1
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Yost PP, Al-Nouman A, Curtiss J. The Rap1 small GTPase affects cell fate or survival and morphogenetic patterning during Drosophila melanogaster eye development. Differentiation 2023; 133:12-24. [PMID: 37437447 PMCID: PMC10528170 DOI: 10.1016/j.diff.2023.06.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 06/06/2023] [Accepted: 06/07/2023] [Indexed: 07/14/2023]
Abstract
The Drosophila melanogaster eye has been instrumental for determining both how cells communicate with one another to determine cell fate, as well as cell morphogenesis and patterning. Here, we describe the effects of the small GTPase Rap1 on the development of multiple cell types in the D. melanogaster eye. Although Rap1 has previously been linked to RTK-Ras-MAPK signaling in eye development, we demonstrate that manipulation of Rap1 activity is modified by increase or decrease of Delta/Notch signaling during several events of cell fate specification in eye development. In addition, we demonstrate that manipulating Rap1 function either in primary pigment cells or in interommatidial cells affects cone cell contact switching, primary pigment cell enwrapment of the ommatidial cluster, and sorting of secondary and tertiary pigment cells. These data suggest that Rap1 has roles in both ommatidial cell recruitment/survival and in ommatidial morphogenesis in the pupal stage. They lay groundwork for future experiments on the role of Rap1 in these events.
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Affiliation(s)
- Philip P Yost
- New Mexico State University, 1780 E University Ave, Las Cruces, NM, 88003, USA
| | | | - Jennifer Curtiss
- New Mexico State University, 1780 E University Ave, Las Cruces, NM, 88003, USA.
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2
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Chohan Y, Eitzman EA, Hawkins WD, Klionsky DJ. Bruchpiloting synaptic connections: Egfr in autophagy-mediated neuronal circuit development. Autophagy 2023; 19:1899-1900. [PMID: 37243688 PMCID: PMC10283405 DOI: 10.1080/15548627.2023.2217015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2023] [Accepted: 05/19/2023] [Indexed: 05/29/2023] Open
Abstract
Macroautophagy/autophagy is involved in many aspects of human development including the formation of neuronal circuits. A recent study from Dutta et al. found that the recruitment of Egfr (Epidermal growth factor receptor) to synapses suppresses autophagic degradation of presynaptic proteins, a requirement for proper neuronal circuit development. The findings suggest that Egfr inactivation during a distinct critical interval in late development results in increased levels of autophagy in the brain and decreased neuronal circuit development. Furthermore, the presence of brp (bruchpilot) in the synapse is critical for proper neuronal functioning over this same period. Dutta and colleagues found that increased autophagy due to Egfr inactivation results in decreased brp levels and, therefore, reduced neuronal connectivity. Through live cell imaging, it was determined that only the synaptic branches that accumulate both Egfr and brp are stabilized, allowing for the persistence of active zones, further supporting the importance of both Egfr and brp in the brain. While Dutta and colleagues collected these data based on studies conducted on Drosophila brains, the findings provide great insight as to how these different proteins may be implicated in human neurology.
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Affiliation(s)
- Yashveer Chohan
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Emily A. Eitzman
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Wayne D. Hawkins
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
| | - Daniel J. Klionsky
- Life Sciences Institute, University of Michigan, Ann Arbor, MI, USA
- Department of Molecular, Cellular and Developmental Biology, University of Michigan, Ann Arbor, MI, USA
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3
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Szinyákovics J, Keresztes F, Kiss EA, Falcsik G, Vellai T, Kovács T. Potent New Targets for Autophagy Enhancement to Delay Neuronal Ageing. Cells 2023; 12:1753. [PMID: 37443788 PMCID: PMC10341134 DOI: 10.3390/cells12131753] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2023] [Revised: 06/28/2023] [Accepted: 06/28/2023] [Indexed: 07/15/2023] Open
Abstract
Autophagy is a lysosomal-dependent degradation process of eukaryotic cells responsible for breaking down unnecessary and damaged intracellular components. Autophagic activity gradually declines with age due to genetic control, and this change contributes to the accumulation of cellular damage at advanced ages, thereby causing cells to lose their functionality and viability. This could be particularly problematic in post-mitotic cells including neurons, the mass destruction of which leads to various neurodegenerative diseases. Here, we aim to uncover new regulatory points where autophagy could be specifically activated and test these potential drug targets in neurodegenerative disease models of Drosophila melanogaster. One possible way to activate autophagy is by enhancing autophagosome-lysosome fusion that creates the autolysosome in which the enzymatic degradation happens. The HOPS (homotypic fusion and protein sorting) and SNARE (Snap receptor) protein complexes regulate the fusion process. The HOPS complex forms a bridge between the lysosome and autophagosome with the assistance of small GTPase proteins. Thus, small GTPases are essential for autolysosome maturation, and among these proteins, Rab2 (Ras-associated binding 2), Rab7, and Arl8 (Arf-like 8) are required to degrade the autophagic cargo. For our experiments, we used Drosophila melanogaster as a model organism. Nerve-specific small GTPases were silenced and overexpressed. We examined the effects of these genetic interventions on lifespan, climbing ability, and autophagy. Finally, we also studied the activation of small GTPases in a Parkinson's disease model. Our results revealed that GTP-locked, constitutively active Rab2 (Rab2-CA) and Arl8 (Arl8-CA) expression reduces the levels of the autophagic substrate p62/Ref(2)P in neurons, extends lifespan, and improves the climbing ability of animals during ageing. However, Rab7-CA expression dramatically shortens lifespan and inhibits autophagy. Rab2-CA expression also increases lifespan in a Parkinson's disease model fly strain overexpressing human mutant (A53T) α-synuclein protein. Data provided by this study suggests that Rab2 and Arl8 serve as potential targets for autophagy enhancement in the Drosophila nervous system. In the future, it might be interesting to assess the effect of Rab2 and Arl8 coactivation on autophagy, and it would also be worthwhile to validate these findings in a mammalian model and human cell lines. Molecules that specifically inhibit Rab2 or Arl8 serve as potent drug candidates to modulate the activity of the autophagic process in treating neurodegenerative pathologies. In the future, it would be reasonable to investigate which GAP enzyme can inhibit Rab2 or Arl8 specifically, but not affect Rab7, with similar medical purposes.
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Affiliation(s)
- Janka Szinyákovics
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
- Doctoral School of Biology, Institute of Biology, ELTE Eötvös Loránd University (ELTE), Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary
- ELKH-ELTE Genetic Research Group, H-1117 Budapest, Hungary
| | - Fanni Keresztes
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
- Doctoral School of Biology, Institute of Biology, ELTE Eötvös Loránd University (ELTE), Pázmány Péter sétány 1/C, H-1117 Budapest, Hungary
| | - Eszter Anna Kiss
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
| | - Gergő Falcsik
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
| | - Tibor Vellai
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
- ELKH-ELTE Genetic Research Group, H-1117 Budapest, Hungary
| | - Tibor Kovács
- Department of Genetics, Eötvös Loránd University (ELTE), H-1117 Budapest, Hungary
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4
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Rotelli MD, Bolling AM, Killion AW, Weinberg AJ, Dixon MJ, Calvi BR. An RNAi Screen for Genes Required for Growth of Drosophila Wing Tissue. G3 (BETHESDA, MD.) 2019; 9:3087-3100. [PMID: 31387856 PMCID: PMC6778782 DOI: 10.1534/g3.119.400581] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Accepted: 07/31/2019] [Indexed: 12/23/2022]
Abstract
Cell division and tissue growth must be coordinated with development. Defects in these processes are the basis for a number of diseases, including developmental malformations and cancer. We have conducted an unbiased RNAi screen for genes that are required for growth in the Drosophila wing, using GAL4-inducible short hairpin RNA (shRNA) fly strains made by the Drosophila RNAi Screening Center. shRNA expression down the center of the larval wing disc using dpp-GAL4, and the central region of the adult wing was then scored for tissue growth and wing hair morphology. Out of 4,753 shRNA crosses that survived to adulthood, 18 had impaired wing growth. FlyBase and the new Alliance of Genome Resources knowledgebases were used to determine the known or predicted functions of these genes and the association of their human orthologs with disease. The function of eight of the genes identified has not been previously defined in Drosophila The genes identified included those with known or predicted functions in cell cycle, chromosome segregation, morphogenesis, metabolism, steroid processing, transcription, and translation. All but one of the genes are similar to those in humans, and many are associated with disease. Knockdown of lin-52, a subunit of the Myb-MuvB transcription factor, or βNACtes6, a gene involved in protein folding and trafficking, resulted in a switch from cell proliferation to an endoreplication growth program through which wing tissue grew by an increase in cell size (hypertrophy). It is anticipated that further analysis of the genes that we have identified will reveal new mechanisms that regulate tissue growth during development.
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Affiliation(s)
- Michael D Rotelli
- Department of Biology, Indiana University, Bloomington, IN 47405 and
| | - Anna M Bolling
- Department of Biology, Indiana University, Bloomington, IN 47405 and
| | - Andrew W Killion
- Department of Biology, Indiana University, Bloomington, IN 47405 and
| | | | - Michael J Dixon
- Department of Biology, Indiana University, Bloomington, IN 47405 and
| | - Brian R Calvi
- Department of Biology, Indiana University, Bloomington, IN 47405 and
- Melvin and Bren Simon Cancer Center, Indiana University, Indianapolis, IN 46202
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5
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Tomlinson A, Mavromatakis YE, Arias R. The role of Sevenless in Drosophila R7 photoreceptor specification. Dev Biol 2019; 454:181-189. [PMID: 31207209 DOI: 10.1016/j.ydbio.2019.06.007] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2019] [Accepted: 06/11/2019] [Indexed: 11/16/2022]
Abstract
Sevenless (Sev) is a Receptor Tyrosine Kinase (RTK) that is required for the specification of the Drosophila R7 photoreceptor. Other Drosophila photoreceptors are specified by the action of another RTK; the Drosophila EGF Receptor (DER). Why Sev is required specifically in the R7 precursor, and the exact role it plays in the cell's fate assignment have long remained unclear. Notch (N) signaling plays many roles in R7 specification, one of which is to prevent DER activity from establishing the photoreceptor fate. Our current model of Sev function is that it hyperactivates the RTK pathway in the R7 precursor to overcome the N-imposed block on photoreceptor specification. From this perspective DER and Sev are viewed as engaging the same transduction machinery, the only difference between them being the level of pathway activation that they induce. To test this model, we generated a Sev/DER chimera in which the intracellular domain of Sev is replaced with that of DER. This chimerical receptor acts indistinguishably from Sev itself; a result that is entirely consistent with the two RTKs sharing identical transduction abilities. A long-standing question in regard to Sev is the function of a hydrophobic domain some 60 amino acids from the initiating Methionine. If this represents a transmembrane domain, it would endow Sev with N-terminal intracellular sequences through which it could engage internal transduction pathways. However, we find that this domain acts as an internal signal peptide, and that there is no Sev N-terminal intracellular domain. phyllopod (phyl) is the target gene of the RTK pathway, and we show that R7 precursors are selectively lost when phyl gene function is mildly compromised, and that other photoreceptors are removed when the gene function is further reduced. This result adds a key piece of evidence for the hyperactivation of the RTK pathway in the R7 precursor. To facilitate the hyperactivation of the RTK pathway, Sev is expressed at high levels. However, when we express DER at the levels at which Sev is expressed, strong gain-of-function effects result, consistent with ligand-independent activation of the receptor. This highlights another key feature of Sev; that it is expressed at high levels yet remains strictly ligand dependent. Finally, we find that activated Sev can rescue R3/4 photoreceptors when their DER function is abrogated. These results are collectively consistent with Sev and DER activating the same transduction machinery, with Sev generating a pathway hyperactivation to overcome the N-imposed block to photoreceptor specification in R7 precursors.
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Affiliation(s)
- Andrew Tomlinson
- Zuckerman Institute, Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, Jerome L. Greene Science Center, Level 9 Room 028, 3227 Broadway, New York, NY, 10027, USA.
| | - Yannis Emmanuel Mavromatakis
- Zuckerman Institute, Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, Jerome L. Greene Science Center, Level 9 Room 028, 3227 Broadway, New York, NY, 10027, USA
| | - Ronald Arias
- Zuckerman Institute, Department of Genetics and Development, College of Physicians and Surgeons of Columbia University, Jerome L. Greene Science Center, Level 9 Room 028, 3227 Broadway, New York, NY, 10027, USA
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6
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Ou M, Wang S, Sun M, An J, Lv H, Zeng X, Hou SX, Xie W. The PDZ-GEF Gef26 regulates synapse development and function via FasII and Rap1 at the Drosophila neuromuscular junction. Exp Cell Res 2018; 374:342-352. [PMID: 30553967 DOI: 10.1016/j.yexcr.2018.12.008] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2018] [Revised: 12/09/2018] [Accepted: 12/12/2018] [Indexed: 12/29/2022]
Abstract
Guanine nucleotide exchange factors (GEFs) are essential for small G proteins to activate their downstream signaling pathways, which are involved in morphogenesis, cell adhesion, and migration. Mutants of Gef26, a PDZ-GEF (PDZ domain-containing guanine nucleotide exchange factor) in Drosophila, exhibit strong defects in wings, eyes, and the reproductive and nervous systems. However, the precise roles of Gef26 in development remain unclear. In the present study, we analyzed the role of Gef26 in synaptic development and function. We identified significant decreases in bouton number and branch length at larval neuromuscular junctions (NMJs) in Gef26 mutants, and these defects were fully rescued by restoring Gef26 expression, indicating that Gef26 plays an important role in NMJ morphogenesis. In addition to the observed defects in NMJ morphology, electrophysiological analyses revealed functional defects at NMJs, and locomotor deficiency appeared in Gef26 mutant larvae. Furthermore, Gef26 regulated NMJ morphogenesis by regulating the level of synaptic Fasciclin II (FasII), a well-studied cell adhesion molecule that functions in NMJ development and remodeling. Finally, our data demonstrate that Gef26-specific small G protein Rap1 worked downstream of Gef26 to regulate the level of FasII at NMJs, possibly through a βPS integrin-mediated signaling pathway. Taken together, our findings define a novel role of Gef26 in regulating NMJ development and function.
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Affiliation(s)
- Mengzhu Ou
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China
| | - Su Wang
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China
| | - Mingkuan Sun
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China
| | - Jinsong An
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China
| | - Huihui Lv
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China
| | - Xiankun Zeng
- Basic Research Laboratory, National Cancer Institute at Frederick, NIH, Frederick, MD 21702, USA
| | - Steven X Hou
- Basic Research Laboratory, National Cancer Institute at Frederick, NIH, Frederick, MD 21702, USA.
| | - Wei Xie
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing 210096, China.
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7
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Rasmussen NR, Dickinson DJ, Reiner DJ. Ras-Dependent Cell Fate Decisions Are Reinforced by the RAP-1 Small GTPase in Caenorhabditiselegans. Genetics 2018; 210:1339-1354. [PMID: 30257933 PMCID: PMC6283165 DOI: 10.1534/genetics.118.301601] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 09/15/2018] [Indexed: 12/15/2022] Open
Abstract
The notoriety of the small GTPase Ras as the most mutated oncoprotein has led to a well-characterized signaling network largely conserved across metazoans. Yet the role of its close relative Rap1 (Ras Proximal), which shares 100% identity between their core effector binding sequences, remains unclear. A long-standing controversy in the field is whether Rap1 also functions to activate the canonical Ras effector, the S/T kinase Raf. We used the developmentally simpler Caenorhabditis elegans, which lacks the extensive paralog redundancy of vertebrates, to examine the role of RAP-1 in two distinct LET-60/Ras-dependent cell fate patterning events: induction of 1° vulval precursor cell (VPC) fate and of the excretory duct cell. Fluorescence-tagged endogenous RAP-1 is localized to plasma membranes and is expressed ubiquitously, with even expression levels across the VPCs. RAP-1 and its activating GEF PXF-1 function cell autonomously and are necessary for maximal induction of 1° VPCs. Critically, mutationally activated endogenous RAP-1 is sufficient both to induce ectopic 1°s and duplicate excretory duct cells. Like endogenous RAP-1, before induction GFP expression from the pxf-1 promoter is uniform across VPCs. However, unlike endogenous RAP-1, after induction GFP expression is increased in presumptive 1°s and decreased in presumptive 2°s. We conclude that RAP-1 is a positive regulator that promotes Ras-dependent inductive fate decisions. We hypothesize that PXF-1 activation of RAP-1 serves as a minor parallel input into the major LET-60/Ras signal through LIN-45/Raf.
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Affiliation(s)
- Neal R Rasmussen
- Institute of Biosciences and Technology, College of Medicine, Texas A&M University, Houston, Texas 77030
| | - Daniel J Dickinson
- Department of Molecular Biosciences, University of Texas, Austin, Texas 78705
| | - David J Reiner
- Institute of Biosciences and Technology, College of Medicine, Texas A&M University, Houston, Texas 77030
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8
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Dorot O, Steller H, Segal D, Horowitz M. Past1 Modulates Drosophila Eye Development. PLoS One 2017; 12:e0169639. [PMID: 28060904 PMCID: PMC5218476 DOI: 10.1371/journal.pone.0169639] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2016] [Accepted: 12/20/2016] [Indexed: 11/24/2022] Open
Abstract
Endocytosis is a multi-step process involving a large number of proteins, both general factors, such as clathrin and adaptor protein complexes, and unique proteins, which modulate specialized endocytic processes, like the EHD proteins. EHDs are a family of Eps15 Homology Domain containing proteins that consists of four mammalian homologs, one C. elegans, one Drosophila melanogaster and two plants orthologs. These membrane-associated proteins are involved in different steps of endocytic trafficking pathways. We have previously shown that the Drosophila EHD ortholog, PAST1, associates predominantly with the plasma membrane. Mutations in Past1 result in defects in endocytosis, male sterility, temperature sensitivity and premature death of the flies. Also, Past1 genetically interacts with Notch. In the present study, we investigated the role of PAST1 in the developing fly eye. In mutant flies lacking PAST1, abnormal differentiation of photoreceptors R1, R6 and R7 was evident, with partial penetrance. Likewise, five cone cells were present instead of four. Expression of transgenic PAST1 resulted in a dominant negative effect, with a phenotype similar to that of the deletion mutant, and appearance of additional inter-ommatidial pigment cells. Our results strongly suggest a role for PAST1 in differentiation of photoreceptors R1/R6/R7 and cone cells of the fly ommatidia.
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Affiliation(s)
- Orly Dorot
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
| | - Hermann Steller
- Howard Hughes Medical Institute, Strang Laboratory of Cancer Research, The Rockefeller University, New York, New York, United States of America
| | - Daniel Segal
- Department of Molecular Microbiology and Biotechnology and the Interdisciplinary Sagol School of Neurosciences, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
| | - Mia Horowitz
- Department of Cell Research and Immunology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Ramat Aviv, Israel
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9
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Apical accumulation of the Sevenless receptor tyrosine kinase during Drosophila eye development is promoted by the small GTPase Rap1. Genetics 2014; 197:1237-50. [PMID: 24899161 DOI: 10.1534/genetics.114.166272] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The Ras/MAPK-signaling pathway plays pivotal roles during development of metazoans by controlling cell proliferation and cell differentiation elicited, in several instances, by receptor tyrosine kinases (RTKs). While the internal mechanism of RTK-driven Ras/MAPK signaling is well understood, far less is known regarding its interplay with other co-required signaling events involved in developmental decisions. In a genetic screen designed to identify new regulators of RTK/Ras/MAPK signaling during Drosophila eye development, we identified the small GTPase Rap1, PDZ-GEF, and Canoe as components contributing to Ras/MAPK-mediated R7 cell differentiation. Rap1 signaling has recently been found to participate in assembling cadherin-based adherens junctions in various fly epithelial tissues. Here, we show that Rap1 activity is required for the integrity of the apical domains of developing photoreceptor cells and that reduced Rap1 signaling hampers the apical accumulation of the Sevenless RTK in presumptive R7 cells. It thus appears that, in addition to its role in cell-cell adhesion, Rap1 signaling controls the partitioning of the epithelial cell membrane, which in turn influences signaling events that rely on apico-basal cell polarity.
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10
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Abstract
The developing Drosophila ommatidium is characterized by two distinct waves of pattern formation. In the first wave, a precluster of five cells is formed by a complex cellular interaction mechanism. In the second wave, cells are systematically recruited to the cluster and directed to their fates by developmental cues presented by differentiating precluster cells. These developmental cues are mediated through the receptor tyrosine kinase (RTK) and Notch (N) signaling pathways and their combined activities are crucial in specifying cell type. The transcription factor Lozenge (Lz) is expressed exclusively in second wave cells. Here, we ectopically supply Lz to precluster cells and concomitantly supply the various RTK/N codes that specify each of three second wave cell fates. We thereby reproduce molecular markers of each of the second wave cell types in precluster cells and draw three inferences. First, we confirm that Lz provides key intrinsic information to second wave cells. We can now combine this with the RTK/N signaling to provide a cell fate specification code that entails both extrinsic and intrinsic information. Second, the reproduction of each second wave cell type in the precluster confirms the accuracy of the RTK/N signaling code. Third, RTK/N signaling and Lz need only be presented to the cells for a short period of time in order to specify their fate.
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Affiliation(s)
- Yannis Emmanuel Mavromatakis
- Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, 701 West 168th Street, New York, NY 10032, USA
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Eguchi K, Yoshioka Y, Yoshida H, Morishita K, Miyata S, Hiai H, Yamaguchi M. The Drosophila DOCK family protein sponge is involved in differentiation of R7 photoreceptor cells. Exp Cell Res 2013; 319:2179-95. [DOI: 10.1016/j.yexcr.2013.05.024] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2013] [Revised: 05/16/2013] [Accepted: 05/18/2013] [Indexed: 01/17/2023]
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12
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Mavromatakis YE, Tomlinson A. Stop and go: antagonistic signals in the specification of the Drosophila R7 photoreceptor viewed from an evolutionary perspective. Fly (Austin) 2012; 6:228-33. [PMID: 22878552 DOI: 10.4161/fly.21102] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
The Drosophila R7 photoreceptor precursor is directed to its fate by signals from adjacent cells that activate its Receptor Tyrosine Kinase (RTK) and Notch (N) signaling pathways. Counter-intuitively, the N activity both promotes and inhibits the photoreceptor fate in the R7 precursor. We offer an evolutionary perspective for this in which earlier ommatidia had fewer photoreceptors and used N to inhibit the addition of any more. When additional photoreceptors were added by evolution, an RTK signal was used to overcome the N inhibition in these cells, and these new additions potently activated N in their neighboring cells, preventing them from also responding to the RTK signal. The R7 precursor also receives this block, and requires robust RTK activation for it to become a photoreceptor. This is achieved by N transcriptionally activating a new RTK, one that is potently activated in the R7 precursor and sufficing to overcome the N inhibition. The unusually high RTK signal in R7 requires additional transduction components not needed when the signal is mild; in R7 the small GTPases Ras and Rap are both required to transduce the signal, but in other photoreceptors Ras alone suffices.
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