101
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Yue Y, Meng Y, Ma H, Hou S, Cao G, Hong W, Shi Y, Guo P, Liu B, Shi F, Yang Y, Jin Y. A large family of Dscam genes with tandemly arrayed 5' cassettes in Chelicerata. Nat Commun 2016; 7:11252. [PMID: 27080167 PMCID: PMC4835542 DOI: 10.1038/ncomms11252] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2015] [Accepted: 03/07/2016] [Indexed: 02/04/2023] Open
Abstract
Drosophila Dscam1 (Down Syndrome Cell Adhesion Molecules) and vertebrate clustered protocadherins (Pcdhs) are two classic examples of the extraordinary isoform diversity from a single genomic locus. Dscam1 encodes 38,016 distinct isoforms via mutually exclusive splicing in D. melanogaster, while the vertebrate clustered Pcdhs utilize alternative promoters to generate isoform diversity. Here we reveal a shortened Dscam gene family with tandemly arrayed 5' cassettes in Chelicerata. These cassette repeats generally comprise two or four exons, corresponding to variable Immunoglobulin 7 (Ig7) or Ig7-8 domains of Drosophila Dscam1. Furthermore, extraordinary isoform diversity has been generated through a combination of alternating promoter and alternative splicing. These sDscams have a high sequence similarity with Drosophila Dscam1, and share striking organizational resemblance to the 5' variable regions of vertebrate clustered Pcdhs. Hence, our findings have important implications for understanding the functional similarities between Drosophila Dscam1 and vertebrate Pcdhs, and may provide further mechanistic insights into the regulation of isoform diversity.
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Affiliation(s)
- Yuan Yue
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Yijun Meng
- College of Life and Environmental Sciences; Hangzhou Normal University, Hangzhou, Zhejiang ZJ310036, China
| | - Hongru Ma
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Shouqing Hou
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Guozheng Cao
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Weiling Hong
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Yang Shi
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Pengjuan Guo
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Baoping Liu
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Feng Shi
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Yun Yang
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
| | - Yongfeng Jin
- Institute of Biochemistry, Innovation Center for Signaling Network, College of Life Sciences, Zhejiang University, Hangzhou, Zhejiang ZJ310058, China
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102
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Peuß R, Wensing KU, Woestmann L, Eggert H, Milutinović B, Sroka MGU, Scharsack JP, Kurtz J, Armitage SAO. Down syndrome cell adhesion molecule 1: testing for a role in insect immunity, behaviour and reproduction. ROYAL SOCIETY OPEN SCIENCE 2016; 3:160138. [PMID: 27152227 PMCID: PMC4852650 DOI: 10.1098/rsos.160138] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 03/22/2016] [Indexed: 05/24/2023]
Abstract
Down syndrome cell adhesion molecule 1 (Dscam1) has wide-reaching and vital neuronal functions although the role it plays in insect and crustacean immunity is less well understood. In this study, we combine different approaches to understand the roles that Dscam1 plays in fitness-related contexts in two model insect species. Contrary to our expectations, we found no short-term modulation of Dscam1 gene expression after haemocoelic or oral bacterial exposure in Tribolium castaneum, or after haemocoelic bacterial exposure in Drosophila melanogaster. Furthermore, RNAi-mediated Dscam1 knockdown and subsequent bacterial exposure did not reduce T. castaneum survival. However, Dscam1 knockdown in larvae resulted in adult locomotion defects, as well as dramatically reduced fecundity in males and females. We suggest that Dscam1 does not always play a straightforward role in immunity, but strongly influences behaviour and fecundity. This study takes a step towards understanding more about the role of this intriguing gene from different phenotypic perspectives.
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103
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Meltzer S, Yadav S, Lee J, Soba P, Younger SH, Jin P, Zhang W, Parrish J, Jan LY, Jan YN. Epidermis-Derived Semaphorin Promotes Dendrite Self-Avoidance by Regulating Dendrite-Substrate Adhesion in Drosophila Sensory Neurons. Neuron 2016; 89:741-55. [PMID: 26853303 PMCID: PMC4760923 DOI: 10.1016/j.neuron.2016.01.020] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2014] [Revised: 05/27/2015] [Accepted: 01/11/2016] [Indexed: 01/15/2023]
Abstract
Precise patterning of dendritic arbors is critical for the wiring and function of neural circuits. Dendrite-extracellular matrix (ECM) adhesion ensures that the dendrites of Drosophila dendritic arborization (da) sensory neurons are properly restricted in a 2D space, and thereby facilitates contact-mediated dendritic self-avoidance and tiling. However, the mechanisms regulating dendrite-ECM adhesion in vivo are poorly understood. Here, we show that mutations in the semaphorin ligand sema-2b lead to a dramatic increase in self-crossing of dendrites due to defects in dendrite-ECM adhesion, resulting in a failure to confine dendrites to a 2D plane. Furthermore, we find that Sema-2b is secreted from the epidermis and signals through the Plexin B receptor in neighboring neurons. Importantly, we find that Sema-2b/PlexB genetically and physically interacts with TORC2 complex, Tricornered (Trc) kinase, and integrins. These results reveal a novel role for semaphorins in dendrite patterning and illustrate how epidermal-derived cues regulate neural circuit assembly.
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Affiliation(s)
- Shan Meltzer
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Smita Yadav
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jiae Lee
- Department of Biology, University of Washington, Seattle, WA 98195, USA
| | - Peter Soba
- Center for Molecular Neurobiology (ZMNH), University of Hamburg Medical School, Falkenried 94, 20251 Hamburg, Germany
| | - Susan H Younger
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Peng Jin
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Wei Zhang
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Jay Parrish
- Department of Biology, University of Washington, Seattle, WA 98195, USA
| | - Lily Yeh Jan
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA
| | - Yuh-Nung Jan
- Howard Hughes Medical Institute, Departments of Physiology, Biochemistry and Biophysics, University of California, San Francisco, San Francisco, CA 94158, USA.
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104
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Cherra SJ, Jin Y. A Two-Immunoglobulin-Domain Transmembrane Protein Mediates an Epidermal-Neuronal Interaction to Maintain Synapse Density. Neuron 2016; 89:325-36. [PMID: 26777275 PMCID: PMC4871750 DOI: 10.1016/j.neuron.2015.12.024] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2015] [Revised: 08/17/2015] [Accepted: 12/08/2015] [Indexed: 02/06/2023]
Abstract
Synaptic maintenance is essential for neural circuit function. In the C. elegans locomotor circuit, motor neurons are in direct contact with the epidermis. Here, we reveal a novel epidermal-neuronal interaction mediated by a two-immunoglobulin domain transmembrane protein, ZIG-10, that is necessary for maintaining cholinergic synapse density. ZIG-10 is localized at the cell surface of epidermis and cholinergic motor neurons, with high levels at areas adjacent to synapses. Loss of zig-10 increases the number of cholinergic excitatory synapses and exacerbates convulsion behavior in a seizure model. Mis-expression of zig-10 in GABAergic inhibitory neurons reduces GABAergic synapse number, dependent on the presence of ZIG-10 in the epidermis. Furthermore, ZIG-10 interacts with the tyrosine kinase SRC-2 to regulate the phagocytic activity of the epidermis to restrict cholinergic synapse number. Our studies demonstrate the highly specific roles of non-neuronal cells in modulating neural circuit function, through neuron-type-specific maintenance of synapse density.
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Affiliation(s)
- Salvatore J. Cherra
- Division of Biological Sciences, Section of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA
| | - Yishi Jin
- Division of Biological Sciences, Section of Neurobiology, University of California, San Diego, La Jolla, CA 92093, USA
- Department of Cellular and Molecular Medicine, University of California, San Diego, La Jolla, CA 92093, USA
- Howard Hughes Medical Institute, University of California, San Diego, La Jolla, CA 92093, USA
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105
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de Wit J, Ghosh A. Specification of synaptic connectivity by cell surface interactions. Nat Rev Neurosci 2015; 17:22-35. [PMID: 26656254 DOI: 10.1038/nrn.2015.3] [Citation(s) in RCA: 192] [Impact Index Per Article: 21.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The molecular diversification of cell surface molecules has long been postulated to impart specific surface identities on neuronal cell types. The existence of unique cell surface identities would allow neurons to distinguish one another and connect with their appropriate target cells. Although progress has been made in identifying cell type-specific surface molecule repertoires and in characterizing their extracellular interactions, determining how this molecular diversity contributes to the precise wiring of neural circuitry has proven challenging. Here, we review the role of the cadherin, neurexin, immunoglobulin and leucine-rich repeat protein superfamilies in the specification of connectivity. The emerging evidence suggests that the concerted actions of these proteins may critically contribute to the assembly of neural circuits.
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Affiliation(s)
- Joris de Wit
- VIB Center for the Biology of Disease and Center for Human Genetics, KU Leuven, Herestraat 49, 3000 Leuven, Belgium
| | - Anirvan Ghosh
- Neuroscience Discovery, Roche Innovation Center Basel, F. Hoffman-La Roche, Grenzacherstrasse 124, 4070 Basel, Switzerland
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106
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RAB-10 Regulates Dendritic Branching by Balancing Dendritic Transport. PLoS Genet 2015; 11:e1005695. [PMID: 26633194 PMCID: PMC4669152 DOI: 10.1371/journal.pgen.1005695] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 10/31/2015] [Indexed: 11/19/2022] Open
Abstract
The construction of a large dendritic arbor requires robust growth and the precise delivery of membrane and protein cargoes to specific subcellular regions of the developing dendrite. How the microtubule-based vesicular trafficking and sorting systems are regulated to distribute these dendritic development factors throughout the dendrite is not well understood. Here we identify the small GTPase RAB-10 and the exocyst complex as critical regulators of dendrite morphogenesis and patterning in the C. elegans sensory neuron PVD. In rab-10 mutants, PVD dendritic branches are reduced in the posterior region of the cell but are excessive in the distal anterior region of the cell. We also demonstrate that the dendritic branch distribution within PVD depends on the balance between the molecular motors kinesin-1/UNC-116 and dynein, and we propose that RAB-10 regulates dendrite morphology by balancing the activity of these motors to appropriately distribute branching factors, including the transmembrane receptor DMA-1. Building a complex dendritic arbor requires tremendous cellular growth, and how membrane and protein components are transported to support a rapidly growing, polarized dendrite remains unclear. We have identified the small GTPase RAB-10 as a key regulator of this process, providing insight into both dendritic development and the control of trafficking by small GTPases.
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107
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Yasunaga KI, Tezuka A, Ishikawa N, Dairyo Y, Togashi K, Koizumi H, Emoto K. Adult Drosophila sensory neurons specify dendritic territories independently of dendritic contacts through the Wnt5-Drl signaling pathway. Genes Dev 2015; 29:1763-75. [PMID: 26302791 PMCID: PMC4561484 DOI: 10.1101/gad.262592.115] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
Here, Yasunaga et al. use Drosophila class IV dendrite arborization (C4da) sensory neurons as a system to investigate how neurons specify dendritic territories during neuronal development. They show that, unlike the larval dendrites, adult C4da dendrites define the dendritic boundary independently of dendritic contacts and that Wnt5 derived from sternites is required for specification of the ventral boundaries of C4da dendrites. These findings provide novel insights into how dendritic territories of neurons develop and the role of the Wnt5–Drl signaling pathway in the contact-independent dendritic boundary specification. Sensory neurons with common functions are often nonrandomly arranged and form dendritic territories in stereotypic spatial patterns throughout the nervous system, yet molecular mechanisms of how neurons specify dendritic territories remain largely unknown. In Drosophila larvae, dendrites of class IV sensory (C4da) neurons completely but nonredundantly cover the whole epidermis, and the boundaries of these tiled dendritic fields are specified through repulsive interactions between homotypic dendrites. Here we report that, unlike the larval C4da neurons, adult C4da neurons rely on both dendritic repulsive interactions and external positional cues to delimit the boundaries of their dendritic fields. We identify Wnt5 derived from sternites, the ventral-most part of the adult abdominal epidermis, as the critical determinant for the ventral boundaries. Further genetic data indicate that Wnt5 promotes dendrite termination on the periphery of sternites through the Ryk receptor family kinase Derailed (Drl) and the Rho GTPase guanine nucleotide exchange factor Trio in C4da neurons. Our findings thus uncover the dendritic contact-independent mechanism that is required for dendritic boundary specification and suggest that combinatory actions of the dendritic contact-dependent and -independent mechanisms may ensure appropriate dendritic territories of a given neuron.
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Affiliation(s)
- Kei-ichiro Yasunaga
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Akane Tezuka
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Natsuko Ishikawa
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Yusuke Dairyo
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Kazuya Togashi
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Hiroyuki Koizumi
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
| | - Kazuo Emoto
- Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Bunkyo-ku, Tokyo 113-0033 Japan
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108
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Synaptic circuits and their variations within different columns in the visual system of Drosophila. Proc Natl Acad Sci U S A 2015; 112:13711-6. [PMID: 26483464 DOI: 10.1073/pnas.1509820112] [Citation(s) in RCA: 153] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We reconstructed the synaptic circuits of seven columns in the second neuropil or medulla behind the fly's compound eye. These neurons embody some of the most stereotyped circuits in one of the most miniaturized of animal brains. The reconstructions allow us, for the first time to our knowledge, to study variations between circuits in the medulla's neighboring columns. This variation in the number of synapses and the types of their synaptic partners has previously been little addressed because methods that visualize multiple circuits have not resolved detailed connections, and existing connectomic studies, which can see such connections, have not so far examined multiple reconstructions of the same circuit. Here, we address the omission by comparing the circuits common to all seven columns to assess variation in their connection strengths and the resultant rates of several different and distinct types of connection error. Error rates reveal that, overall, <1% of contacts are not part of a consensus circuit, and we classify those contacts that supplement (E+) or are missing from it (E-). Autapses, in which the same cell is both presynaptic and postsynaptic at the same synapse, are occasionally seen; two cells in particular, Dm9 and Mi1, form ≥ 20-fold more autapses than do other neurons. These results delimit the accuracy of developmental events that establish and normally maintain synaptic circuits with such precision, and thereby address the operation of such circuits. They also establish a precedent for error rates that will be required in the new science of connectomics.
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109
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Rubinstein R, Thu CA, Goodman KM, Wolcott HN, Bahna F, Mannepalli S, Ahlsen G, Chevee M, Halim A, Clausen H, Maniatis T, Shapiro L, Honig B. Molecular logic of neuronal self-recognition through protocadherin domain interactions. Cell 2015; 163:629-42. [PMID: 26478182 DOI: 10.1016/j.cell.2015.09.026] [Citation(s) in RCA: 116] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2015] [Revised: 07/17/2015] [Accepted: 08/27/2015] [Indexed: 12/27/2022]
Abstract
Self-avoidance, a process preventing interactions of axons and dendrites from the same neuron during development, is mediated in vertebrates through the stochastic single-neuron expression of clustered protocadherin protein isoforms. Extracellular cadherin (EC) domains mediate isoform-specific homophilic binding between cells, conferring cell recognition through a poorly understood mechanism. Here, we report crystal structures for the EC1-EC3 domain regions from four protocadherin isoforms representing the α, β, and γ subfamilies. All are rod shaped and monomeric in solution. Biophysical measurements, cell aggregation assays, and computational docking reveal that trans binding between cells depends on the EC1-EC4 domains, which interact in an antiparallel orientation. We also show that the EC6 domains are required for the formation of cis-dimers. Overall, our results are consistent with a model in which protocadherin cis-dimers engage in a head-to-tail interaction between EC1-EC4 domains from apposed cell surfaces, possibly forming a zipper-like protein assembly, and thus providing a size-dependent self-recognition mechanism.
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Affiliation(s)
- Rotem Rubinstein
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA
| | - Chan Aye Thu
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Kerry Marie Goodman
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Holly Noelle Wolcott
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Fabiana Bahna
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA
| | - Seetha Mannepalli
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Goran Ahlsen
- Department of Systems Biology, Columbia University, New York, NY 10032, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA
| | - Maxime Chevee
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Adnan Halim
- Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Henrik Clausen
- Copenhagen Center for Glycomics, Departments of Cellular and Molecular Medicine, Faculty of Health Sciences, University of Copenhagen, 2200 Copenhagen N, Denmark
| | - Tom Maniatis
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Lawrence Shapiro
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA.
| | - Barry Honig
- Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Department of Systems Biology, Columbia University, New York, NY 10032, USA; Department of Medicine, Columbia University, New York, NY 10032, USA; Zuckerman Mind Brain Behavior Institute, Columbia University, New York, NY 10032, USA; Howard Hughes Medical Institute, Columbia University, New York, NY 10032, USA.
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110
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Allorecognition proteins in an invertebrate exhibit homophilic interactions. Curr Biol 2015; 25:2845-2850. [PMID: 26455308 DOI: 10.1016/j.cub.2015.09.030] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2015] [Revised: 08/31/2015] [Accepted: 09/11/2015] [Indexed: 11/21/2022]
Abstract
Sessile colonial invertebrates-animals such as sponges, corals, bryozoans, and ascidians-can distinguish between their own tissues and those of conspecifics upon contact [1]. This ability, called allorecognition, mediates spatial competition and can prevent stem cell parasitism by ensuring that colonies only fuse with self or close kin. In every taxon studied to date, allorecognition is controlled by one or more highly polymorphic genes [2-8]. However, in no case is it understood how the proteins encoded by these genes discriminate self from non-self. In the cnidarian Hydractinia symbiolongicarpus, allorecognition is controlled by at least two highly polymorphic allorecognition genes, Alr1 and Alr2 [3, 5, 9-12]. Sequence variation at each gene predicts allorecognition in laboratory strains such that colonies reject if they do not share a common allele at either locus, fuse temporarily if they share an allele at only one locus, or fuse permanently if they share an allele at both genes [5, 9]. Here, we show that the gene products of Alr1 and Alr2 (Alr1 and Alr2) are self-ligands with extraordinary specificity. Using an in vitro cell aggregation assay, we found that Alr1 and Alr2 bind to themselves homophilically across opposing cell membranes. For both proteins, each isoform bound only to itself or to an isoform of nearly identical sequence. These results provide a mechanistic explanation for the exquisite specificity of Hydractinia allorecognition. Our results also indicate that hydroids have evolved a molecular strategy of self-recognition that is unique among characterized allorecognition systems within and outside invertebrates.
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111
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Abstract
The nervous system is populated by numerous types of neurons, each bearing a dendritic arbor with a characteristic morphology. These type-specific features influence many aspects of a neuron's function, including the number and identity of presynaptic inputs and how inputs are integrated to determine firing properties. Here, we review the mechanisms that regulate the construction of cell type-specific dendrite patterns during development. We focus on four aspects of dendrite patterning that are particularly important in determining the function of the mature neuron: (a) dendrite shape, including branching pattern and geometry of the arbor; (b) dendritic arbor size;
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Affiliation(s)
| | - Joshua R Sanes
- Center for Brain Science and Department of Molecular and Cellular Biology, Harvard University, Cambridge, Massachusetts 02138;
| | - Jeremy N Kay
- Departments of Neurobiology and Ophthalmology, Duke University School of Medicine, Durham, North Carolina 27710;
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112
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Garrett AM, Burgess RW. Self-awareness in the retina. eLife 2015; 4. [PMID: 26305501 PMCID: PMC4548409 DOI: 10.7554/elife.10233] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Proteins called gamma-protocadherins are essential for the establishment of working circuits of neurons in the retina.
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113
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Kostadinov D, Sanes JR. Protocadherin-dependent dendritic self-avoidance regulates neural connectivity and circuit function. eLife 2015; 4. [PMID: 26140686 PMCID: PMC4548410 DOI: 10.7554/elife.08964] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2015] [Accepted: 07/02/2015] [Indexed: 12/30/2022] Open
Abstract
Dendritic and axonal arbors of many neuronal types exhibit self-avoidance, in which branches repel each other. In some cases, these neurites interact with those of neighboring neurons, a phenomenon called self/non-self discrimination. The functional roles of these processes remain unknown. In this study, we used retinal starburst amacrine cells (SACs), critical components of a direction-selective circuit, to address this issue. In SACs, both processes are mediated by the gamma-protocadherins (Pcdhgs), a family of 22 recognition molecules. We manipulated Pcdhg expression in SACs and recorded from them and their targets, direction-selective ganglion cells (DSGCs). SACs form autapses when self-avoidance is disrupted and fail to form connections with other SACs when self/non-self discrimination is perturbed. Pcdhgs are also required to prune connections between closely spaced SACs. These alterations degrade the direction selectivity of DSGCs. Thus, self-avoidance, self/non-self discrimination, and synapse elimination are essential for proper function of a circuit that computes directional motion. DOI:http://dx.doi.org/10.7554/eLife.08964.001 Nerve cells (or neurons) connect to one another to form circuits that control the animal's behavior. Typically, each neuron receives signals from other cells via branch-like structures called dendrites. Each specific type of neuron has a characteristic pattern of branched dendrites, which is different from the pattern of other types of neuron. Therefore, it is reasonable to imagine that the shape of these branches can influence how the neuron works; however, this idea has rarely been tested experimentally. Different processes are known to act together to control the pattern of the branched dendrites. For example, dendrites in some neurons avoid other dendrites from the same neuron. This phenomenon is referred to as ‘self-avoidance’. In some of these cases, the same dendrites freely interact with the dendrites of neighboring neurons of the same type; this is called ‘self/non-self discrimination’. It is not clear, however, how these two processes influence the activity of neural circuits. Both self-avoidance and self/non-self discrimination rely on the expression of genes that encode so-called recognition molecules. Kostadinov and Sanes have now altered the expression of these genes in mice to see the effect that disrupting these two phenomena has on a set of neurons called ‘starburst amacrine cells’ that are found at the back the eye. The dendrites of starburst amacrine cells generate signals when objects move across the animal's field of vision. These dendrites then signal to other starburst amacrine cells and to so-called ‘direction-selective ganglion cells’, which in turn send this information to the brain for further processing. The experiments revealed that these disruptions affected the connections between the dendrites. Starburst amacrine cells that lacked self-avoidance mistakenly formed connections with themselves—as if they mistook their own dendrites for those of other starburst cells. In contrast, neurons that lacked self/non-self discrimination made the opposite mistake, and rarely formed connections with each other—as if they mistook the dendrites of other starbursts for their own. Disruptions to either phenomenon interfered with the activity of the direction-selective ganglion cells. Following on from the work of Kostadinov and Sanes, the next challenges include uncovering how the recognition molecules help with self-avoidance and self/non-self discrimination. It will also be important to examine whether the conclusions based on one type of neurons can be generalized to others that also exhibit these two phenomena. DOI:http://dx.doi.org/10.7554/eLife.08964.002
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Affiliation(s)
- Dimitar Kostadinov
- Center for Brain Science, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
| | - Joshua R Sanes
- Center for Brain Science, Department of Molecular and Cellular Biology, Harvard University, Cambridge, United States
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114
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Raj B, Blencowe B. Alternative Splicing in the Mammalian Nervous System: Recent Insights into Mechanisms and Functional Roles. Neuron 2015; 87:14-27. [DOI: 10.1016/j.neuron.2015.05.004] [Citation(s) in RCA: 321] [Impact Index Per Article: 35.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
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115
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116
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Coughlin GM, Kurrasch DM. Protocadherins and hypothalamic development: do they play an unappreciated role? J Neuroendocrinol 2015; 27:544-55. [PMID: 25845440 DOI: 10.1111/jne.12280] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/11/2015] [Revised: 03/26/2015] [Accepted: 03/27/2015] [Indexed: 12/17/2022]
Abstract
Normal brain development requires coordinated cell movements at precise times. It has long been established that cell-cell adhesion proteins of the cadherin superfamily are involved in the adhesion and sorting of cells during tissue morphogenesis. In the present review, we focus on protocadherins, which form the largest subfamily of the cadherin superfamily and mediate homophilic cell-cell adhesion in the developing brain. These molecules are highly expressed during neural development and the exact roles that they play are still emerging. Although, historically, protocadherins were considered to provide mechanical and chemical connections between adjacent cells, recent research suggests that they may also serve as molecular identity markers of neurones to help guide cell recognition and sorting, cell migration, outgrowth of neuronal processes, and synapse formation. This phenomenon of single cell diversity stems, in part, from the vast variation in protein structure, genomic organisation and molecular function of the protocadherins. Although expression profiles and genetic manipulations have provided evidence for the role of protocadherins in the developing brain, we have only begun to construct a complete understanding of protocadherin function. We examine our current understanding of how protocadherins influence brain development and discuss the possible roles for this large superfamily within the hypothalamus. We conclude that further research into these underappreciated but vitally important genes will shed insight into hypothalamic development and perhaps the underlying aetiology of neuroendocrine disorders.
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Affiliation(s)
- G M Coughlin
- Department of Medical Genetics, University of Calgary, Calgary, AB, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
| | - D M Kurrasch
- Department of Medical Genetics, University of Calgary, Calgary, AB, Canada
- Alberta Children's Hospital Research Institute, University of Calgary, Calgary, AB, Canada
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Sterne GR, Kim JH, Ye B. Dysregulated Dscam levels act through Abelson tyrosine kinase to enlarge presynaptic arbors. eLife 2015; 4. [PMID: 25988807 PMCID: PMC4434255 DOI: 10.7554/elife.05196] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Accepted: 04/15/2015] [Indexed: 11/20/2022] Open
Abstract
Increased expression of Down Syndrome Cell Adhesion Molecule (Dscam) is implicated in the pathogenesis of brain disorders such as Down syndrome (DS) and fragile X syndrome (FXS). Here, we show that the cellular defects caused by dysregulated Dscam levels can be ameliorated by genetic and pharmacological inhibition of Abelson kinase (Abl) both in Dscam-overexpressing neurons and in a Drosophila model of fragile X syndrome. This study offers Abl as a potential therapeutic target for treating brain disorders associated with dysregulated Dscam expression. DOI:http://dx.doi.org/10.7554/eLife.05196.001 Information is transmitted through the brain by cells called neurons, which are connected into specific circuits and networks. As the brain develops, several different signaling molecules control how the connections between neurons develop. If these signals occur at the wrong time or wrong place, or in the wrong amount, the neurons may not connect in the right way; this is the cause of several brain disorders. One of the signaling molecules that helps neural circuits to form in the developing brain is the Dscam protein. Having too much Dscam has been linked to neurons with enlarged presynaptic terminals. Presynaptic terminals are the parts of each neuron that send information on to the next cell, and when they are enlarged it results in the neuron not being able to communicate with other neurons in a targeted way. People with brain disorders including Down syndrome, epilepsy and possibly fragile X syndrome often have excessive amounts of Dscam. It was not known precisely how Dscam signals within neurons. Sterne, Kim and Ye have now investigated this by exploring the effects of Dscam on a group of well-known neurons in the larvae of the fruit fly species Drosophila. The presynaptic terminals of single neurons in this group were labeled in the larvae using a genetic marker. This revealed that the neurons of larvae that had been engineered to produce too much Dscam had larger presynaptic terminals than normal. Further investigation showed that for Dscam to influence how a presynaptic terminal grows, it must interact with another signaling protein called Abelson tyrosine kinase (or Abl for short). Therefore, the larger presynaptic terminals seen in larvae that produce too much Dscam are a result of the Dscam protein activating too much Abl. There are several drugs that are approved for use in humans that suppress the activity of Abl. Sterne, Kim and Ye used two of these to treat fruit fly larvae, and found that they reversed the detrimental effects of extra Dscam on the larvae's neural circuit. Furthermore, the drugs fixed neural defects in a fruit fly model designed to reproduce the symptoms of fragile X syndrome. Overall, the results presented by Sterne, Kim and Ye suggest that suppressing the abnormally high activity of the Abl protein could be a way of treating the brain disorders caused by having excessive amounts of the Dscam protein. The next step is to test whether Dscam and Abl interact in the same way in mammals and whether the proposed treatment is effective in treating mammalian models of disorders that involve dysregulated Dscam signaling. DOI:http://dx.doi.org/10.7554/eLife.05196.002
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Affiliation(s)
- Gabriella R Sterne
- Life Sciences Institute, University of Michigan, Ann Arbor, United States
| | - Jung Hwan Kim
- Life Sciences Institute, University of Michigan, Ann Arbor, United States
| | - Bing Ye
- Life Sciences Institute, University of Michigan, Ann Arbor, United States
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Roy CK, Olson S, Graveley BR, Zamore PD, Moore MJ. Assessing long-distance RNA sequence connectivity via RNA-templated DNA-DNA ligation. eLife 2015; 4. [PMID: 25866926 PMCID: PMC4442144 DOI: 10.7554/elife.03700] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2014] [Accepted: 04/12/2015] [Indexed: 02/04/2023] Open
Abstract
Many RNAs, including pre-mRNAs and long non-coding RNAs, can be thousands of nucleotides long and undergo complex post-transcriptional processing. Multiple sites of alternative splicing within a single gene exponentially increase the number of possible spliced isoforms, with most human genes currently estimated to express at least ten. To understand the mechanisms underlying these complex isoform expression patterns, methods are needed that faithfully maintain long-range exon connectivity information in individual RNA molecules. In this study, we describe SeqZip, a methodology that uses RNA-templated DNA–DNA ligation to retain and compress connectivity between distant sequences within single RNA molecules. Using this assay, we test proposed coordination between distant sites of alternative exon utilization in mouse Fn1, and we characterize the extraordinary exon diversity of Drosophila melanogaster Dscam1. DOI:http://dx.doi.org/10.7554/eLife.03700.001 A flow chart can show how an outcome can be achieved from a particular start point by breaking down an activity into a list of possible steps. Often, a flow chart contains several alternative steps, not all of which are taken every time the flow chart is used. The same can be said of genes, which are biological instructions that often contain many options within their DNA sequences. Proteins—which perform many roles in cells—are built following the instructions contained in genes. First, the DNA sequence of the gene is copied. This produces a molecule of ribonucleic acid (RNA), which is able to move around the cell to find the machinery that can use the genetic information to make a protein. Genes and their RNA copies contain instructions with more steps—called exons—than are necessary to make a working protein, so extra exons are removed (‘spliced’) from the RNA copies. Different combinations of exons can be removed, so splicing can make different versions of the RNA called isoforms. These allow a single gene to build many different proteins. In fruit flies, for example, the different exons of the gene Dscam1 can be spliced into one of 38,016 unique RNA isoforms. Current technology only allows researchers to deduce the sequence of RNA molecules by combining sequences recorded from short fragments of the molecule. However, before splicing, RNA molecules tend to be much longer than this, so this restricts our understanding of the RNA isoforms found in cells. Here, Roy et al. devised and tested a new method called SeqZip to solve this problem. SeqZip uses short fragments of DNA called ligamers that can only stick to the sections of RNA that will remain after the molecule has been spliced. After splicing, the ligamers can be stuck together to make a DNA replica of the spliced RNA. The end product is at least 49 times shorter than the original RNA, so it is easier to sequence. In addition, the combinations of the ligamers in the DNA replica show which exons of a specific gene are kept and which ones are spliced out. To test the method, Roy et al. studied a mouse gene that has six RNA isoforms. SeqZip reduced the length of the RNA by five times and made it possible to measure how frequently the different isoforms naturally arise. Roy et al. also used SeqZip to work out which isoforms of the Dscam1 gene are used at different stages in the life of fruit fly larvae. SeqZip can provide insights into how complex organisms like flies, mice, and humans have evolved with relatively few—a little over 20,000—genes in their genomes. DOI:http://dx.doi.org/10.7554/eLife.03700.002
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Affiliation(s)
- Christian K Roy
- RNA Therapeutics Institute, Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, United States
| | - Sara Olson
- Institute for Systems Genomics, Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, United States
| | - Brenton R Graveley
- Institute for Systems Genomics, Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, United States
| | - Phillip D Zamore
- RNA Therapeutics Institute, Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, United States
| | - Melissa J Moore
- RNA Therapeutics Institute, Howard Hughes Medical Institute, University of Massachusetts Medical School, Worcester, United States
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Wilken MS, Brzezinski JA, La Torre A, Siebenthall K, Thurman R, Sabo P, Sandstrom RS, Vierstra J, Canfield TK, Hansen RS, Bender MA, Stamatoyannopoulos J, Reh TA. DNase I hypersensitivity analysis of the mouse brain and retina identifies region-specific regulatory elements. Epigenetics Chromatin 2015; 8:8. [PMID: 25972927 PMCID: PMC4429822 DOI: 10.1186/1756-8935-8-8] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 01/27/2015] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The brain, spinal cord, and neural retina comprise the central nervous system (CNS) of vertebrates. Understanding the regulatory mechanisms that underlie the enormous cell-type diversity of the CNS is a significant challenge. Whole-genome mapping of DNase I-hypersensitive sites (DHSs) has been used to identify cis-regulatory elements in many tissues. We have applied this approach to the mouse CNS, including developing and mature neural retina, whole brain, and two well-characterized brain regions, the cerebellum and the cerebral cortex. RESULTS For the various regions and developmental stages of the CNS that we analyzed, there were approximately the same number of DHSs; however, there were many DHSs unique to each CNS region and developmental stage. Many of the DHSs are likely to mark enhancers that are specific to the specific CNS region and developmental stage. We validated the DNase I mapping approach for identification of CNS enhancers using the existing VISTA Browser database and with in vivo and in vitro electroporation of the retina. Analysis of transcription factor consensus sites within the DHSs shows distinct region-specific profiles of transcriptional regulators particular to each region. Clustering developmentally dynamic DHSs in the retina revealed enrichment of developmental stage-specific transcriptional regulators. Additionally, we found reporter gene activity in the retina driven from several previously uncharacterized regulatory elements surrounding the neurodevelopmental gene Otx2. Identification of DHSs shared between mouse and human showed region-specific differences in the evolution of cis-regulatory elements. CONCLUSIONS Overall, our results demonstrate the potential of genome-wide DNase I mapping to cis-regulatory questions regarding the regional diversity within the CNS. These data represent an extensive catalogue of potential cis-regulatory elements within the CNS that display region and temporal specificity, as well as a set of DHSs common to CNS tissues. Further examination of evolutionary conservation of DHSs between CNS regions and different species may reveal important cis-regulatory elements in the evolution of the mammalian CNS.
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Affiliation(s)
- Matthew S Wilken
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Box 357420, Seattle, WA 98195 USA ; Molecular and Cellular Biology Program, University of Washington, MCB Program Office, T-466 Health Sciences Building, Box 357275, Seattle, WA 98195 USA
| | - Joseph A Brzezinski
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Box 357420, Seattle, WA 98195 USA ; Department of Ophthalmology, University of Colorado School of Medicine, 1675 Aurora Court, Aurora, CO 80045 USA
| | - Anna La Torre
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Box 357420, Seattle, WA 98195 USA
| | - Kyle Siebenthall
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Robert Thurman
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Peter Sabo
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Richard S Sandstrom
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Jeff Vierstra
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Theresa K Canfield
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - R Scott Hansen
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Michael A Bender
- Department of Pediatrics, University of Washington, 1959 NE Pacific St, Health Sciences Building, Seattle, WA Box 356320, 98195 USA ; Clinical Research Division, Fred Hutchinson Cancer Research Center, 1100 Fairview Avenue North, Seattle, WA 98109 USA
| | - John Stamatoyannopoulos
- Department of Genome Sciences, University of Washington, Foege Building S-250, 3720 15th Ave NE, Box 355065, Seattle, WA 98195 USA
| | - Thomas A Reh
- Department of Biological Structure, University of Washington, 1959 NE Pacific Street, Box 357420, Seattle, WA 98195 USA
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Meguro R, Hishida R, Tsukano H, Yoshitake K, Imamura R, Tohmi M, Kitsukawa T, Hirabayashi T, Yagi T, Takebayashi H, Shibuki K. Impaired clustered protocadherin-α leads to aggregated retinogeniculate terminals and impaired visual acuity in mice. J Neurochem 2015; 133:66-72. [PMID: 25650227 DOI: 10.1111/jnc.13053] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2014] [Revised: 01/16/2015] [Accepted: 01/26/2015] [Indexed: 11/26/2022]
Abstract
Clustered protocadherins (cPcdhs) comprising cPcdh-α, -β, and -γ, encode a large family of cadherin-like cell-adhesion molecules specific to neurons. Impairment of cPcdh-α results in abnormal neuronal projection patterns in specific brain areas. To elucidate the role of cPcdh-α in retinogeniculate projections, we investigated the morphological patterns of retinogeniculate terminals in the lateral geniculate (LG) nucleus of mice with impaired cPcdh-α. We found huge aggregated retinogeniculate terminals in the dorsal LG nucleus, whereas no such aggregated terminals derived from the retina were observed in the olivary pretectal nucleus and the ventral LG nucleus. These aggregated terminals appeared between P10 and P14, just before eye opening and at the beginning of the refinement stage of the retinogeniculate projections. Reduced visual acuity was observed in adult mice with impaired cPcdh-α, whereas the orientation selectivity and direction selectivity of neurons in the primary visual cortex were apparently normal. These findings suggest that cPcdh-α is required for adequate spacing of retinogeniculate projections, which may be essential for normal development of visual acuity.
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Affiliation(s)
- Reiko Meguro
- Division of Neurobiology and Anatomy, Graduate School of Medical and Dental Sciences, Niigata University, Niigata, Japan
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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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Thu CA, Chen WV, Rubinstein R, Chevee M, Wolcott HN, Felsovalyi KO, Tapia JC, Shapiro L, Honig B, Maniatis T. Single-cell identity generated by combinatorial homophilic interactions between α, β, and γ protocadherins. Cell 2015; 158:1045-1059. [PMID: 25171406 DOI: 10.1016/j.cell.2014.07.012] [Citation(s) in RCA: 154] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2014] [Revised: 06/18/2014] [Accepted: 07/07/2014] [Indexed: 02/07/2023]
Abstract
Individual mammalian neurons stochastically express distinct repertoires of α, β, and γ protocadherin (Pcdh) proteins, which function in neural circuit assembly. We report that all three subfamilies of clustered Pcdhs can engage in specific homophilic interactions, that cell surface delivery of Pcdhα isoforms requires cis interactions with other Pcdhs, and that the extracellular cadherin domain EC6 plays a critical role in this process. Examination of homophilic interactions between specific combinations of multiple Pcdh isoforms revealed that Pcdh combinatorial recognition specificities depend on the identity of all of the expressed isoforms. A single mismatched Pcdh isoform can interfere with these combinatorial homophilic interactions. A theoretical analysis reveals that assembly of Pcdh isoforms into multimeric recognition units and the observed tolerance for mismatched isoforms can generate cell surface diversity sufficient for single-cell identity. However, the competing demands of nonself discrimination and self-recognition place limitations on the mechanisms by which homophilic recognition units can function.
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Affiliation(s)
- Chan Aye Thu
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 701 W 168th Street, New York, NY 10032, USA
| | - Weisheng V Chen
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 701 W 168th Street, New York, NY 10032, USA
| | - Rotem Rubinstein
- Center for Computational Biology and Bioinformatics, Columbia University Medical Center, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Department of System Biology, Columbia University, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Howard Hughes Medical Institute
| | - Maxime Chevee
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 701 W 168th Street, New York, NY 10032, USA
| | - Holly N Wolcott
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, New York, NY 10032, USA
| | - Klara O Felsovalyi
- Center for Computational Biology and Bioinformatics, Columbia University Medical Center, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Department of System Biology, Columbia University, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Howard Hughes Medical Institute
| | - Juan Carlos Tapia
- Department of Neuroscience, Columbia University, 1051 Riverside Drive, New York, NY 10032, USA
| | - Lawrence Shapiro
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, New York, NY 10032, USA; Department of System Biology, Columbia University, 1130 St. Nicholas Avenue, New York, NY 10032, USA
| | - Barry Honig
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 1150 St. Nicholas Avenue, Russ Berrie Pavilion, New York, NY 10032, USA; Center for Computational Biology and Bioinformatics, Columbia University Medical Center, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Department of System Biology, Columbia University, 1130 St. Nicholas Avenue, New York, NY 10032, USA; Howard Hughes Medical Institute.
| | - Tom Maniatis
- Department of Biochemistry and Molecular Biophysics, Columbia University Medical Center, 701 W 168th Street, New York, NY 10032, USA.
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Abstract
The complex, branched morphology of dendrites is a cardinal feature of neurons and has been used as a criterion for cell type identification since the beginning of neurobiology. Regulated dendritic outgrowth and branching during development form the basis of receptive fields for neurons and are essential for the wiring of the nervous system. The cellular and molecular mechanisms of dendritic morphogenesis have been an intensely studied area. In this review, we summarize the major experimental systems that have contributed to our understandings of dendritic development as well as the intrinsic and extrinsic mechanisms that instruct the neurons to form cell type-specific dendritic arbors.
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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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Komulainen E, Zdrojewska J, Freemantle E, Mohammad H, Kulesskaya N, Deshpande P, Marchisella F, Mysore R, Hollos P, Michelsen KA, Mågard M, Rauvala H, James P, Coffey ET. JNK1 controls dendritic field size in L2/3 and L5 of the motor cortex, constrains soma size, and influences fine motor coordination. Front Cell Neurosci 2014; 8:272. [PMID: 25309320 PMCID: PMC4162472 DOI: 10.3389/fncel.2014.00272] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2014] [Accepted: 08/20/2014] [Indexed: 11/23/2022] Open
Abstract
Genetic anomalies on the JNK pathway confer susceptibility to autism spectrum disorders, schizophrenia, and intellectual disability. The mechanism whereby a gain or loss of function in JNK signaling predisposes to these prevalent dendrite disorders, with associated motor dysfunction, remains unclear. Here we find that JNK1 regulates the dendritic field of L2/3 and L5 pyramidal neurons of the mouse motor cortex (M1), the main excitatory pathway controlling voluntary movement. In Jnk1-/- mice, basal dendrite branching of L5 pyramidal neurons is increased in M1, as is cell soma size, whereas in L2/3, dendritic arborization is decreased. We show that JNK1 phosphorylates rat HMW-MAP2 on T1619, T1622, and T1625 (Uniprot P15146) corresponding to mouse T1617, T1620, T1623, to create a binding motif, that is critical for MAP2 interaction with and stabilization of microtubules, and dendrite growth control. Targeted expression in M1 of GFP-HMW-MAP2 that is pseudo-phosphorylated on T1619, T1622, and T1625 increases dendrite complexity in L2/3 indicating that JNK1 phosphorylation of HMW-MAP2 regulates the dendritic field. Consistent with the morphological changes observed in L2/3 and L5, Jnk1-/- mice exhibit deficits in limb placement and motor coordination, while stride length is reduced in older animals. In summary, JNK1 phosphorylates HMW-MAP2 to increase its stabilization of microtubules while at the same time controlling dendritic fields in the main excitatory pathway of M1. Moreover, JNK1 contributes to normal functioning of fine motor coordination. We report for the first time, a quantitative Sholl analysis of dendrite architecture, and of motor behavior in Jnk1-/- mice. Our results illustrate the molecular and behavioral consequences of interrupted JNK1 signaling and provide new ground for mechanistic understanding of those prevalent neuropyschiatric disorders where genetic disruption of the JNK pathway is central.
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Affiliation(s)
- Emilia Komulainen
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Justyna Zdrojewska
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Erika Freemantle
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Hasan Mohammad
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | | | - Prasannakumar Deshpande
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Francesca Marchisella
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Raghavendra Mysore
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | - Patrik Hollos
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
| | | | - Mats Mågard
- Institute for Immune Technology, Medicon Village, University of Lund Lund, Sweden
| | - Heikki Rauvala
- Neuroscience Center, University of Helsinki Helsinki, Finland
| | - Peter James
- Institute for Immune Technology, Medicon Village, University of Lund Lund, Sweden
| | - Eleanor T Coffey
- Turku Centre for Biotechnology, Åbo Akademi University and University of Turku Turku, Finland
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Abstract
Precise connectivity in neuronal circuits is a prerequisite for proper brain function. The dauntingly complex environment encountered by axons and dendrites, even after navigation to their target area, prompts the question of how specificity of synaptic connections arises during development. We review developmental strategies and molecular mechanisms that are used by neurons to ensure their precise matching of pre- and postsynaptic elements. The emerging theme is that each circuit uses a combination of simple mechanisms to achieve its refined, often complex connectivity pattern. At increasing levels of resolution, from lamina choice to subcellular targeting, similar signaling concepts are reemployed to narrow the choice of potential matches. Temporal control over synapse development and synapse elimination further ensures the specificity of connections in the nervous system.
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Affiliation(s)
- Shaul Yogev
- Department of Biology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305;
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127
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Abstract
Post-transcriptional pre-mRNA splicing has emerged as a critical step in the gene expression cascade greatly influencing diversification and spatiotemporal control of the proteome in many developmental processes. The percentage of genes targeted by alternative splicing (AS) is shown to be over 95% in humans and 60% in Drosophila. Therefore, it is evident that deregulation of this process underlies many genetic diseases. Among all tissues, the brain shows the highest transcriptome diversity, which is not surprising in view of the complex inter- and intracellular networks underlying the development of this organ. Reports of isoforms known to function at different steps during Drosophila nervous system development are rapidly increasing as well as knowledge on their regulation and function, highlighting the role of AS during neuronal development in Drosophila.
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Affiliation(s)
- Carmen Mohr
- Institute of Human Genetics, University Medical Center Freiburg , Freiburg , Germany
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128
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Caviglia S, Luschnig S. Tube fusion: Making connections in branched tubular networks. Semin Cell Dev Biol 2014; 31:82-90. [DOI: 10.1016/j.semcdb.2014.03.018] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2014] [Revised: 03/03/2014] [Accepted: 03/14/2014] [Indexed: 11/16/2022]
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129
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Tsai L, Barnea G. A critical period defined by axon-targeting mechanisms in the murine olfactory bulb. Science 2014; 344:197-200. [PMID: 24723611 DOI: 10.1126/science.1248806] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The olfactory system remains plastic throughout life because of continuous neurogenesis of sensory neurons in the nose and inhibitory interneurons in the olfactory bulb. Here, we reveal that transgenic expression of an odorant receptor has non-cell autonomous effects on axons expressing this receptor from the endogenous gene. Perinatal expression of transgenic odorant receptor causes rerouting of like axons to new glomeruli, whereas expression after the sensory map is established does not lead to rerouting. Further, chemical ablation of the map after rerouting does not restore the normal map, even when the transgenic receptor is no longer expressed. Our results reveal that glomeruli are designated as targets for sensory neurons expressing specific odorant receptors during a critical period in the formation of the olfactory sensory map.
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Affiliation(s)
- Lulu Tsai
- Department of Neuroscience, Brown University, Providence, RI 02912, USA
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130
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Machamer JB, Collins SE, Lloyd TE. The ALS gene FUS regulates synaptic transmission at the Drosophila neuromuscular junction. Hum Mol Genet 2014; 23:3810-22. [PMID: 24569165 DOI: 10.1093/hmg/ddu094] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Mutations in the RNA binding protein Fused in sarcoma (FUS) are estimated to account for 5-10% of all inherited cases of amyotrophic lateral sclerosis (ALS), but the function of FUS in motor neurons is poorly understood. Here, we investigate the early functional consequences of overexpressing wild-type or ALS-associated mutant FUS proteins in Drosophila motor neurons, and compare them to phenotypes arising from loss of the Drosophila homolog of FUS, Cabeza (Caz). We find that lethality and locomotor phenotypes correlate with levels of FUS transgene expression, indicating that toxicity in developing motor neurons is largely independent of ALS-linked mutations. At the neuromuscular junction (NMJ), overexpression of either wild-type or mutant FUS results in decreased number of presynaptic active zones and altered postsynaptic glutamate receptor subunit composition, coinciding with a reduction in synaptic transmission as a result of both reduced quantal size and quantal content. Interestingly, expression of human FUS downregulates endogenous Caz levels, demonstrating that FUS autoregulation occurs in motor neurons in vivo. However, loss of Caz from motor neurons increases synaptic transmission as a result of increased quantal size, suggesting that the loss of Caz in animals expressing FUS does not contribute to motor deficits. These data demonstrate that FUS/Caz regulates NMJ development and plays an evolutionarily conserved role in modulating the strength of synaptic transmission in motor neurons.
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Affiliation(s)
| | | | - Thomas E Lloyd
- Department of Neurology, and The Solomon H. Snyder Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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131
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Miura SK, Martins A, Zhang KX, Graveley BR, Zipursky SL. Probabilistic splicing of Dscam1 establishes identity at the level of single neurons. Cell 2014; 155:1166-77. [PMID: 24267895 DOI: 10.1016/j.cell.2013.10.018] [Citation(s) in RCA: 74] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/27/2013] [Accepted: 10/09/2013] [Indexed: 11/17/2022]
Abstract
The Drosophila Dscam1 gene encodes a vast number of cell recognition molecules through alternative splicing. These exhibit isoform-specific homophilic binding and regulate self-avoidance, the tendency of neurites from the same cell to repel one another. Genetic experiments indicate that different cells must express different isoforms. How this is achieved is unknown, as expression of alternative exons in vivo has not been shown. Here, we modified the endogenous Dscam1 locus to generate splicing reporters for all variants of exon 4. We demonstrate that splicing does not occur in a cell-type-specific fashion, that cells sharing the same anatomical location in different individuals express different exon 4 variants, and that the splicing pattern in a given neuron can change over time. We conclude that splicing is probabilistic. This is compatible with a widespread role in neural circuit assembly through self-avoidance and is incompatible with models in which specific isoforms of Dscam1 mediate homophilic recognition between processes of different cells.
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Affiliation(s)
- Satoru K Miura
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
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Abstract
Oppositely directed projections of some homologous neurons in the developing CNS of the medicinal leech (Hirudo verbana), such as the AP cells, undergo a form of contact-dependent homolog avoidance. Embryonic APs extend axons within the connective nerve toward adjacent ganglia, in which they meet and form gap junctions (GJs) with the oppositely directed axons of their segmental homologs, stop growing, and are later permanently retracted (Wolszon et al., 1994a,b). However, early deletion of an AP neuron leads to resumed growth and permanent maintenance of the projections of neighboring APs. Here we test the hypothesis that a GJ-based signaling mechanism is responsible for this instance of homolog avoidance. We demonstrate that selective knockdown of GJ gene Hve-inx1 expression in single embryonic APs, by expressing a short-hairpin interfering RNA, leads to continued growth of the projections of the cell toward, into, and beyond adjacent ganglia. Moreover, the projections of the APs in adjacent ganglia also resume growth, mimicking their responses to cell deletion. Continued growth was also observed when two different INX1 mutant transgenes that abolish dye coupling between APs were expressed. These include a mutant transgene that effectively downregulates all GJ plaques that include the INX1 protein and a closed channel INX1 mutant that retains the adhesive cellular binding characteristic of INX1 GJs but not the open channel pore function. Our results add GJ intercellular communication to the list of molecular signaling mechanisms that can act as mediators of growth-inhibiting cell-cell interactions that define the topography of neuronal arbors.
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