1
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Sakagami H, Shiroshima T, Nemoto N, Niimura T, Sugawara T, Hara Y, Saito K, Okubo T, Fukaya M. Disruption of Iqsec1 in mice leads to embryonic lethality with reduced large apical vacuoles in the visceral endoderm. FEBS Lett 2025; 599:581-591. [PMID: 39561249 DOI: 10.1002/1873-3468.15058] [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: 08/30/2024] [Revised: 10/01/2024] [Accepted: 10/24/2024] [Indexed: 11/21/2024]
Abstract
Iqsec1 (IQ motif and Sec7 domain-containing protein 1), also known as BRAG2 (Brefeldin A-resistant Arf-GEF 2), is a guanine nucleotide exchange factor that regulates membrane trafficking, cytoskeletal organization, and signal transduction by activating class II and III ADP-ribosylation factors. To investigate the physiological role of Iqsec1 at the whole animal level, we generated Iqsec1-deficient mice using CRISPR/Cas9-mediated gene editing. Nearly all Iqsec1-/- mice (99%) exhibited embryonic lethality with severe growth retardation. Electron microscopy revealed that Iqsec1-/- embryos at embryonic day 8.5 lacked large apical vacuoles in visceral endoderm cells of the yolk sac, compared with controls. These findings suggest that Iqsec1 plays a critical role in embryogenesis, likely through regulation of membrane trafficking in visceral endoderm cells.
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Affiliation(s)
- Hiroyuki Sakagami
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Tomoko Shiroshima
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Noriko Nemoto
- Bio-imaging Center, Kitasato University School of Medicine, Sagamihara, Japan
| | - Tomoko Niimura
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Takeyuki Sugawara
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Yoshinobu Hara
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Koji Saito
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
| | - Tadashi Okubo
- Department of Laboratory Animal Science, Kitasato University School of Medicine, Sagamihara, Japan
| | - Masahiro Fukaya
- Department of Anatomy, Kitasato University School of Medicine, Sagamihara, Japan
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2
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Kidd T, Evans T. Analysis of Axon Guidance in the Drosophila Embryo. Cold Spring Harb Protoc 2024; 2024:pdb.top108109. [PMID: 37419653 DOI: 10.1101/pdb.top108109] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 07/09/2023]
Abstract
The establishment of neural connectivity is a major part of neural development. The central nervous system (CNS) midline is the most characterized axon guidance choice point, and work in Drosophila has played a pivotal role in understanding the molecular mechanisms responsible. Axons respond to attractive cues such as Netrin via the Frazzled receptor, and repulsive cues such as Slit via Robo receptors. Both signals are expressed at the CNS midline, affect pioneer axons, and have dramatic effects on the axon scaffold as a whole. Here, we focus on previous research analyzing classic mutants in the Slit/Robo pathway, which can readily be detected with a dissecting microscope. We also discuss analyzing these mutants in a teaching lab situation. The combination of sophisticated genetics and reliable axonal markers in Drosophila allows phenotypic analysis to be performed at the single-cell level. The elaborate architecture of neurons is very sensitive to disruption by genetic mutations, allowing the effects of novel mutations to be easily detected and assessed.
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Affiliation(s)
- Thomas Kidd
- Department of Biology, University of Nevada, Reno, Nevada 89557, USA
| | - Timothy Evans
- Department of Biological Sciences, University of Arkansas, Fayetteville, Arkansas 72701, USA
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3
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Lübke S, Braukmann C, Rexer KH, Cigoja L, Rout P, Önel SF. The Abl-interactor Abi suppresses the function of the BRAG2 GEF family member Schizo. Biol Open 2024; 13:bio058666. [PMID: 34897417 PMCID: PMC10810563 DOI: 10.1242/bio.058666] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2021] [Accepted: 11/27/2021] [Indexed: 11/20/2022] Open
Abstract
Guanine nucleotide exchange factors (GEF) of the BRAG subfamily activate small Arf GTPases, which are pivotal regulators of intracellular membrane traffic and actin dynamics. Consequently, BRAG proteins have been implicated to regulate the surface levels of adhesive and signaling receptors. However, not much is known about the mechanism leading to the regulation of these surface proteins. In this study, we found that the Drosophila BRAG GEF Schizo interacts physically with the Abl-interactor (Abi). schizo mutants display severe defects in myoblast fusion during syncytial muscle formation and show increased amounts of the cell adhesion protein N-cadherin. We demonstrate that the schizo myoblast fusion phenotype can be rescued by the expression of the Schizo GEF (Sec7) and membrane-binding (pleckstrin homology) domain. Furthermore, the expression of the Sec7-PH domain in a wild-type background decreases the amounts of N-cadherin and impairs myoblast fusion. These findings support the notion that the Sec7-PH domain serves as a constitutive-active form of Schizo. Using a yeast-two hybrid assay, we show that the SH3 domain of Abi interacts with the N-terminal region of Schizo. This region is also able to bind to the cytodomain of the cell adhesion molecule N-cadherin. To shed light on the function of Schizo and Abi in N-cadherin removal, we employed epistasis experiments in different developmental contexts of Drosophila. These studies point towards a new model for the regulation of Schizo. We propose that the binding of Abi to the N-terminal part of Schizo antagonizes Schizo function to inhibit N-cadherin removal.
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Affiliation(s)
- Stefanie Lübke
- Fachbereich Medizin, Department for Molecular Cell Physiology, Institute for Physiology and Pathophysiology, Philipps-Universität Marburg, Emil-Mannkopff-Str. 2, 35037 Marburg, Germany
- Fachbereich Biologie, Department for Developmental Biology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodeling, GRK 2213, Philipps-Universität Marburg, Marburg, Germany
| | - Carina Braukmann
- Fachbereich Biologie, Department for Developmental Biology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
| | - Karl-Heinz Rexer
- Fachbereich Biologie, Department for Biodiversity of Plants, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
| | - Lubjinka Cigoja
- Fachbereich Biologie, Department for Developmental Biology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
| | - Pratiti Rout
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodeling, GRK 2213, Philipps-Universität Marburg, Marburg, Germany
- Fachbereich Biologie, Department for Molecular Embryology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
| | - Susanne F. Önel
- Fachbereich Medizin, Department for Molecular Cell Physiology, Institute for Physiology and Pathophysiology, Philipps-Universität Marburg, Emil-Mannkopff-Str. 2, 35037 Marburg, Germany
- Fachbereich Biologie, Department for Developmental Biology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
- DFG Research Training Group, Membrane Plasticity in Tissue Development and Remodeling, GRK 2213, Philipps-Universität Marburg, Marburg, Germany
- Fachbereich Biologie, Department for Molecular Embryology, Philipps-Universität Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany
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4
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Mountford HS, Hill A, Barnett AL, Newbury DF. Genome-Wide Association Study of Motor Coordination. Front Hum Neurosci 2021; 15:669902. [PMID: 34177493 PMCID: PMC8219980 DOI: 10.3389/fnhum.2021.669902] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Accepted: 05/10/2021] [Indexed: 11/13/2022] Open
Abstract
The ability to finely control our movement is key to achieving many of the educational milestones and life-skills we develop throughout our lives. Despite the centrality of coordination to early development, there is a vast gap in our understanding of the underlying biology. Like most complex traits, both genetics and environment influence motor coordination, however, the specific genes, early environmental risk factors and molecular pathways are unknown. Previous studies have shown that about 5% of school-age children experience unexplained difficulties with motor coordination. These children are said to have Developmental Coordination Disorder (DCD). For children with DCD, these motor coordination difficulties significantly impact their everyday life and learning. DCD is associated with poorer academic achievement, reduced quality of life, it can constrain career opportunities and increase the risk of mental health issues in adulthood. Despite the high prevalence of coordination difficulties, many children remain undiagnosed by healthcare professionals. Compounding under-diagnosis in the clinic, research into the etiology of DCD is severely underrepresented in the literature. Here we present the first genome-wide association study to examine the genetic basis of early motor coordination in the context of motor difficulties. Using data from the Avon Longitudinal Study of Parents and Children we generate a derived measure of motor coordination from four components of the Movement Assessment Battery for Children, providing an overall measure of coordination across the full range of ability. We perform the first genome-wide association analysis focused on motor coordination (N = 4542). No single nucleotide polymorphisms (SNPs) met the threshold for genome-wide significance, however, 59 SNPs showed suggestive associations. Three regions contained multiple suggestively associated SNPs, within five preliminary candidate genes: IQSEC1, LRCC1, SYNJ2B2, ADAM20, and ADAM21. Association to the gene IQSEC1 suggests a potential link to axon guidance and dendritic projection processes as a potential underlying mechanism of motor coordination difficulties. This represents an interesting potential mechanism, and whilst further validation is essential, it generates a direct window into the biology of motor coordination difficulties. This research has identified potential biological drivers of DCD, a first step towards understanding this common, yet neglected neurodevelopmental disorder.
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Affiliation(s)
- Hayley S. Mountford
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, United Kingdom
| | - Amanda Hill
- Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, United Kingdom
| | - Anna L. Barnett
- Centre for Psychological Research, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, United Kingdom
| | - Dianne F. Newbury
- Department of Biological and Medical Sciences, Faculty of Health and Life Sciences, Oxford Brookes University, Oxford, United Kingdom
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5
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Rozés-Salvador V, González-Billault C, Conde C. The Recycling Endosome in Nerve Cell Development: One Rab to Rule Them All? Front Cell Dev Biol 2020; 8:603794. [PMID: 33425908 PMCID: PMC7793921 DOI: 10.3389/fcell.2020.603794] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2020] [Accepted: 11/11/2020] [Indexed: 12/13/2022] Open
Abstract
Endocytic recycling is an intracellular process that returns internalized molecules back to the plasma membrane and plays crucial roles not only in the reuse of receptor molecules but also in the remodeling of the different components of this membrane. This process is required for a diversity of cellular events, including neuronal morphology acquisition and functional regulation, among others. The recycling endosome (RE) is a key vesicular component involved in endocytic recycling. Recycling back to the cell surface may occur with the participation of several different Rab proteins, which are master regulators of membrane/protein trafficking in nerve cells. The RE consists of a network of interconnected and functionally distinct tubular subdomains that originate from sorting endosomes and transport their cargoes along microtubule tracks, by fast or slow recycling pathways. Different populations of REs, particularly those formed by Rab11, Rab35, and Arf6, are associated with a myriad of signaling proteins. In this review, we discuss the cumulative evidence suggesting the existence of heterogeneous domains of REs, controlling different aspects of neurogenesis, with a particular focus on the commonalities and singularities of these REs and their contribution to nerve development and differentiation in several animal models.
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Affiliation(s)
- Victoria Rozés-Salvador
- Instituto de Investigación Médica Mercedes y Martín Ferreyra INIMEC-CONICET-UNC, Córdoba, Argentina.,Instituto de Ciencias Básicas, Universidad Nacional de Villa María, Córdoba, Argentina
| | - Christian González-Billault
- Department of Biology, Faculty of Sciences, Universidad de Chile, Santiago, Chile.,Department of Neurosciences, Faculty of Medicine, Universidad de Chile, Santiago, Chile.,Geroscience Center for Brain Health and Metabolism, Santiago, Chile.,The Buck Institute for Research on Aging, Novato, CA, United States
| | - Cecilia Conde
- Instituto de Investigación Médica Mercedes y Martín Ferreyra INIMEC-CONICET-UNC, Córdoba, Argentina
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6
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Ansar M, Chung HL, Al-Otaibi A, Elagabani MN, Ravenscroft TA, Paracha SA, Scholz R, Abdel Magid T, Sarwar MT, Shah SF, Qaisar AA, Makrythanasis P, Marcogliese PC, Kamsteeg EJ, Falconnet E, Ranza E, Santoni FA, Aldhalaan H, Al-Asmari A, Faqeih EA, Ahmed J, Kornau HC, Bellen HJ, Antonarakis SE. Bi-allelic Variants in IQSEC1 Cause Intellectual Disability, Developmental Delay, and Short Stature. Am J Hum Genet 2019; 105:907-920. [PMID: 31607425 DOI: 10.1016/j.ajhg.2019.09.013] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Accepted: 09/11/2019] [Indexed: 12/30/2022] Open
Abstract
We report two consanguineous families with probands that exhibit intellectual disability, developmental delay, short stature, aphasia, and hypotonia in which homozygous non-synonymous variants were identified in IQSEC1 (GenBank: NM_001134382.3). In a Pakistani family, the IQSEC1 segregating variant is c.1028C>T (p.Thr343Met), while in a Saudi Arabian family the variant is c.962G>A (p.Arg321Gln). IQSEC1-3 encode guanine nucleotide exchange factors for the small GTPase ARF6 and their loss affects a variety of actin-dependent cellular processes, including AMPA receptor trafficking at synapses. The ortholog of IQSECs in the fly is schizo and its loss affects growth cone guidance at the midline in the CNS, also an actin-dependent process. Overexpression of the reference IQSEC1 cDNA in wild-type flies is lethal, but overexpression of the two variant IQSEC1 cDNAs did not affect viability. Loss of schizo caused embryonic lethality that could be rescued to 2nd instar larvae by moderate expression of the human reference cDNA. However, the p.Arg321Gln and p.Thr343Met variants failed to rescue embryonic lethality. These data indicate that the variants behave as loss-of-function mutations. We also show that schizo in photoreceptors is required for phototransduction. Finally, mice with a conditional Iqsec1 deletion in cortical neurons exhibited an increased density of dendritic spines with an immature morphology. The phenotypic similarity of the affecteds and the functional experiments in flies and mice indicate that IQSEC1 variants are the cause of a recessive disease with intellectual disability, developmental delay, and short stature, and that axonal guidance and dendritic projection defects as well as dendritic spine dysgenesis may underlie disease pathogenesis.
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7
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Kinoshita-Kawada M, Hasegawa H, Hongu T, Yanagi S, Kanaho Y, Masai I, Mishima T, Chen X, Tsuboi Y, Rao Y, Yuasa-Kawada J, Wu JY. A crucial role for Arf6 in the response of commissural axons to Slit. Development 2019; 146:dev172106. [PMID: 30674481 PMCID: PMC6382006 DOI: 10.1242/dev.172106] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2018] [Accepted: 01/14/2019] [Indexed: 12/23/2022]
Abstract
A switch in the response of commissural axons to the repellent Slit is crucial for ensuring that they cross the ventral midline only once. However, the underlying mechanisms remain to be elucidated. We have found that both endocytosis and recycling of Robo1 receptor are crucial for modulating Slit sensitivity in vertebrate commissural axons. Robo1 endocytosis and its recycling back to the cell surface maintained the stability of axonal Robo1 during Slit stimulation. We identified Arf6 guanosine triphosphatase and its activators, cytohesins, as previously unknown components in Slit-Robo1 signalling in vertebrate commissural neurons. Slit-Robo1 signalling activated Arf6. The Arf6-deficient mice exhibited marked defects in commissural axon midline crossing. Our data showed that a Robo1 endocytosis-triggered and Arf6-mediated positive-feedback strengthens the Slit response in commissural axons upon their midline crossing. Furthermore, the cytohesin-Arf6 pathways modulated this self-enhancement of the Slit response before and after midline crossing, resulting in a switch that reinforced robust regulation of axon midline crossing. Our study provides insights into endocytic trafficking-mediated mechanisms for spatiotemporally controlled axonal responses and uncovers new players in the midline switch in Slit responsiveness of commissural axons.
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Affiliation(s)
- Mariko Kinoshita-Kawada
- Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan
- Department of Neurology, Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
- Department of Neurology, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan
| | - Hiroshi Hasegawa
- Department of Physiological Chemistry, Faculty of Medicine and Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Tsunaki Hongu
- Department of Physiological Chemistry, Faculty of Medicine and Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Shigeru Yanagi
- Laboratory of Molecular Biochemistry, School of Life Sciences, Tokyo University of Pharmacy and Life Sciences, Hachioji, Tokyo 192-0392, Japan
| | - Yasunori Kanaho
- Department of Physiological Chemistry, Faculty of Medicine and Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
| | - Ichiro Masai
- Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan
| | - Takayasu Mishima
- Department of Neurology, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan
| | - Xiaoping Chen
- Department of Neurology, Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
| | - Yoshio Tsuboi
- Department of Neurology, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan
| | - Yi Rao
- State Key Laboratory of Biomembrane and Membrane Biology, Peking-Tsinghua Center for Life Sciences, PKU-IDG/McGovern Institute for Brain Research, Peking University School of Life Sciences, Beijing 100871, China
| | - Junichi Yuasa-Kawada
- Developmental Neurobiology Unit, Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan
- Department of Neurology, Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
- Department of Neurology, Faculty of Medicine, Fukuoka University, Fukuoka 814-0180, Japan
- Center for Advanced Medical Innovation, Kyushu University, Fukuoka 812-8582, Japan
- Department of Clinical Chemistry and Laboratory Medicine, Kyushu University Graduate School of Medical Sciences, Fukuoka 812-8582, Japan
| | - Jane Y Wu
- Department of Neurology, Lurie Comprehensive Cancer Center, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA
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8
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EGFR/ARF6 regulation of Hh signalling stimulates oncogenic Ras tumour overgrowth. Nat Commun 2017; 8:14688. [PMID: 28281543 PMCID: PMC5353614 DOI: 10.1038/ncomms14688] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2016] [Accepted: 01/20/2017] [Indexed: 12/15/2022] Open
Abstract
Multiple signalling events interact in cancer cells. Oncogenic Ras cooperates with Egfr, which cannot be explained by the canonical signalling paradigm. In turn, Egfr cooperates with Hedgehog signalling. How oncogenic Ras elicits and integrates Egfr and Hedgehog signals to drive overgrowth remains unclear. Using a Drosophila tumour model, we show that Egfr cooperates with oncogenic Ras via Arf6, which functions as a novel regulator of Hh signalling. Oncogenic Ras induces the expression of Egfr ligands. Egfr then signals through Arf6, which regulates Hh transport to promote Hh signalling. Blocking any step of this signalling cascade inhibits Hh signalling and correspondingly suppresses the growth of both, fly and human cancer cells harbouring oncogenic Ras mutations. These findings highlight a non-canonical Egfr signalling mechanism, centered on Arf6 as a novel regulator of Hh signalling. This explains both, the puzzling requirement of Egfr in oncogenic Ras-mediated overgrowth and the cooperation between Egfr and Hedgehog. EGFR signalling is required for oncogenic Ras driven tumorigenesis. In this study, using a Drosophila tumour model the authors demonstrate that depletion of Arf6, a Ras-related GTP-binding protein activated by EGFR, supresses oncogenic Ras driven overgrowth via modulation of Hedgehog signalling.
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9
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Grossmann AH, Zhao H, Jenkins N, Zhu W, Richards JR, Yoo JH, Winter JM, Rich B, Mleynek TM, Li DY, Odelberg SJ. The small GTPase ARF6 regulates protein trafficking to control cellular function during development and in disease. Small GTPases 2016; 10:1-12. [PMID: 28001501 DOI: 10.1080/21541248.2016.1259710] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
The activation of the small GTPase ARF6 has been implicated in promoting several pathological processes related to vascular instability and tumor formation, growth, and metastasis. ARF6 also plays a vital role during embryonic development. Recent studies have suggested that ARF6 carries out these disparate functions primarily by controlling protein trafficking within the cell. ARF6 helps direct proteins to intracellular or extracellular locations where they function in normal cellular responses during development and in pathological processes later in life. This transport of proteins is accomplished through a variety of mechanisms, including endocytosis and recycling, microvesicle release, and as yet uncharacterized processes. This Commentary will explore the functions of ARF6, while focusing on the role of this small GTPase in development and postnatal physiology, regulating barrier function and diseases associated with its loss, and tumor formation, growth, and metastasis.
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Affiliation(s)
- Allie H Grossmann
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,b Department of Pathology , University of Utah , Salt Lake City , UT , USA.,c ARUP Laboratories, University of Utah , Salt Lake City , UT , USA
| | - Helong Zhao
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Noah Jenkins
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Weiquan Zhu
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,d Department of Medicine , Division of Cardiovascular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Jackson R Richards
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,e Department of Oncological Sciences , University of Utah , Salt Lake City , UT , USA
| | - Jae Hyuk Yoo
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,e Department of Oncological Sciences , University of Utah , Salt Lake City , UT , USA
| | - Jacob M Winter
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Bianca Rich
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Tara M Mleynek
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA
| | - Dean Y Li
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,d Department of Medicine , Division of Cardiovascular Medicine, University of Utah , Salt Lake City , UT , USA.,e Department of Oncological Sciences , University of Utah , Salt Lake City , UT , USA.,f Department of Human Genetics , University of Utah , Salt Lake City , UT , USA.,g Sichuan Provincial Key Laboratory for Human Disease Gene Study , Sichuan Provincial People's Hospital, Chinese Academy of Sciences , Chengdu , China.,h Department of Cardiology , VA Salt Lake City Health Care System , Salt Lake City , UT , USA.,i Navigen Inc. , Salt Lake City , UT , USA
| | - Shannon J Odelberg
- a Department of Medicine , Program in Molecular Medicine, University of Utah , Salt Lake City , UT , USA.,d Department of Medicine , Division of Cardiovascular Medicine, University of Utah , Salt Lake City , UT , USA.,j Department of Neurobiology and Anatomy , University of Utah , Salt Lake City , UT , USA
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10
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Abstract
The IQSec/BRAG proteins are a subfamily of Arf-nucleotide exchange factors. Since their discovery almost 15 y ago, the BRAGs have been reported to be involved in diverse physiological processes from myoblast fusion, neuronal pathfinding and angiogenesis, to pathophysiological processes including X-linked intellectual disability and tumor metastasis. In this review we will address how, in each of these situations, the BRAGs are thought to regulate the surface levels of adhesive and signaling receptors. While in most cases BRAGs are thought to enhance the endocytosis of these receptors, how they achieve this remains unclear. Similarly, while all 3 BRAG proteins contain calmodulin-binding IQ motifs, little is known about how their activities might be regulated by calcium. These are some of the questions that are likely to form the basis of future research.
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Affiliation(s)
- Ryan S D'Souza
- a Department of Cell Biology , University of Virginia Health System , Charlottesville , VA , USA
| | - James E Casanova
- a Department of Cell Biology , University of Virginia Health System , Charlottesville , VA , USA
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11
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Kashi VP, Hatley ME, Galindo RL. Probing for a deeper understanding of rhabdomyosarcoma: insights from complementary model systems. Nat Rev Cancer 2015; 15:426-39. [PMID: 26105539 PMCID: PMC4599785 DOI: 10.1038/nrc3961] [Citation(s) in RCA: 87] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Rhabdomyosarcoma (RMS) is a mesenchymal malignancy composed of neoplastic primitive precursor cells that exhibit histological features of myogenic differentiation. Despite intensive conventional multimodal therapy, patients with high-risk RMS typically suffer from aggressive disease. The lack of directed therapies against RMS emphasizes the need to further uncover the molecular underpinnings of the disease. In this Review, we discuss the notable advances in the model systems now available to probe for new RMS-targetable pathogenetic mechanisms, and the possibilities for enhanced RMS therapeutics and improved clinical outcomes.
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Affiliation(s)
- Venkatesh P Kashi
- Department of Pathology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9072, USA
| | - Mark E Hatley
- Department of Oncology, St. Jude Children's Research Hospital, 262 Danny Thomas Place, Memphis, Tennessee 38105, USA
| | - Rene L Galindo
- 1] Department of Pathology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9072, USA. [2] Department of Molecular Biology, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9148, USA. [3] Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, 5323 Harry Hines Boulevard, Dallas, Texas 75390-9063, USA
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Ribeiro JMC, Genta FA, Sorgine MHF, Logullo R, Mesquita RD, Paiva-Silva GO, Majerowicz D, Medeiros M, Koerich L, Terra WR, Ferreira C, Pimentel AC, Bisch PM, Leite DC, Diniz MMP, Junior JLDSGV, Da Silva ML, Araujo RN, Gandara ACP, Brosson S, Salmon D, Bousbata S, González-Caballero N, Silber AM, Alves-Bezerra M, Gondim KC, Silva-Neto MAC, Atella GC, Araujo H, Dias FA, Polycarpo C, Vionette-Amaral RJ, Fampa P, Melo ACA, Tanaka AS, Balczun C, Oliveira JHM, Gonçalves RLS, Lazoski C, Rivera-Pomar R, Diambra L, Schaub GA, Garcia ES, Azambuja P, Braz GRC, Oliveira PL. An insight into the transcriptome of the digestive tract of the bloodsucking bug, Rhodnius prolixus. PLoS Negl Trop Dis 2014; 8:e2594. [PMID: 24416461 PMCID: PMC3886914 DOI: 10.1371/journal.pntd.0002594] [Citation(s) in RCA: 149] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2013] [Accepted: 11/04/2013] [Indexed: 12/14/2022] Open
Abstract
The bloodsucking hemipteran Rhodnius prolixus is a vector of Chagas' disease, which affects 7-8 million people today in Latin America. In contrast to other hematophagous insects, the triatomine gut is compartmentalized into three segments that perform different functions during blood digestion. Here we report analysis of transcriptomes for each of the segments using pyrosequencing technology. Comparison of transcript frequency in digestive libraries with a whole-body library was used to evaluate expression levels. All classes of digestive enzymes were highly expressed, with a predominance of cysteine and aspartic proteinases, the latter showing a significant expansion through gene duplication. Although no protein digestion is known to occur in the anterior midgut (AM), protease transcripts were found, suggesting secretion as pro-enzymes, being possibly activated in the posterior midgut (PM). As expected, genes related to cytoskeleton, protein synthesis apparatus, protein traffic, and secretion were abundantly transcribed. Despite the absence of a chitinous peritrophic membrane in hemipterans - which have instead a lipidic perimicrovillar membrane lining over midgut epithelia - several gut-specific peritrophin transcripts were found, suggesting that these proteins perform functions other than being a structural component of the peritrophic membrane. Among immunity-related transcripts, while lysozymes and lectins were the most highly expressed, several genes belonging to the Toll pathway - found at low levels in the gut of most insects - were identified, contrasting with a low abundance of transcripts from IMD and STAT pathways. Analysis of transcripts related to lipid metabolism indicates that lipids play multiple roles, being a major energy source, a substrate for perimicrovillar membrane formation, and a source for hydrocarbons possibly to produce the wax layer of the hindgut. Transcripts related to amino acid metabolism showed an unanticipated priority for degradation of tyrosine, phenylalanine, and tryptophan. Analysis of transcripts related to signaling pathways suggested a role for MAP kinases, GTPases, and LKBP1/AMP kinases related to control of cell shape and polarity, possibly in connection with regulation of cell survival, response of pathogens and nutrients. Together, our findings present a new view of the triatomine digestive apparatus and will help us understand trypanosome interaction and allow insights into hemipteran metabolic adaptations to a blood-based diet.
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Affiliation(s)
- José M. C. Ribeiro
- Section of Vector Biology, Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Rockville, Maryland, United States of America
| | - Fernando A. Genta
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Marcos H. F. Sorgine
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Raquel Logullo
- Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Rafael D. Mesquita
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Gabriela O. Paiva-Silva
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - David Majerowicz
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Marcelo Medeiros
- Instituto Nacional de Metrologia Qualidade e Tecnologia, Diretoria de Metrologia Aplicada às Ciências da Vida, Programa de Biotecnologia, Prédio 27, CEP 25250-020, Duque de Caxias, Rio de Janeiro, Brazil
| | - Leonardo Koerich
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Genética, Instituto de Biologia, Universidade Federal do Rio de Janeiro, CEP 21944-970, Rio de Janeiro, Brazil
| | - Walter R. Terra
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Clélia Ferreira
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - André C. Pimentel
- Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, Brazil
| | - Paulo M. Bisch
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Daniel C. Leite
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Michelle M. P. Diniz
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - João Lídio da S. G. V. Junior
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
- Center for Technological Innovation, Evandro Chagas Institute, Ananindeua, Pará, Brazil
| | - Manuela L. Da Silva
- Instituto Nacional de Metrologia Qualidade e Tecnologia, Diretoria de Metrologia Aplicada às Ciências da Vida, Programa de Biotecnologia, Prédio 27, CEP 25250-020, Duque de Caxias, Rio de Janeiro, Brazil
- Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Ricardo N. Araujo
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Parasitologia do Instituto de Ciências Biológicas da Universidade Federal de Minas Gerais, Belo Horizonte, Minas Gerais, Brazil
| | - Ana Caroline P. Gandara
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sébastien Brosson
- Institute for Molecular Biology and Medicine (IBMM), Université Libre de Bruxelles, Gosselies, Belgium
| | - Didier Salmon
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Sabrina Bousbata
- Institute for Molecular Biology and Medicine (IBMM), Université Libre de Bruxelles, Gosselies, Belgium
| | | | - Ariel Mariano Silber
- Departamento de Parasitologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, São Paulo, Brazil
| | - Michele Alves-Bezerra
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Katia C. Gondim
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Mário Alberto C. Silva-Neto
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Georgia C. Atella
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Helena Araujo
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Institute for Biomedical Sciences, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Felipe A. Dias
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Carla Polycarpo
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Raquel J. Vionette-Amaral
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Patrícia Fampa
- Instituto de Biologia, DBA, UFRRJ, Seropédica, Rio de Janeiro, Brazil
| | - Ana Claudia A. Melo
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Aparecida S. Tanaka
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Bioquímica, Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, Brazil
| | - Carsten Balczun
- Zoology/Parasitology Group, Ruhr-Universität, Bochum, Germany
| | - José Henrique M. Oliveira
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Renata L. S. Gonçalves
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
| | - Cristiano Lazoski
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Departamento de Genética, Instituto de Biologia, Universidade Federal do Rio de Janeiro, CEP 21944-970, Rio de Janeiro, Brazil
| | - Rolando Rivera-Pomar
- Centro Regional de Estudios Genomicos, Universidad Nacional de La Plata, Florencio Varela, Argentina
- Centro de Bioinvestigaciones, Universidad Nacional del Noroeste de Buenos Aires, Pergamino, Argentina
| | - Luis Diambra
- Centro Regional de Estudios Genomicos, Universidad Nacional de La Plata, Florencio Varela, Argentina
| | | | - Elói S. Garcia
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Patrícia Azambuja
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto Oswaldo Cruz, Fundação Oswaldo Cruz, Rio de Janeiro, Rio de Janeiro, Brazil
| | - Glória R. C. Braz
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Department of Biochemistry, Institute of Chemistry, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
| | - Pedro L. Oliveira
- Instituto Nacional de Ciência e Tecnologia em Entomologia Molecular, Federal University of Rio de Janeiro, Rio de Janeiro, Brazil
- Instituto de Bioquímica Médica, Programa de Biotecnologia e Biologia Molecular, Universidade Federal do Rio de Janeiro, Rio de Janeiro, Brazil
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The Arf-GEF Schizo/Loner regulates N-cadherin to induce fusion competence of Drosophila myoblasts. Dev Biol 2012; 368:18-27. [DOI: 10.1016/j.ydbio.2012.04.031] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2011] [Revised: 03/30/2012] [Accepted: 04/27/2012] [Indexed: 01/19/2023]
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Abstract
The fusion of myoblasts into multinucleate syncytia plays a fundamental role in muscle function, as it supports the formation of extended sarcomeric arrays, or myofibrils, within a large volume of cytoplasm. Principles learned from the study of myoblast fusion not only enhance our understanding of myogenesis, but also contribute to our perspectives on membrane fusion and cell-cell fusion in a wide array of model organisms and experimental systems. Recent studies have advanced our views of the cell biological processes and crucial proteins that drive myoblast fusion. Here, we provide an overview of myoblast fusion in three model systems that have contributed much to our understanding of these events: the Drosophila embryo; developing and regenerating mouse muscle; and cultured rodent muscle cells.
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Affiliation(s)
- Susan M Abmayr
- Stowers Institute for Medical Research, Kansas City, MO 64110, USA.
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15
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Johnson RI, Sedgwick A, D'Souza-Schorey C, Cagan RL. Role for a Cindr-Arf6 axis in patterning emerging epithelia. Mol Biol Cell 2011; 22:4513-26. [PMID: 21976699 PMCID: PMC3226471 DOI: 10.1091/mbc.e11-04-0305] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The fly pupal eye is used to explore dArf6 activity regulated by the Arf GTPase–activating proteins (ArfGAPs) dAsap and dArfGAP3 and Arf GTP exchange factors Schizo and dPsd, which promote cellular extensions that presage cell rearrangements. The adaptor protein Cindr bound to dArfGAP3 and dAsap to sequester ArfGAP function to Neph1/nephrin adhesion complexes, liberating active dArf6 elsewhere. Patterning of the Drosophila pupal eye is characterized by precise cell movements. In this paper, we demonstrate that these movements require an Arf regulatory cycle that connects surface receptors to actin-based movement. dArf6 activity—regulated by the Arf GTPase–activating proteins (ArfGAPs) dAsap and dArfGAP3 and the Arf GTP exchange factors Schizo and dPsd—promoted large cellular extensions; time-lapse microscopy indicated that these extensions presage cell rearrangements into correct epithelial niches. During this process, the Drosophila eye also requires interactions between surface Neph1/nephrin adhesion receptors Roughest and Hibris, which bind the adaptor protein Cindr (CD2AP). We provide evidence that Cindr forms a physical complex with dArfGAP3 and dAsap. Our data suggest this interaction sequesters ArfGAP function to liberate active dArf6 elsewhere in the cell. We propose that a Neph1/nephrin–Cindr/ArfGAP complex accumulates to limit local Arf6 activity and stabilize adherens junctions. Our model therefore links surface adhesion via an Arf6 regulatory cascade to dynamic modeling of the cytoskeleton, accounting for precise cell movements that organize the functional retinal field. Further, we demonstrate a similar relationship between the mammalian Cindr orthologue CD2AP and Arf6 activity in cell motility assays. We propose that this Cindr/CD2AP-mediated regulation of Arf6 is a widely used mechanism in emerging epithelia.
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Affiliation(s)
- Ruth I Johnson
- Department of Developmental and Regenerative Biology, Mount Sinai School of Medicine, New York, NY 10029, USA
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16
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Haralalka S, Abmayr SM. Myoblast fusion in Drosophila. Exp Cell Res 2010; 316:3007-13. [PMID: 20580706 DOI: 10.1016/j.yexcr.2010.05.018] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2010] [Revised: 05/13/2010] [Accepted: 05/17/2010] [Indexed: 10/19/2022]
Abstract
The body wall musculature of a Drosophila larva is composed of an intricate pattern of 30 segmentally repeated muscle fibers in each abdominal hemisegment. Each muscle fiber has unique spatial and behavioral characteristics that include its location, orientation, epidermal attachment, size and pattern of innervation. Many, if not all, of these properties are dictated by founder cells, which determine the muscle pattern and seed the fusion process. Myofibers are then derived from fusion between a specific founder cell and several fusion competent myoblasts (FCMs) fusing with as few as 3-5 FCMs in the small muscles on the most ventral side of the embryo and as many as 30 FCMs in the larger muscles on the dorsal side of the embryo. The focus of the present review is the formation of the larval muscles in the developing embryo, summarizing the major issues and players in this process. We have attempted to emphasize experimentally-validated details of the mechanism of myoblast fusion and distinguish these from the theoretically possible details that have not yet been confirmed experimentally. We also direct the interested reader to other recent reviews that discuss myoblast fusion in Drosophila, each with their own perspective on the process [1-4]. With apologies, we use gene nomenclature as specified by Flybase (http://flybase.org) but provide Table 1 with alternative names and references.
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Affiliation(s)
- Shruti Haralalka
- Stowers Institute for Medical Research, 1000 E. 50th Street, Kansas City, MO 64110, USA
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17
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Abstract
In Drosophila, as in mammals, myoblast fusion is fundamental for development. This fusion process has two distinct phases that share common ultrastructural features and at least some molecular players between Drosophila and vertebrates. Here, we integrate the latest data on the key molecular players and ultrastructural features found during myoblast fusion into a new working model to explain this fundamental cellular process. At cell-cell contact sites, a protein complex (FuRMAS) serves as a signalling centre and might restrict the area of membrane fusion. The FuRMAS consists of a ring of cell adhesion molecules, signalling proteins, and F-actin. Regulated F-actin branching plays a pivotal role in myoblast fusion with regard to vesicle transport, fusion pore formation, and expansion as well as the integration of the fusion-competent myoblast into the growing myotube. Interestingly, local F-actin accumulation is a typical feature of other transient adhesive structures such as the immunological synapse, podosomes, and invadopodia. Developmental Dynamics 238:1513-1525, 2009. (c) 2009 Wiley-Liss, Inc.
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Affiliation(s)
- Susanne-Filiz Onel
- Philipps-Universität Marburg, Fachbereich Biologie, Entwicklungsbiologie, Marburg, Germany
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18
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Raghu P, Coessens E, Manifava M, Georgiev P, Pettitt T, Wood E, Garcia-Murillas I, Okkenhaug H, Trivedi D, Zhang Q, Razzaq A, Zaid O, Wakelam M, O'Kane CJ, Ktistakis N. Rhabdomere biogenesis in Drosophila photoreceptors is acutely sensitive to phosphatidic acid levels. ACTA ACUST UNITED AC 2009; 185:129-45. [PMID: 19349583 PMCID: PMC2700502 DOI: 10.1083/jcb.200807027] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Phosphatidic acid (PA) is postulated to have both structural and signaling functions during membrane dynamics in animal cells. In this study, we show that before a critical time period during rhabdomere biogenesis in Drosophila melanogaster photoreceptors, elevated levels of PA disrupt membrane transport to the apical domain. Lipidomic analysis shows that this effect is associated with an increase in the abundance of a single, relatively minor molecular species of PA. These transport defects are dependent on the activation state of Arf1. Transport defects via PA generated by phospholipase D require the activity of type I phosphatidylinositol (PI) 4 phosphate 5 kinase, are phenocopied by knockdown of PI 4 kinase, and are associated with normal endoplasmic reticulum to Golgi transport. We propose that PA levels are critical for apical membrane transport events required for rhabdomere biogenesis.
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Affiliation(s)
- Padinjat Raghu
- Inositide Laboratory, Babraham Institute, Babraham Research Campus, Cambridge, England, UK.
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19
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Abstract
AbstractSkeletal muscle formation, growth and repair depend on myoblast fusion events. Therefore, in-depth understanding of the underlying molecular mechanisms controlling these events that ultimately lead to skeletal muscle formation may be fundamental for developing new therapies for tissue repair. To this end, the greatest advances in furthering understanding myoblast fusion has been made in Drosophila. Recent studies have shown that transient F-actin structures, so-called actin plugs or foci, are known to form at the site of contacting myoblasts. Indeed, actin regulators of the WASP family that control the activation of the Arp2/3 complex and thereby branched F-actin formation have been demonstrated to be crucial for myoblast fusion. Myoblast-specific cell adhesion molecules seem to be involved in the recruitment of WASP family members to the site of myoblast fusion and form a Fusion-Restricted Myogenic-Adhesive Structure (FuRMAS). Currently, the exact role of the FuRMAS is not completely understood. However, recent studies indicate that WASP-dependent F-actin regulation is required for fusion pore formation as well as for the correct integration of fusing myoblasts into the growing muscle. In this review, I discuss latest cellular studies, and recent genetic and biochemical analyses on actin regulation during myoblast fusion.
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Abstract
Slit was identified in Drosophila embryo as a gene involved in the patterning of larval cuticle. It was later shown that Slit is synthesized in the fly central nervous system by midline glia cells. Slit homologues have since been found in C. elegans and many vertebrate species, from amphibians, fishes, birds to mammals. A single slit was isolated in invertebrates, whereas there are three slit genes (slit1-slit3) in mammals, that have around 60% homology. All encodes large ECM glycoproteins of about 200 kDa (Fig. 1A), comprising, from their N terminus to their C terminus, a long stretch of four leucine rich repeats (LRR) connected by disulphide bonds, seven to nine EGF repeats, a domain, named ALPS (Agrin, Perlecan, Laminin, Slit) or laminin G-like module (see ref 17), and a cystein knot (Fig. 1A). Alternative spliced transcripts have been reported for Drosophila Slit2, human Slit2 and Slit3, and Slit1. Moreover, two Slit1 isoforms exist in zebrafish as a consequence of gene duplication. Last, in mammals, two Slit2 isoforms can be purified from brain extracts, a long 200 kDa one and a shorter 150 kDa form (Slit2-N) that was shown to result from the proteolytic processing of full-length Slit2. Human Slit and Slit3 and Drosophila Slit are also cleaved by an unknown protease in a large N-terminal fragment and a shorter C-terminal fragment, suggesting conserved mechanisms for Slit cleavage across species. Moreover, Slit fragments have different cell association characteristics in cell culture suggesting that they may also have different extents of diffusion, different binding properties, and, hence, different functional activities in vivo. This conclusion is supported by in vitro data showing that full-length Slit2 functions as an antagonist of Slit2-N in the DRG branching assay, and that Slit2-N, not full-length Slit2, causes collapse of OB growth cones. In addition, Slit1-N and full-length Slit1 can induce branching of cortical neurons (see below), but only full-length Slit1 repels cortical axons. Structure-function analysis in vertebrates and Drosophila demonstrated that the LRRs of Slits are required and sufficient to mediate their repulsive activities in neurons. More recent detailed structure function analysis of the LRR domains of Drosophila Slit, revealed that the active site of Slit (at least regarding its pro-angiogenic activity) is located on the second of the fourth LRR (LRR2), which is highly conserved between Slits. Slit can also dimerize through the LRR4 domain and the cystein knot.However, a Slit1 spliced-variant that lacks the cysteine knot and does not dimerize is still able to repel OB axons.
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Andrews GL, Tanglao S, Farmer WT, Morin S, Brotman S, Berberoglu MA, Price H, Fernandez GC, Mastick GS, Charron F, Kidd T. Dscam guides embryonic axons by Netrin-dependent and -independent functions. Development 2008; 135:3839-48. [PMID: 18948420 DOI: 10.1242/dev.023739] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Developing axons are attracted to the CNS midline by Netrin proteins and other as yet unidentified signals. Netrin signals are transduced in part by Frazzled (Fra)/DCC receptors. Genetic analysis in Drosophila indicates that additional unidentified receptors are needed to mediate the attractive response to Netrin. Analysis of Bolwig's nerve reveals that Netrin mutants have a similar phenotype to Down Syndrome Cell Adhesion Molecule (Dscam) mutants. Netrin and Dscam mutants display dose sensitive interactions, suggesting that Dscam could act as a Netrin receptor. We show using cell overlay assays that Netrin binds to fly and vertebrate Dscam, and that Dscam binds Netrin with the same affinity as DCC. At the CNS midline, we find that Dscam and its paralog Dscam3 act redundantly to promote midline crossing. Simultaneous genetic knockout of the two Dscam genes and the Netrin receptor fra produces a midline crossing defect that is stronger than the removal of Netrin proteins, suggesting that Dscam proteins also function in a pathway parallel to Netrins. Additionally, overexpression of Dscam in axons that do not normally cross the midline is able to induce ectopic midline crossing, consistent with an attractive receptor function. Our results support the model that Dscam proteins function as attractive receptors for Netrin and also act in parallel to Frazzled/DCC. Furthermore, the results suggest that Dscam proteins have the ability to respond to multiple ligands and act as receptors for an unidentified midline attractive cue. These functions in axon guidance have implications for the pathogenesis of Down Syndrome.
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Affiliation(s)
- Gracie L Andrews
- Department of Biology/ms 314, University of Nevada, Reno, NV 89557, USA
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22
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Dyer N, Rebollo E, Domínguez P, Elkhatib N, Chavrier P, Daviet L, González C, González-Gaitán M. Spermatocyte cytokinesis requires rapid membrane addition mediated by ARF6 on central spindle recycling endosomes. Development 2008; 134:4437-47. [PMID: 18039970 DOI: 10.1242/dev.010983] [Citation(s) in RCA: 85] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
The dramatic cell shape changes during cytokinesis require the interplay between microtubules and the actomyosin contractile ring, and addition of membrane to the plasma membrane. Numerous membrane-trafficking components localize to the central spindle during cytokinesis, but it is still unclear how this machinery is targeted there and how membrane trafficking is coordinated with cleavage furrow ingression. Here we use an arf6 null mutant to show that the endosomal GTPase ARF6 is required for cytokinesis in Drosophila spermatocytes. ARF6 is enriched on recycling endosomes at the central spindle, but it is required neither for central spindle nor actomyosin contractile ring assembly, nor for targeting of recycling endosomes to the central spindle. However, in arf6 mutants the cleavage furrow regresses because of a failure in rapid membrane addition to the plasma membrane. We propose that ARF6 promotes rapid recycling of endosomal membrane stores during cytokinesis, which is critical for rapid cleavage furrow ingression.
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Affiliation(s)
- Naomi Dyer
- Max Planck Institute of Molecular Cell Biology and Genetics, Pfotenhauerstrasse 108, 01307 Dresden, Germany
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23
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Abstract
Myogenic differentiation in Drosophila melanogaster, as in many other organisms, involves the generation of multinucleate muscle fibers through the fusion of myoblasts. Prior to fusion, the myoblasts become specified as one of two distinct cell types. They then become competent to fuse and express genes associated with cell recognition and adhesion. Initially, cell-type- specific adhesion molecules mediate recognition and fusion between these two distinct populations of myoblasts. Intracellular proteins that are essential for the fusion process are then recruited to points of cell-cell contact at the membrane, where the cell surface molecules have become localized. Many of these cytosolic proteins contribute to reorganization of the cytoskeleton through activation of small guanosine triphosphatases and recruitment of actin nucleating proteins. Following the initial fusion event, the ultimate size of the syncytia is achieved through multiple rounds of fusion between the developing syncytia and mononucleate myoblasts. Ultrastructural changes associated with cell fusion include recruitment of electron-dense vesicles to points of cell-cell contact, resolution of these vesicles into fusion plaques, fusion pore formation, and membrane vesiculation. This chapter reviews our current understanding of the genes, pathways, and ultrastructural events associated with fusion in the Drosophila embryo, giving rise to multinucleate syncytia that will be used throughout larval life.
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Affiliation(s)
- Susan M Abmayr
- The Stowers Institute for Medical Research, Kansas City, MO, USA
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24
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Abstract
Small G proteins play a central role in the organization of the secretory and endocytic pathways. The majority of such small G proteins are members of the Rab family, which are anchored to the bilayer by C-terminal prenyl groups. However, the recruitment of some effectors, including vesicle coat proteins, is mediated by a second class of small G proteins that is unique in having an N-terminal amphipathic helix that becomes available for membrane insertion upon GTP binding. Sar1, Arf1, and Arf6 are the best-characterized members of this ADP-ribosylation factor (Arf) family. In addition, all eukaryotes contain additional distantly related G proteins, often called Arf like, or Arls. The complete Arf family in humans has 29 members. The roles of these related G proteins are poorly understood, but recent work has shown that some are involved in membrane traffic or organizing the cytoskeleton. Here we review what is known about all the members of the Arf family, along with the known regulatory molecules that convert them between GDP- and GTP-bound states.
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25
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Abstract
The ADP ribosylation factors (Arfs) are a family of small, ubiquitously expressed and evolutionarily conserved guanosine triphosphatases that are key regulators of vesicular transport in eukaryotic cells (D'Souza-Schorey C, Chavrier P. ARF proteins: roles in membrane traffic and beyond. Nat Rev Mol Cell Biol 2006;7:347-358). Although Arfs are best known for their role in the nucleation of coat protein assembly at a variety of intracellular locations, it is increasingly apparent that they are also integral components in a number of important signaling pathways that are regulated by extracellular cues. The activation of Arfs is catalyzed by a family of guanine nucleotide exchange factors (GEFs), referred to as the Sec7 family, based on homology of their catalytic domains to the yeast Arf GEF, sec7p. While there are only six mammalian Arfs, the human genome encodes 15 Sec7 family members, which can be divided into five classes based on related domain organization. Some of this diversity arises from the tissue-specific expression of certain isoforms, but all mammalian cells appear to express at least six Arf GEFs, suggesting that Arf activation is under extensive regulatory control. Here we review recent progress in our understanding of the structure, localization and biology of the different classes of Arf GEFs.
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Affiliation(s)
- James E Casanova
- Department of Cell Biology, University of Virginia Health System, Charlottesville, VA 22908-0732, USA.
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26
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Jaworski J. ARF6 in the nervous system. Eur J Cell Biol 2007; 86:513-24. [PMID: 17559968 DOI: 10.1016/j.ejcb.2007.04.007] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2007] [Revised: 04/11/2007] [Accepted: 04/18/2007] [Indexed: 01/19/2023] Open
Abstract
Actin cytoskeleton dynamics and membrane trafficking are tightly connected and are among the most important driving forces of neuronal development, basic synaptic transmission events, and synaptic plasticity. One group of proteins involved in coordination of these two processes is the family of ADP ribosylation factors (ARFs) regulating actin dynamics, lipid modification and membrane trafficking. ARF6 is the only member of the ARF family that can simultaneously regulate actin cytoskeleton changes and membrane exchange between plasma membrane and endocytic compartments. The presence of ARF6 and its guanine nucleotide exchange factors (GEFs) and GTPase-activating proteins (GAPs) in the brain, as well as its capability to regulate several aspects of neuronal development and synaptic plasticity, has been recently demonstrated. The main purpose of this review is to present the current knowledge about how ARF6 can influence morphological processes crucial for proper formation of the neuronal circuits in the brain, including dendrite and axon differentiation, development of dendritic arbor complexity and dendritic spine formation. Potential effects of ARF6 on synaptic events resulting from its ability to control exo- and endocytosis will be also discussed.
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Affiliation(s)
- Jacek Jaworski
- Laboratory of Molecular and Cell Neurobiology, International Institute of Molecular and Cell Biology, Ks. Trojdena St. 4, PL-02-109, Warsaw, Poland.
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27
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Sánchez-Soriano N, Tear G, Whitington P, Prokop A. Drosophila as a genetic and cellular model for studies on axonal growth. Neural Dev 2007; 2:9. [PMID: 17475018 PMCID: PMC1876224 DOI: 10.1186/1749-8104-2-9] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2007] [Accepted: 05/02/2007] [Indexed: 11/10/2022] Open
Abstract
One of the most fascinating processes during nervous system development is the establishment of stereotypic neuronal networks. An essential step in this process is the outgrowth and precise navigation (pathfinding) of axons and dendrites towards their synaptic partner cells. This phenomenon was first described more than a century ago and, over the past decades, increasing insights have been gained into the cellular and molecular mechanisms regulating neuronal growth and navigation. Progress in this area has been greatly assisted by the use of simple and genetically tractable invertebrate model systems, such as the fruit fly Drosophila melanogaster. This review is dedicated to Drosophila as a genetic and cellular model to study axonal growth and demonstrates how it can and has been used for this research. We describe the various cellular systems of Drosophila used for such studies, insights into axonal growth cones and their cytoskeletal dynamics, and summarise identified molecular signalling pathways required for growth cone navigation, with particular focus on pathfinding decisions in the ventral nerve cord of Drosophila embryos. These Drosophila-specific aspects are viewed in the general context of our current knowledge about neuronal growth.
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Affiliation(s)
- Natalia Sánchez-Soriano
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
| | - Guy Tear
- MRC Centre for Developmental Neurobiology, Guy's Campus, King's College, London, UK
| | - Paul Whitington
- Department of Anatomy and Cell Biology, University of Melbourne, Victoria, Australia
| | - Andreas Prokop
- The Wellcome Trust Centre for Cell-Matrix Research, Faculty of Life Sciences, The University of Manchester, Manchester, UK
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28
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Kesper DA, Stute C, Buttgereit D, Kreisköther N, Vishnu S, Fischbach KF, Renkawitz-Pohl R. Myoblast fusion in Drosophila melanogaster is mediated through a fusion-restricted myogenic-adhesive structure (FuRMAS). Dev Dyn 2007; 236:404-15. [PMID: 17146786 DOI: 10.1002/dvdy.21035] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
During myogenesis in Drosophila embryos, a prominent adhesive structure is formed between precursor cells and fusion-competent myoblasts (fcms). Here, we show that Duf/Kirre and its interaction partners Rols7 (found in founder myoblasts and growing myotubes) and Sns (found in fcms) are organized in a ring-structure at the contact points of fcms with precursor cells, while cytoskeletal components like F-actin and Titin are centered in this ring in both cell types. The cytoplasmic protein Blow colocalizes with the actin plugs in fcms after cell adhesion. Furthermore, the requirement of additional as yet unidentified components was demonstrated by using mammalian C2C12 myoblasts. In this study, we propose that the fusion-restricted myogenic-adhesive structure (FuRMAS) is pivotal in linking cell adhesion as well as local F-actin assembly and dynamics to downstream events that ultimately lead to plasma membrane fusion. Moreover, we suggest that the FuRMAS may restrict the area of membrane breakdown.
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Affiliation(s)
- Dörthe Andrea Kesper
- Philipps-Universität Marburg, Fachbereich Biologie, Entwicklungsbiologie, Marburg, Germany
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29
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Dunphy JL, Moravec R, Ly K, Lasell TK, Melancon P, Casanova JE. The Arf6 GEF GEP100/BRAG2 regulates cell adhesion by controlling endocytosis of beta1 integrins. Curr Biol 2006; 16:315-20. [PMID: 16461286 PMCID: PMC3600433 DOI: 10.1016/j.cub.2005.12.032] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2005] [Revised: 12/16/2005] [Accepted: 12/19/2005] [Indexed: 01/03/2023]
Abstract
The small GTPase Arf6 has been shown to regulate the post-endocytic trafficking of a subset of membrane proteins, including beta1 integrins, and inhibition of Arf6 function impairs both cell adhesion and motility. The activity of Arf GTPases is regulated by a large family of guanine nucleotide exchange factors (GEFs). Arf-GEP100/BRAG2 is a GEF with reported specificity for Arf6 in vitro, but it is otherwise poorly characterized. Here we report that BRAG2 exists in two ubiquitously expressed isoforms, which we call BRAG2a and BRAG2b, both of which can activate Arf6 in vivo. Depletion of endogenous BRAG2 by siRNA leads to dramatic effects in the cell periphery; one such effect is an accumulation of beta1 integrin on the cell surface and a corresponding enhancement of cell attachment and spreading on fibronectin-coated substrates. In contrast, depletion of Arf6 leads to intracellular accumulation of beta1 integrin and reduced adhesion and spreading. These findings suggest that Arf6 regulates both endocytosis and recycling of beta1 integrins and that BRAG2 functions selectively to activate Arf6 during integrin internalization.
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Affiliation(s)
- Jillian L. Dunphy
- Department of Cell Biology, University of Virginia Health Sciences Center, Box 800732, Charlottesville, Virginia 22908
| | - Radim Moravec
- Department of Cell Biology, University of Virginia Health Sciences Center, Box 800732, Charlottesville, Virginia 22908
| | - Kim Ly
- Department of Cell Biology, University of Virginia Health Sciences Center, Box 800732, Charlottesville, Virginia 22908
| | - Troy K. Lasell
- Department of Cell Biology, University of Alberta, 5-35 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada
| | - Paul Melancon
- Department of Cell Biology, University of Alberta, 5-35 Medical Sciences Building, Edmonton, Alberta T6G 2H7, Canada
| | - James E. Casanova
- Department of Cell Biology, University of Virginia Health Sciences Center, Box 800732, Charlottesville, Virginia 22908
- Correspondence:
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30
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Abstract
How axons in the developing nervous system successfully navigate to their correct targets is a fundamental problem in neurobiology. Understanding the mechanisms that mediate axon guidance will give important insight into how the nervous system is correctly wired during development and may have implications for therapeutic approaches to developmental brain disorders and nerve regeneration. Achieving this understanding will require unraveling the molecular logic that ensures the proper expression and localization of axon guidance cues and receptors, and elucidating the signaling events that regulate the growth cone cytoskeleton in response to guidance receptor activation. Studies of axon guidance at the midline of many experimental systems, from the ventral midline of Drosophila to the vertebrate spinal cord, have led to important mechanistic insights into the complex problem of wiring the nervous system. Here we review recent advances in understanding the regulation of midline axon guidance, with a particular emphasis on the contributions made from molecular genetic studies of invertebrate model systems.
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Affiliation(s)
- David S Garbe
- Department of Neuroscience, University of Pennsylvania, School of Medicine, Philadelphia, PA 19104, USA
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31
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Forsthoefel DJ, Liebl EC, Kolodziej PA, Seeger MA. The Abelson tyrosine kinase, the Trio GEF and Enabled interact with the Netrin receptor Frazzled in Drosophila. Development 2005; 132:1983-94. [PMID: 15790972 DOI: 10.1242/dev.01736] [Citation(s) in RCA: 98] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The attractive Netrin receptor Frazzled (Fra), and the signaling molecules Abelson tyrosine kinase (Abl), the guanine nucleotide-exchange factor Trio,and the Abl substrate Enabled (Ena), all regulate axon pathfinding at the Drosophila embryonic CNS midline. We detect genetic and/or physical interactions between Fra and these effector molecules that suggest that they act in concert to guide axons across the midline. Mutations in Abland trio dominantly enhance fra and Netrin mutant CNS phenotypes, and fra;Abl and fra;trio double mutants display a dramatic loss of axons in a majority of commissures. Conversely,heterozygosity for ena reduces the severity of the CNS phenotype in fra, Netrin and trio,Abl mutants. Consistent with an in vivo role for these molecules as effectors of Fra signaling, heterozygosity for Abl, trio or ena reduces the number of axons that inappropriately cross the midline in embryos expressing the chimeric Robo-Fra receptor. Fra interacts physically with Abl and Trio in GST-pulldown assays and in co-immunoprecipitation experiments. In addition, tyrosine phosphorylation of Trio and Fra is elevated in S2 cells when Abl levels are increased. Together, these data suggest that Abl, Trio, Ena and Fra are integrated into a complex signaling network that regulates axon guidance at the CNS midline.
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Affiliation(s)
- David J Forsthoefel
- The Ohio State University, Department of Molecular Genetics and Center for Molecular Neurobiology, Columbus, OH 43210, USA
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32
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Abstract
In the developing nervous system, growth cones follow specific trajectories to reach their target area and ultimately connect with their correct postsynaptic partners. This review focuses on studies in both Drosophila and vertebrates to highlight that mutual interactions between neurons and glia are essential in forming specific neuronal connections. Glia signal to neurons to direct pathfinding and targeting of axons, as well as to stabilize and refine axonal branches within the target area. Equally, neurons provide crucial information to glia, supporting their migration and correct positioning.
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Affiliation(s)
- Carole Chotard
- National Institute for Medical Research, Division of Molecular Neurobiology, The Ridgeway, London NW7 1AA, UK
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