1
|
Karagyaur M, Primak A, Bozov K, Sheleg D, Arbatsky M, Dzhauari S, Illarionova M, Semina E, Samokhodskaya L, Klimovich P, Velichko A, Drach M, Sotskaya E, Popov V, Rubina K, Parfenenko M, Makus J, Tsygankov B, Tkachuk V, Neyfeld E. Novel missense variants in brain morphogenic genes associated with depression and schizophrenia. Front Psychiatry 2024; 15:1338168. [PMID: 38699454 PMCID: PMC11063365 DOI: 10.3389/fpsyt.2024.1338168] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/14/2023] [Accepted: 04/05/2024] [Indexed: 05/05/2024] Open
Abstract
Introduction Impaired function of brain morphogenic genes is considered one of the predisposing factors for the manifestation of psychiatric and cognitive disorders, such as paranoid schizophrenia (SCZ) and major depressive disorder (MDD). Identification of such genes (genes of neurotrophic factors and guidance molecules among them) and their deleterious genetic variants serves as a key to diagnosis, prevention, and possibly treatment of such disorders. In this study, we have examined the prevalence of genomic variants in brain morphogenic genes in individuals with SCZ and MDD within a Russian population. Methods We have performed whole-exome sequencing of 21 DNA samples: 11 from individuals with SCZ and 10 with MDD, followed by ARMS (Amplification-Refractory Mutation System) based screening of detected single nucleotide variants (SNVs) in larger groups: 102 for individuals with SCZ, 79 for those with MDD and 103 for healthy donors. Results Whole-exome sequencing has revealed 226 missense mutations in 79 genes (out of 140 studied), some of which occur in patients with psychiatric disorders significantly more frequently than in healthy donors. We have identified previously undescribed genomic variants in brain morphogenic genes: CDH2 (rs1944294-T and rs17445840-T), DCHS2 (rs11935573-G and rs12500437-G/T) and CDH23 (rs1227051-G/A), significantly associated with the incidence of SCZ and MDD in the Russian population. For some SNVs (rs6265-T, rs1944294-T, rs11935573-G, rs4760-G) sex-biased differences in their prevalence between SCZ/MDD patients and healthy donors was detected. Discussion However, the functional significance of the SNVs identified has still to be confirmed in cellular and animal models. Once it is fulfilled, these SNVs have the potential to complement the diagnostic toolbox for assessing susceptibility to mental disorders. The data obtained indirectly confirm the importance of adequate brain structure formation for its correct functioning and preservation of mental health.
Collapse
Affiliation(s)
- Maxim Karagyaur
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
- Institute for Regenerative Medicine, Medical Research and Education Center, Lomonosov Moscow State University, Moscow, Russia
| | - Alexandra Primak
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Kirill Bozov
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Dmitriy Sheleg
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
- Federal State Budgetary Educational Institution of the Higher Education “A.I. Yevdokimov Moscow State University of Medicine and Dentistry” of the Ministry of Healthcare of the Russian Federation, Moscow, Russia
| | - Mikhail Arbatsky
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Stalik Dzhauari
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Maria Illarionova
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Ekaterina Semina
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Larisa Samokhodskaya
- Medical Research and Education Center, Lomonosov Moscow State University, Moscow, Russia
| | - Polina Klimovich
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Arkadiy Velichko
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Mikhail Drach
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | | | - Vladimir Popov
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Kseniya Rubina
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Mariia Parfenenko
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Julia Makus
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
| | - Boris Tsygankov
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
- Federal State Budgetary Educational Institution of the Higher Education “A.I. Yevdokimov Moscow State University of Medicine and Dentistry” of the Ministry of Healthcare of the Russian Federation, Moscow, Russia
| | - Vsevolod Tkachuk
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
- Institute for Regenerative Medicine, Medical Research and Education Center, Lomonosov Moscow State University, Moscow, Russia
| | - Elena Neyfeld
- Faculty of Medicine, Lomonosov Moscow State University, Moscow, Russia
- Federal State Budgetary Educational Institution of the Higher Education “A.I. Yevdokimov Moscow State University of Medicine and Dentistry” of the Ministry of Healthcare of the Russian Federation, Moscow, Russia
| |
Collapse
|
2
|
Agi E, Reifenstein ET, Wit C, Schneider T, Kauer M, Kehribar M, Kulkarni A, von Kleist M, Hiesinger PR. Axonal self-sorting without target guidance in Drosophila visual map formation. Science 2024; 383:1084-1092. [PMID: 38452066 DOI: 10.1126/science.adk3043] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2023] [Accepted: 02/01/2024] [Indexed: 03/09/2024]
Abstract
The idea of guidance toward a target is central to axon pathfinding and brain wiring in general. In this work, we show how several thousand axonal growth cones self-pattern without target-dependent guidance during neural superposition wiring in Drosophila. Ablation of all target lamina neurons or loss of target adhesion prevents the stabilization but not the development of the pattern. Intravital imaging at the spatiotemporal resolution of growth cone dynamics in intact pupae and data-driven dynamics simulations reveal a mechanism by which >30,000 filopodia do not explore potential targets, but instead simultaneously generate and navigate a dynamic filopodial meshwork that steers growth directions. Hence, a guidance mechanism can emerge from the interactions of the axons being guided, suggesting self-organization as a more general feature of brain wiring.
Collapse
Affiliation(s)
- Egemen Agi
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Eric T Reifenstein
- Department of Mathematics, Free University of Berlin, 14195 Berlin, Germany
| | - Charlotte Wit
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Teresa Schneider
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Monika Kauer
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Melinda Kehribar
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Abhishek Kulkarni
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| | - Max von Kleist
- Department of Mathematics, Free University of Berlin, 14195 Berlin, Germany
| | - P Robin Hiesinger
- Division of Neurobiology, Free University of Berlin, 14195 Berlin, Germany
| |
Collapse
|
3
|
Wolterhoff N, Hiesinger PR. Synaptic promiscuity in brain development. Curr Biol 2024; 34:R102-R116. [PMID: 38320473 PMCID: PMC10849093 DOI: 10.1016/j.cub.2023.12.037] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2024]
Abstract
Precise synaptic connectivity is a prerequisite for the function of neural circuits, yet individual neurons, taken out of their developmental context, readily form unspecific synapses. How does the genome encode brain wiring in light of this apparent contradiction? Synaptic specificity is the outcome of a long series of developmental processes and mechanisms before, during and after synapse formation. How much promiscuity is permissible or necessary at the moment of synaptic partner choice depends on the extent to which prior development restricts available partners or subsequent development corrects initially made synapses. Synaptic promiscuity at the moment of choice can thereby play important roles in the development of precise connectivity, but also facilitate developmental flexibility and robustness. In this review, we assess the experimental evidence for the prevalence and roles of promiscuous synapse formation during brain development. Many well-established experimental approaches are based on developmental genetic perturbation and an assessment of synaptic connectivity only in the adult; this can make it difficult to pinpoint when a given defect or mechanism occurred. In many cases, such studies reveal mechanisms that restrict partner availability already prior to synapse formation. Subsequently, at the moment of choice, factors including synaptic competency, interaction dynamics and molecular recognition further restrict synaptic partners. The discussion of the development of synaptic specificity through the lens of synaptic promiscuity suggests an algorithmic process based on neurons capable of promiscuous synapse formation that are continuously prevented from making the wrong choices, with no single mechanism or developmental time point sufficient to explain the outcome.
Collapse
Affiliation(s)
- Neele Wolterhoff
- Division of Neurobiology, Free University Berlin, 14195 Berlin, Germany
| | - P Robin Hiesinger
- Division of Neurobiology, Free University Berlin, 14195 Berlin, Germany.
| |
Collapse
|
4
|
Koff M, Monagas-Valentin P, Novikov B, Chandel I, Panin V. Protein O-mannosylation: one sugar, several pathways, many functions. Glycobiology 2023; 33:911-926. [PMID: 37565810 PMCID: PMC10859634 DOI: 10.1093/glycob/cwad067] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2023] [Revised: 07/23/2023] [Accepted: 07/31/2023] [Indexed: 08/12/2023] Open
Abstract
Recent research has unveiled numerous important functions of protein glycosylation in development, homeostasis, and diseases. A type of glycosylation taking the center stage is protein O-mannosylation, a posttranslational modification conserved in a wide range of organisms, from yeast to humans. In animals, protein O-mannosylation plays a crucial role in the nervous system, whereas protein O-mannosylation defects cause severe neurological abnormalities and congenital muscular dystrophies. However, the molecular and cellular mechanisms underlying protein O-mannosylation functions and biosynthesis remain not well understood. This review outlines recent studies on protein O-mannosylation while focusing on the functions in the nervous system, summarizes the current knowledge about protein O-mannosylation biosynthesis, and discusses the pathologies associated with protein O-mannosylation defects. The evolutionary perspective revealed by studies in the Drosophila model system are also highlighted. Finally, the review touches upon important knowledge gaps in the field and discusses critical questions for future research on the molecular and cellular mechanisms associated with protein O-mannosylation functions.
Collapse
Affiliation(s)
- Melissa Koff
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Pedro Monagas-Valentin
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Boris Novikov
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Ishita Chandel
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| | - Vladislav Panin
- Department of Biochemistry and Biophysics, AgriLife Research, Texas A&M University, College Station, College Station, TX 77843, United States
| |
Collapse
|
5
|
Wit CB, Hiesinger PR. Neuronal filopodia: From stochastic dynamics to robustness of brain morphogenesis. Semin Cell Dev Biol 2023; 133:10-19. [PMID: 35397971 DOI: 10.1016/j.semcdb.2022.03.038] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2021] [Revised: 03/26/2022] [Accepted: 03/29/2022] [Indexed: 12/30/2022]
Abstract
Brain development relies on dynamic morphogenesis and interactions of neurons. Filopodia are thin and highly dynamic membrane protrusions that are critically required for neuronal development and neuronal interactions with the environment. Filopodial interactions are typically characterized by non-deterministic dynamics, yet their involvement in developmental processes leads to stereotypic and robust outcomes. Here, we discuss recent advances in our understanding of how filopodial dynamics contribute to neuronal differentiation, migration, axonal and dendritic growth and synapse formation. Many of these advances are brought about by improved methods of live observation in intact developing brains. Recent findings integrate known and novel roles ranging from exploratory sensors and decision-making agents to pools for selection and mechanical functions. Different types of filopodial dynamics thereby reveal non-deterministic subcellular decision-making processes as part of genetically encoded brain development.
Collapse
Affiliation(s)
- Charlotte B Wit
- Devision of Neurobiology, Institute of Biology, Freie Universität Berlin, Berlin, Germany
| | - P Robin Hiesinger
- Devision of Neurobiology, Institute of Biology, Freie Universität Berlin, Berlin, Germany.
| |
Collapse
|
6
|
Zou Y. Inter-growth cone communications mediated by planar cell polarity pathway in axon guidance. Dev Biol 2022; 490:50-52. [PMID: 35788000 DOI: 10.1016/j.ydbio.2022.06.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 06/21/2022] [Accepted: 06/29/2022] [Indexed: 11/26/2022]
Abstract
The emergence of exquisitely organized axonal projections is one of the greatest wonders of nervous system development. In addition to growing along stereotyped directions, axons join one another as they extend to form highly organized projections. Axon-axon interactions are essential for axon guidance during nervous system wiring. Axonal growth cones recognize cell surface guidance cues on axons and either grow along the axons or away from the axons. However, it is less well understood whether and how the growth cones communicate with each other and, if so, what do these interactions mean. Recent studies from our lab provided direct evidence that the growth cones do interact with each other during axon pathfinding. And this interaction is regulated by highly regulated protein-protein interactions among components of the planar cell polarity pathway. The disruption of these interactions lead to guidance defects and disorganization of axons. We propose that these local inter-growth cone PCP signaling reinforces and increases the sensitivity of the growth cone response to shallow Wnt gradients to turn in a precise and organized fashion.
Collapse
Affiliation(s)
- Yimin Zou
- Department of Neurobiology, School of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093, USA.
| |
Collapse
|
7
|
Ji W, Wu LF, Altschuler SJ. Analysis of growth cone extension in standardized coordinates highlights self-organization rules during wiring of the Drosophila visual system. PLoS Genet 2021; 17:e1009857. [PMID: 34731164 PMCID: PMC8565740 DOI: 10.1371/journal.pgen.1009857] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2021] [Accepted: 10/04/2021] [Indexed: 11/19/2022] Open
Abstract
A fascinating question in neuroscience is how ensembles of neurons, originating from different locations, extend to the proper place and by the right time to create precise circuits. Here, we investigate this question in the Drosophila visual system, where photoreceptors re-sort in the lamina to form the crystalline-like neural superposition circuit. The repeated nature of this circuit allowed us to establish a data-driven, standardized coordinate system for quantitative comparison of sparsely perturbed growth cones within and across specimens. Using this common frame of reference, we investigated the extension of the R3 and R4 photoreceptors, which is the only pair of symmetrically arranged photoreceptors with asymmetric target choices. Specifically, we found that extension speeds of the R3 and R4 growth cones are inherent to their cell identities. The ability to parameterize local regularity in tissue organization facilitated the characterization of ensemble cellular behaviors and dissection of mechanisms governing neural circuit formation.
Collapse
Affiliation(s)
- Weiyue Ji
- Biophysics Graduate Group, University of California, San Francisco, San Francisco, California, United States of America
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, United States of America
| | - Lani F. Wu
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, United States of America
| | - Steven J. Altschuler
- Department of Pharmaceutical Chemistry, University of California, San Francisco, San Francisco, California, United States of America
| |
Collapse
|
8
|
Winkler B, Funke D, Benmimoun B, Spéder P, Rey S, Logan MA, Klämbt C. Brain inflammation triggers macrophage invasion across the blood-brain barrier in Drosophila during pupal stages. SCIENCE ADVANCES 2021; 7:eabh0050. [PMID: 34705495 PMCID: PMC8550232 DOI: 10.1126/sciadv.abh0050] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The nervous system is shielded from circulating immune cells by the blood-brain barrier (BBB). During infections and autoimmune diseases, macrophages can enter the brain where they participate in pathogen elimination but can also cause tissue damage. Here, we establish a Drosophila model to study macrophage invasion into the inflamed brain. We show that the immune deficiency (Imd) pathway, but not the Toll pathway, is responsible for attraction and invasion of hemolymph-borne macrophages across the BBB during pupal stages. Macrophage recruitment is mediated by glial, but not neuronal, induction of the Imd pathway through expression of Pvf2. Within the brain, macrophages can phagocytose synaptic material and reduce locomotor abilities and longevity. Similarly, we show that central nervous system infection by group B Streptococcus elicits macrophage recruitment in an Imd-dependent manner. This suggests that evolutionarily conserved inflammatory responses require a delicate balance between beneficial and detrimental activities.
Collapse
Affiliation(s)
- Bente Winkler
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Badestr. 9, 48149 Münster, Germany
| | - Dominik Funke
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Badestr. 9, 48149 Münster, Germany
| | - Billel Benmimoun
- Brain Plasticity in response to the Environment, Institut Pasteur, UMR3738 CNRS, 75015 Paris, France
| | - Pauline Spéder
- Brain Plasticity in response to the Environment, Institut Pasteur, UMR3738 CNRS, 75015 Paris, France
| | - Simone Rey
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Badestr. 9, 48149 Münster, Germany
| | - Mary A. Logan
- Jungers Center for Neurosciences Research, Oregon Health and Science University, Portland, OR 97239, USA
| | - Christian Klämbt
- Institut für Neuro- und Verhaltensbiologie, Universität Münster, Badestr. 9, 48149 Münster, Germany
- Corresponding author.
| |
Collapse
|
9
|
Neural specification, targeting, and circuit formation during visual system assembly. Proc Natl Acad Sci U S A 2021; 118:2101823118. [PMID: 34183440 DOI: 10.1073/pnas.2101823118] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Like other sensory systems, the visual system is topographically organized: Its sensory neurons, the photoreceptors, and their targets maintain point-to-point correspondence in physical space, forming a retinotopic map. The iterative wiring of circuits in the visual system conveniently facilitates the study of its development. Over the past few decades, experiments in Drosophila have shed light on the principles that guide the specification and connectivity of visual system neurons. In this review, we describe the main findings unearthed by the study of the Drosophila visual system and compare them with similar events in mammals. We focus on how temporal and spatial patterning generates diverse cell types, how guidance molecules distribute the axons and dendrites of neurons within the correct target regions, how vertebrates and invertebrates generate their retinotopic map, and the molecules and mechanisms required for neuronal migration. We suggest that basic principles used to wire the fly visual system are broadly applicable to other systems and highlight its importance as a model to study nervous system development.
Collapse
|
10
|
Arguello JR, Abuin L, Armida J, Mika K, Chai PC, Benton R. Targeted molecular profiling of rare olfactory sensory neurons identifies fate, wiring, and functional determinants. eLife 2021; 10:63036. [PMID: 33666172 PMCID: PMC7993999 DOI: 10.7554/elife.63036] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2020] [Accepted: 03/04/2021] [Indexed: 02/06/2023] Open
Abstract
Determining the molecular properties of neurons is essential to understand their development, function and evolution. Using Targeted DamID (TaDa), we characterize RNA polymerase II occupancy and chromatin accessibility in selected Ionotropic receptor (Ir)-expressing olfactory sensory neurons in Drosophila. Although individual populations represent a minute fraction of cells, TaDa is sufficiently sensitive and specific to identify the expected receptor genes. Unique Ir expression is not consistently associated with differences in chromatin accessibility, but rather to distinct transcription factor profiles. Genes that are heterogeneously expressed across populations are enriched for neurodevelopmental factors, and we identify functions for the POU-domain protein Pdm3 as a genetic switch of Ir neuron fate, and the atypical cadherin Flamingo in segregation of neurons into discrete glomeruli. Together this study reveals the effectiveness of TaDa in profiling rare neural populations, identifies new roles for a transcription factor and a neuronal guidance molecule, and provides valuable datasets for future exploration.
Collapse
Affiliation(s)
- J Roman Arguello
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland.,Department of Ecology and Evolution Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland.,Swiss Institute of Bioinformatics, Lausanne, Switzerland
| | - Liliane Abuin
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland
| | - Jan Armida
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland
| | - Kaan Mika
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland
| | - Phing Chian Chai
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland
| | - Richard Benton
- Center for Integrative Genomics Faculty of Biology and Medicine University of Lausanne, Lausanne, Switzerland
| |
Collapse
|
11
|
Heckman EL, Doe CQ. Establishment and Maintenance of Neural Circuit Architecture. J Neurosci 2021; 41:1119-1129. [PMID: 33568445 PMCID: PMC7888231 DOI: 10.1523/jneurosci.1143-20.2020] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2020] [Revised: 11/29/2020] [Accepted: 12/09/2020] [Indexed: 02/03/2023] Open
Abstract
The ability to sense the world, process information, and navigate the environment depends on the assembly and continuous function of neural circuits in the brain. Within the past two decades, new technologies have rapidly advanced our understanding of how neural circuits are wired during development and how they are stably maintained, often for years. Electron microscopy reconstructions of model organism connectomes have provided a map of the stereotyped (and variable) connections in the brain; advanced light microscopy techniques have enabled direct observation of the cellular dynamics that underlie circuit construction and maintenance; transcriptomic and proteomic surveys of both developing and mature neurons have provided insights into the molecular and genetic programs governing circuit establishment and maintenance; and advanced genetic techniques have allowed for high-throughput discovery of wiring regulators. These tools have empowered scientists to rapidly generate and test hypotheses about how circuits establish and maintain connectivity. Thus, the set of principles governing circuit formation and maintenance have been expanded. These principles are discussed in this review.
Collapse
Affiliation(s)
- Emily L Heckman
- Institute of Neuroscience, Institute of Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene, Oregon 97403
| | - Chris Q Doe
- Institute of Neuroscience, Institute of Molecular Biology, Howard Hughes Medical Institute, University of Oregon, Eugene, Oregon 97403
| |
Collapse
|
12
|
Han X, Wang M, Liu C, Trush O, Takayama R, Akiyama T, Naito T, Tomomizu T, Imamura K, Sato M. DWnt4 and DWnt10 Regulate Morphogenesis and Arrangement of Columnar Units via Fz2/PCP Signaling in the Drosophila Brain. Cell Rep 2020; 33:108305. [PMID: 33113378 DOI: 10.1016/j.celrep.2020.108305] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 09/13/2020] [Accepted: 10/02/2020] [Indexed: 01/09/2023] Open
Abstract
Columns are structural and functional units of the brain. However, the mechanism of column formation remains unclear. The medulla of the fly visual center shares features with the mammalian cerebral cortex, such as columnar and layered structures, and provides a good opportunity to study the mechanisms of column formation. Column formation is initiated by three core neurons in the medulla, namely, Mi1, R8, and R7. The proper orientation of neurons is required for the orientation and arrangement of multiple columns. Their orientations may be under the control of planar cell polarity (PCP) signaling, because it is known to regulate the orientation of cells in two-dimensional tissue structures. In this study, we demonstrate that the ligands DWnt4 and DWnt10 expressed specifically in the ventral medulla and dorsal medulla, respectively, globally regulate the columnar arrangement and orientation of Mi1 and R8 terminals through Fz2/PCP signaling in a three-dimensional space.
Collapse
Affiliation(s)
- Xujun Han
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; Nano Life Science Institute, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Miaoxing Wang
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Chuyan Liu
- Laboratory of Developmental Neurobiology, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Olena Trush
- Laboratory of Developmental Neurobiology, Graduate School of Medical Sciences, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Rie Takayama
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Takaaki Akiyama
- Division of Electrical Engineering and Computer Science, Graduate School of Natural Science and Technology, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Toshiki Naito
- Graduate School of Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Takeshi Tomomizu
- Graduate School of Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Kousuke Imamura
- Faculty of Electrical, Information and Communication Engineering, Institute of Science and Engineering, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan
| | - Makoto Sato
- Mathematical Neuroscience Unit, Institute for Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan; Graduate School of Frontier Science Initiative, Kanazawa University, 13-1 Takaramachi, Kanazawa, Ishikawa 920-8640, Japan.
| |
Collapse
|
13
|
Zelhof AC, Mahato S, Liang X, Rylee J, Bergh E, Feder LE, Larsen ME, Britt SG, Friedrich M. The brachyceran de novo gene PIP82, a phosphorylation target of aPKC, is essential for proper formation and maintenance of the rhabdomeric photoreceptor apical domain in Drosophila. PLoS Genet 2020; 16:e1008890. [PMID: 32579558 PMCID: PMC7340324 DOI: 10.1371/journal.pgen.1008890] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2020] [Revised: 07/07/2020] [Accepted: 05/27/2020] [Indexed: 11/18/2022] Open
Abstract
The Drosophila apical photoreceptor membrane is defined by the presence of two distinct morphological regions, the microvilli-based rhabdomere and the stalk membrane. The subdivision of the apical membrane contributes to the geometrical positioning and the stereotypical morphology of the rhabdomeres in compound eyes with open rhabdoms and neural superposition. Here we describe the characterization of the photoreceptor specific protein PIP82. We found that PIP82's subcellular localization demarcates the rhabdomeric portion of the apical membrane. We further demonstrate that PIP82 is a phosphorylation target of aPKC. PIP82 localization is modulated by phosphorylation, and in vivo, the loss of the aPKC/Crumbs complex results in an expansion of the PIP82 localization domain. The absence of PIP82 in photoreceptors leads to misshapped rhabdomeres as a result of misdirected cellular trafficking of rhabdomere proteins. Comparative analyses reveal that PIP82 originated de novo in the lineage leading to brachyceran Diptera, which is also characterized by the transition from fused to open rhabdoms. Taken together, these findings define a novel factor that delineates and maintains a specific apical membrane domain, and offers new insights into the functional organization and evolutionary history of the Drosophila retina.
Collapse
Affiliation(s)
- Andrew C. Zelhof
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Simpla Mahato
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Xulong Liang
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Jonathan Rylee
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Emma Bergh
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Lauren E. Feder
- Department of Biology, Indiana University, Bloomington, Indiana, United States of America
| | - Matthew E. Larsen
- Department of Neurology and Ophthalmology, Dell Medical School, University of Texas, Austin, Texas, United States of America
| | - Steven G. Britt
- Department of Neurology and Ophthalmology, Dell Medical School, University of Texas, Austin, Texas, United States of America
| | - Markus Friedrich
- Department of Biological Sciences, Wayne State University, Detroit, Michigan, United States of America
| |
Collapse
|
14
|
Sanes JR, Zipursky SL. Synaptic Specificity, Recognition Molecules, and Assembly of Neural Circuits. Cell 2020; 181:536-556. [DOI: 10.1016/j.cell.2020.04.008] [Citation(s) in RCA: 68] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2020] [Revised: 03/23/2020] [Accepted: 04/06/2020] [Indexed: 01/02/2023]
|
15
|
N-Cadherin Is Critical for the Survival of Germ Cells, the Formation of Steroidogenic Cells, and the Architecture of Developing Mouse Gonads. Cells 2019; 8:cells8121610. [PMID: 31835801 PMCID: PMC6952792 DOI: 10.3390/cells8121610] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2019] [Revised: 12/05/2019] [Accepted: 12/09/2019] [Indexed: 01/10/2023] Open
Abstract
Normal gonad development assures the fertility of the individual. The properly functioning gonads must contain a sufficient number of the viable germ cells, possess a correct architecture and tissue structure, and assure the proper hormonal regulation. This is achieved by the interplay between the germ cells and different types of somatic cells. N-cadherin coded by the Cdh2 gene plays a critical role in this interplay. To gain an insight into the role of N-cadherin in the development of mouse gonads, we used the Cre-loxP system to knock out N-cadherin separately in two cell lines: the SF1+ somatic cells and the OCT4+ germ cells. We observed that N-cadherin plays a key role in the survival of both female and male germ cells. However, the N-cadherin is not necessary for the differentiation of the Sertoli cells or the initiation of the formation of testis cords or ovigerous cords. In the later stages of gonad development, N-cadherin is important for the maintenance of testis cord structure and is required for the formation of steroidogenic cells. In the ovaries, N-cadherin is necessary for the formation of the ovarian follicles. These results indicate that N-cadherin plays a major role in gonad differentiation, structuralization, and function.
Collapse
|
16
|
Li R, Liang Y, Zheng S, He Q, Yang L. The atypical cadherin flamingo determines the competence of neurons for activity-dependent fine-scale topography. Mol Brain 2019; 12:109. [PMID: 31823796 PMCID: PMC6905094 DOI: 10.1186/s13041-019-0531-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2019] [Accepted: 11/28/2019] [Indexed: 11/10/2022] Open
Abstract
The topographic projection of afferent terminals into two-dimensional maps is essential for sensory systems to encode the locations of sensory stimuli. In vertebrates, guidance cues are critical for establishing a coarse topographic map, while neuronal activity directs fine-scale topography between adjacent afferent terminals. However, the molecular mechanism underlying activity-dependent fine-scale topography is not well known. Studies in the Drosophila visual system have demonstrated that cell-adhesion molecules direct fine-scale topography, but whether or not these molecules are involved in activity-dependent fine-scale topography remains to be determined. We previously reported that the nociceptors in Drosophila larvae form an activity-dependent fine-scale topographic system. The establishment of this system is instructed by the level of neuronal activity in individual nociceptors. Here, we show that the atypical cadherin Flamingo (Fmi) is required for establishing the nociceptor topographic map. We found that the topographic defect caused by loss of fmi was epistatic to the inhibition of neuronal activity and the overexpression of the activity-regulated gene Trim9. These results suggest that Fmi and neuronal activity interact to regulate fine-scale topography. This study provides a link between neuronal activity and the cell-adhesion molecule in the establishment of fine-scale topography.
Collapse
Affiliation(s)
- Ruonan Li
- School of Medicine, Dalian University, Dalian, 116622, Liaoning, China.,Institute of Health Sciences, China Medical University, Shenyang, 110112, China
| | - Yuhua Liang
- School of Medicine, Dalian University, Dalian, 116622, Liaoning, China
| | - Siyang Zheng
- Life Sciences Institute, Dalian National University, Dalian, 116600, Liaoning, China
| | - Qun He
- School of Medicine, Dalian University, Dalian, 116622, Liaoning, China
| | - Limin Yang
- School of Medicine, Dalian University, Dalian, 116622, Liaoning, China. .,Chronic Disease Research Center, Dalian Key Laboratory, Dalian, 116622, Liaoning, China. .,School of Medicine, Jiamusi University, Jiamusi, 154007, Heilongjiang, China.
| |
Collapse
|
17
|
Xu C, Theisen E, Maloney R, Peng J, Santiago I, Yapp C, Werkhoven Z, Rumbaut E, Shum B, Tarnogorska D, Borycz J, Tan L, Courgeon M, Griffin T, Levin R, Meinertzhagen IA, de Bivort B, Drugowitsch J, Pecot MY. Control of Synaptic Specificity by Establishing a Relative Preference for Synaptic Partners. Neuron 2019; 103:865-877.e7. [PMID: 31300277 PMCID: PMC6728174 DOI: 10.1016/j.neuron.2019.06.006] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2018] [Revised: 04/19/2019] [Accepted: 06/11/2019] [Indexed: 02/07/2023]
Abstract
The ability of neurons to identify correct synaptic partners is fundamental to the proper assembly and function of neural circuits. Relative to other steps in circuit formation such as axon guidance, our knowledge of how synaptic partner selection is regulated is severely limited. Drosophila Dpr and DIP immunoglobulin superfamily (IgSF) cell-surface proteins bind heterophilically and are expressed in a complementary manner between synaptic partners in the visual system. Here, we show that in the lamina, DIP mis-expression is sufficient to promote synapse formation with Dpr-expressing neurons and that disrupting DIP function results in ectopic synapse formation. These findings indicate that DIP proteins promote synapses to form between specific cell types and that in their absence, neurons synapse with alternative partners. We propose that neurons have the capacity to synapse with a broad range of cell types and that synaptic specificity is achieved by establishing a preference for specific partners.
Collapse
Affiliation(s)
- Chundi Xu
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA.
| | - Emma Theisen
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Ryan Maloney
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Jing Peng
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Ivan Santiago
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Clarence Yapp
- Image and Data Analysis Core, Harvard Medical School, Boston, MA 02115, USA
| | - Zachary Werkhoven
- Center for Brain Science and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Elijah Rumbaut
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Bryan Shum
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Dorota Tarnogorska
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Jolanta Borycz
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Liming Tan
- Department of Biological Chemistry, HHMI, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Maximilien Courgeon
- Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA
| | - Tessa Griffin
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Raina Levin
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Ian A Meinertzhagen
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Benjamin de Bivort
- Center for Brain Science and Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA
| | - Jan Drugowitsch
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA
| | - Matthew Y Pecot
- Department of Neurobiology, Harvard Medical School, 220 Longwood Ave, Boston, MA 02115, USA.
| |
Collapse
|
18
|
Abstract
The brain's synaptic networks endow an animal with powerfully adaptive biological behavior. Maps of such synaptic circuits densely reconstructed in those model brains that can be examined and manipulated by genetic means offer the best prospect for understanding the underlying biological bases of behavior. That prospect is now technologically feasible and a scientifically enabling possibility in neurobiology, much as genomics has been in molecular biology and genetics. In Drosophila, two major advances are in electron microscopic technology, using focused ion beam-scanning electron microscopy (FIB-SEM) milling to capture and align digital images, and in computer-aided reconstruction of neuron morphologies. The last decade has witnessed enormous progress in detailed knowledge of the actual synaptic circuits formed by real neurons. Advances in various brain regions that heralded identification of the motion-sensing circuits in the optic lobe are now extending to other brain regions, with the prospect of encompassing the fly's entire nervous system, both brain and ventral nerve cord.
Collapse
Affiliation(s)
- Louis K Scheffer
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147-2408, USA;
| | - Ian A Meinertzhagen
- Janelia Research Campus, Howard Hughes Medical Institute, Ashburn, Virginia 20147-2408, USA; .,Department of Psychology and Neuroscience and Department of Biology, Life Sciences Centre, Dalhousie University, Halifax, Canada B3H 4R2
| |
Collapse
|
19
|
Abstract
How the nervous system is wired has been a central question of neuroscience since the inception of the field, and many of the foundational discoveries and conceptual advances have been made through the study of invertebrate experimental organisms, including Caenorhabditis elegans and Drosophila melanogaster. Although many guidance molecules and receptors have been identified, recent experiments have shed light on the many modes of action for these pathways. Here, we summarize the recent progress in determining how the physical and temporal constraints of the surrounding environment provide instructive regulations in nervous system wiring. We use Netrin and its receptors as an example to analyze the complexity of how they guide neurite outgrowth. In neurite repair, conserved injury detection and response-signaling pathways regulate gene expression and cytoskeletal dynamics. We also describe recent developments in the research on molecular mechanisms of neurite regeneration in worms and flies.
Collapse
Affiliation(s)
- Claire E Richardson
- Department of Biology, Stanford University, Stanford, California 94305, USA;
| | - Kang Shen
- Department of Biology, Stanford University, Stanford, California 94305, USA; .,Howard Hughes Medical Institute, Stanford University, Stanford, California 94305, USA
| |
Collapse
|
20
|
Zhao C, Zhang C, Xing Z, Ahmad Z, Li JS, Chang MW. Pharmacological effects of natural Ganoderma and its extracts on neurological diseases: A comprehensive review. Int J Biol Macromol 2019; 121:1160-1178. [DOI: 10.1016/j.ijbiomac.2018.10.076] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2018] [Revised: 10/06/2018] [Accepted: 10/14/2018] [Indexed: 01/13/2023]
|
21
|
Synaptic structural protein dysfunction leads to altered excitation inhibition ratios in models of autism spectrum disorder. Pharmacol Res 2018; 139:207-214. [PMID: 30465851 DOI: 10.1016/j.phrs.2018.11.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/30/2018] [Revised: 11/08/2018] [Accepted: 11/12/2018] [Indexed: 01/01/2023]
Abstract
Genetics is believed to play a key role in the development of Autism Spectrum Disorder (ASD) and a plethora of potential candidate genes have been identified by genetic characterization of patients, their family members and controls. To make sense of this information investigators have searched for common pathways and downstream properties of neural networks that are regulated by these genes. For instance, several candidate genes encode synaptic proteins, and one hypothesis that has emerged is that disruption of the synaptic excitation and inhibition (E/I) balance would destabilize neural processing and lead to ASD phenotypes. Some compelling evidence for this has come from the analyses of mouse and culture models with defects in synaptic structural proteins, which influence several aspects of synapse biology and is the subject of this review. Remaining challenges include identifying the specifics that distinguish ASD from other psychiatric diseases and designing more direct tests of the E/I balance hypothesis.
Collapse
|
22
|
Millard SS, Pecot MY. Strategies for assembling columns and layers in the Drosophila visual system. Neural Dev 2018; 13:11. [PMID: 29875010 PMCID: PMC5991427 DOI: 10.1186/s13064-018-0106-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2017] [Accepted: 04/24/2018] [Indexed: 11/23/2022] Open
Abstract
A striking feature of neural circuit structure is the arrangement of neurons into regularly spaced ensembles (i.e. columns) and neural connections into parallel layers. These patterns of organization are thought to underlie precise synaptic connectivity and provide a basis for the parallel processing of information. In this article we discuss in detail specific findings that contribute to a framework for understanding how columns and layers are assembled in the Drosophila visual system, and discuss their broader implications.
Collapse
Affiliation(s)
- S. Sean Millard
- School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072 Australia
| | - Matthew Y. Pecot
- Department of Neurobiology, Harvard Medical School, Boston, MA 02115 USA
| |
Collapse
|
23
|
Abstract
In general, neurons in insects and many other invertebrate groups are individually recognizable, enabling us to assign an index number to specific neurons in a manner which is rarely possible in a vertebrate brain. This endows many studies on insect nervous systems with the opportunity to document neurons with great precision, so that in favourable cases we can return to the same neuron or neuron type repeatedly so as to recognize many separate morphological classes. The visual system of the fly's compound eye particularly provides clear examples of the accuracy of neuron wiring, allowing numerical comparisons between representatives of the same cell type, and estimates of the accuracy of their wiring.
Collapse
Affiliation(s)
- Ian A Meinertzhagen
- a Department of Psychology and Neuroscience , Life Sciences Centre, Dalhousie University , Halifax , Canada.,b Janelia Research Campus of Howard Hughes Medical Institute , Ashburn , VA , USA
| |
Collapse
|
24
|
Astigarraga S, Douthit J, Tarnogorska D, Creamer MS, Mano O, Clark DA, Meinertzhagen IA, Treisman JE. Drosophila Sidekick is required in developing photoreceptors to enable visual motion detection. Development 2018; 145:dev.158246. [PMID: 29361567 DOI: 10.1242/dev.158246] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Accepted: 01/09/2018] [Indexed: 12/15/2022]
Abstract
The assembly of functional neuronal circuits requires growth cones to extend in defined directions and recognize the correct synaptic partners. Homophilic adhesion between vertebrate Sidekick proteins promotes synapse formation between retinal neurons involved in visual motion detection. We show here that Drosophila Sidekick accumulates in specific synaptic layers of the developing motion detection circuit and is necessary for normal optomotor behavior. Sidekick is required in photoreceptors, but not in their target lamina neurons, to promote the alignment of lamina neurons into columns and subsequent sorting of photoreceptor axons into synaptic modules based on their precise spatial orientation. Sidekick is also localized to the dendrites of the direction-selective T4 and T5 cells, and is expressed in some of their presynaptic partners. In contrast to its vertebrate homologs, Sidekick is not essential for T4 and T5 to direct their dendrites to the appropriate layers or to receive synaptic contacts. These results illustrate a conserved requirement for Sidekick proteins in establishing visual motion detection circuits that is achieved through distinct cellular mechanisms in Drosophila and vertebrates.
Collapse
Affiliation(s)
- Sergio Astigarraga
- Skirball Institute for Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Jessica Douthit
- Skirball Institute for Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| | - Dorota Tarnogorska
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4R2, Canada
| | - Matthew S Creamer
- Interdepartmental Neuroscience Program, Yale University, Kline Biology Tower Room 224, 219 Whitney Avenue, New Haven, CT 06511, USA
| | - Omer Mano
- Department of Molecular, Cellular and Developmental Biology, Yale University, Kline Biology Tower Room 224, 219 Whitney Avenue, New Haven, CT 06511, USA
| | - Damon A Clark
- Interdepartmental Neuroscience Program, Yale University, Kline Biology Tower Room 224, 219 Whitney Avenue, New Haven, CT 06511, USA
| | - Ian A Meinertzhagen
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, 1355 Oxford Street, Halifax, NS B3H 4R2, Canada
| | - Jessica E Treisman
- Skirball Institute for Biomolecular Medicine and Department of Cell Biology, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
| |
Collapse
|
25
|
Abstract
The activity and maintenance of neurons requires substantial metabolic energy, resulting in selective pressure to decrease resource consumption by the nervous system. The wiring economy principle proposes that animals have evolved mechanisms that wire circuits efficiently by minimizing neurite length. Computational modeling of neuronal morphology, microcircuit organization, and neural networks reveals that wiring economy is a significant determinant of nervous system layout. The strategies for reducing wiring costs are shared across phyla and point to the possibility of generalizable rules that specify the development of efficient nervous systems. As the developmental mechanisms underpinning wiring economy are only now being elucidated, whether the molecular basis of this phenomenon is the result of conserved genetic programs or convergent evolution remains to be determined.
Collapse
Affiliation(s)
- Irving E Wang
- Department of Neurobiology, Stanford University, Stanford, CA 94305, USA
| | - Thomas R Clandinin
- Department of Neurobiology, Stanford University, Stanford, CA 94305, USA.
| |
Collapse
|
26
|
Abstract
The brain is a network of neurons, one that generates behaviour, and knowing the former is crucial to understanding the latter. Identifying the exact network of synaptic connections, or connectome, of the fly's central nervous system is now a major objective in Drosophila neurobiology, one that has been initiated in several laboratories, especially the Janelia Research Campus of the Howard Hughes Medical Institute. Progress is most advanced in the optic neuropiles of the visual system. The effort to derive a connectome from these and other neuropile regions is proceeding by various methods of electron microscopy, especially focused-ion beam milling scanning electron microscopy, and relies upon - but is to be carefully distinguished from - published light microscopic methods that reveal the projections of genetically labelled cell types. The latter reveal those neurons that come into close proximity and are therefore candidate synaptic partners. Synaptic partnerships are not in fact reliably revealed by such candidate pairs, anatomical connections often revealing unexpected pathways. Synaptic partnerships identified from ultrastructural features provide a strong heuristic basis to interpret not only functional interactions between identified neurons, but also a powerful means to predict such interactions, and suggest functional pathways not readily predicted from existing experimental evidence. The analysis of circuit function may proceed cell by cell, by examining the behavioural outcome of either interrupting or restoring function to any one element in an anatomically defined circuit, but can be foiled by degeneracy in pathway elements. Circuit information can also be used to identify and analyse circuit motifs, and their role in higher-order network properties. These attempts in Drosophila anticipate parallel attempts in other systems, notably the inner plexiform layer of the vertebrate retina, and augment the one complete connectome already available to us, that available for 30 years in the nematode Caenorhabditis elegans.
Collapse
Affiliation(s)
- Ian A Meinertzhagen
- a Department of Psychology and Neuroscience, Life Sciences Centre , Dalhousie University , Halifax , Canada ;,b Janelia Research Campus of Howard Hughes Medical Institute , Ashburn , VA , USA
| |
Collapse
|
27
|
Plazaola-Sasieta H, Fernández-Pineda A, Zhu Q, Morey M. Untangling the wiring of the Drosophila visual system: developmental principles and molecular strategies. J Neurogenet 2017; 31:231-249. [DOI: 10.1080/01677063.2017.1391249] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Haritz Plazaola-Sasieta
- Department of Genetics, Microbiology and Statistics; School of Biology and Institute of Biomedicine of the University of Barcelona (IBUB), University of Barcelona, Barcelona, Spain
| | - Alejandra Fernández-Pineda
- Department of Genetics, Microbiology and Statistics; School of Biology and Institute of Biomedicine of the University of Barcelona (IBUB), University of Barcelona, Barcelona, Spain
| | - Qi Zhu
- Department of Genetics, Microbiology and Statistics; School of Biology and Institute of Biomedicine of the University of Barcelona (IBUB), University of Barcelona, Barcelona, Spain
| | - Marta Morey
- Department of Genetics, Microbiology and Statistics; School of Biology and Institute of Biomedicine of the University of Barcelona (IBUB), University of Barcelona, Barcelona, Spain
| |
Collapse
|
28
|
Lefebvre JL. Neuronal territory formation by the atypical cadherins and clustered protocadherins. Semin Cell Dev Biol 2017; 69:111-121. [DOI: 10.1016/j.semcdb.2017.07.040] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2017] [Revised: 07/24/2017] [Accepted: 07/25/2017] [Indexed: 02/04/2023]
|
29
|
Kremer MC, Jung C, Batelli S, Rubin GM, Gaul U. The glia of the adult Drosophila nervous system. Glia 2017; 65:606-638. [PMID: 28133822 PMCID: PMC5324652 DOI: 10.1002/glia.23115] [Citation(s) in RCA: 160] [Impact Index Per Article: 22.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2016] [Revised: 12/22/2016] [Accepted: 12/29/2016] [Indexed: 12/11/2022]
Abstract
Glia play crucial roles in the development and homeostasis of the nervous system. While the GLIA in the Drosophila embryo have been well characterized, their study in the adult nervous system has been limited. Here, we present a detailed description of the glia in the adult nervous system, based on the analysis of some 500 glial drivers we identified within a collection of synthetic GAL4 lines. We find that glia make up ∼10% of the cells in the nervous system and envelop all compartments of neurons (soma, dendrites, axons) as well as the nervous system as a whole. Our morphological analysis suggests a set of simple rules governing the morphogenesis of glia and their interactions with other cells. All glial subtypes minimize contact with their glial neighbors but maximize their contact with neurons and adapt their macromorphology and micromorphology to the neuronal entities they envelop. Finally, glial cells show no obvious spatial organization or registration with neuronal entities. Our detailed description of all glial subtypes and their regional specializations, together with the powerful genetic toolkit we provide, will facilitate the functional analysis of glia in the mature nervous system. GLIA 2017 GLIA 2017;65:606–638
Collapse
Affiliation(s)
- Malte C Kremer
- Gene Center and Department of Biochemistry, Center of Protein Science Munich (CIPSM), Ludwig-Maximilians-University Munich, Germany.,Janelia Research Campus, Howard Hughes Medical Institute, Helix Drive, Ashburn, Virginia
| | - Christophe Jung
- Gene Center and Department of Biochemistry, Center of Protein Science Munich (CIPSM), Ludwig-Maximilians-University Munich, Germany
| | - Sara Batelli
- Gene Center and Department of Biochemistry, Center of Protein Science Munich (CIPSM), Ludwig-Maximilians-University Munich, Germany
| | - Gerald M Rubin
- Janelia Research Campus, Howard Hughes Medical Institute, Helix Drive, Ashburn, Virginia
| | - Ulrike Gaul
- Gene Center and Department of Biochemistry, Center of Protein Science Munich (CIPSM), Ludwig-Maximilians-University Munich, Germany
| |
Collapse
|
30
|
Kolodkin AL, Hiesinger PR. Wiring visual systems: common and divergent mechanisms and principles. Curr Opin Neurobiol 2017; 42:128-135. [PMID: 28064004 PMCID: PMC5316370 DOI: 10.1016/j.conb.2016.12.006] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2016] [Revised: 12/16/2016] [Accepted: 12/16/2016] [Indexed: 10/20/2022]
Abstract
The study of visual systems has a rich history, leading to the discovery and understanding of basic principles underlying the elaboration of neuronal connectivity. Recent work in model organisms such as fly, fish and mouse has yielded a wealth of new insights into visual system wiring. Here, we consider how axonal and dendritic patterning in columns and laminae influence synaptic partner selection in these model organisms. We highlight similarities and differences among disparate visual systems with the goal of identifying common and divergent principles for visual system wiring.
Collapse
Affiliation(s)
- Alex L Kolodkin
- The Solomon H. Snyder Department of Neuroscience and Howard Hughes Medical Institute, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
| | - P Robin Hiesinger
- Division of Neurobiology of the Institute for Biology, Free University Berlin, Germany.
| |
Collapse
|
31
|
Yang C, Li X, Wang C, Fu S, Li H, Guo Z, Zhao S, Lin J. N-cadherin regulates beta-catenin signal and its misexpression perturbs commissural axon projection in the developing chicken spinal cord. J Mol Histol 2016; 47:541-554. [PMID: 27650519 DOI: 10.1007/s10735-016-9698-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2016] [Accepted: 09/14/2016] [Indexed: 12/31/2022]
Abstract
N-cadherin is a calcium-sensitive cell adhesion molecule that plays an important role in the formation of the neural circuit and the development of the nervous system. In the present study, we investigated the function of N-cadherin in cell-cell connection in vitro with HEK293T cells, and in commissural axon projections in the developing chicken spinal cord using in ovo electroporation. Cell-cell connections increased with N-cadherin overexpression in HEK293T cells, while cell contacts disappeared after co-transfection with an N-cadherin-shRNA plasmid. The knockdown of N-cadherin caused the accumulation of β-catenin in the nucleus, supporting the notion that N-cadherin regulates β-catenin signaling in vitro. Furthermore, N-cadherin misexpression perturbed commissural axon projections in the spinal cord. The overexpression of N-cadherin reduced the number of axons that projected alongside the contralateral margin of the floor plate, and formed intermediate longitudinal commissural axons. In contrast, the knockdown of N-cadherin perturbed commissural axon projections significantly, affecting the projections alongside the contralateral margin of the floor plate, but did not affect intermediate longitudinal commissural axons. Taken together, these findings suggest that N-cadherin regulates commissural axon projections in the developing chicken spinal cord.
Collapse
Affiliation(s)
- Ciqing Yang
- College of Life Science and Technology, Xinxiang Medical University, Xinxiang, 453003, China.,Henan Key Laboratory of Medical Tissue Regeneration, Xinxiang, 453003, China
| | - Xiaoying Li
- College of Life Science and Technology, Xinxiang Medical University, Xinxiang, 453003, China
| | - Congrui Wang
- Henan Key Laboratory of Medical Tissue Regeneration, Xinxiang, 453003, China
| | - Sulei Fu
- College of Life Science and Technology, Xinxiang Medical University, Xinxiang, 453003, China
| | - Han Li
- College of Life Science and Technology, Xinxiang Medical University, Xinxiang, 453003, China.,Advanced Medical and Dental Institute, Universiti Sains Malaysia, 13200, Bertam, Penang, Malaysia
| | - Zhikun Guo
- Henan Key Laboratory of Medical Tissue Regeneration, Xinxiang, 453003, China
| | - Shanting Zhao
- College of Veterinary Medicine, Northwest A&F University, Yangling, 712100, China
| | - Juntang Lin
- College of Life Science and Technology, Xinxiang Medical University, Xinxiang, 453003, China. .,Henan Key Laboratory of Medical Tissue Regeneration, Xinxiang, 453003, China. .,Institute of Anatomy I, Jena University Hospital, 07743, Jena, Germany.
| |
Collapse
|
32
|
Tadros W, Xu S, Akin O, Yi CH, Shin GJE, Millard SS, Zipursky SL. Dscam Proteins Direct Dendritic Targeting through Adhesion. Neuron 2016; 89:480-93. [PMID: 26844831 DOI: 10.1016/j.neuron.2015.12.026] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2015] [Revised: 11/11/2015] [Accepted: 12/07/2015] [Indexed: 11/17/2022]
Abstract
Cell recognition molecules are key regulators of neural circuit assembly. The Dscam family of recognition molecules in Drosophila has been shown to regulate interactions between neurons through homophilic repulsion. This is exemplified by Dscam1 and Dscam2, which together repel dendrites of lamina neurons, L1 and L2, in the visual system. By contrast, here we show that Dscam2 directs dendritic targeting of another lamina neuron, L4, through homophilic adhesion. Through live imaging and genetic mosaics to dissect interactions between specific cells, we show that Dscam2 is required in L4 and its target cells for correct dendritic targeting. In a genetic screen, we identified Dscam4 as another regulator of L4 targeting which acts with Dscam2 in the same pathway to regulate this process. This ensures tiling of the lamina neuropil through heterotypic interactions. Thus, different combinations of Dscam proteins act through distinct mechanisms in closely related neurons to pattern neural circuits.
Collapse
Affiliation(s)
- Wael Tadros
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Shuwa Xu
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Orkun Akin
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Caroline H Yi
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Grace Ji-Eun Shin
- School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia
| | - S Sean Millard
- School of Biomedical Sciences, The University of Queensland, Brisbane QLD 4072, Australia
| | - S Lawrence Zipursky
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
| |
Collapse
|
33
|
Poliak S, Norovich AL, Yamagata M, Sanes JR, Jessell TM. Muscle-type Identity of Proprioceptors Specified by Spatially Restricted Signals from Limb Mesenchyme. Cell 2016; 164:512-25. [PMID: 26824659 DOI: 10.1016/j.cell.2015.12.049] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/04/2015] [Revised: 11/18/2015] [Accepted: 12/22/2015] [Indexed: 11/20/2022]
Abstract
The selectivity with which proprioceptive sensory neurons innervate their central and peripheral targets implies that they exhibit distinctions in muscle-type identity. The molecular correlates of proprioceptor identity and its origins remain largely unknown, however. In screens to define muscle-type proprioceptor character, we find all-or-none differences in gene expression for proprioceptors that control antagonistic muscles at a single hindlimb joint. Analysis of three of these genes, cadherin13 (cdh13), semaphorin5a (sema5a), and cartilage-acidic protein-1 (crtac1), reveals expression in proprioceptor subsets that supply muscle groups located at restricted dorsoventral and proximodistal domains of the limb. Genetically altering the dorsoventral character of the limb mesenchyme elicits a change in the profile of proprioceptor cdh13, sema5a, and crtac1 expression. These findings indicate that proprioceptors acquire aspects of their muscle-type identity in response to mesenchymal signals expressed in restricted proximodistal and dorsoventral domains of the developing limb.
Collapse
Affiliation(s)
- Sebastian Poliak
- Department of Neuroscience, Biochemistry, and Molecular Biophysics, Columbia University, New York, NY 10032, USA
| | - Amy L Norovich
- Department of Biological Sciences, Columbia University, New York, NY 10032, USA
| | - Masahito Yamagata
- Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Joshua R Sanes
- Department of Molecular and Cellular Biology and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA
| | - Thomas M Jessell
- Department of Neuroscience, Biochemistry, and Molecular Biophysics, Columbia University, New York, NY 10032, USA; Howard Hughes Medical Institute, Kavli Institute for Brain Science, Columbia University, New York, NY 10032, USA.
| |
Collapse
|
34
|
Hassan BA, Hiesinger PR. Beyond Molecular Codes: Simple Rules to Wire Complex Brains. Cell 2016; 163:285-91. [PMID: 26451480 DOI: 10.1016/j.cell.2015.09.031] [Citation(s) in RCA: 71] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Indexed: 11/30/2022]
Abstract
Molecular codes, like postal zip codes, are generally considered a robust way to ensure the specificity of neuronal target selection. However, a code capable of unambiguously generating complex neural circuits is difficult to conceive. Here, we re-examine the notion of molecular codes in the light of developmental algorithms. We explore how molecules and mechanisms that have been considered part of a code may alternatively implement simple pattern formation rules sufficient to ensure wiring specificity in neural circuits. This analysis delineates a pattern-based framework for circuit construction that may contribute to our understanding of brain wiring.
Collapse
Affiliation(s)
- Bassem A Hassan
- Center for the Biology of Disease, VIB, 3000 Leuven, Belgium; Center for Human Genetics, University of Leuven School of Medicine, 3000 Leuven, Belgium.
| | - P Robin Hiesinger
- Division of Neurobiology, Institute for Biology, Freie Universität Berlin, 14195 Berlin, Germany; NeuroCure Cluster of Excellence, Charite Universitätsmedizin Berlin, 10117 Berlin, Germany.
| |
Collapse
|
35
|
Özel MN, Langen M, Hassan BA, Hiesinger PR. Filopodial dynamics and growth cone stabilization in Drosophila visual circuit development. eLife 2015; 4. [PMID: 26512889 PMCID: PMC4728134 DOI: 10.7554/elife.10721] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 10/26/2015] [Indexed: 01/04/2023] Open
Abstract
Filopodial dynamics are thought to control growth cone guidance, but the types and roles of growth cone dynamics underlying neural circuit assembly in a living brain are largely unknown. To address this issue, we have developed long-term, continuous, fast and high-resolution imaging of growth cone dynamics from axon growth to synapse formation in cultured Drosophila brains. Using R7 photoreceptor neurons as a model we show that >90% of the growth cone filopodia exhibit fast, stochastic dynamics that persist despite ongoing stepwise layer formation. Correspondingly, R7 growth cones stabilize early and change their final position by passive dislocation. N-Cadherin controls both fast filopodial dynamics and growth cone stabilization. Surprisingly, loss of N-Cadherin causes no primary targeting defects, but destabilizes R7 growth cones to jump between correct and incorrect layers. Hence, growth cone dynamics can influence wiring specificity without a direct role in target recognition and implement simple rules during circuit assembly. DOI:http://dx.doi.org/10.7554/eLife.10721.001 Genes encode complicated developmental processes, but it is clear that genetic information cannot encode each and every individual connection that forms between the nerve cells in a brain. Instead, the individual cells and nerve endings must make decisions during brain development. Up until now, few examples were known for how these nerve endings move and choose their paths and partners in a living, developing brain. The fruit fly Drosophila provides a useful model to explore the ‘wiring’ of nerve cells in the brain, partly because a fruit fly’s brain develops within a few days. However, most previous studies have relied on identifying mutant flies with disrupted brain wiring and studying them using still images. Now, Özel et al. have developed a new imaging method that has enough resolution and speed over sufficiently long periods to track the growing nerve endings in a developing fly brain. The method was applied to a model nerve cell in the fly’s visual system. This revealed that most of this nerve’s dynamic changes are short-lived and random, and appear to help to stabilize the developing nerve ending, rather than guide it to a target. Özel et al. also found that a protein called N-Cadherin, previously thought to be required for the targeting of developing nerve endings, actually plays a role in their stabilization. These findings uncover the roles of changes in nerve endings during long-term brain development; this was previously largely unknown for any organism. The next stage in this research will involve further analyses of both wild type and mutant flies to try and work out general principles about how the brain develops via the decoding of genetic information. DOI:http://dx.doi.org/10.7554/eLife.10721.002
Collapse
Affiliation(s)
- Mehmet Neset Özel
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States.,Division of Neurobiology, Institute for Biology, Freie Universität Berlin, Berlin, Germany.,NeuroCure Cluster of Excellence, Charite Universitätsmedizin Berlin, Berlin, Germany
| | - Marion Langen
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States
| | - Bassem A Hassan
- Center for the Biology of Disease, Vlaams Instituut voor Biotechnologie, Leuven, Belgium.,Center for Human Genetics, University of Leuven School of Medicine, Leuven, Belgium
| | - P Robin Hiesinger
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, United States.,Division of Neurobiology, Institute for Biology, Freie Universität Berlin, Berlin, Germany.,NeuroCure Cluster of Excellence, Charite Universitätsmedizin Berlin, Berlin, Germany
| |
Collapse
|
36
|
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: 151] [Impact Index Per Article: 16.8] [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.
Collapse
|
37
|
Abstract
In this issue of Cell, Langen et al. use time-lapse multiphoton microscopy to show how Drosophila photoreceptor growth cones find their targets. Based on the observed dynamics, they develop a simple developmental algorithm recapitulating the highly complex connectivity pattern of these neurons, suggesting a basic framework for establishing wiring specificity.
Collapse
Affiliation(s)
- Mathias F Wernet
- Center for Genomics and Systems Biology, New York University Abu Dhabi (NYUAD), 129188 Saadiyat Island, Abu Dhabi, UAE
| | - Claude Desplan
- Center for Genomics and Systems Biology, New York University Abu Dhabi (NYUAD), 129188 Saadiyat Island, Abu Dhabi, UAE; Department of Biology, New York University, 100 Washington Square East, New York, NY 10003, USA.
| |
Collapse
|
38
|
Bomer N, den Hollander W, Ramos YFM, Bos SD, van der Breggen R, Lakenberg N, Pepers BA, van Eeden AE, Darvishan A, Tobi EW, Duijnisveld BJ, van den Akker EB, Heijmans BT, van Roon-Mom WMC, Verbeek FJ, van Osch GJVM, Nelissen RGHH, Slagboom PE, Meulenbelt I. Underlying molecular mechanisms of DIO2 susceptibility in symptomatic osteoarthritis. Ann Rheum Dis 2015; 74:1571-9. [PMID: 24695009 PMCID: PMC4516000 DOI: 10.1136/annrheumdis-2013-204739] [Citation(s) in RCA: 65] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2013] [Revised: 03/14/2014] [Accepted: 03/15/2014] [Indexed: 11/30/2022]
Abstract
OBJECTIVES To investigate how the genetic susceptibility gene DIO2 confers risk to osteoarthritis (OA) onset in humans and to explore whether counteracting the deleterious effect could contribute to novel therapeutic approaches. METHODS Epigenetically regulated expression of DIO2 was explored by assessing methylation of positional CpG-dinucleotides and the respective DIO2 expression in OA-affected and macroscopically preserved articular cartilage from end-stage OA patients. In a human in vitro chondrogenesis model, we measured the effects when thyroid signalling during culturing was either enhanced (excess T3 or lentiviral induced DIO2 overexpression) or decreased (iopanoic acid). RESULTS OA-related changes in methylation at a specific CpG dinucleotide upstream of DIO2 caused significant upregulation of its expression (β=4.96; p=0.0016). This effect was enhanced and appeared driven specifically by DIO2 rs225014 risk allele carriers (β=5.58, p=0.0006). During in vitro chondrogenesis, DIO2 overexpression resulted in a significant reduced capacity of chondrocytes to deposit extracellular matrix (ECM) components, concurrent with significant induction of ECM degrading enzymes (ADAMTS5, MMP13) and markers of mineralisation (ALPL, COL1A1). Given their concurrent and significant upregulation of expression, this process is likely mediated via HIF-2α/RUNX2 signalling. In contrast, we showed that inhibiting deiodinases during in vitro chondrogenesis contributed to prolonged cartilage homeostasis as reflected by significant increased deposition of ECM components and attenuated upregulation of matrix degrading enzymes. CONCLUSIONS Our findings show how genetic variation at DIO2 could confer risk to OA and raised the possibility that counteracting thyroid signalling may be a novel therapeutic approach.
Collapse
Affiliation(s)
- Nils Bomer
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- IDEAL, The Netherlands
| | | | | | - Steffan D Bos
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- Genomics Initiative, sponsored by the NCHA, Leiden, The Netherlands
| | | | - Nico Lakenberg
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
| | - Barry A Pepers
- Department of Human Genetics, LUMC, Leiden, The Netherlands
| | | | - Arash Darvishan
- Department of Imaging & BioInformatics, LIACS, Leiden, The Netherlands
| | - Elmar W Tobi
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- IDEAL, The Netherlands
| | | | - Erik B van den Akker
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- The Delft Bioinformatics Lab, Delft University of Technology, Delft, The Netherlands
| | - Bastiaan T Heijmans
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- Genomics Initiative, sponsored by the NCHA, Leiden, The Netherlands
| | | | - Fons J Verbeek
- Department of Imaging & BioInformatics, LIACS, Leiden, The Netherlands
| | - Gerjo J V M van Osch
- Department of Orthopaedics, Erasmus MC, Rotterdam, The Netherlands
- Deptartment of Otorhinolaryngology, Erasmus MC, Rotterdam, The Netherlands
| | | | - P Eline Slagboom
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- IDEAL, The Netherlands
- Genomics Initiative, sponsored by the NCHA, Leiden, The Netherlands
| | - Ingrid Meulenbelt
- Department of Molecular Epidemiology, LUMC, Leiden, The Netherlands
- Genomics Initiative, sponsored by the NCHA, Leiden, The Netherlands
| |
Collapse
|
39
|
Genetically Encoded Spy Peptide Fusion System to Detect Plasma Membrane-Localized Proteins In Vivo. ACTA ACUST UNITED AC 2015. [PMID: 26211362 DOI: 10.1016/j.chembiol.2015.06.020] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Membrane proteins are the main gatekeepers of cellular state, especially in neurons, serving either to maintain homeostasis or instruct response to synaptic input or other external signals. Visualization of membrane protein localization and trafficking in live cells facilitates understanding the molecular basis of cellular dynamics. We describe here a method for specifically labeling the plasma membrane-localized fraction of heterologous membrane protein expression using channelrhodopsins as a case study. We show that the genetically encoded, covalent binding SpyTag and SpyCatcher pair from the Streptococcus pyogenes fibronectin-binding protein FbaB can selectively label membrane-localized proteins in living cells in culture and in vivo in Caenorhabditis elegans. The SpyTag/SpyCatcher covalent labeling method is highly specific, modular, and stable in living cells. We have used the binding pair to develop a channelrhodopsin membrane localization assay that is amenable to high-throughput screening for opsin discovery and engineering.
Collapse
|
40
|
Petrovic M, Schmucker D. Axonal wiring in neural development: Target-independent mechanisms help to establish precision and complexity. Bioessays 2015; 37:996-1004. [DOI: 10.1002/bies.201400222] [Citation(s) in RCA: 35] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
- Milan Petrovic
- Neuronal Wiring Laboratory; VIB; Leuven Belgium
- Department of Oncology, School of Medicine; University of Leuven; Leuven Belgium
| | - Dietmar Schmucker
- Neuronal Wiring Laboratory; VIB; Leuven Belgium
- Department of Oncology, School of Medicine; University of Leuven; Leuven Belgium
| |
Collapse
|
41
|
Mencarelli C, Pichaud F. Orthodenticle Is Required for the Expression of Principal Recognition Molecules That Control Axon Targeting in the Drosophila Retina. PLoS Genet 2015; 11:e1005303. [PMID: 26114289 PMCID: PMC4482733 DOI: 10.1371/journal.pgen.1005303] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Accepted: 05/27/2015] [Indexed: 11/18/2022] Open
Abstract
Parallel processing of neuronal inputs relies on assembling neural circuits into distinct synaptic-columns and layers. This is orchestrated by matching recognition molecules between afferent growth cones and target areas. Controlling the expression of these molecules during development is crucial but not well understood. The developing Drosophila visual system is a powerful genetic model for addressing this question. In this model system, the achromatic R1-6 photoreceptors project their axons in the lamina while the R7 and R8 photoreceptors, which are involved in colour detection, project their axons to two distinct synaptic-layers in the medulla. Here we show that the conserved homeodomain transcription factor Orthodenticle (Otd), which in the eye is a main regulator of rhodopsin expression, is also required for R1-6 photoreceptor synaptic-column specific innervation of the lamina. Our data indicate that otd function in these photoreceptors is largely mediated by the recognition molecules flamingo (fmi) and golden goal (gogo). In addition, we find that otd regulates synaptic-layer targeting of R8. We demonstrate that during this process, otd and the R8-specific transcription factor senseless/Gfi1 (sens) function as independent transcriptional inputs that are required for the expression of fmi, gogo and the adhesion molecule capricious (caps), which govern R8 synaptic-layer targeting. Our work therefore demonstrates that otd is a main component of the gene regulatory network that regulates synaptic-column and layer targeting in the fly visual system. Establishing neural circuits during brain development relies on the ability for neurons to find their appropriate targets, a task that depends on recognition molecules whose expression must be tightly controlled. Very little is known of the factors that control the expression of these molecules. Here we have used the genetically amenable fly retina to address this issue. We identify Orthodenticle, a protein involved in mammalian brain development, as a main component of a new genetic cascade controlling the expression of recognition molecules that govern the wiring of the fly retina. Our work raises the issue that Orthodenticle might play a similar role in mammals. It also sheds new light on the genetic basis for wiring a model neural circuit during development.
Collapse
Affiliation(s)
- Chiara Mencarelli
- MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom
| | - Franck Pichaud
- MRC Laboratory for Molecular Cell Biology, University College London, London, United Kingdom
- * E-mail:
| |
Collapse
|
42
|
The Developmental Rules of Neural Superposition in Drosophila. Cell 2015; 162:120-33. [PMID: 26119341 DOI: 10.1016/j.cell.2015.05.055] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2014] [Revised: 03/21/2015] [Accepted: 05/15/2015] [Indexed: 11/17/2022]
Abstract
Complicated neuronal circuits can be genetically encoded, but the underlying developmental algorithms remain largely unknown. Here, we describe a developmental algorithm for the specification of synaptic partner cells through axonal sorting in the Drosophila visual map. Our approach combines intravital imaging of growth cone dynamics in developing brains of intact pupae and data-driven computational modeling. These analyses suggest that three simple rules are sufficient to generate the seemingly complex neural superposition wiring of the fly visual map without an elaborate molecular matchmaking code. Our computational model explains robust and precise wiring in a crowded brain region despite extensive growth cone overlaps and provides a framework for matching molecular mechanisms with the rules they execute. Finally, ordered geometric axon terminal arrangements that are not required for neural superposition are a side product of the developmental algorithm, thus elucidating neural circuit connectivity that remained unexplained based on adult structure and function alone.
Collapse
|
43
|
Fine-scale topography in sensory systems: insights from Drosophila and vertebrates. J Comp Physiol A Neuroethol Sens Neural Behav Physiol 2015; 201:911-20. [PMID: 26091779 DOI: 10.1007/s00359-015-1022-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2014] [Revised: 06/07/2015] [Accepted: 06/08/2015] [Indexed: 10/23/2022]
Abstract
To encode the positions of sensory stimuli, sensory circuits form topographic maps in the central nervous system through specific point-to-point connections between pre- and postsynaptic neurons. In vertebrate visual systems, the establishment of topographic maps involves the formation of a coarse topography followed by that of fine-scale topography that distinguishes the axon terminals of neighboring neurons. It is known that intrinsic differences in the form of broad gradients of guidance molecules instruct coarse topography while neuronal activity is required for fine-scale topography. On the other hand, studies in the Drosophila visual system have shown that intrinsic differences in cell adhesion among the axon terminals of neighboring neurons instruct the fine-scale topography. Recent studies on activity-dependent topography in the Drosophila somatosensory system have revealed a role of neuronal activity in creating molecular differences among sensory neurons for establishing fine-scale topography, implicating a conserved principle. Here we review the findings in both Drosophila and vertebrates and propose an integrated model for fine-scale topography.
Collapse
|
44
|
Abstract
During brain development, billions of neurons organize into highly specific circuits. To form specific circuits, neurons must build the appropriate types of synapses with appropriate types of synaptic partners while avoiding incorrect partners in a dense cellular environment. Defining the cellular and molecular rules that govern specific circuit formation has significant scientific and clinical relevance because fine scale connectivity defects are thought to underlie many cognitive and psychiatric disorders. Organizing specific neural circuits is an enormously complicated developmental process that requires the concerted action of many molecules, neural activity, and temporal events. This review focuses on one class of molecules postulated to play an important role in target selection and specific synapse formation: the classic cadherins. Cadherins have a well-established role in epithelial cell adhesion, and although it has long been appreciated that most cadherins are expressed in the brain, their role in synaptic specificity is just beginning to be unraveled. Here, we review past and present studies implicating cadherins as active participants in the formation, function, and dysfunction of specific neural circuits and pose some of the major remaining questions.
Collapse
Affiliation(s)
- Raunak Basu
- a Department of Neurobiology and Anatomy ; University of Utah ; Salt Lake City , UT USA
| | | | | |
Collapse
|
45
|
Boyan G, Williams L, Liu Y. Conserved patterns of axogenesis in the panarthropod brain. ARTHROPOD STRUCTURE & DEVELOPMENT 2015; 44:101-112. [PMID: 25483803 DOI: 10.1016/j.asd.2014.11.003] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/14/2014] [Revised: 10/11/2014] [Accepted: 11/24/2014] [Indexed: 06/04/2023]
Abstract
Neuropils in the cerebral midline of Panarthropoda exhibit a wide spectrum of neuroarchitectures--from rudimentary to highly elaborated--and which at first sight defy a unifying neuroarchitectural principle. Developmental approaches have shown that in model arthropods such as insects, conserved cellular and molecular mechanisms first establish a simple axon scaffold in the brain. However, to be adapted for adult life, this immature ground plan is transformed by a developmental process--known in the grasshopper as "fascicle switching"--in which subsets of neurons systematically redirect their growth cones at stereotypic locations across the brain midline. A topographic system of choice points along the transverse brain axis where axons decussate features in all panarthropods studied even though different modes of neurogenesis and varying degrees of neuropilar elaboration are involved. This suggests that the molecular mechanisms regulating choice point selection may be conserved. In combination with recent cladistic interpretations of arthropod phylogeny based on nuclear protein-coding sequences the data argue for this topographic decussation as having evolved early and being a conserved feature of the Panarthropoda. Differences in elaboration likely reflect both the extent to which neuropilar reorganization has progressed during development and the lifestyle of the individual organism.
Collapse
Affiliation(s)
- George Boyan
- Developmental Neurobiology Group, Biocenter, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany.
| | - Leslie Williams
- Developmental Neurobiology Group, Biocenter, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany
| | - Yu Liu
- Developmental Neurobiology Group, Biocenter, Ludwig-Maximilians-Universität, Grosshadernerstrasse 2, 82152 Planegg-Martinsried, Germany
| |
Collapse
|
46
|
Friedman LG, Benson DL, Huntley GW. Cadherin-based transsynaptic networks in establishing and modifying neural connectivity. Curr Top Dev Biol 2015; 112:415-65. [PMID: 25733148 DOI: 10.1016/bs.ctdb.2014.11.025] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
It is tacitly understood that cell adhesion molecules (CAMs) are critically important for the development of cells, circuits, and synapses in the brain. What is less clear is what CAMs continue to contribute to brain structure and function after the early period of development. Here, we focus on the cadherin family of CAMs to first briefly recap their multidimensional roles in neural development and then to highlight emerging data showing that with maturity, cadherins become largely dispensible for maintaining neuronal and synaptic structure, instead displaying new and narrower roles at mature synapses where they critically regulate dynamic aspects of synaptic signaling, structural plasticity, and cognitive function. At mature synapses, cadherins are an integral component of multiprotein networks, modifying synaptic signaling, morphology, and plasticity through collaborative interactions with other CAM family members as well as a variety of neurotransmitter receptors, scaffolding proteins, and other effector molecules. Such recognition of the ever-evolving functions of synaptic cadherins may yield insight into the pathophysiology of brain disorders in which cadherins have been implicated and that manifest at different times of life.
Collapse
Affiliation(s)
- Lauren G Friedman
- Fishberg Department of Neuroscience, Friedman Brain Institute and the Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, USA
| | - Deanna L Benson
- Fishberg Department of Neuroscience, Friedman Brain Institute and the Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, USA
| | - George W Huntley
- Fishberg Department of Neuroscience, Friedman Brain Institute and the Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, USA.
| |
Collapse
|
47
|
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.
Collapse
Affiliation(s)
- Shaul Yogev
- Department of Biology, Howard Hughes Medical Institute, Stanford University, Stanford, California 94305;
| | | |
Collapse
|
48
|
Schmidt ERE, Brignani S, Adolfs Y, Lemstra S, Demmers J, Vidaki M, Donahoo ALS, Lilleväli K, Vasar E, Richards LJ, Karagogeos D, Kolk SM, Pasterkamp RJ. Subdomain-mediated axon-axon signaling and chemoattraction cooperate to regulate afferent innervation of the lateral habenula. Neuron 2014; 83:372-387. [PMID: 25033181 DOI: 10.1016/j.neuron.2014.05.036] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/21/2014] [Indexed: 11/20/2022]
Abstract
A dominant feature of neural circuitry is the organization of neuronal projections and synapses into specific brain nuclei or laminae. Lamina-specific connectivity is controlled by the selective expression of extracellular guidance and adhesion molecules in the target field. However, how (sub)nucleus-specific connections are established and whether axon-derived cues contribute to subdomain targeting are largely unknown. Here, we demonstrate that the lateral subnucleus of the habenula (lHb) determines its own afferent innervation by sending out efferent projections that express the cell adhesion molecule LAMP to reciprocally collect and guide dopaminergic afferents to the lHb-a phenomenon we term subdomain-mediated axon-axon signaling. This process of reciprocal axon-axon interactions cooperates with lHb-specific chemoattraction mediated by Netrin-1, which controls axon target entry, to ensure specific innervation of the lHb. We propose that cooperation between pretarget reciprocal axon-axon signaling and subdomain-restricted instructive cues provides a highly precise and general mechanism to establish subdomain-specific neural circuitry.
Collapse
Affiliation(s)
- Ewoud Roberto Eduard Schmidt
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands
| | - Sara Brignani
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands
| | - Youri Adolfs
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands
| | - Suzanne Lemstra
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands
| | - Jeroen Demmers
- Proteomics Centre and Department of Cell Biology, Erasmus University Medical Centre, Dr Molewaterplein 50, 3015 GE Rotterdam, the Netherlands
| | - Marina Vidaki
- Department of Basic Science, Faculty of Medicine, University of Crete and Institute of Molecular Biology and Biotechnology, Vassilika Vouton, Heraklion GR-7110, Greece
| | - Amber-Lee Skye Donahoo
- Queensland Brain Institute and The School of Biomedical Sciences, University of Queensland, Building 79, St Lucia Campus, Brisbane, QLD 4067, Australia
| | - Kersti Lilleväli
- Department of Physiology, Institute of Biomedicine and Translational Medicine, University of Tartu, Ravila 19, 50411 Tartu, Estonia
| | - Eero Vasar
- Department of Physiology, Institute of Biomedicine and Translational Medicine, University of Tartu, Ravila 19, 50411 Tartu, Estonia
| | - Linda Jane Richards
- Queensland Brain Institute and The School of Biomedical Sciences, University of Queensland, Building 79, St Lucia Campus, Brisbane, QLD 4067, Australia
| | - Domna Karagogeos
- Department of Basic Science, Faculty of Medicine, University of Crete and Institute of Molecular Biology and Biotechnology, Vassilika Vouton, Heraklion GR-7110, Greece
| | - Sharon Margriet Kolk
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands
| | - Ronald Jeroen Pasterkamp
- Department of Translational Neuroscience, Brain Center Rudolf Magnus, University Medical Center Utrecht, Universiteitsweg 100, 3584 CG Utrecht, the Netherlands.
| |
Collapse
|
49
|
Agi E, Langen M, Altschuler SJ, Wu LF, Zimmermann T, Hiesinger PR. The evolution and development of neural superposition. J Neurogenet 2014; 28:216-32. [PMID: 24912630 PMCID: PMC4245170 DOI: 10.3109/01677063.2014.922557] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Visual systems have a rich history as model systems for the discovery and understanding of basic principles underlying neuronal connectivity. The compound eyes of insects consist of up to thousands of small unit eyes that are connected by photoreceptor axons to set up a visual map in the brain. The photoreceptor axon terminals thereby represent neighboring points seen in the environment in neighboring synaptic units in the brain. Neural superposition is a special case of such a wiring principle, where photoreceptors from different unit eyes that receive the same input converge upon the same synaptic units in the brain. This wiring principle is remarkable, because each photoreceptor in a single unit eye receives different input and each individual axon, among thousands others in the brain, must be sorted together with those few axons that have the same input. Key aspects of neural superposition have been described as early as 1907. Since then neuroscientists, evolutionary and developmental biologists have been fascinated by how such a complicated wiring principle could evolve, how it is genetically encoded, and how it is developmentally realized. In this review article, we will discuss current ideas about the evolutionary origin and developmental program of neural superposition. Our goal is to identify in what way the special case of neural superposition can help us answer more general questions about the evolution and development of genetically “hard-wired” synaptic connectivity in the brain.
Collapse
Affiliation(s)
- Egemen Agi
- Green Center for Systems Biology, University of Texas Southwestern Medical Center , Dallas, TX , USA
| | | | | | | | | | | |
Collapse
|
50
|
Schwabe T, Borycz JA, Meinertzhagen IA, Clandinin TR. Differential adhesion determines the organization of synaptic fascicles in the Drosophila visual system. Curr Biol 2014; 24:1304-1313. [PMID: 24881879 PMCID: PMC4500537 DOI: 10.1016/j.cub.2014.04.047] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2013] [Revised: 03/20/2014] [Accepted: 04/24/2014] [Indexed: 01/20/2023]
Abstract
BACKGROUND Neuronal circuits in worms, flies, and mammals are organized so as to minimize wiring length for a functional number of synaptic connections, a phenomenon called wiring optimization. However, the molecular mechanisms that establish optimal wiring during development are unknown. We addressed this question by studying the role of N-cadherin in the development of optimally wired neurite fascicles in the peripheral visual system of Drosophila. RESULTS Photoreceptor axons surround the dendrites of their postsynaptic targets, called lamina cells, within a concentric fascicle called a cartridge. N-cadherin is expressed at higher levels in lamina cells than in photoreceptors, and all genetic manipulations that invert these relative differences displace lamina cells to the periphery and relocate photoreceptor axon terminals into the center. CONCLUSIONS Differential expression of a single cadherin is both necessary and sufficient to determine cartridge structure because it positions the most-adhesive elements that make the most synapses at the core and the less-adhesive elements that make fewer synapses at the periphery. These results suggest a general model by which differential adhesion can be utilized to determine the relative positions of axons and dendrites to establish optimal wiring.
Collapse
Affiliation(s)
- Tina Schwabe
- Department of Neurobiology, Stanford University, Stanford, CA 94305, USA
| | - Jolanta A Borycz
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Ian A Meinertzhagen
- Department of Psychology and Neuroscience, Life Sciences Centre, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Thomas R Clandinin
- Department of Neurobiology, Stanford University, Stanford, CA 94305, USA.
| |
Collapse
|