1
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Hizawa K, Sasaki T, Arimura N. A comparative overview of DSCAM and its multifunctional roles in Drosophila and vertebrates. Neurosci Res 2024; 202:1-7. [PMID: 38141781 DOI: 10.1016/j.neures.2023.12.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2023] [Revised: 11/21/2023] [Accepted: 12/14/2023] [Indexed: 12/25/2023]
Abstract
DSCAM (Down syndrome cell adhesion molecule) is a unique neuronal adhesion protein with extensively documented multifaceted functionalities. DSCAM also has interesting properties in vertebrates and invertebrates, respectively. In Drosophila species, particularly, Dscam exhibits remarkable genetic diversity, with tens of thousands of splicing isoforms that modulate the specificity of neuronal wiring. Interestingly, this splice variant diversity of Dscam is absent in vertebrates. DSCAM plays a pivotal role in mitigating excessive adhesion between identical cell types, thereby maintaining the structural and functional coherence of neural networks. DSCAM contributes to the oversight of selective intercellular interactions such as synaptogenesis; however, the precise regulatory mechanisms underlying the promotion and inhibition of cell adhesion involved remain unclear. In this review, we aim to delineate the distinct molecules that interact with DSCAM and their specific roles within the biological landscapes of Drosophila and vertebrates. By integrating these comparative insights, we aim to elucidate the multifunctional nature of DSCAM, particularly its capacity to facilitate or deter intercellular adhesion.
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Affiliation(s)
- Kento Hizawa
- Department of Pharmacology, Faculty of Pharmaceutical Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba Ward, Sendai, Miyagi 980-8578, Japan
| | - Takuya Sasaki
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba Ward, Sendai, Miyagi 980-8578, Japan
| | - Nariko Arimura
- Department of Pharmacology, Graduate School of Pharmaceutical Sciences, Tohoku University, 6-3, Aoba, Aramaki, Aoba Ward, Sendai, Miyagi 980-8578, Japan.
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2
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Dong H, Li J, Wu Q, Jin Y. Confluence and convergence of Dscam and Pcdh cell-recognition codes. Trends Biochem Sci 2023; 48:1044-1057. [PMID: 37839971 DOI: 10.1016/j.tibs.2023.09.001] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2023] [Revised: 09/02/2023] [Accepted: 09/08/2023] [Indexed: 10/17/2023]
Abstract
The ability of neurites of the same neuron to avoid each other (self-avoidance) is a conserved feature in both invertebrates and vertebrates. The key to self-avoidance is the generation of a unique subset of cell-surface proteins in individual neurons engaging in isoform-specific homophilic interactions that drive neurite repulsion rather than adhesion. Among these cell-surface proteins are fly Dscam1 and vertebrate clustered protocadherins (cPcdhs), as well as the recently characterized shortened Dscam (sDscam) in the Chelicerata. Herein, we review recent advances in our understanding of how cPcdh, Dscam, and sDscam cell-surface recognition codes are expressed and translated into cellular functions essential for neural wiring.
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Affiliation(s)
- Haiyang Dong
- The First Affiliated Hospital, School of Medicine, Zhejiang University, 310006, Hangzhou, China; MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, ZJ310058, China
| | - Jinhuan Li
- Center for Comparative Biomedicine, Ministry of Education Key Laboratory of Systems Biomedicine, State Key Laboratory of Systems Medicine for Cancer, Institute of Systems Biomedicine, Shanghai Jiao Tong University, Shanghai 200240, China
| | - Qiang Wu
- Center for Comparative Biomedicine, Ministry of Education Key Laboratory of Systems Biomedicine, State Key Laboratory of Systems Medicine for Cancer, Institute of Systems Biomedicine, Shanghai Jiao Tong University, Shanghai 200240, China.
| | - Yongfeng Jin
- The First Affiliated Hospital, School of Medicine, Zhejiang University, 310006, Hangzhou, China; MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang, ZJ310058, China.
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3
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Zhang X, Zhang X, Zong S, Shen G, Zhao Y, Li W, Wang Q. The extracellular non-variable region of Dscam promotes bacterial clearance by promoting phagocytosis of hemocytes in Eriocheir sinensis. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2023; 138:104541. [PMID: 36108933 DOI: 10.1016/j.dci.2022.104541] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/07/2022] [Revised: 09/07/2022] [Accepted: 09/07/2022] [Indexed: 06/15/2023]
Abstract
As the most typical example of mRNA variable splicing, Down Syndrome Cell Adhesion Molecule (Dscam) can produce a large number of mRNA isomers. It plays an important role not only in the nervous system, but also in the immune system. In Eriocheir sinensis, the extracellular region of Dscam has three variable domains, which can produce 25, 34 and 18 exons and encode the N-terminal region of immunoglobulin (Ig) 2 and Ig3 domains, and the entire Ig7 domain, respectively. In addition to three variable domains, the extracellular non-variable region of Dscam also includes many Ig domains and fibronectin type III (FNIII) domains. However, the role of the extracellular non-variable region function of Dscam in the immune defense of E. sinensis is unclear. In this study, we focused on the role of the extracellular non-variable region of Dscam in crab immune defense. The results indicate that the extracellular non-variable region of Dscam can bind bacteria and has bacteriostatic function. At the same time, the extracellular non-variable region of Dscam can also directly promote bacterial clearance by promoting phagocytosis of hemocytes.
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Affiliation(s)
- Xiaoli Zhang
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China
| | - Xiaona Zhang
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China
| | - Shibo Zong
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China
| | - Guoqing Shen
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China
| | - Yuehong Zhao
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China
| | - Weiwei Li
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China.
| | - Qun Wang
- Laboratory of Invertebrate Immunological Defense & Reproductive Biology, School of Life Sciences, East China Normal University, Shanghai, China.
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4
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Williams DL, Sikora VM, Hammer MA, Amin S, Brinjikji T, Brumley EK, Burrows CJ, Carrillo PM, Cromer K, Edwards SJ, Emri O, Fergle D, Jenkins MJ, Kaushik K, Maydan DD, Woodard W, Clowney EJ. May the Odds Be Ever in Your Favor: Non-deterministic Mechanisms Diversifying Cell Surface Molecule Expression. Front Cell Dev Biol 2022; 9:720798. [PMID: 35087825 PMCID: PMC8787164 DOI: 10.3389/fcell.2021.720798] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2021] [Accepted: 11/24/2021] [Indexed: 12/30/2022] Open
Abstract
How does the information in the genome program the functions of the wide variety of cells in the body? While the development of biological organisms appears to follow an explicit set of genomic instructions to generate the same outcome each time, many biological mechanisms harness molecular noise to produce variable outcomes. Non-deterministic variation is frequently observed in the diversification of cell surface molecules that give cells their functional properties, and is observed across eukaryotic clades, from single-celled protozoans to mammals. This is particularly evident in immune systems, where random recombination produces millions of antibodies from only a few genes; in nervous systems, where stochastic mechanisms vary the sensory receptors and synaptic matching molecules produced by different neurons; and in microbial antigenic variation. These systems employ overlapping molecular strategies including allelic exclusion, gene silencing by constitutive heterochromatin, targeted double-strand breaks, and competition for limiting enhancers. Here, we describe and compare five stochastic molecular mechanisms that produce variety in pathogen coat proteins and in the cell surface receptors of animal immune and neuronal cells, with an emphasis on the utility of non-deterministic variation.
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Affiliation(s)
- Donnell L. Williams
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, United States
| | - Veronica Maria Sikora
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Max A. Hammer
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Sayali Amin
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Taema Brinjikji
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Emily K. Brumley
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Connor J. Burrows
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Paola Michelle Carrillo
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Kirin Cromer
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Summer J. Edwards
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Olivia Emri
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Daniel Fergle
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - M. Jamal Jenkins
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, United States
| | - Krishangi Kaushik
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Daniella D. Maydan
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - Wrenn Woodard
- MCDB 464 – Cellular Diversity in the Immune and Nervous Systems, University of Michigan, Ann Arbor, MI, United States
| | - E. Josephine Clowney
- Department of Molecular, Cellular and Developmental Biology, The University of Michigan, Ann Arbor, MI, United States
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5
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Rebboah E, Reese F, Williams K, Balderrama-Gutierrez G, McGill C, Trout D, Rodriguez I, Liang H, Wold BJ, Mortazavi A. Mapping and modeling the genomic basis of differential RNA isoform expression at single-cell resolution with LR-Split-seq. Genome Biol 2021; 22:286. [PMID: 34620214 PMCID: PMC8495978 DOI: 10.1186/s13059-021-02505-w] [Citation(s) in RCA: 26] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2021] [Accepted: 09/20/2021] [Indexed: 11/24/2022] Open
Abstract
The rise in throughput and quality of long-read sequencing should allow unambiguous identification of full-length transcript isoforms. However, its application to single-cell RNA-seq has been limited by throughput and expense. Here we develop and characterize long-read Split-seq (LR-Split-seq), which uses combinatorial barcoding to sequence single cells with long reads. Applied to the C2C12 myogenic system, LR-split-seq associates isoforms to cell types with relative economy and design flexibility. We find widespread evidence of changing isoform expression during differentiation including alternative transcription start sites (TSS) and/or alternative internal exon usage. LR-Split-seq provides an affordable method for identifying cluster-specific isoforms in single cells.
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Affiliation(s)
- Elisabeth Rebboah
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Fairlie Reese
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Katherine Williams
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Gabriela Balderrama-Gutierrez
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Cassandra McGill
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Diane Trout
- Division of Biology, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Isaryhia Rodriguez
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Heidi Liang
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA
| | - Barbara J Wold
- Division of Biology, California Institute of Technology, Pasadena, CA, 91125, USA
| | - Ali Mortazavi
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA, 92697, USA.
- Center for Complex Biological Systems, University of California, Irvine, Irvine, CA, 92697, USA.
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6
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Zhang Z, So K, Peterson R, Bauer M, Ng H, Zhang Y, Kim JH, Kidd T, Miura P. Elav-Mediated Exon Skipping and Alternative Polyadenylation of the Dscam1 Gene Are Required for Axon Outgrowth. Cell Rep 2020; 27:3808-3817.e7. [PMID: 31242415 PMCID: PMC7092717 DOI: 10.1016/j.celrep.2019.05.083] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2018] [Revised: 04/18/2019] [Accepted: 05/22/2019] [Indexed: 12/19/2022] Open
Abstract
Many metazoan genes express alternative long 3′ UTR isoforms in the nervous system, but their functions remain largely unclear. In Drosophila melanogaster, the Dscam1 gene generates short and long (Dscam1-L) 3′ UTR isoforms because of alternative polyadenylation (APA). Here, we found that the RNA-binding protein Embryonic Lethal Abnormal Visual System (Elav) impacts Dscam1 biogenesis at two levels, including regulation of long 3′ UTR biogenesis and skipping of an upstream exon (exon 19). MinION long-read sequencing confirmed the connectivity of this alternative splicing event to the long 3′ UTR. Knockdown or CRISPR deletion of Dscam1-L impaired axon outgrowth in Drosophila. The Dscam1 long 3′ UTR was found to be required for correct Elav-mediated skipping of exon 19. Elav thus co-regulates APA and alternative splicing to generate specific Dscam1 transcripts that are essential for neural development. This coupling of APA to alternative splicing might represent a new class of regulated RNA processing. Like most metazoan genes, Dscam1 expresses alternative short and long 3′ UTR mRNAs. Zhang et al. find that loss of Dscam1 long 3′ UTR transcripts impairs axon outgrowth in Drosophila. Long-read sequencing reveals that these long 3′ UTR mRNAs preferentially skip an upstream exon, altering Dscam1 amino acid sequence.
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Affiliation(s)
- Zhiping Zhang
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Kevin So
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Ryan Peterson
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Matthew Bauer
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Henry Ng
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Yong Zhang
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Jung Hwan Kim
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Thomas Kidd
- Department of Biology, University of Nevada, Reno, Reno, NV, USA
| | - Pedro Miura
- Department of Biology, University of Nevada, Reno, Reno, NV, USA.
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7
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Sergeeva AP, Katsamba PS, Cosmanescu F, Brewer JJ, Ahlsen G, Mannepalli S, Shapiro L, Honig B. DIP/Dpr interactions and the evolutionary design of specificity in protein families. Nat Commun 2020; 11:2125. [PMID: 32358559 PMCID: PMC7195491 DOI: 10.1038/s41467-020-15981-8] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 04/06/2020] [Indexed: 01/10/2023] Open
Abstract
Differential binding affinities among closely related protein family members underlie many biological phenomena, including cell-cell recognition. Drosophila DIP and Dpr proteins mediate neuronal targeting in the fly through highly specific protein-protein interactions. We show here that DIPs/Dprs segregate into seven specificity subgroups defined by binding preferences between their DIP and Dpr members. We then describe a sequence-, structure- and energy-based computational approach, combined with experimental binding affinity measurements, to reveal how specificity is coded on the canonical DIP/Dpr interface. We show that binding specificity of DIP/Dpr subgroups is controlled by "negative constraints", which interfere with binding. To achieve specificity, each subgroup utilizes a different combination of negative constraints, which are broadly distributed and cover the majority of the protein-protein interface. We discuss the structural origins of negative constraints, and potential general implications for the evolutionary origins of binding specificity in multi-protein families.
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Affiliation(s)
- Alina P Sergeeva
- Department of Systems Biology, Columbia University, New York, NY, USA
| | - Phinikoula S Katsamba
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA
| | - Filip Cosmanescu
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA
| | - Joshua J Brewer
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA
| | - Goran Ahlsen
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA
| | - Seetha Mannepalli
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA
| | - Lawrence Shapiro
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA.
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA.
| | - Barry Honig
- Department of Systems Biology, Columbia University, New York, NY, USA.
- Zuckerman Mind, Brain and Behavior Institute, Columbia University, New York, NY, USA.
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY, USA.
- Department of Medicine, Columbia University, New York, NY, USA.
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8
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Ng TH, Kurtz J. Dscam in immunity: A question of diversity in insects and crustaceans. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2020; 105:103539. [PMID: 31734281 DOI: 10.1016/j.dci.2019.103539] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 11/07/2019] [Accepted: 11/09/2019] [Indexed: 06/10/2023]
Abstract
In insects and crustaceans, thousands of Down syndrome cell adhesion molecules (Dscam) can be generated by alternative splicing of variable exons from a single-locus gene, Dscam-hv. This extraordinarily versatile gene (38,016 protein isoforms produced in Drosophila) was first proposed to be involved in exon guidance and subsequently implicated in immunity as a hypervariable immune molecule. Almost 20 y after discovery of Dscam-hv, there have been many studies in insects and crustaceans regarding roles of Dscam in immunity, with many similarities and concurrently, many differences. Here, we review the current status of Dscam-hv, presented as a comparison of similarities and differences in insects and crustaceans and discuss hypotheses of Dscam functions in immunity.
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Affiliation(s)
- Tze Hann Ng
- Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, 48149, Münster, Germany
| | - Joachim Kurtz
- Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, 48149, Münster, Germany.
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9
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Gunady MK, Mount SM, Corrada Bravo H. Yanagi: Fast and interpretable segment-based alternative splicing and gene expression analysis. BMC Bioinformatics 2019; 20:421. [PMID: 31409274 PMCID: PMC6693274 DOI: 10.1186/s12859-019-2947-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Accepted: 06/12/2019] [Indexed: 12/13/2022] Open
Abstract
Background Ultra-fast pseudo-alignment approaches are the tool of choice in transcript-level RNA sequencing (RNA-seq) analyses. Unfortunately, these methods couple the tasks of pseudo-alignment and transcript quantification. This coupling precludes the direct usage of pseudo-alignment to other expression analyses, including alternative splicing or differential gene expression analysis, without including a non-essential transcript quantification step. Results In this paper, we introduce a transcriptome segmentation approach to decouple these two tasks. We propose an efficient algorithm to generate maximal disjoint segments given a transcriptome reference library on which ultra-fast pseudo-alignment can be used to produce per-sample segment counts. We show how to apply these maximally unambiguous count statistics in two specific expression analyses – alternative splicing and gene differential expression – without the need of a transcript quantification step. Our experiments based on simulated and experimental data showed that the use of segment counts, like other methods that rely on local coverage statistics, provides an advantage over approaches that rely on transcript quantification in detecting and correctly estimating local splicing in the case of incomplete transcript annotations. Conclusions The transcriptome segmentation approach implemented in Yanagi exploits the computational and space efficiency of pseudo-alignment approaches. It significantly expands their applicability and interpretability in a variety of RNA-seq analyses by providing the means to model and capture local coverage variation in these analyses. Electronic supplementary material The online version of this article (10.1186/s12859-019-2947-6) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Mohamed K Gunady
- Department of Computer Science, University of Maryland, College Park, Maryland, USA.,Center for Bioinformatics and Computational Biology, University of Maryland, College Park, Maryland, USA
| | - Stephen M Mount
- Department of Cell Biology and Molecular Genetics, University of Maryland, College Park, Maryland, USA
| | - Héctor Corrada Bravo
- Department of Computer Science, University of Maryland, College Park, Maryland, USA. .,Center for Bioinformatics and Computational Biology, University of Maryland, College Park, Maryland, USA.
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10
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Inter-axonal recognition organizes Drosophila olfactory map formation. Sci Rep 2019; 9:11554. [PMID: 31399611 PMCID: PMC6689066 DOI: 10.1038/s41598-019-47924-9] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Accepted: 07/26/2019] [Indexed: 11/20/2022] Open
Abstract
Olfactory systems across the animal kingdom show astonishing similarities in their morphological and functional organization. In mouse and Drosophila, olfactory sensory neurons are characterized by the selective expression of a single odorant receptor (OR) type and by the OR class-specific connection in the olfactory brain center. Monospecific OR expression in mouse provides each sensory neuron with a unique recognition identity underlying class-specific axon sorting into synaptic glomeruli. Here we show that in Drosophila, although OR genes are not involved in sensory neuron connectivity, afferent sorting via OR class-specific recognition defines a central mechanism of odortopic map formation. Sensory neurons mutant for the Ig-domain receptor Dscam converge into ectopic glomeruli with single OR class identity independent of their target cells. Mosaic analysis showed that Dscam prevents premature recognition among sensory axons of the same OR class. Single Dscam isoform expression in projecting axons revealed the importance of Dscam diversity for spatially restricted glomerular convergence. These data support a model in which the precise temporal-spatial regulation of Dscam activity controls class-specific axon sorting thereby indicating convergent evolution of olfactory map formation via self-patterning of sensory neurons.
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11
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A genome-wide search for new imprinted genes in the human placenta identifies DSCAM as the first imprinted gene on chromosome 21. Eur J Hum Genet 2018; 27:49-60. [PMID: 30206355 DOI: 10.1038/s41431-018-0267-3] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Revised: 07/16/2018] [Accepted: 08/23/2018] [Indexed: 11/08/2022] Open
Abstract
We identified, through a genome-wide search for new imprinted genes in the human placenta, DSCAM (Down Syndrome Cellular Adhesion Molecule) as a paternally expressed imprinted gene. Our work revealed the presence of a Differentially Methylated Region (DMR), located within intron 1 that might regulate the imprinting in the region. This DMR showed a maternal allele methylation, compatible with its paternal expression. We showed that DSCAM is present in endothelial cells and the syncytiotrophoblast layer of the human placenta. In mouse, Dscam expression is biallelic in foetal brain and placenta excluding any possible imprinting in these tissues. This gene encodes a cellular adhesion molecule mainly known for its role in neurone development but its function in the placenta remains unclear. We report here the first imprinted gene located on human chromosome 21 with potential clinical implications.
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12
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Armitage SAO, Kurtz J, Brites D, Dong Y, Du Pasquier L, Wang HC. Dscam1 in Pancrustacean Immunity: Current Status and a Look to the Future. Front Immunol 2017. [PMID: 28649249 PMCID: PMC5465998 DOI: 10.3389/fimmu.2017.00662] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The Down syndrome cell adhesion molecule 1 (Dscam1) gene is an extraordinary example of diversity: by combining alternatively spliced exons, thousands of isoforms can be produced from just one gene. So far, such diversity in this gene has only been found in insects and crustaceans, and its essential part in neural wiring has been well-characterized for Drosophila melanogaster. Ten years ago evidence from D. melanogaster showed that the Dscam1 gene is involved in insect immune defense and work on Anopheles gambiae indicated that it is a hypervariable immune receptor. These exciting findings showed that via processes of somatic diversification insects have the possibility to produce unexpected immune molecule diversity, and it was hypothesized that Dscam1 could provide the mechanistic underpinnings of specific immune responses. Since these first publications the quest to understand the function of this gene has uncovered fascinating insights from insects and crustaceans. However, we are still far from a complete understanding of how Dscam1 functions in relation to parasites and pathogens and its full relevance for the immune system. In this Hypothesis and Theory article, we first briefly introduce Dscam1 and what we know so far about how it might function in immunity. By focusing on seven questions, we then share our sometimes contrasting thoughts on what the evidence tells us so far, what essential experiments remain to be done, and the future prospects, with the aim to provide a multiangled view on what this fascinating gene has to do with immune defense.
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Affiliation(s)
- Sophie A O Armitage
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Joachim Kurtz
- Institute for Evolution and Biodiversity, University of Münster, Münster, Germany
| | - Daniela Brites
- Tuberculosis Research Unit, Swiss Tropical and Public Health Institute, Basel, Switzerland.,Zoological Institute, University of Basel, Basel, Switzerland
| | - Yuemei Dong
- Department of Molecular Microbiology and Immunology, Bloomberg School of Public Health, John Hopkins University, Baltimore, MD, United States
| | | | - Han-Ching Wang
- Department of Biotechnology and Bioindustry Sciences, College of Bioscience and Biotechnology, National Cheng Kung University, Tainan, Taiwan
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13
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Abstract
Neurons form precise patterns of connections. The cellular recognition mechanisms regulating the selection of synaptic partners are poorly understood. As final mediators of cell-cell interactions, cell surface and secreted molecules (CSMs) are expected to play important roles in this process. To gain insight into how neurons discriminate synaptic partners, we profiled the transcriptomes of 7 closely related neurons forming distinct synaptic connections in discrete layers in the medulla neuropil of the fly visual system. Our sequencing data revealed that each one of these neurons expresses a unique combination of hundreds of CSMs at the onset of synapse formation. We show that 21 paralogs of the defective proboscis extension response (Dpr) family are expressed in a unique cell-type-specific fashion, consistent with the distinct connectivity pattern of each neuron profiled. Expression analysis of their cognate binding partners, the 9 members of the Dpr interacting protein (DIP) family, revealed complementary layer-specific expression in the medulla, suggestive of interactions between neurons expressing Dpr and those expressing DIP in the same layer. Through coexpression analysis and correlation to connectome data, we identify neurons expressing DIP as a subset of the synaptic partners of the neurons expressing Dpr. We propose that Dpr-DIP interactions regulate patterns of connectivity between the neurons expressing them.
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Affiliation(s)
- Marta Morey
- a Department de Genètica , Facultat de Biologia and Institut de Biomedicina de la Universitat de Barcelona (IBUB) , Barcelona Spain
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14
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Tan L, Zhang KX, Pecot MY, Nagarkar-Jaiswal S, Lee PT, Takemura SY, McEwen JM, Nern A, Xu S, Tadros W, Chen Z, Zinn K, Bellen HJ, Morey M, Zipursky SL. Ig Superfamily Ligand and Receptor Pairs Expressed in Synaptic Partners in Drosophila. Cell 2016; 163:1756-69. [PMID: 26687360 DOI: 10.1016/j.cell.2015.11.021] [Citation(s) in RCA: 125] [Impact Index Per Article: 15.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2015] [Revised: 09/27/2015] [Accepted: 11/10/2015] [Indexed: 12/30/2022]
Abstract
Information processing relies on precise patterns of synapses between neurons. The cellular recognition mechanisms regulating this specificity are poorly understood. In the medulla of the Drosophila visual system, different neurons form synaptic connections in different layers. Here, we sought to identify candidate cell recognition molecules underlying this specificity. Using RNA sequencing (RNA-seq), we show that neurons with different synaptic specificities express unique combinations of mRNAs encoding hundreds of cell surface and secreted proteins. Using RNA-seq and protein tagging, we demonstrate that 21 paralogs of the Dpr family, a subclass of immunoglobulin (Ig)-domain containing proteins, are expressed in unique combinations in homologous neurons with different layer-specific synaptic connections. Dpr interacting proteins (DIPs), comprising nine paralogs of another subclass of Ig-containing proteins, are expressed in a complementary layer-specific fashion in a subset of synaptic partners. We propose that pairs of Dpr/DIP paralogs contribute to layer-specific patterns of synaptic connectivity.
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Affiliation(s)
- Liming Tan
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Kelvin Xi Zhang
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Matthew Y Pecot
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Sonal Nagarkar-Jaiswal
- Department of Molecular and Human Genetics, HHMI, Baylor College of Medicine, Houston, TX 77030, USA
| | - Pei-Tseng Lee
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Shin-Ya Takemura
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - Jason M McEwen
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Aljoscha Nern
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147, USA
| | - Shuwa Xu
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Wael Tadros
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Zhenqing Chen
- Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA
| | - Kai Zinn
- Division of Biology and Biological Engineering, California Institute of Technology, Pasadena, CA 91125, USA
| | - Hugo J Bellen
- Department of Molecular and Human Genetics, HHMI, Baylor College of Medicine, Houston, TX 77030, USA; Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Marta Morey
- Departament de Genètica, Facultat de Biologia and Institut de Biomedicina (IBUB) de la Universitat de Barcelona, Barcelona 08028, Spain.
| | - S Lawrence Zipursky
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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15
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Morales Diaz H, Mejares E, Newman-Smith E, Smith WC. ACAM, a novel member of the neural IgCAM family, mediates anterior neural tube closure in a primitive chordate. Dev Biol 2016; 409:288-296. [PMID: 26542009 DOI: 10.1016/j.ydbio.2015.10.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 10/30/2015] [Accepted: 10/30/2015] [Indexed: 01/18/2023]
Abstract
The neural IgCAM family of cell adhesion molecules, which includes NCAM and related molecules, has evolved via gene duplication and alternative splicing to allow for a wide range of isoforms with distinct functions and homophilic binding properties. A search for neural IgCAMs in ascidians (Ciona intestinalis, Ciona savignyi, and Phallusia mammillata) has identified a novel set of truncated family members that, unlike the known members, lack fibronectin III domains and consist of only repeated Ig domains. Within the tunicates this form appears to be unique to the ascidians, and it was designated ACAM, for Ascidian Cell Adhesion Molecule. In C. intestinalis ACAM is expressed in the developing neural plate and neural tube, with strongest expression in the anterior sensory vesicle precursor. Unlike the two other conventional neural IgCAMs in C. intestinalis, which are expressed maternally and throughout the morula and blastula stages, ACAM expression initiates at the gastrula stage. Moreover, C. intestinalis ACAM is a target of the homeodomain transcription factor OTX, which plays an essential role in the development of the anterior central nervous system. Morpholino (MO) knockdown shows that ACAM is required for neural tube closure. In MO-injected embryos neural tube closure was normal caudally, but the anterior neuropore remained open. A similar phenotype was seen with overexpression of a secreted version of ACAM. The presence of ACAM in ascidians highlights the diversity of this gene family in morphogenesis and neurodevelopment.
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Affiliation(s)
- Heidi Morales Diaz
- Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, United States
| | - Emil Mejares
- Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, United States
| | - Erin Newman-Smith
- Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, United States
| | - William C Smith
- Molecular, Cellular and Developmental Biology, University of California Santa Barbara, Santa Barbara, CA, United States.
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16
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Armitage SAO, Peuss R, Kurtz J. Dscam and pancrustacean immune memory - a review of the evidence. DEVELOPMENTAL AND COMPARATIVE IMMUNOLOGY 2015; 48:315-323. [PMID: 24657209 DOI: 10.1016/j.dci.2014.03.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/07/2014] [Revised: 03/04/2014] [Accepted: 03/09/2014] [Indexed: 06/03/2023]
Abstract
Evidence is accumulating for a memory-like phenomenon in the immune defence of invertebrates. Down syndrome cell adhesion molecule (Dscam) has been proposed as a key candidate for a somatically diversified receptor system in the crustaceans and insects (Pancrustacea) that could enable challenge-specific protection. However, what is the evidence for an involvement of Dscam in pancrustacean immune memory, and in particular specificity? Here we review the current state of the art, and discuss hypotheses of how Dscam could be involved in immunity. We conclude that while there is increasing evidence for the involvement of Dscam in pancrustacean immunity, crucial experiments to address whether it plays a role in specificity upon secondary encounter with a pathogen still remain to be done.
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Affiliation(s)
- Sophie A O Armitage
- Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, 48149 Münster, Germany.
| | - Robert Peuss
- Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, 48149 Münster, Germany.
| | - Joachim Kurtz
- Institute for Evolution and Biodiversity, University of Münster, Hüfferstrasse 1, 48149 Münster, Germany.
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17
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Lyons DB, Magklara A, Goh T, Sampath SC, Schaefer A, Schotta G, Lomvardas S. Heterochromatin-mediated gene silencing facilitates the diversification of olfactory neurons. Cell Rep 2014; 9:884-92. [PMID: 25437545 PMCID: PMC4251488 DOI: 10.1016/j.celrep.2014.10.001] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2014] [Revised: 08/29/2014] [Accepted: 09/27/2014] [Indexed: 01/26/2023] Open
Abstract
An astounding property of the nervous system is its cellular diversity. This diversity, which was initially realized by morphological and electrophysiological differences, is ultimately produced by variations in gene-expression programs. In most cases, these variations are determined by external cues. However, a growing number of neuronal types have been identified in which inductive signals cannot explain the few but decisive transcriptional differences that cause cell diversification. Here, we show that heterochromatic silencing, which we find is governed by histone methyltransferases G9a (KMT1C) and GLP (KMT1D), is essential for stochastic and singular olfactory receptor (OR) expression. Deletion of G9a and GLP dramatically reduces the complexity of the OR transcriptome, resulting in transcriptional domination by a few ORs and loss of singularity in OR expression. Thus, our data suggest that, in addition to its previously known functions, heterochromatin creates an epigenetic platform that affords stochastic, mutually exclusive gene choices and promotes cellular diversity.
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Affiliation(s)
- David B Lyons
- Tetrad Program, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Angeliki Magklara
- Division of Biomedical Research, Institute of Molecular Biology and Biotechnology, Foundation for Research and Technology-Hellas, 45110 Ioannina, Greece
| | - Tracie Goh
- Department of Anatomy, University of California, San Francisco, San Francisco, CA 94920, USA
| | - Srihari C Sampath
- Laboratory of Immune Cell Epigenetics and Signaling, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Anne Schaefer
- Laboratory of Immune Cell Epigenetics and Signaling, The Rockefeller University, 1230 York Avenue, New York, NY 10065, USA
| | - Gunnar Schotta
- Munich Center for Integrated Protein Science, Adolf-Butenandt-Institute, Ludwig Maximilian University, Schillerstrasse 44, 80336 Munich, Germany
| | - Stavros Lomvardas
- Tetrad Program, University of California, San Francisco, San Francisco, CA 94158, USA; Department of Anatomy, University of California, San Francisco, San Francisco, CA 94920, USA.
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18
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Quantitative profiling of Drosophila melanogaster Dscam1 isoforms reveals no changes in splicing after bacterial exposure. PLoS One 2014; 9:e108660. [PMID: 25310676 PMCID: PMC4195611 DOI: 10.1371/journal.pone.0108660] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2014] [Accepted: 08/25/2014] [Indexed: 01/01/2023] Open
Abstract
The hypervariable Dscam1 (Down syndrome cell adhesion molecule 1) gene can produce thousands of different ectodomain isoforms via mutually exclusive alternative splicing. Dscam1 appears to be involved in the immune response of some insects and crustaceans. It has been proposed that the diverse isoforms may be involved in the recognition of, or the defence against, diverse parasite epitopes, although evidence to support this is sparse. A prediction that can be generated from this hypothesis is that the gene expression of specific exons and/or isoforms is influenced by exposure to an immune elicitor. To test this hypothesis, we for the first time, use a long read RNA sequencing method to directly investigate the Dscam1 splicing pattern after exposing adult Drosophila melanogaster and a S2 cell line to live Escherichia coli. After bacterial exposure both models showed increased expression of immune-related genes, indicating that the immune system had been activated. However there were no changes in total Dscam1 mRNA expression. RNA sequencing further showed that there were no significant changes in individual exon expression and no changes in isoform splicing patterns in response to bacterial exposure. Therefore our studies do not support a change of D. melanogaster Dscam1 isoform diversity in response to live E. coli. Nevertheless, in future this approach could be used to identify potentially immune-related Dscam1 splicing regulation in other host species or in response to other pathogens.
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19
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Haney RA, Ayoub NA, Clarke TH, Hayashi CY, Garb JE. Dramatic expansion of the black widow toxin arsenal uncovered by multi-tissue transcriptomics and venom proteomics. BMC Genomics 2014; 15:366. [PMID: 24916504 PMCID: PMC4058007 DOI: 10.1186/1471-2164-15-366] [Citation(s) in RCA: 62] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 05/08/2014] [Indexed: 12/22/2022] Open
Abstract
Background Animal venoms attract enormous interest given their potential for pharmacological discovery and understanding the evolution of natural chemistries. Next-generation transcriptomics and proteomics provide unparalleled, but underexploited, capabilities for venom characterization. We combined multi-tissue RNA-Seq with mass spectrometry and bioinformatic analyses to determine venom gland specific transcripts and venom proteins from the Western black widow spider (Latrodectus hesperus) and investigated their evolution. Results We estimated expression of 97,217 L. hesperus transcripts in venom glands relative to silk and cephalothorax tissues. We identified 695 venom gland specific transcripts (VSTs), many of which BLAST and GO term analyses indicate may function as toxins or their delivery agents. ~38% of VSTs had BLAST hits, including latrotoxins, inhibitor cystine knot toxins, CRISPs, hyaluronidases, chitinase, and proteases, and 59% of VSTs had predicted protein domains. Latrotoxins are venom toxins that cause massive neurotransmitter release from vertebrate or invertebrate neurons. We discovered ≥ 20 divergent latrotoxin paralogs expressed in L. hesperus venom glands, significantly increasing this biomedically important family. Mass spectrometry of L. hesperus venom identified 49 proteins from VSTs, 24 of which BLAST to toxins. Phylogenetic analyses showed venom gland specific gene family expansions and shifts in tissue expression. Conclusions Quantitative expression analyses comparing multiple tissues are necessary to identify venom gland specific transcripts. We present a black widow venom specific exome that uncovers a trove of diverse toxins and associated proteins, suggesting a dynamic evolutionary history. This justifies a reevaluation of the functional activities of black widow venom in light of its emerging complexity. Electronic supplementary material The online version of this article (doi:10.1186/1471-2164-15-366) contains supplementary material, which is available to authorized users.
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Affiliation(s)
| | | | | | | | - Jessica E Garb
- Department of Biological Sciences, University of Massachusetts, Lowell, MA 01854, USA.
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20
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Affiliation(s)
- S. Lawrence Zipursky
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1662;
| | - Wesley B. Grueber
- Department of Physiology and Cellular Biophysics, Department of Neuroscience, College of Physicians and Surgeons, Columbia University Medical Center, New York, NY 10032;
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21
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Transcriptomic analysis of postmortem brain identifies dysregulated splicing events in novel candidate genes for schizophrenia. Schizophr Res 2012; 142:188-99. [PMID: 23062752 PMCID: PMC3502694 DOI: 10.1016/j.schres.2012.09.015] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/11/2012] [Revised: 09/17/2012] [Accepted: 09/19/2012] [Indexed: 01/20/2023]
Abstract
The diverse spatial and temporal expression of alternatively spliced transcript isoforms shapes neurodevelopment and plays a major role in neuronal adaptability. Although alternative splicing is extremely common in the brain, its role in mental illnesses such as schizophrenia has received little attention. To examine this relationship, postmortem brain tissue was obtained from 20 individuals with schizophrenia (SZ) and 20 neuropsychiatrically normal comparison subjects. Gray matter samples were extracted from two brain regions implicated in the disorder: Brodmann Area 10 and caudate. Affymetrix Human Gene 1.0 ST arrays were used on four subjects per group to attain an initial profile of differential expression of transcribed elements within and across brain regions in SZ. Numerous genes of interest with altered mRNA transcripts were identified by microarray through the differential expression of particular exons and 3' untranslated regions (UTRs) between diagnostic groups. Select microarray results--including dysregulation of ENAH exon 11a and CPNE3 3'UTR--were verified by qRTPCR and replicated in the remaining independent sample of 16 SZ patients and 16 normal comparison subjects. These results, if further replicated, clearly illustrate the importance of Identifying transcriptomic variants in expression studies, and implicate novel candidate genes in the disorder.
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22
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Alternative splicing: functional diversity among voltage-gated calcium channels and behavioral consequences. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:1522-9. [PMID: 23022282 DOI: 10.1016/j.bbamem.2012.09.018] [Citation(s) in RCA: 87] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2012] [Revised: 09/15/2012] [Accepted: 09/19/2012] [Indexed: 12/14/2022]
Abstract
Neuronal voltage-gated calcium channels generate rapid, transient intracellular calcium signals in response to membrane depolarization. Neuronal Ca(V) channels regulate a range of cellular functions and are implicated in a variety of neurological and psychiatric diseases including epilepsy, Parkinson's disease, chronic pain, schizophrenia, and bipolar disorder. Each mammalian Cacna1 gene has the potential to generate tens to thousands of Ca(V) channels by alternative pre-mRNA splicing, a process that adds fine granulation to the pool of Ca(V) channel structures and functions. The precise composition of Ca(V) channel splice isoform mRNAs expressed in each cell are controlled by cell-specific splicing factors. The activity of splicing factors are in turn regulated by molecules that encode various cellular features, including cell-type, activity, metabolic states, developmental state, and other factors. The cellular and behavioral consequences of individual sites of Ca(V) splice isoforms are being elucidated, as are the cell-specific splicing factors that control splice isoform selection. Altered patterns of alternative splicing of Ca(V) pre-mRNAs can alter behavior in subtle but measurable ways, with the potential to influence drug efficacy and disease severity. This article is part of a Special Issue entitled: Calcium channels.
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23
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Abstract
The nuclear receptors (NRs) of metazoans are an ancient family of transcription factors defined by conserved DNA- and ligand-binding domains (DBDs and LBDs, respectively). The Drosophila melanogaster genome project revealed 18 canonical NRs (with DBDs and LBDs both present) and 3 receptors with the DBD only. Annotation of subsequently sequenced insect genomes revealed only minor deviations from this pattern. A renewed focus on functional analysis of the isoforms of insect NRs is therefore required to understand the diverse roles of these transcription factors in embryogenesis, metamorphosis, reproduction, and homeostasis. One insect NR, ecdysone receptor (EcR), functions as a receptor for the ecdysteroid molting hormones of insects. Researchers have developed nonsteroidal ecdysteroid agonists for EcR that disrupt molting and can be used as safe pesticides. An exciting new technology allows EcR to be used in chimeric, ligand-inducible gene-switch systems with applications in pest management and medicine.
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Affiliation(s)
- Susan E Fahrbach
- Department of Biology, Wake Forest University, Winston-Salem, North Carolina 27109, USA.
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24
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Glatt SJ, Cohen OS, Faraone SV, Tsuang MT. Dysfunctional gene splicing as a potential contributor to neuropsychiatric disorders. Am J Med Genet B Neuropsychiatr Genet 2011; 156B:382-92. [PMID: 21438146 PMCID: PMC3082621 DOI: 10.1002/ajmg.b.31181] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Accepted: 02/18/2011] [Indexed: 12/31/2022]
Abstract
Alternative pre-mRNA splicing is a major mechanism by which the proteomic diversity of eukaryotic genomes is amplified. Much akin to neuropsychiatric disorders themselves, alternative splicing events can be influenced by genetic, developmental, and environmental factors. Here, we review the evidence that abnormalities of splicing may contribute to the liability toward these disorders. First, we introduce the phenomenon of alternative splicing and describe the processes involved in its regulation. We then review the evidence for specific splicing abnormalities in a wide range of neuropsychiatric disorders, including psychotic disorders (schizophrenia), affective disorders (bipolar disorder and major depressive disorder), suicide, substance abuse disorders (cocaine abuse and alcoholism), and neurodevelopmental disorders (autism). Next, we provide a theoretical reworking of the concept of "gene-focused" epidemiologic and neurobiologic investigations. Lastly, we suggest potentially fruitful lines for future research that should illuminate the nature, extent, causes, and consequences of alternative splicing abnormalities in neuropsychiatric disorders.
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Affiliation(s)
- Stephen J. Glatt
- Psychiatric Genetic Epidemiology & Neurobiology Laboratory (PsychGENe Lab); Departments of Psychiatry and Behavioral Sciences & Neuroscience and Physiology; Medical Genetics Research Center; SUNY Upstate Medical University; Syracuse, NY 13210; U.S.A,To whom correspondence should be addressed: SUNY Upstate Medical University, 750 East Adams Street, Weiskotten Hall, Room 3283, Syracuse, NY 13210, U.S.A., , Facsimile: (315) 464-7744, Telephone: (315) 464-7742
| | - Ori S. Cohen
- Psychiatric Genetic Epidemiology & Neurobiology Laboratory (PsychGENe Lab); Departments of Psychiatry and Behavioral Sciences & Neuroscience and Physiology; Medical Genetics Research Center; SUNY Upstate Medical University; Syracuse, NY 13210; U.S.A
| | - Stephen V. Faraone
- Psychiatric Genetic Epidemiology & Neurobiology Laboratory (PsychGENe Lab); Departments of Psychiatry and Behavioral Sciences & Neuroscience and Physiology; Medical Genetics Research Center; SUNY Upstate Medical University; Syracuse, NY 13210; U.S.A
| | - Ming T. Tsuang
- Center for Behavioral Genomics; Department of Psychiatry; Institute of Genomic Medicine; University of California, San Diego; 9500 Gilman Drive; La Jolla, CA 92039; U.S.A, Veterans Affairs San Diego Healthcare System; 3350 La Jolla Village Drive; San Diego, CA 92161; U.S.A, Harvard Institute of Psychiatric Epidemiology and Genetics; Harvard Departments of Epidemiology and Psychiatry; 25 Shattuck Street; Boston, MA 02115; U.S.A
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25
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Olson S, Blanchette M, Park J, Savva Y, Yeo GW, Yeakley JM, Rio DC, Graveley BR. A regulator of Dscam mutually exclusive splicing fidelity. Nat Struct Mol Biol 2011; 14:1134-40. [PMID: 21188797 DOI: 10.1038/nsmb1339] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The Down syndrome cell adhesion molecule (Dscam) gene has essential roles in neural wiring and pathogen recognition in Drosophila melanogaster. Dscam encodes 38,016 distinct isoforms via extensive alternative splicing. The 95 alternative exons in Dscam are organized into clusters that are spliced in a mutually exclusive manner. The exon 6 cluster contains 48 variable exons and uses a complex system of competing RNA structures to ensure that only one variable exon is included. Here we show that the heterogeneous nuclear ribonucleoprotein hrp36 acts specifically within, and throughout, the exon 6 cluster to prevent the inclusion of multiple exons. Moreover, hrp36 prevents serine/arginine-rich proteins from promoting the ectopic inclusion of multiple exon 6 variants. Thus, the fidelity of mutually exclusive splicing in the exon 6 cluster is governed by an intricate combination of alternative RNA structures and a globally acting splicing repressor.
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Affiliation(s)
- Sara Olson
- Department of Genetics and Developmental Biology, University of Connecticut Health Center, 263 Farmington Avenue, Farmington, Connecticut 06030-3301, USA
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26
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Grueber WB, Sagasti A. Self-avoidance and tiling: Mechanisms of dendrite and axon spacing. Cold Spring Harb Perspect Biol 2010; 2:a001750. [PMID: 20573716 DOI: 10.1101/cshperspect.a001750] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The spatial pattern of branches within axonal or dendritic arbors and the relative arrangement of neighboring arbors with respect to one another impact a neuron's potential connectivity. Although arbors can adopt diverse branching patterns to suit their functions, evenly spread branches that avoid clumping or overlap are a common feature of many axonal and dendritic arbors. The degree of overlap between neighboring arbors innervating a surface is also characteristic within particular neuron types. The arbors of some populations of neurons innervate a target with a comprehensive and nonoverlapping "tiled" arrangement, whereas those of others show substantial territory overlap. This review focuses on cellular and molecular studies that have provided insight into the regulation of spatial arrangements of neurite branches within and between arbors. These studies have revealed principles that govern arbor arrangements in dendrites and axons in both vertebrates and invertebrates. Diverse molecular mechanisms controlling the spatial patterning of sister branches and neighboring arbors have begun to be elucidated.
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Affiliation(s)
- Wesley B Grueber
- Department of Physiology and Cellular Biophysics, Department of Neuroscience, Columbia University Medical Center, New York, New York 10032, USA.
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27
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Loya CM, Van Vactor D, Fulga TA. Understanding neuronal connectivity through the post-transcriptional toolkit. Genes Dev 2010; 24:625-35. [PMID: 20360381 DOI: 10.1101/gad.1907710] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Post-transcriptional regulatory mechanisms have emerged as a critical component underlying the diversification and spatiotemporal control of the proteome during the establishment of precise neuronal connectivity. These mechanisms have been shown to be important for virtually all stages of assembling a neural network, from neurite guidance, branching, and growth to synapse morphogenesis and function. From the moment a gene is transcribed, it undergoes a series of post-transcriptional regulatory modifications in the nucleus and cytoplasm until its final deployment as a functional protein. Initially, a message is subjected to extensive structural regulation through alternative splicing, which is capable of greatly expanding the protein repertoire by generating, in some cases, thousands of functionally distinct isoforms from a single gene locus. Then, RNA packaging into neuronal transport granules and recognition by RNA-binding proteins and/or microRNAs is capable of restricting protein synthesis to selective locations and under specific input conditions. This ability of the post-transcriptional apparatus to expand the informational content of a cell and control the deployment of proteins in both spatial and temporal dimensions is a feature well adapted for the extreme morphological properties of neural cells. In this review, we describe recent advances in understanding how post-transcriptional regulatory mechanisms refine the proteomic complexity required for the assembly of intricate and specific neural networks.
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Affiliation(s)
- Carlos M Loya
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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28
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Regulation of Complex Brain Wiring via Diverse Ig Receptor Arising from a Single Gene. J Oral Biosci 2010. [DOI: 10.1016/s1349-0079(10)80020-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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29
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Lee C, Kim N, Roy M, Graveley BR. Massive expansions of Dscam splicing diversity via staggered homologous recombination during arthropod evolution. RNA (NEW YORK, N.Y.) 2010; 16:91-105. [PMID: 19934230 PMCID: PMC2802040 DOI: 10.1261/rna.1812710] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2009] [Accepted: 09/15/2009] [Indexed: 05/26/2023]
Abstract
The arthropod Down syndrome cell adhesion molecule (Dscam) gene can generate tens of thousands of protein isoforms via combinatorial splicing of numerous alternative exons encoding immunoglobulin variable domains organized into three clusters referred to as the exon 4, 6, and 9 clusters. Dscam protein diversity is important for nervous system development and immune functions. We have performed extensive phylogenetic analyses of Dscam from 20 arthropods (each containing between 46 and 96 alternative exons) to reconstruct the detailed history of exon duplication and loss events that built this remarkable system over 450 million years of evolution. Whereas the structure of the exon 4 cluster is ancient, the exon 6 and 9 clusters have undergone massive, independent expansions in each insect lineage. An analysis of nearly 2000 duplicated exons enabled detailed reconstruction of the timing, location, and boundaries of these duplication events. These data clearly show that new Dscam exons have arisen continuously throughout arthropod evolution and that this process is still occurring in the exon 6 and 9 clusters. Recently duplicated regions display boundaries corresponding to a single exon and the adjacent intron. The boundaries, homology, location, clustering, and relative frequencies of these duplication events strongly suggest that staggered homologous recombination is the major mechanism by which new Dscam exons evolve. These data provide a remarkably detailed picture of how complex gene structure evolves and reveal the molecular mechanism behind this process.
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Affiliation(s)
- Christopher Lee
- Department of Chemistry and Biochemistry, Center for Computational Biology, Institute for Genomics and Proteomics, Molecular BiologyInstitute, University of California at Los Angeles, Los Angeles, California 90095-1570, USA.
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DSCAM functions as a netrin receptor in commissural axon pathfinding. Proc Natl Acad Sci U S A 2009; 106:2951-6. [PMID: 19196994 DOI: 10.1073/pnas.0811083106] [Citation(s) in RCA: 124] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Down syndrome cell adhesion molecule (DSCAM) is required for axon guidance and dendrite arborization. How DSCAM functions in vertebrates is not well understood. Here we show that DSCAM is expressed on commissural axons and interacts with Netrin-1, a prototypical guidance cue for commissural axons. The knockdown of DSCAM by specific siRNA or blockage of DSCAM signaling by overexpression of a mutant lacking its intracellular domain inhibits netrin-induced axon outgrowth and commissural axon turning in vitro. SiRNA-mediated knockdown of DSCAM in ovo causes defects in commissural axon projection and pathfinding. In transfected cells, DSCAM by itself, in the absence of DCC, is capable of mediating netrin signaling in activating phosphorylation of Fyn and Pak1. These findings demonstrate an essential role of vertebrate DSCAM in axon guidance, indicating that DSCAM functions as a receptor of netrin-1. Our data suggest previously unexpected complexity in receptors that mediate vertebrate netrin signaling.
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Wu Z, Jia X, de la Cruz L, Su XC, Marzolf B, Troisch P, Zak D, Hamilton A, Whittle B, Yu D, Sheahan D, Bertram E, Aderem A, Otting G, Goodnow CC, Hoyne GF. Memory T cell RNA rearrangement programmed by heterogeneous nuclear ribonucleoprotein hnRNPLL. Immunity 2009; 29:863-75. [PMID: 19100700 DOI: 10.1016/j.immuni.2008.11.004] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2008] [Revised: 09/16/2008] [Accepted: 11/04/2008] [Indexed: 11/26/2022]
Abstract
Differentiation of memory cells involves DNA-sequence changes in B lymphocytes but is less clearly defined in T cells. RNA rearrangement is identified here as a key event in memory T cell differentiation by analysis of a mouse mutation that altered the proportions of naive and memory T cells and crippled the process of Ptprc exon silencing needed to generate CD45RO in memory T cells. A single substitution in a memory-induced RNA-binding protein, hnRNPLL, destabilized an RNA-recognition domain that bound with micromolar affinity to RNA containing the Ptprc exon-silencing sequence. Hnrpll mutation selectively diminished T cell accumulation in peripheral lymphoid tissues but not proliferation. Exon-array analysis of Hnrpll mutant naive and memory T cells revealed an extensive program of alternative mRNA splicing in memory T cells, coordinated by hnRNPLL. A remarkable overlap with alternative splicing in neural tissues may reflect a co-opted strategy for diversifying memory T cells.
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Affiliation(s)
- Zuopeng Wu
- John Curtin School of Medical Research, Australian Phenomics Facility, Australian National University, Canberra ACT 0200, Australia
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32
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Schmucker D, Chen B. Dscam and DSCAM: complex genes in simple animals, complex animals yet simple genes. Genes Dev 2009; 23:147-56. [DOI: 10.1101/gad.1752909] [Citation(s) in RCA: 129] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
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33
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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: 91] [Impact Index Per Article: 5.7] [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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Ly A, Nikolaev A, Suresh G, Zheng Y, Tessier-Lavigne M, Stein E. DSCAM is a netrin receptor that collaborates with DCC in mediating turning responses to netrin-1. Cell 2008; 133:1241-54. [PMID: 18585357 DOI: 10.1016/j.cell.2008.05.030] [Citation(s) in RCA: 194] [Impact Index Per Article: 12.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2007] [Revised: 03/03/2008] [Accepted: 05/14/2008] [Indexed: 01/29/2023]
Abstract
During nervous system development, spinal commissural axons project toward and across the ventral midline. They are guided in part by netrin-1, made by midline cells, which attracts the axons by activating the netrin receptor DCC. However, previous studies suggest that additional receptor components are required. Here, we report that the Down's syndrome Cell Adhesion Molecule (DSCAM), a candidate gene implicated in the mental retardation phenotype of Down's syndrome, is expressed on spinal commissural axons, binds netrin-1, and is necessary for commissural axons to grow toward and across the midline. DSCAM and DCC can each mediate a turning response of these neurons to netrin-1. Similarly, Xenopus spinal neurons exogenously expressing DSCAM can be attracted by netrin-1 independently of DCC. These results show that DSCAM is a receptor that can mediate turning responses to netrin-1 and support a key role for netrin/DSCAM signaling in commissural axon guidance in vertebrates.
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Affiliation(s)
- Alice Ly
- Department of Molecular, Cellular, and Developmental Biology, Yale University, 266 Whitney Avenue, New Haven, CT 06520, USA
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35
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Chen Z, Gore BB, Long H, Ma L, Tessier-Lavigne M. Alternative splicing of the Robo3 axon guidance receptor governs the midline switch from attraction to repulsion. Neuron 2008; 58:325-32. [PMID: 18466743 DOI: 10.1016/j.neuron.2008.02.016] [Citation(s) in RCA: 185] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Revised: 01/29/2007] [Accepted: 02/15/2008] [Indexed: 11/19/2022]
Abstract
Alternative splicing provides a means to increase the complexity of gene function in numerous biological processes, including nervous system wiring. Navigating axons switch responses from attraction to repulsion at intermediate targets, allowing them to grow to each intermediate target and then to move on. The mechanisms underlying this switch remain poorly characterized. We previously showed that the Slit receptor Robo3 is required for spinal commissural axons to enter and cross the midline intermediate target. We report here the existence of two functionally antagonistic isoforms of Robo3 with distinct carboxy termini arising from alternative splicing. Robo3.1 is deployed on the precrossing and crossing portions of commissural axons and allows midline crossing by silencing Slit repulsion. Robo3.2 becomes expressed on the postcrossing portion and blocks midline recrossing, favoring Slit repulsion. The tight spatial regulation of opponent splice variants helps ensure high-fidelity transition of axonal responses from attraction to repulsion at the midline.
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Affiliation(s)
- Zhe Chen
- Division of Research, Genentech Inc., 1 DNA Way, South San Francisco, CA 94080, USA
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36
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Sanghamitra M, Talukder I, Singarapu N, Sindhu KV, Kateriya S, Goswami SK. WD-40 repeat protein SG2NA has multiple splice variants with tissue restricted and growth responsive properties. Gene 2008; 420:48-56. [PMID: 18571342 DOI: 10.1016/j.gene.2008.04.016] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2007] [Revised: 04/14/2008] [Accepted: 04/15/2008] [Indexed: 10/22/2022]
Abstract
SG2NA is a member of the striatin family of WD-40 repeat proteins with potential scaffolding functions. It was originally identified as a tumor antigen with increased expression during S to G2 phase of cell cycle. We report here that mouse SG2NA has at least five novel splice variants of which two are devoid of the carboxyl terminal WD-40 repeats. The variants of SG2NA are generated by alternative splicing at the exon 7-9 regions and differ in their expression profiles in various tissues tested. While the 83, 78, 38 and 35 kDa variants are present in both brain and heart, the 87 kDa form is brain specific. Also, the expression of 35 kDa variant is more in neonatal than in adult tissues. Western analysis suggests that the SG2NA isoforms differentially respond to growth stimuli. Upon serum stimulation, while the 35 kDa variant is increased, the 78 kDa form is diminished. Splicing variation of SG2NA is conserved in metazoan evolution. In embryonic chicken there are at least four variants of which one is present in brain but absent in heart. Taken together, splicing variation of SG2NA might have some critical roles in differentiation and maturation in metazoan cells.
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Affiliation(s)
- Mishra Sanghamitra
- School of Life Sciences, Jawaharlal Nehru University, New Delhi 110067, India
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37
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38
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Farrar NR, Spencer GE. Pursuing a 'turning point' in growth cone research. Dev Biol 2008; 318:102-11. [PMID: 18436201 DOI: 10.1016/j.ydbio.2008.03.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2007] [Revised: 03/05/2008] [Accepted: 03/06/2008] [Indexed: 01/13/2023]
Abstract
Growth cones are highly motile structures found at the leading edge of developing and regenerating nerve processes. Their role in axonal pathfinding has been well established and many guidance cues that influence growth cone behavior have now been identified. Many studies are now providing insights into the transduction and integration of signals in the growth cone, though a full understanding of growth cone behavior still eludes us. This review focuses on recent studies adding to the growing body of literature on growth cone behavior, focusing particularly on the level of autonomy the growth cone possesses and the role of local protein synthesis.
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Affiliation(s)
- Nathan R Farrar
- Department of Biological Sciences, Brock University, 500 Glenridge Avenue, St. Catharines, Ontario, Canada L2S 3A1
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39
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Dscam and Sidekick proteins direct lamina-specific synaptic connections in vertebrate retina. Nature 2008; 451:465-9. [PMID: 18216854 DOI: 10.1038/nature06469] [Citation(s) in RCA: 291] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/31/2007] [Accepted: 11/12/2007] [Indexed: 11/08/2022]
Abstract
Synaptic circuits in the retina transform visual input gathered by photoreceptors into messages that retinal ganglion cells (RGCs) send to the brain. Processes of retinal interneurons (amacrine and bipolar cells) form synapses on dendrites of RGCs in the inner plexiform layer (IPL). The IPL is divided into at least 10 parallel sublaminae; subsets of interneurons and RGCs arborize and form synapses in just one or a few of them. These lamina-specific circuits determine the visual features to which RGC subtypes respond. Here we show that four closely related immunoglobulin superfamily (IgSF) adhesion molecules--Dscam (Down's syndrome cell adhesion molecule), DscamL (refs 6-9), Sidekick-1 and Sidekick-2 (ref. 10)--are expressed in chick by non-overlapping subsets of interneurons and RGCs that form synapses in distinct IPL sublaminae. Moreover, each protein is concentrated within the appropriate sublaminae and each mediates homophilic adhesion. Loss- and gain-of-function studies in vivo indicate that these IgSF members participate in determining the IPL sublaminae in which synaptic partners arborize and connect. Thus, vertebrate Dscams, like Drosophila Dscams, play roles in neural connectivity. Together, our results on Dscams and Sidekicks suggest the existence of an IgSF code for laminar specificity in retina and, by implication, in other parts of the central nervous system.
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40
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Haas BJ. Analysis of alternative splicing in plants with bioinformatics tools. Curr Top Microbiol Immunol 2008; 326:17-37. [PMID: 18630745 DOI: 10.1007/978-3-540-76776-3_2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Alternative splicing is a molecular mechanism utilized by a broad range of eukaryotes to extend the repertoire of functions encoded by single genes and to posttranscriptionally regulate gene expression. Recent analyses of expressed transcript sequences aligned to the complete genomes of Arabidopsis and rice indicate that alternative splicing in plants is prevalent and exhibits several features similar to other higher eukaryotes including mouse and human. This chapter reviews the computational strategies employed to study alternative splicing with bioinformatics tools and the recent findings from analyses performed on plants by applying such methods.
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Affiliation(s)
- B J Haas
- B.J. Haas Broad Institute, 7 Cambridge Center, Cambridge, MA 02142, USA.
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41
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Schmucker D. Molecular diversity of Dscam: recognition of molecular identity in neuronal wiring. Nat Rev Neurosci 2007; 8:915-20. [PMID: 18026165 DOI: 10.1038/nrn2256] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Our understanding of how the enormously complex task of interconnecting millions of nerve cells is accomplished remains rudimentary. What molecular mechanisms control its exquisite specificity? Can we pinpoint single molecular interactions that might help to explain some of the specificity requirements that underlie neuronal wiring? A series of recent studies on the molecular diversity of the Drosophila melanogaster cell-surface receptor Down syndrome cell-adhesion molecule (Dscam) provide one exceptional example of a novel mechanistic model of neuronal-wiring specificity, progressing from structural studies of single protein-protein interactions to biochemical analysis in vitro and to an understanding of complex neuronal differentiation at the single-cell or tissue levels.
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Affiliation(s)
- Dietmar Schmucker
- Department of Neurobiology, Harvard Medical School, and at the Dana-Faber Cancer Institute, 1 Jimmy Fund Way, Boston, Massachusetts 02115, USA.
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42
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Abstract
Alternative pre-mRNA splicing has an important role in the control of neuronal gene expression. Many neuronal proteins are structurally diversified through the differential inclusion and exclusion of sequences in the final spliced mRNA. Here, we discuss common mechanisms of splicing regulation and provide examples of how alternative splicing has important roles in neuronal development and mature neuron function. Finally, we describe regulatory proteins that control the splicing of some neuronally expressed transcripts.
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Affiliation(s)
- Qin Li
- Howard Hughes Medical Institute, University of California, Los Angeles, 6-762 MacDonald Research Laboratories, 675 Charles E. Young Drive South, Los Angeles, California 90095, USA
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43
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Wojtowicz WM, Wu W, Andre I, Qian B, Baker D, Zipursky SL. A vast repertoire of Dscam binding specificities arises from modular interactions of variable Ig domains. Cell 2007; 130:1134-45. [PMID: 17889655 PMCID: PMC2707357 DOI: 10.1016/j.cell.2007.08.026] [Citation(s) in RCA: 173] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 08/08/2007] [Accepted: 08/10/2007] [Indexed: 11/15/2022]
Abstract
Dscam encodes a family of cell surface proteins required for establishing neural circuits in Drosophila. Alternative splicing of Drosophila Dscam can generate 19,008 distinct extracellular domains containing different combinations of three variable immunoglobulin domains. To test the binding properties of many Dscam isoforms, we developed a high-throughput ELISA-based binding assay. We provide evidence that 95% (>18,000) of Dscam isoforms exhibit striking isoform-specific homophilic binding. We demonstrate that each of the three variable domains binds to the same variable domain in an opposing isoform and identify the structural elements that mediate this self-binding of each domain. These studies demonstrate that self-binding domains can assemble in different combinations to generate an enormous family of homophilic binding proteins. We propose that this vast repertoire of Dscam recognition molecules is sufficient to provide each neuron with a unique identity and homotypic binding specificity, thereby allowing neuronal processes to distinguish between self and nonself.
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Affiliation(s)
- Woj M. Wojtowicz
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles California, USA
| | - Wei Wu
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles California, USA
| | - Ingemar Andre
- Department of Biochemistry, Howard Hughes Medical Institute, University of Washington, Seattle, Washington, USA
| | - Bin Qian
- Department of Biochemistry, Howard Hughes Medical Institute, University of Washington, Seattle, Washington, USA
| | - David Baker
- Department of Biochemistry, Howard Hughes Medical Institute, University of Washington, Seattle, Washington, USA
| | - S. Lawrence Zipursky
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles California, USA
- Correspondence:
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44
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Hattori D, Demir E, Kim HW, Viragh E, Zipursky SL, Dickson BJ. Dscam diversity is essential for neuronal wiring and self-recognition. Nature 2007; 449:223-7. [PMID: 17851526 PMCID: PMC2691715 DOI: 10.1038/nature06099] [Citation(s) in RCA: 162] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2007] [Accepted: 07/17/2007] [Indexed: 11/08/2022]
Abstract
Neurons are thought to use diverse families of cell-surface molecules for cell recognition during circuit assembly. In Drosophila, alternative splicing of the Down syndrome cell adhesion molecule (Dscam) gene potentially generates 38,016 closely related transmembrane proteins of the immunoglobulin superfamily, each comprising one of 19,008 alternative ectodomains linked to one of two alternative transmembrane segments. These ectodomains show isoform-specific homophilic binding, leading to speculation that Dscam proteins mediate cell recognition. Genetic studies have established that Dscam is required for neural circuit assembly, but the extent to which isoform diversity contributes to this process is not known. Here we provide conclusive evidence that Dscam diversity is essential for circuit assembly. Using homologous recombination, we reduced the entire repertoire of Dscam ectodomains to just a single isoform. Neural circuits in these mutants are severely disorganized. Furthermore, we show that it is crucial for neighbouring neurons to express distinct isoforms, but that the specific identity of the isoforms expressed in an individual neuron is unimportant. We conclude that Dscam diversity provides each neuron with a unique identity by which it can distinguish its own processes from those of other neurons, and that this self-recognition is essential for wiring the Drosophila brain.
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Affiliation(s)
- Daisuke Hattori
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, California 90049, USA
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45
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Gao FB. Molecular and cellular mechanisms of dendritic morphogenesis. Curr Opin Neurobiol 2007; 17:525-32. [PMID: 17933513 DOI: 10.1016/j.conb.2007.08.004] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2007] [Revised: 08/03/2007] [Accepted: 08/24/2007] [Indexed: 11/28/2022]
Abstract
Dendrites exhibit unique cell type-specific branching patterns and targeting specificity that are crucially important for neuronal function and connectivity. Recent evidence indicates that highly complex transcriptional regulatory networks dictate various aspects of dendritic outgrowth, branching, and routing. In addition to other intrinsic molecular pathways such as membrane protein trafficking, interactions between neighboring dendritic branches also contribute to the final specification of dendritic morphology. Nonredundant coverage by dendrites of same type of neurons, known as tiling, requires the actions of the Tricornered/Furry (Sax-1/Sax-2) signaling pathway. However, the dendrites of a neuron do not crossover each other, a process called self-avoidance that is mediated by Down's syndrome cell adhesion molecule (Dscam). Those exciting findings have enhanced significantly our understanding of dendritic morphogenesis and revealed the magnitude of complexity in the underlying molecular regulatory networks.
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Affiliation(s)
- Fen-Biao Gao
- Gladstone Institute of Neurological Disease, and Department of Neurology, University of California, San Francisco, CA 94158, United States.
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46
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Protocadherin family: diversity, structure, and function. Curr Opin Cell Biol 2007; 19:584-92. [DOI: 10.1016/j.ceb.2007.09.006] [Citation(s) in RCA: 167] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2007] [Accepted: 09/05/2007] [Indexed: 12/13/2022]
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47
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48
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Millard SS, Flanagan JJ, Pappu KS, Wu W, Zipursky SL. Dscam2 mediates axonal tiling in the Drosophila visual system. Nature 2007; 447:720-4. [PMID: 17554308 PMCID: PMC2691714 DOI: 10.1038/nature05855] [Citation(s) in RCA: 116] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2007] [Accepted: 04/17/2007] [Indexed: 01/25/2023]
Abstract
Sensory processing centres in both the vertebrate and the invertebrate brain are often organized into reiterated columns, thus facilitating an internal topographic representation of the external world. Cells within each column are arranged in a stereotyped fashion and form precise patterns of synaptic connections within discrete layers. These connections are largely confined to a single column, thereby preserving the spatial information from the periphery. Other neurons integrate this information by connecting to multiple columns. Restricting axons to columns is conceptually similar to tiling. Axons and dendrites of neighbouring neurons of the same class use tiling to form complete, yet non-overlapping, receptive fields. It is thought that, at the molecular level, cell-surface proteins mediate tiling through contact-dependent repulsive interactions, but proteins serving this function have not yet been identified. Here we show that the immunoglobulin superfamily member Dscam2 restricts the connections formed by L1 lamina neurons to columns in the Drosophila visual system. Our data support a model in which Dscam2 homophilic interactions mediate repulsion between neurites of L1 cells in neighbouring columns. We propose that Dscam2 is a tiling receptor for L1 neurons.
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Affiliation(s)
- S Sean Millard
- Howard Hughes Medical Institute, Department of Biological Chemistry, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, California 90095, USA
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49
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Abstract
Dendrites from the same neuron usually avoid contact with one another, a behavior known as self-avoidance. In this issue of Neuron and in the upcoming May 4, 2007 issue of Cell, a pair of studies by Soba et al. and Hughes et al. and a study by Matthews et al., respectively, identify products from the highly alternatively spliced Dscam gene as central to this behavior in Drosophila. Signaling induced by adhesion between identical isoforms triggers repulsion between sister dendrites.
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Affiliation(s)
- Thomas Kidd
- Biology Department/MS 314, University of Nevada, Reno, NV 89557, USA.
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50
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Matthews BJ, Kim ME, Flanagan JJ, Hattori D, Clemens JC, Zipursky SL, Grueber WB. Dendrite self-avoidance is controlled by Dscam. Cell 2007; 129:593-604. [PMID: 17482551 DOI: 10.1016/j.cell.2007.04.013] [Citation(s) in RCA: 269] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2006] [Revised: 02/07/2007] [Accepted: 04/09/2007] [Indexed: 10/23/2022]
Abstract
Dendrites distinguish between sister branches and those of other cells. Self-recognition can often lead to repulsion, a process termed "self-avoidance." Here we demonstrate that dendrite self-avoidance in Drosophila da sensory neurons requires cell-recognition molecules encoded by the Dscam locus. By alternative splicing, Dscam encodes a vast number of cell-surface proteins of the immunoglobulin superfamily. We demonstrate that interactions between identical Dscam isoforms on the cell surface underlie self-recognition, while the cytoplasmic tail converts this recognition to dendrite repulsion. Sister dendrites expressing the same isoforms engage in homophilic repulsion. By contrast, Dscam diversity ensures that inappropriate repulsive interactions between dendrites sharing the same receptive field do not occur. The selectivity of Dscam-mediated cell interactions is likely to be widely important in the developing fly nervous system, where processes of cells must distinguish between self and nonself during the construction of neural circuits.
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Affiliation(s)
- Benjamin J Matthews
- Center for Neurobiology and Behavior, Columbia University, New York, NY 10032, USA
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