmful effects of free 3OH-K are diminished by its sub-cellular compartmentalization. Sequestering of 3OH-K enables the quenching of its toxicity through conversion to brown pigment or conjugation to proteins. This work enabled us to decouple the role of these KP genes in ommochrome formation from their role in retinal homeostasis. Additionally, it puts forward new hypotheses on the importance of the balance of KP metabolites and their compartmentalization in disease alleviation.
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Affiliation(s)
- Sarita Hebbar
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Sofia Traikov
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Catrin Hälsig
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
| | - Elisabeth Knust
- Max-Planck-Institute of Molecular Cell Biology and Genetics, Dresden, Germany
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4
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Križaj D, Cordeiro S, Strauß O. Retinal TRP channels: Cell-type-specific regulators of retinal homeostasis and multimodal integration. Prog Retin Eye Res 2023; 92:101114. [PMID: 36163161 PMCID: PMC9897210 DOI: 10.1016/j.preteyeres.2022.101114] [Citation(s) in RCA: 17] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/03/2022] [Accepted: 08/08/2022] [Indexed: 02/05/2023]
Abstract
Transient receptor potential (TRP) channels are a widely expressed family of 28 evolutionarily conserved cationic ion channels that operate as primary detectors of chemical and physical stimuli and secondary effectors of metabotropic and ionotropic receptors. In vertebrates, the channels are grouped into six related families: TRPC, TRPV, TRPM, TRPA, TRPML, and TRPP. As sensory transducers, TRP channels are ubiquitously expressed across the body and the CNS, mediating critical functions in mechanosensation, nociception, chemosensing, thermosensing, and phototransduction. This article surveys current knowledge about the expression and function of the TRP family in vertebrate retinas, which, while dedicated to transduction and transmission of visual information, are highly susceptible to non-visual stimuli. Every retinal cell expresses multiple TRP subunits, with recent evidence establishing their critical roles in paradigmatic aspects of vertebrate vision that include TRPM1-dependent transduction of ON bipolar signaling, TRPC6/7-mediated ganglion cell phototransduction, TRP/TRPL phototransduction in Drosophila and TRPV4-dependent osmoregulation, mechanotransduction, and regulation of inner and outer blood-retina barriers. TRP channels tune light-dependent and independent functions of retinal circuits by modulating the intracellular concentration of the 2nd messenger calcium, with emerging evidence implicating specific subunits in the pathogenesis of debilitating diseases such as glaucoma, ocular trauma, diabetic retinopathy, and ischemia. Elucidation of TRP channel involvement in retinal biology will yield rewards in terms of fundamental understanding of vertebrate vision and therapeutic targeting to treat diseases caused by channel dysfunction or over-activation.
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Affiliation(s)
- David Križaj
- Departments of Ophthalmology, Neurobiology, and Bioengineering, University of Utah, Salt Lake City, USA
| | - Soenke Cordeiro
- Institute of Physiology, Faculty of Medicine, Christian-Albrechts-University Kiel, Germany
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité - Universitätsmedizin Berlin, a Corporate Member of Freie Universität, Humboldt-University, The Berlin Institute of Health, Berlin, Germany.
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5
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Kumari A, Ghosh A, Kolay S, Raghu P. Septins tune lipid kinase activity and PI(4,5)P 2 turnover during G-protein–coupled PLC signalling in vivo. Life Sci Alliance 2022; 5:5/6/e202101293. [PMID: 35277468 PMCID: PMC8921834 DOI: 10.26508/lsa.202101293] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 02/23/2022] [Accepted: 02/25/2022] [Indexed: 11/24/2022] Open
Abstract
Phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] hydrolysis by phospholipase C (PLC) is a conserved mechanism of signalling. Given the low abundance of PI(4,5)P2, its hydrolysis needs to be coupled to resynthesis to ensure continued PLC activity; however, the mechanism by which depletion is coupled to resynthesis remains unknown. PI(4,5)P2 synthesis is catalyzed by the phosphorylation of phosphatidylinositol 4 phosphate (PI4P) by phosphatidylinositol 4 phosphate 5 kinase (PIP5K). In Drosophila photoreceptors, photon absorption is transduced into PLC activity and during this process, PI(4,5)P2 is resynthesized by a PIP5K. However, the mechanism by which PIP5K activity is coupled to PI(4,5)P2 hydrolysis is unknown. In this study, we identify a unique isoform dPIP5KL, that is both necessary and sufficient to mediate PI(4,5)P2 synthesis during phototransduction. Depletion of PNUT, a non-redundant subunit of the septin family, enhances dPIP5KL activity in vitro and PI(4,5)P2 resynthesis in vivo; co-depletion of dPIP5KL reverses the enhanced rate of PI(4,5)P2 resynthesis in vivo. Thus, our work defines a septin-mediated mechanism through which PIP5K activity is coupled to PLC-mediated PI(4,5)P2 hydrolysis.
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Affiliation(s)
- Aastha Kumari
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bengaluru, India
| | - Avishek Ghosh
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bengaluru, India
- Department of Surgery, Vascular Biology Program, Boston Children’s Hospital, Harvard Medical School, Boston, MA, USA
| | - Sourav Kolay
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bengaluru, India
- UT Southwestern Medical Center, Dallas, TX, USA
| | - Padinjat Raghu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bengaluru, India
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6
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The Role of Membrane Lipids in Light-Activation of Drosophila TRP Channels. Biomolecules 2022; 12:biom12030382. [PMID: 35327573 PMCID: PMC8945425 DOI: 10.3390/biom12030382] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2022] [Revised: 02/21/2022] [Accepted: 02/23/2022] [Indexed: 12/28/2022] Open
Abstract
Transient Receptor Potential (TRP) channels constitute a large superfamily of polymodal channel proteins with diverse roles in many physiological and sensory systems that function both as ionotropic and metabotropic receptors. From the early days of TRP channel discovery, membrane lipids were suggested to play a fundamental role in channel activation and regulation. A prominent example is the Drosophila TRP and TRP-like (TRPL) channels, which are predominantly expressed in the visual system of Drosophila. Light activation of the TRP and TRPL channels, the founding members of the TRP channel superfamily, requires activation of phospholipase Cβ (PLC), which hydrolyzes phosphatidylinositol 4,5-bisphosphate (PIP2) into Diacylglycerol (DAG) and Inositol 1, 4,5-trisphosphate (IP3). However, the events required for channel gating downstream of PLC activation are still under debate and led to several hypotheses regarding the mechanisms by which lipids gate the channels. Despite many efforts, compelling evidence of the involvement of DAG accumulation, PIP2 depletion or IP3-mediated Ca2+ release in light activation of the TRP/TRPL channels are still lacking. Exogeneous application of poly unsaturated fatty acids (PUFAs), a product of DAG hydrolysis was demonstrated as an efficient way to activate the Drosophila TRP/TRPL channels. However, compelling evidence for the involvement of PUFAs in physiological light-activation of the TRP/TRPL channels is still lacking. Light-induced mechanical force generation was measured in photoreceptor cells prior to channel opening. This mechanical force depends on PLC activity, suggesting that the enzymatic activity of PLC converting PIP2 into DAG generates membrane tension, leading to mechanical gating of the channels. In this review, we will present the roles of membrane lipids in light activation of Drosophila TRP channels and present the many advantages of this model system in the exploration of TRP channel activation under physiological conditions.
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Raghu P, Basak B, Krishnan H. Emerging perspectives on multidomain phosphatidylinositol transfer proteins. Biochim Biophys Acta Mol Cell Biol Lipids 2021; 1866:158984. [PMID: 34098114 PMCID: PMC7611342 DOI: 10.1016/j.bbalip.2021.158984] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2021] [Revised: 05/23/2021] [Accepted: 05/25/2021] [Indexed: 12/09/2022]
Abstract
The phosphatidylinositol transfer protein domain (PITPd) is an evolutionarily conserved protein that is able to transfer phosphatidylinositol between membranes in vitro and in vivo. However some animal genomes also include genes that encode proteins where the PITPd is found in cis with a number of additional domains and recent large scale genome sequencing efforts indicate that this type of multidomain architecture is widespread in the animal kingdom. In Drosophila photoreceptors, the multidomain phosphatidylinositol transfer protein RDGB is required to regulate phosphoinositide turnover during G-protein activated phospholipase C signalling. Recent studies in flies and mammalian cell culture models have begun to elucidate functions for the non-PITPd of RDGB and its vertebrate orthologs. We review emerging evidence on the genomics, functional and cell biological perspectives of these multi-domain PITPd containing proteins.
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Affiliation(s)
- Padinjat Raghu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India.
| | - Bishal Basak
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India
| | - Harini Krishnan
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India
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8
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Basak B, Krishnan H, Raghu P. Interdomain interactions regulate the localization of a lipid transfer protein at ER-PM contact sites. Biol Open 2021; 10:bio.057422. [PMID: 33597200 PMCID: PMC7990853 DOI: 10.1242/bio.057422] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
During phospholipase C-β (PLC-β) signalling in Drosophila photoreceptors, the phosphatidylinositol transfer protein (PITP) RDGB, is required for lipid transfer at endoplasmic reticulum (ER)–plasma membrane (PM) contact sites (MCS). Depletion of RDGB or its mis-localization away from the ER–PM MCS results in multiple defects in photoreceptor function. Previously, the interaction between the FFAT motif of RDGB and the integral ER protein dVAP-A was shown to be essential for accurate localization to ER–PM MCS. Here, we report that the FFAT/dVAP-A interaction alone is insufficient to localize RDGB accurately; this also requires the function of the C-terminal domains, DDHD and LNS2. Mutations in each of these domains results in mis-localization of RDGB leading to loss of function. While the LNS2 domain is necessary, it is not sufficient for the correct localization of RDGB, which also requires the C-terminal DDHD domain. The function of the DDHD domain is mediated through an intramolecular interaction with the LNS2 domain. Thus, interactions between the additional domains in a multi-domain PITP together lead to accurate localization at the MCS and signalling function. This article has an associated First Person interview with the first author of the paper. Summary: This study demonstrates interdomain interactions within a phosphatidylinositol transfer protein that regulate its localization and function at an ER-PM membrane contact site.
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Affiliation(s)
- Bishal Basak
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India
| | - Harini Krishnan
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India
| | - Padinjat Raghu
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bengaluru 560065, India
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9
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Trivedi D, CM V, Bisht K, Janardan V, Pandit A, Basak B, H S, Ramesh N, Raghu P. A genome engineering resource to uncover principles of cellular organization and tissue architecture by lipid signaling. eLife 2020; 9:e55793. [PMID: 33320085 PMCID: PMC7771963 DOI: 10.7554/elife.55793] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Accepted: 12/14/2020] [Indexed: 12/14/2022] Open
Abstract
Phosphoinositides (PI) are key regulators of cellular organization in eukaryotes and genes that tune PI signaling are implicated in human disease mechanisms. Biochemical analyses and studies in cultured cells have identified a large number of proteins that can mediate PI signaling. However, the role of such proteins in regulating cellular processes in vivo and development in metazoans remains to be understood. Here, we describe a set of CRISPR-based genome engineering tools that allow the manipulation of each of these proteins with spatial and temporal control during metazoan development. We demonstrate the use of these reagents to deplete a set of 103 proteins individually in the Drosophila eye and identify several new molecules that control eye development. Our work demonstrates the power of this resource in uncovering the molecular basis of tissue homeostasis during normal development and in human disease biology.
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Affiliation(s)
- Deepti Trivedi
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Vinitha CM
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Karishma Bisht
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Vishnu Janardan
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Awadhesh Pandit
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Bishal Basak
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Shwetha H
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Navyashree Ramesh
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, GKVK CampusBangaloreIndia
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10
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Hebbar S, Schuhmann K, Shevchenko A, Knust E. Hydroxylated sphingolipid biosynthesis regulates photoreceptor apical domain morphogenesis. J Cell Biol 2020; 219:211460. [PMID: 33048164 PMCID: PMC7557679 DOI: 10.1083/jcb.201911100] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2019] [Revised: 08/07/2020] [Accepted: 09/08/2020] [Indexed: 01/04/2023] Open
Abstract
Apical domains of epithelial cells often undergo dramatic changes during morphogenesis to form specialized structures, such as microvilli. Here, we addressed the role of lipids during morphogenesis of the rhabdomere, the microvilli-based photosensitive organelle of Drosophila photoreceptor cells. Shotgun lipidomics analysis performed on mutant alleles of the polarity regulator crumbs, exhibiting varying rhabdomeric growth defects, revealed a correlation between increased abundance of hydroxylated sphingolipids and abnormal rhabdomeric growth. This could be attributed to an up-regulation of fatty acid hydroxylase transcription. Indeed, direct genetic perturbation of the hydroxylated sphingolipid metabolism modulated rhabdomere growth in a crumbs mutant background. One of the pathways targeted by sphingolipid metabolism turned out to be the secretory route of newly synthesized Rhodopsin, a major rhabdomeric protein. In particular, altered biosynthesis of hydroxylated sphingolipids impaired apical trafficking via Rab11, and thus apical membrane growth. The intersection of lipid metabolic pathways with apical domain growth provides a new facet to our understanding of apical growth during morphogenesis.
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11
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Nath VR, Mishra S, Basak B, Trivedi D, Raghu P. Extended synaptotagmin regulates membrane contact site structure and lipid transfer function in vivo. EMBO Rep 2020; 21:e50264. [PMID: 32716137 DOI: 10.15252/embr.202050264] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2020] [Revised: 06/12/2020] [Accepted: 06/22/2020] [Indexed: 12/20/2022] Open
Abstract
Inter-organelle communication between closely apposed membranes is proposed at membrane contact sites (MCS). However, the regulation of MCS structure and their functional relevance in vivo remain debated. The extended synaptotagmins (Esyt) are evolutionarily conserved proteins proposed to function at MCS. However, loss of all three Esyts in yeast or mammals shows minimal phenotypes questioning the functional importance of Esyt. We report that in Drosophila photoreceptors, MCS number is regulated by PLCβ activity. Photoreceptors of a null allele of Drosophila extended synaptotagmin (dEsyt) show loss of ER-PM MCS. Loss of dEsyt results in mislocalization of RDGB, an MCS localized lipid transfer protein, required for photoreceptor structure and function, ultimately leading to retinal degeneration. dEsyt depletion enhanced the retinal degeneration, reduced light responses and slower rates of plasma membrane PIP2 resynthesis seen in rdgB mutants. Thus, dEsyt function and PLCβ signaling regulate ER-PM MCS structure and lipid transfer in Drosophila photoreceptors.
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Affiliation(s)
- Vaisaly R Nath
- National Centre for Biological Sciences-TIFR, Bangalore, India.,School of Biotechnology, Amrita Vishwa Vidyapeetham, Amritapuri, Kollam, Kerala, India
| | - Shirish Mishra
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Bishal Basak
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Deepti Trivedi
- National Centre for Biological Sciences-TIFR, Bangalore, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, Bangalore, India
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12
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Thakur R, Naik A, Panda A, Raghu P. Regulation of Membrane Turnover by Phosphatidic Acid: Cellular Functions and Disease Implications. Front Cell Dev Biol 2019; 7:83. [PMID: 31231646 PMCID: PMC6559011 DOI: 10.3389/fcell.2019.00083] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2019] [Accepted: 05/03/2019] [Indexed: 01/23/2023] Open
Abstract
Phosphatidic acid (PA) is a simple glycerophospholipid with a well-established role as an intermediate in phospholipid biosynthesis. In addition to its role in lipid biosynthesis, PA has been proposed to act as a signaling molecule that modulates several aspects of cell biology including membrane transport. PA can be generated in eukaryotic cells by several enzymes whose activity is regulated in the context of signal transduction and enzymes that can metabolize PA thus terminating its signaling activity have also been described. Further, several studies have identified PA binding proteins and changes in their activity are proposed to be mediators of the signaling activity of this lipid. Together these enzymes and proteins constitute a PA signaling toolkit that mediates the signaling functions of PA in cells. Recently, a number of novel genetic models for the analysis of PA function in vivo and analytical methods to quantify PA levels in cells have been developed and promise to enhance our understanding of PA functions. Studies of several elements of the PA signaling toolkit in a single cell type have been performed and are presented to provide a perspective on our understanding of the biochemical and functional organization of pools of PA in a eukaryotic cell. Finally, we also provide a perspective on the potential role of PA in human disease, synthesizing studies from model organisms, human disease genetics and analysis using recently developed PLD inhibitors.
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Affiliation(s)
- Rajan Thakur
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Amruta Naik
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Aniruddha Panda
- National Centre for Biological Sciences-TIFR, Bengaluru, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, Bengaluru, India
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13
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Weigelt CM, Hahn O, Arlt K, Gruhn M, Jahn AJ, Eßer J, Werner JA, Klein C, Büschges A, Grönke S, Partridge L. Loss of miR-210 leads to progressive retinal degeneration in Drosophila melanogaster. Life Sci Alliance 2019; 2:2/1/e201800149. [PMID: 30670478 PMCID: PMC6343102 DOI: 10.26508/lsa.201800149] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2018] [Revised: 01/10/2019] [Accepted: 01/11/2019] [Indexed: 12/22/2022] Open
Abstract
Depletion of miRNA-210 disrupts photoreceptor integrity and visual function in Drosophila melanogaster. miRNAs are small, non-coding RNAs that regulate gene expression post-transcriptionally. We used small RNA sequencing to identify tissue-specific miRNAs in the adult brain, thorax, gut, and fat body of Drosophila melanogaster. One of the most brain-specific miRNAs that we identified was miR-210, an evolutionarily highly conserved miRNA implicated in the regulation of hypoxia in mammals. In Drosophila, we show that miR-210 is specifically expressed in sensory organs, including photoreceptors. miR-210 knockout mutants are not sensitive toward hypoxia but show progressive degradation of photoreceptor cells, accompanied by decreased photoreceptor potential, demonstrating an important function of miR-210 in photoreceptor maintenance and survival.
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Affiliation(s)
| | - Oliver Hahn
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Katharina Arlt
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Matthias Gruhn
- Department for Animal Physiology, Biocenter Cologne, Institute of Zoology, Cologne, Germany
| | - Annika J Jahn
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | - Jacqueline Eßer
- Max Planck Institute for Biology of Ageing, Cologne, Germany
| | | | - Corinna Klein
- Cluster of Excellence-Cellular Stress Responses in Aging-Associated Diseases Research Centre, University of Cologne, Cologne, Germany
| | - Ansgar Büschges
- Department for Animal Physiology, Biocenter Cologne, Institute of Zoology, Cologne, Germany
| | | | - Linda Partridge
- Max Planck Institute for Biology of Ageing, Cologne, Germany .,Institute of Healthy Ageing, Genetics, Evolution and Environment, University College London, London, UK
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14
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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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15
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Balakrishnan SS, Basu U, Shinde D, Thakur R, Jaiswal M, Raghu P. Regulation of PI4P levels by PI4KIIIα during G-protein-coupled PLC signaling in Drosophila photoreceptors. J Cell Sci 2018; 131:jcs.217257. [PMID: 29980590 DOI: 10.1242/jcs.217257] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2018] [Accepted: 06/27/2018] [Indexed: 12/27/2022] Open
Abstract
The activation of phospholipase C (PLC) is a conserved mechanism of receptor-activated cell signaling at the plasma membrane. PLC hydrolyzes the minor membrane lipid phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], and continued signaling requires the resynthesis and availability of PI(4,5)P2 at the plasma membrane. PI(4,5)P2 is synthesized by the phosphorylation of phosphatidylinositol 4-phosphate (PI4P). Thus, a continuous supply of PI4P is essential to support ongoing PLC signaling. While the enzyme PI4KA has been identified as performing this function in cultured mammalian cells, its function in the context of an in vivo physiological model has not been established. In this study, we show that, in Drosophila photoreceptors, PI4KIIIα activity is required to support signaling during G-protein-coupled PLC activation. Depletion of PI4KIIIα results in impaired electrical responses to light, and reduced plasma membrane levels of PI4P and PI(4,5)P2 Depletion of the conserved proteins Efr3 and TTC7 [also known as StmA and L(2)k14710, respectively, in flies], which assemble PI4KIIIα at the plasma membrane, also results in an impaired light response and reduced plasma membrane PI4P and PI(4,5)P2 levels. Thus, PI4KIIIα activity at the plasma membrane generates PI4P and supports PI(4,5)P2 levels during receptor activated PLC signaling.
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Affiliation(s)
- Sruthi S Balakrishnan
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Urbashi Basu
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Dhananjay Shinde
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Rajan Thakur
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Manish Jaiswal
- TIFR Center for Interdisciplinary Science, Hyderabad 500107, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
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16
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Liu CH, Bollepalli MK, Long SV, Asteriti S, Tan J, Brill JA, Hardie RC. Genetic dissection of the phosphoinositide cycle in Drosophila photoreceptors. J Cell Sci 2018; 131:jcs.214478. [PMID: 29567856 DOI: 10.1242/jcs.214478] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2017] [Accepted: 03/16/2018] [Indexed: 11/20/2022] Open
Abstract
Phototransduction in Drosophila is mediated by phospholipase C-dependent hydrolysis of PIP2-, and is an important model for phosphoinositide signalling. Although generally assumed to operate by generic machinery conserved from yeast to mammals, some key elements of the phosphoinositide cycle have yet to be identified in Drosophila photoreceptors. Here, we used transgenic flies expressing fluorescently tagged probes (P4M and TbR332H), which allow in vivo quantitative measurements of PI4P and PIP2 dynamics in photoreceptors of intact living flies. Using mutants and RNA interference for candidate genes potentially involved in phosphoinositide turnover, we identified Drosophila PI4KIIIα (CG10260) as the PI4-kinase responsible for PI4P synthesis in the photoreceptor membrane. Our results also indicate that PI4KIIIα activity requires rbo (the Drosophila orthologue of Efr3) and CG8325 (orthologue of YPP1), both of which are implicated as scaffolding proteins necessary for PI4KIIIα activity in yeast and mammals. However, our evidence indicates that the recently reported central role of dPIP5K59B (CG3682) in PIP2 synthesis in the rhabdomeres should be re-evaluated; although PIP2 resynthesis was suppressed by RNAi directed against dPIP5K59B, little or no defect was detected in a reportedly null mutant (dPIP5K18 ).
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Affiliation(s)
- Che-Hsiung Liu
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Murali K Bollepalli
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Samuel V Long
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Sabrina Asteriti
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
| | - Julie Tan
- Program in Cell Biology, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, 686 Bay Street, Room 15.9716, Toronto, ON M5G 0A4, Canada.,Department of Molecular Genetics, University of Toronto, Room 4396, Medical Sciences Building, 1 King's College Circle, Toronto, ON M5S 1A8, Canada
| | - Julie A Brill
- Program in Cell Biology, The Hospital for Sick Children, Peter Gilgan Centre for Research and Learning, 686 Bay Street, Room 15.9716, Toronto, ON M5G 0A4, Canada.,Department of Molecular Genetics, University of Toronto, Room 4396, Medical Sciences Building, 1 King's College Circle, Toronto, ON M5S 1A8, Canada
| | - Roger C Hardie
- Department of Physiology, Development and Neuroscience, Cambridge University, Downing St, Cambridge CB2 3EG, United Kingdom
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17
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Suratekar R, Panda A, Raghu P, Krishna S. Evidence of sinks and sources in the phospholipase C-activated PIP2
cycle. FEBS Lett 2018; 592:962-972. [DOI: 10.1002/1873-3468.12998] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2017] [Revised: 01/22/2018] [Accepted: 02/01/2018] [Indexed: 11/12/2022]
Affiliation(s)
- Rohit Suratekar
- Simons Centre for the Study of Living Machines; National Centre for Biological Sciences, TIFR; Bengaluru India
| | - Aniruddha Panda
- National Centre for Biological Sciences, TIFR; Bengaluru India
- Manipal University; Manipal India
| | - Padinjat Raghu
- National Centre for Biological Sciences, TIFR; Bengaluru India
| | - Sandeep Krishna
- Simons Centre for the Study of Living Machines; National Centre for Biological Sciences, TIFR; Bengaluru India
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18
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Yadav S, Thakur R, Georgiev P, Deivasigamani S, Krishnan H, Ratnaparkhi G, Raghu P. RDGBα localization and function at membrane contact sites is regulated by FFAT-VAP interactions. J Cell Sci 2018; 131:jcs.207985. [PMID: 29180517 DOI: 10.1242/jcs.207985] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2017] [Accepted: 11/20/2017] [Indexed: 12/27/2022] Open
Abstract
Phosphatidylinositol transfer proteins (PITPs) are essential regulators of PLC signalling. The PI transfer domain (PITPd) of multi-domain PITPs is reported to be sufficient for in vivo function, questioning the relevance of other domains in the protein. In Drosophila photoreceptors, loss of RDGBα, a multi-domain PITP localized to membrane contact sites (MCSs), results in multiple defects during PLC signalling. Here, we report that the PITPd of RDGBα does not localize to MCSs and fails to support function during strong PLC stimulation. We show that the MCS localization of RDGBα depends on the interaction of its FFAT motif with dVAP-A. Disruption of the FFAT motif (RDGBFF/AA) or downregulation of dVAP-A, both result in mis-localization of RDGBα and are associated with loss of function. Importantly, the ability of the PITPd in full-length RDGBFF/AA to rescue mutant phenotypes was significantly worse than that of the PITPd alone, indicating that an intact FFAT motif is necessary for PITPd activity in vivo Thus, the interaction between the FFAT motif and dVAP-A confers not only localization but also intramolecular regulation on lipid transfer by the PITPd of RDGBα. This article has an associated First Person interview with the first author of the paper.
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Affiliation(s)
- Shweta Yadav
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Rajan Thakur
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India.,Shanmugha Arts, Science, Technology & Research Academy, Thanjavur 613401, India
| | - Plamen Georgiev
- Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
| | | | - Harini Krishnan
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Girish Ratnaparkhi
- Department of Biology, Indian Institute of Science Education and Research, Pune 411021, India
| | - Padinjat Raghu
- Cellular Organization and Signalling, National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
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19
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Topological organisation of the phosphatidylinositol 4,5-bisphosphate-phospholipase C resynthesis cycle: PITPs bridge the ER-PM gap. Biochem J 2017; 473:4289-4310. [PMID: 27888240 DOI: 10.1042/bcj20160514c] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2016] [Revised: 09/08/2016] [Accepted: 09/12/2016] [Indexed: 12/13/2022]
Abstract
Phospholipase C (PLC) is a receptor-regulated enzyme that hydrolyses phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) at the plasma membrane (PM) triggering three biochemical consequences, the generation of soluble inositol 1,4,5-trisphosphate (IP3), membrane-associated diacylglycerol (DG) and the consumption of PM PI(4,5)P2 Each of these three signals triggers multiple molecular processes impacting key cellular properties. The activation of PLC also triggers a sequence of biochemical reactions, collectively referred to as the PI(4,5)P2 cycle that culminates in the resynthesis of this lipid. The biochemical intermediates of this cycle and the enzymes that mediate these reactions are topologically distributed across two membrane compartments, the PM and the endoplasmic reticulum (ER). At the PM, the DG formed during PLC activation is rapidly converted into phosphatidic acid (PA) that needs to be transported to the ER where the machinery for its conversion into PI is localised. Conversely, PI from the ER needs to be rapidly transferred to the PM where it can be phosphorylated by lipid kinases to regenerate PI(4,5)P2 Thus, two lipid transport steps between membrane compartments through the cytosol are required for the replenishment of PI(4,5)P2 at the PM. Here, we review the topological constraints in the PI(4,5)P2 cycle and current understanding how these constraints are overcome during PLC signalling. In particular, we discuss the role of lipid transfer proteins in this process. Recent findings on the biochemical properties of a membrane-associated lipid transfer protein of the PITP family, PITPNM proteins (alternative name RdgBα/Nir proteins) that localise to membrane contact sites are discussed. Studies in both Drosophila and mammalian cells converge to provide a resolution to the conundrum of reciprocal transfer of PA and PI during PLC signalling.
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20
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Kamalesh K, Trivedi D, Toscano S, Sharma S, Kolay S, Raghu P. Phosphatidylinositol 5-phosphate 4-kinase regulates early endosomal dynamics during clathrin-mediated endocytosis. J Cell Sci 2017; 130:2119-2133. [PMID: 28507272 PMCID: PMC5536888 DOI: 10.1242/jcs.202259] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2017] [Accepted: 05/09/2017] [Indexed: 12/19/2022] Open
Abstract
Endocytic turnover is essential for the regulation of the protein composition and function of the plasma membrane, and thus affects the plasma membrane levels of many receptors. In Drosophila melanogaster photoreceptors, photon absorption by the G-protein-coupled receptor (GPCR) rhodopsin 1 (Rh1; also known as NinaE) triggers its endocytosis through clathrin-mediated endocytosis (CME). We find that CME of Rh1 is regulated by phosphatidylinositol 5 phosphate 4-kinase (PIP4K). Flies lacking PIP4K show mislocalization of Rh1 on expanded endomembranes within the cell body. This mislocalization of Rh1 was dependent on the formation of an expanded Rab5-positive compartment. The Rh1-trafficking defect in PIP4K-depleted cells could be suppressed by downregulating Rab5 function or by selectively reconstituting PIP4K in the PI3P-enriched early endosomal compartment of photoreceptors. We also found that loss of PIP4K was associated with increased CME and an enlarged Rab5-positive compartment in cultured Drosophila cells. Collectively, our findings define PIP4K as a novel regulator of early endosomal homeostasis during CME.
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Affiliation(s)
- Kumari Kamalesh
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India.,Department of Biological Sciences, Tata Institute of Fundamental Research, Dr. Homi Bhabha Road, Colaba, Mumbai 400005, India
| | - Deepti Trivedi
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Sarah Toscano
- Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
| | - Sanjeev Sharma
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Sourav Kolay
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India.,Manipal University, Madhav Nagar, Manipal, Karnataka 576104, India
| | - Padinjat Raghu
- National Centre for Biological Sciences-TIFR, GKVK Campus, Bellary Road, Bangalore 560065, India
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21
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The Drosophila photoreceptor as a model system for studying signalling at membrane contact sites. Biochem Soc Trans 2016; 44:447-51. [PMID: 27068953 DOI: 10.1042/bst20150256] [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: 01/25/2016] [Indexed: 01/08/2023]
Abstract
Several recent studies have demonstrated the existence of membrane contact sites (MCS) between intracellular organelles in eukaryotic cells. Recent exciting studies have also demonstrated the existence of biomolecular interactions at these contact sites in mediating changes in the membrane composition of the cellular compartments. However, the role of such contact sites in regulating organelle function and physiological processes remains less clear. In this review we discuss the existence of a contact site between the plasma membrane (PM) and the endoplasmic reticulum (ER) inDrosophilaphotoreceptors. Further, we discuss the role of specific proteins present at this location in regulating phospholipid turnover and its impact in regulating a physiological process, namely phototransduction.
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22
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Thakur R, Panda A, Coessens E, Raj N, Yadav S, Balakrishnan S, Zhang Q, Georgiev P, Basak B, Pasricha R, Wakelam MJ, Ktistakis NT, Raghu P. Phospholipase D activity couples plasma membrane endocytosis with retromer dependent recycling. eLife 2016; 5. [PMID: 27848911 PMCID: PMC5125754 DOI: 10.7554/elife.18515] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2016] [Accepted: 11/14/2016] [Indexed: 01/11/2023] Open
Abstract
During illumination, the light-sensitive plasma membrane (rhabdomere) of Drosophila photoreceptors undergoes turnover with consequent changes in size and composition. However, the mechanism by which illumination is coupled to rhabdomere turnover remains unclear. We find that photoreceptors contain a light-dependent phospholipase D (PLD) activity. During illumination, loss of PLD resulted in an enhanced reduction in rhabdomere size, accumulation of Rab7 positive, rhodopsin1-containing vesicles (RLVs) in the cell body and reduced rhodopsin protein. These phenotypes were associated with reduced levels of phosphatidic acid, the product of PLD activity and were rescued by reconstitution with catalytically active PLD. In wild-type photoreceptors, during illumination, enhanced PLD activity was sufficient to clear RLVs from the cell body by a process dependent on Arf1-GTP levels and retromer complex function. Thus, during illumination, PLD activity couples endocytosis of RLVs with their recycling to the plasma membrane thus maintaining plasma membrane size and composition. DOI:http://dx.doi.org/10.7554/eLife.18515.001 Certain cells in the eye contain a receptor protein known as rhodopsin that enables them to detect light. Rhodopsin is found in distinct patches on the membrane surrounding each of these “photoreceptor” cells and the number of rhodopsin molecules present controls how sensitive the cell is to light. In humans, vitamin A deficiency or genetic defects can decrease the number of rhodopsin molecules on the membrane, leading to difficulty in seeing in dim light. Fruit fly eyes also contain rhodopsin. Exposure to normal levels of light triggers parts of the membranes of fly photoreceptor cells to detach and move into the interior of the cell. These internalized pieces of membrane have two possible fates: they can either be destroyed or recycled back to the cell surface. This membrane turnover adjusts the size of the membrane surrounding the cell and the number of rhodopsin molecules in it to regulate the cell’s sensitivity to light. It is crucial that turnover is tightly regulated in order to maintain the integrity of the cell membrane. However, it is not clear how the process is regulated during light exposure. Thakur et al. set out to address this question in fruit flies. The experiments show that an enzyme called phospholipase D is activated when photoreceptors are exposed to light. Active phospholipase D – which generates a molecule called phosphatidic acid – coordinates the internalization of pieces of membrane with the recycling of rhodopsin back to the cell surface. Thakur et al. generated fly mutants that lacked phospholipase D and in these animals the internalized rhodopsin was not transported back to the cell membrane. This caused the membrane to shrink in size and decreased the number of rhodopsin molecules in it. As a result, the photoreceptor cells became less sensitive to light. The findings of Thakur et al. show that in response to normal levels of light, phospholipase D balances membrane internalization and recycling to maintain the size and rhodopsin composition of the membrane. Future challenges will be to work out exactly how phospholipase D is activated and how phosphatidic acid tunes membrane internalization and recycling. DOI:http://dx.doi.org/10.7554/eLife.18515.002
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Affiliation(s)
- Rajan Thakur
- National Centre for Biological Sciences, Bangalore, India.,Shanmugha Arts, Science, Technology & Research Academy, Thanjavur, India
| | - Aniruddha Panda
- National Centre for Biological Sciences, Bangalore, India.,Manipal University, Karnataka, India
| | - Elise Coessens
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
| | - Nikita Raj
- National Centre for Biological Sciences, Bangalore, India
| | - Shweta Yadav
- National Centre for Biological Sciences, Bangalore, India
| | | | - Qifeng Zhang
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
| | - Plamen Georgiev
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
| | - Bishal Basak
- National Centre for Biological Sciences, Bangalore, India
| | - Renu Pasricha
- National Centre for Biological Sciences, Bangalore, India
| | | | | | - Padinjat Raghu
- National Centre for Biological Sciences, Bangalore, India
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23
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Yadav S, Garner K, Georgiev P, Li M, Gomez-Espinosa E, Panda A, Mathre S, Okkenhaug H, Cockcroft S, Raghu P. RDGBα, a PtdIns-PtdOH transfer protein, regulates G-protein-coupled PtdIns(4,5)P2 signalling during Drosophila phototransduction. J Cell Sci 2015. [PMID: 26203165 PMCID: PMC4582195 DOI: 10.1242/jcs.173476] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Many membrane receptors activate phospholipase C (PLC) during signalling, triggering changes in the levels of several plasma membrane lipids including phosphatidylinositol (PtdIns), phosphatidic acid (PtdOH) and phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P2]. It is widely believed that exchange of lipids between the plasma membrane and endoplasmic reticulum (ER) is required to restore lipid homeostasis during PLC signalling, yet the mechanism remains unresolved. RDGBα (hereafter RDGB) is a multi-domain protein with a PtdIns transfer protein (PITP) domain (RDGB-PITPd). We find that, in vitro, the RDGB-PITPd binds and transfers both PtdOH and PtdIns. In Drosophila photoreceptors, which experience high rates of PLC activity, RDGB function is essential for phototransduction. We show that binding of PtdIns to RDGB-PITPd is essential for normal phototransduction; however, this property is insufficient to explain the in vivo function because another Drosophila PITP (encoded by vib) that also binds PtdIns cannot rescue the phenotypes of RDGB deletion. In RDGB mutants, PtdIns(4,5)P2 resynthesis at the plasma membrane following PLC activation is delayed and PtdOH levels elevate. Thus RDGB couples the turnover of both PtdIns and PtdOH, key lipid intermediates during G-protein-coupled PtdIns(4,5)P2 turnover.
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Affiliation(s)
- Shweta Yadav
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India
| | - Kathryn Garner
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Plamen Georgiev
- Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
| | - Michelle Li
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Evelyn Gomez-Espinosa
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Aniruddha Panda
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Manipal University, Madhav Nagar, Manipal, Karnataka 576104, India
| | - Swarna Mathre
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Manipal University, Madhav Nagar, Manipal, Karnataka 576104, India
| | | | - Shamshad Cockcroft
- Department of Neuroscience, Physiology and Pharmacology, University College, London WC1E 6JJ, UK
| | - Padinjat Raghu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore, Karnataka 560065, India Inositide Laboratory, Babraham Institute, Cambridge CB22 3AT, UK
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24
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Chakrabarti P, Kolay S, Yadav S, Kumari K, Nair A, Trivedi D, Raghu P. A dPIP5K dependent pool of phosphatidylinositol 4,5 bisphosphate (PIP2) is required for G-protein coupled signal transduction in Drosophila photoreceptors. PLoS Genet 2015; 11:e1004948. [PMID: 25633995 PMCID: PMC4310717 DOI: 10.1371/journal.pgen.1004948] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2014] [Accepted: 12/09/2014] [Indexed: 12/02/2022] Open
Abstract
Multiple PIP2 dependent molecular processes including receptor activated phospholipase C activity occur at the neuronal plasma membranes, yet levels of this lipid at the plasma membrane are remarkably stable. Although the existence of unique pools of PIP2 supporting these events has been proposed, the mechanism by which they are generated is unclear. In Drosophila photoreceptors, the hydrolysis of PIP2 by G-protein coupled phospholipase C activity is essential for sensory transduction of photons. We identify dPIP5K as an enzyme essential for PIP2 re-synthesis in photoreceptors. Loss of dPIP5K causes profound defects in the electrical response to light and light-induced PIP2 dynamics at the photoreceptor membrane. Overexpression of dPIP5K was able to accelerate the rate of PIP2 synthesis following light induced PIP2 depletion. Other PIP2 dependent processes such as endocytosis and cytoskeletal function were unaffected in photoreceptors lacking dPIP5K function. These results provide evidence for the existence of a unique dPIP5K dependent pool of PIP2 required for normal Drosophila phototransduction. Our results define the existence of multiple pools of PIP2 in photoreceptors generated by distinct lipid kinases and supporting specific molecular processes at neuronal membranes. PIP2 has been implicated in multiple functions at the plasma membrane. Some of these require its hydrolysis by receptor-activated phospholipase C, whereas others, such as membrane transport and cytoskeletal function, involve the interaction of the intact lipid with cellular proteins. The mechanistic basis underlying the segregation of these two classes of PIP2 dependent functions is unknown; it has been postulated that this might involve unique pools of PIP2 generated by distinct phosphoinsoitide kinases. We have studied this question in Drosophila photoreceptors, a model system where sensory transduction requires robust phospholipase C mediated PIP2 hydrolysis. We find that the activity of phosphatidylinositol-4-phosphate 5 kinase encoded by dPIP5K is required to support normal sensory transduction and PIP2 dynamics in photoreceptors. Remarkably, non-PLC dependent functions of PIP2, such as vesicular transport and the actin cytoskeleton, were unaffected in dPIP5K mutants. Thus, dPIP5K supports a pool of PIP2 that is readily available to PLC, but has no role in sustaining other non-PLC mediated PIP2 dependent processes. These findings support the existence of at least two non-overlapping pools of PIP2 at the plasma membrane, and provide a platform for future studies of PIP2 regulation at the plasma membrane.
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Affiliation(s)
| | - Sourav Kolay
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bangalore, India
- Manipal University, Madhav Nagar, Manipal, Karnataka, India
| | - Shweta Yadav
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bangalore, India
| | - Kamalesh Kumari
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bangalore, India
- Department of Biological Sciences, Tata Institute of Fundamental Research, Colaba, Mumbai, India
| | - Amit Nair
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
| | - Deepti Trivedi
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
| | - Padinjat Raghu
- Inositide Laboratory, Babraham Institute, Cambridge, United Kingdom
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bangalore, India
- * E-mail:
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25
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Balakrishnan SS, Basu U, Raghu P. Phosphoinositide signalling in Drosophila. Biochim Biophys Acta Mol Cell Biol Lipids 2014; 1851:770-84. [PMID: 25449646 DOI: 10.1016/j.bbalip.2014.10.010] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2014] [Revised: 10/08/2014] [Accepted: 10/22/2014] [Indexed: 01/28/2023]
Abstract
Phosphoinositides (PtdInsPs) are lipids that mediate a range of conserved cellular processes in eukaryotes. These include the transduction of ligand binding to cell surface receptors, vesicular transport and cytoskeletal function. The nature and functions of PtdInsPs were initially elucidated through biochemical experiments in mammalian cells. However, over the years, genetic and cell biological analysis in a range of model organisms including S. cerevisiae, D. melanogaster and C. elegans have contributed to an understanding of the involvement of PtdInsPs in these cellular events. The fruit fly Drosophila is an excellent genetic model for the analysis of cell and developmental biology as well as physiological processes, particularly analysis of the complex relationship between the cell types of a metazoan in mediating animal physiology. PtdInsP signalling pathways are underpinned by enzymes that synthesise and degrade these molecules and also by proteins that bind to these lipids in cells. In this review we provide an overview of the current understanding of PtdInsP signalling in Drosophila. We provide a comparative genomic analysis of the PtdInsP signalling toolkit between Drosophila and mammalian systems. We also review some areas of cell and developmental biology where analysis in Drosophila might provide insights into the role of this lipid-signalling pathway in metazoan biology. This article is part of a Special Issue entitled Phosphoinositides.
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Affiliation(s)
- Sruthi S Balakrishnan
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Urbashi Basu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India
| | - Padinjat Raghu
- National Centre for Biological Sciences, TIFR-GKVK Campus, Bellary Road, Bangalore 560065, India.
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Gurudev N, Yuan M, Knust E. chaoptin, prominin, eyes shut and crumbs form a genetic network controlling the apical compartment of Drosophila photoreceptor cells. Biol Open 2014; 3:332-41. [PMID: 24705015 PMCID: PMC4021355 DOI: 10.1242/bio.20147310] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The apical surface of epithelial cells is often highly specialised to fulfil cell type-specific functions. Many epithelial cells expand their apical surface by forming microvilli, actin-based, finger-like membrane protrusions. The apical surface of Drosophila photoreceptor cells (PRCs) forms tightly packed microvilli, which are organised into the photosensitive rhabdomeres. As previously shown, the GPI-anchored adhesion protein Chaoptin is required for the stability of the microvilli, whereas the transmembrane protein Crumbs is essential for proper rhabdomere morphogenesis. Here we show that chaoptin synergises with crumbs to ensure optimal rhabdomere width. In addition, reduction of crumbs ameliorates morphogenetic defects observed in PRCs mutant for prominin and eyes shut, known antagonists of chaoptin. These results suggest that these four genes provide a balance of adhesion and anti-adhesion to maintain microvilli development and maintenance. Similar to crumbs mutant PRCs, PRCs devoid of prominin or eyes shut undergo light-dependent retinal degeneration. Given the observation that human orthologues of crumbs, prominin and eyes shut result in progressive retinal degeneration and blindness, the Drosophila eye is ideally suited to unravel the genetic and cellular mechanisms that ensure morphogenesis of PRCs and their maintenance under light-mediated stress.
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Affiliation(s)
- Nagananda Gurudev
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
| | - Michaela Yuan
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
| | - Elisabeth Knust
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, D-01307 Dresden, Germany
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Cockcroft S, Garner K. Potential role for phosphatidylinositol transfer protein (PITP) family in lipid transfer during phospholipase C signalling. Adv Biol Regul 2013; 53:280-291. [PMID: 23916246 DOI: 10.1016/j.jbior.2013.07.007] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2013] [Revised: 07/11/2013] [Accepted: 07/12/2013] [Indexed: 06/02/2023]
Abstract
The hallmark of mammalian phosphatidylinositol transfer proteins (PITPs) is to transfer phosphatidylinositol between membrane compartments. In the mammalian genome, there are three genes that code for soluble PITP proteins, PITPα, PITPβ and RdgBβ and two genes that code for membrane-associated multi-domain proteins (RdgBαI and II) containing a PITP domain. PITPα and PITPβ constitute Class I PITPs whilst the RdgB proteins constitute Class II proteins based on sequence analysis. The PITP domain of both Class I and II can sequester one molecule of phosphatidylinositol (PI) in its hydrophobic cavity. Therefore, in principle, PITPs are therefore ideally poised to couple phosphatidylinositol delivery to the PI kinases for substrate provision for phospholipases C during cell activation. Since phosphatidylinositol (4,5)bisphosphate plays critical roles in cells, particularly at the plasma membrane, where it is a substrate for both phospholipase C and phosphoinositide-3-kinases as well as required as an intact lipid to regulate ion channels and the actin cytoskeleton, homeostatic mechanisms to maintain phosphatidylinositol(4,5)bisphosphate levels are vital. To maintain phosphatidylinositol levels, phospholipase C activation inevitably leads to the resynthesis of PI at the endoplasmic reticulum where the enzymes are located. Phosphatidic acid generated at the plasma membrane during phospholipase C activation needs to move to the ER for conversion to PI and here we provide evidence that Class II PITPs are also able to bind and transport phosphatidic acid. Thus RdgB proteins could couple PA and PI transport bidirectionally during phospholipase C signalling.
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Affiliation(s)
- Shamshad Cockcroft
- Dept. of Neuroscience, Physiology and Pharmacology, Division of Biosciences, University College London, London WC1E 6JJ, UK.
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Sengupta S, Barber TR, Xia H, Ready DF, Hardie RC. Depletion of PtdIns(4,5)P₂ underlies retinal degeneration in Drosophila trp mutants. J Cell Sci 2013; 126:1247-59. [PMID: 23378018 DOI: 10.1242/jcs.120592] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
The prototypical transient receptor potential (TRP) channel is the major light-sensitive, and Ca(2+)-permeable channel in the microvillar photoreceptors of Drosophila. TRP channels are activated following hydrolysis of phosphatidylinositol 4,5-bisphosphate [PtdIns(4,5)P₂] by the key effector enzyme phospholipase C (PLC). Mutants lacking TRP channels undergo light-dependent retinal degeneration, as a consequence of the reduced Ca(2+) influx. It has been proposed that degeneration is caused by defects in the Ca(2+)-dependent visual pigment cycle, which result in accumulation of toxic phosphorylated metarhodopsin-arrestin complexes (MPP-Arr2). Here we show that two interventions, which prevent accumulation of MPP-Arr2, namely rearing under red light or eliminating the C-terminal rhodopsin phosphorylation sites, failed to rescue degeneration in trp mutants. Instead, degeneration in trp mutants reared under red light was rescued by mutation of PLC. Degeneration correlated closely with the light-induced depletion of PtdIns(4,5)P₂ that occurs in trp mutants due to failure of Ca(2+)-dependent inhibition of PLC. Severe retinal degeneration was also induced in the dark in otherwise wild-type flies by overexpression of a bacterial PtdInsPn phosphatase (SigD) to deplete PtdIns(4,5)P₂. In degenerating trp photoreceptors, phosphorylated Moesin, a PtdIns(4,5)P₂-regulated membrane-cytoskeleton linker essential for normal microvillar morphology, was found to delocalize from the rhabdomere and there was extensive microvillar actin depolymerisation. The results suggest that compromised light-induced Ca(2+) influx, due to loss of TRP channels, leads to PtdIns(4,5)P₂ depletion, resulting in dephosphorylation of Moesin, actin depolymerisation and disintegration of photoreceptor structure.
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Affiliation(s)
- Sukanya Sengupta
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK.
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