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Aiken J, Holzbaur ELF. Spastin locally amplifies microtubule dynamics to pattern the axon for presynaptic cargo delivery. Curr Biol 2024; 34:1687-1704.e8. [PMID: 38554708 PMCID: PMC11042977 DOI: 10.1016/j.cub.2024.03.010] [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: 07/31/2023] [Revised: 01/10/2024] [Accepted: 03/08/2024] [Indexed: 04/02/2024]
Abstract
Neurons rely on the long-range trafficking of synaptic components to form and maintain the complex neural networks that encode the human experience. With a single neuron capable of forming thousands of distinct en passant synapses along its axon, spatially precise delivery of the necessary synaptic components is paramount. How these synapses are patterned, as well as how the efficient delivery of synaptic components is regulated, remains largely unknown. Here, we reveal a novel role for the microtubule (MT)-severing enzyme spastin in locally enhancing MT polymerization to influence presynaptic cargo pausing and retention along the axon. In human neurons derived from induced pluripotent stem cells (iPSCs), we identify sites stably enriched for presynaptic components along the axon prior to the robust assembly of mature presynapses apposed by postsynaptic contacts. These sites are capable of cycling synaptic vesicles, are enriched with spastin, and are hotspots for new MT growth and synaptic vesicle precursor (SVP) pausing/retention. The disruption of neuronal spastin level or activity, by CRISPRi-mediated depletion, transient overexpression, or pharmacologic inhibition of enzymatic activity, interrupts the localized enrichment of dynamic MT plus ends and diminishes SVP accumulation. Using an innovative human heterologous synapse model, where microfluidically isolated human axons recognize and form presynaptic connections with neuroligin-expressing non-neuronal cells, we reveal that neurons deficient for spastin do not achieve the same level of presynaptic component accumulation as control neurons. We propose a model where spastin acts locally as an amplifier of MT polymerization to pattern specific regions of the axon for synaptogenesis and guide synaptic cargo delivery.
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Affiliation(s)
- Jayne Aiken
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Erika L F Holzbaur
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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2
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Frankel EB, Tiroumalechetty A, Henry PS, Su Z, Wu Y, Kurshan PT. Protein-lipid interactions drive presynaptic assembly upstream of cell adhesion molecules. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.17.567618. [PMID: 38014115 PMCID: PMC10680821 DOI: 10.1101/2023.11.17.567618] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2023]
Abstract
Textbook models of synaptogenesis position cell adhesion molecules such as neurexin as initiators of synapse assembly. Here we discover a mechanism for presynaptic assembly that occurs prior to neurexin recruitment, while supporting a role for neurexin in synapse maintenance. We find that the cytosolic active zone scaffold SYD-1 interacts with membrane phospholipids to promote active zone protein clustering at the plasma membrane, and subsequently recruits neurexin to stabilize those clusters. Employing molecular dynamics simulations to model intrinsic interactions between SYD-1 and lipid bilayers followed by in vivo tests of these predictions, we find that PIP2-interacting residues in SYD-1's C2 and PDZ domains are redundantly necessary for proper active zone assembly. Finally, we propose that the uncharacterized yet evolutionarily conserved short γ isoform of neurexin represents a minimal neurexin sequence that can stabilize previously assembled presynaptic clusters, potentially a core function of this critical protein.
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Affiliation(s)
- Elisa B Frankel
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | | | - Parise S Henry
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Zhaoqian Su
- Data Science Institute, Vanderbilt University, 1001 19th Ave S, Nashville, TN, 37212
| | - Yinghao Wu
- Department of Systems and Computational Biology, Albert Einstein College of Medicine, Bronx, NY 10461
| | - Peri T Kurshan
- Department of Neuroscience, Albert Einstein College of Medicine, Bronx, NY 10461
- Lead Contact
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3
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Aiken J, Holzbaur ELF. Spastin locally amplifies microtubule dynamics to pattern the axon for presynaptic cargo delivery. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.08.08.552320. [PMID: 37609249 PMCID: PMC10441300 DOI: 10.1101/2023.08.08.552320] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Neurons rely on long-range trafficking of synaptic components to form and maintain the complex neural networks that encode the human experience. With a single neuron capable of forming thousands of distinct en passant synapses along its axon, spatially precise delivery of the necessary synaptic components is paramount. How these synapses are patterned, and how efficient delivery of synaptic components is regulated, remains largely unknown. Here, we reveal a novel role for the microtubule severing enzyme spastin in locally enhancing microtubule polymerization to influence presynaptic cargo pausing and retention along the axon. In human neurons derived from induced pluripotent stem cells (iPSCs), we identify sites stably enriched for presynaptic components, termed 'protosynapses', which are distributed along the axon prior to the robust assembly of mature presynapses apposed by postsynaptic contacts. These sites are capable of cycling synaptic vesicles, are enriched with spastin, and are hotspots for new microtubule growth and synaptic vesicle precursor (SVP) pausing/retention. Disruption of neuronal spastin, either by CRISPRi-mediated depletion or transient overexpression, interrupts the localized enrichment of dynamic microtubule plus ends and diminishes SVP accumulation. Using an innovative human heterologous synapse model, where microfluidically isolated human axons recognize and form presynaptic connections with neuroligin-expressing non-neuronal cells, we reveal that neurons deficient for spastin do not achieve the same level of presynaptic component accumulation as control neurons. We propose a model where spastin acts locally as an amplifier of microtubule polymerization to pattern specific regions of the axon for synaptogenesis and guide synaptic cargo delivery.
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Affiliation(s)
- Jayne Aiken
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
| | - Erika L F Holzbaur
- Department of Physiology, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA
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4
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Falkovich R, Danielson EW, Perez de Arce K, Wamhoff EC, Strother J, Lapteva AP, Sheng M, Cottrell JR, Bathe M. A synaptic molecular dependency network in knockdown of autism- and schizophrenia-associated genes revealed by multiplexed imaging. Cell Rep 2023; 42:112430. [PMID: 37099425 DOI: 10.1016/j.celrep.2023.112430] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/24/2022] [Revised: 01/29/2023] [Accepted: 04/08/2023] [Indexed: 04/27/2023] Open
Abstract
The complex functions of neuronal synapses depend on their tightly interconnected protein network, and their dysregulation is implicated in the pathogenesis of autism spectrum disorders and schizophrenia. However, it remains unclear how synaptic molecular networks are altered biochemically in these disorders. Here, we apply multiplexed imaging to probe the effects of RNAi knockdown of 16 autism- and schizophrenia-associated genes on the simultaneous joint distribution of 10 synaptic proteins, observing several protein composition phenotypes associated with these risk genes. We apply Bayesian network analysis to infer hierarchical dependencies among eight excitatory synaptic proteins, yielding predictive relationships that can only be accessed with single-synapse, multiprotein measurements performed simultaneously in situ. Finally, we find that central features of the network are affected similarly across several distinct gene knockdowns. These results offer insight into the convergent molecular etiology of these widespread disorders and provide a general framework to probe subcellular molecular networks.
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Affiliation(s)
- Reuven Falkovich
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Eric W Danielson
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Karen Perez de Arce
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Eike-C Wamhoff
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Juliana Strother
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Anna P Lapteva
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Morgan Sheng
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA; Picower Institute for Learning and Memory, Massachusetts Institute of Technology, Cambridge, MA, USA
| | - Jeffrey R Cottrell
- Stanley Center for Psychiatric Research, Broad Institute of MIT and Harvard, Cambridge, MA, USA
| | - Mark Bathe
- Department of Biological Engineering, Massachusetts Institute of Technology, Cambridge, MA, USA; Broad Institute of MIT and Harvard, Cambridge, MA, USA; Harvard Medical School Initiative for RNA Medicine, Harvard University, Cambridge, MA, USA.
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5
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Junion G, Jagla K. Diversification of muscle types in Drosophila embryos. Exp Cell Res 2022; 410:112950. [PMID: 34838813 DOI: 10.1016/j.yexcr.2021.112950] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 11/22/2021] [Accepted: 11/24/2021] [Indexed: 12/31/2022]
Abstract
Drosophila embryonic somatic muscles represent a simple and tractable model system to study the gene regulatory networks that control diversification of cell types. Somatic myogenesis in Drosophila is initiated by intrinsic action of the mesodermal master gene twist, which activates a cascade of transcriptional outputs including myogenic differentiation factor Mef2, which triggers all aspects of the myogenic differentiation program. In parallel, the expression of a combinatorial code of identity transcription factors (iTFs) defines discrete particular features of each muscle fiber, such as number of fusion events, and specific attachment to tendon cells or innervation, thus ensuring diversification of muscle types. Here, we take the example of a subset of lateral transverse (LT) muscles and discuss how the iTF code and downstream effector genes progressively define individual LT properties such as fusion program, attachment and innervation. We discuss new challenges in the field including the contribution of posttranscriptional and epitranscriptomic regulation of gene expression in the diversification of cell types.
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Affiliation(s)
- Guillaume Junion
- Genetics Reproduction and Development Institute (iGReD), CNRS UMR6293, INSERM U1103, University of Clermont Auvergne, Clermont-Ferrand, France
| | - Krzysztof Jagla
- Genetics Reproduction and Development Institute (iGReD), CNRS UMR6293, INSERM U1103, University of Clermont Auvergne, Clermont-Ferrand, France.
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6
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Jeong S. Molecular Mechanisms Underlying Motor Axon Guidance in Drosophila. Mol Cells 2021; 44:549-556. [PMID: 34385406 PMCID: PMC8424136 DOI: 10.14348/molcells.2021.0129] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2021] [Revised: 06/29/2021] [Accepted: 07/02/2021] [Indexed: 11/30/2022] Open
Abstract
Decoding the molecular mechanisms underlying axon guidance is key to precise understanding of how complex neural circuits form during neural development. Although substantial progress has been made over the last three decades in identifying numerous axon guidance molecules and their functional roles, little is known about how these guidance molecules collaborate to steer growth cones to their correct targets. Recent studies in Drosophila point to the importance of the combinatorial action of guidance molecules, and further show that selective fasciculation and defasciculation at specific choice points serve as a fundamental strategy for motor axon guidance. Here, I discuss how attractive and repulsive guidance cues cooperate to ensure the recognition of specific choice points that are inextricably linked to selective fasciculation and defasciculation, and correct pathfinding decision-making.
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Affiliation(s)
- Sangyun Jeong
- Division of Life Sciences (Molecular Biology Major), Department of Bioactive Material Sciences, and Research Center of Bioactive Materials, Jeonbuk National University, Jeonju 54896, Korea
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7
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Bjorke B, Weller KG, Jones LE, Robinson GE, Vesser M, Chen L, Gage PJ, Gould TW, Mastick GS. Oculomotor nerve guidance and terminal branching requires interactions with differentiating extraocular muscles. Dev Biol 2021; 476:272-281. [PMID: 33905720 PMCID: PMC8284410 DOI: 10.1016/j.ydbio.2021.04.006] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2019] [Revised: 04/20/2021] [Accepted: 04/20/2021] [Indexed: 11/25/2022]
Abstract
Muscle function is dependent on innervation by the correct motor nerves. Motor nerves are composed of motor axons which extend through peripheral tissues as a compact bundle, then diverge to create terminal nerve branches to specific muscle targets. As motor nerves approach their targets, they undergo a transition where the fasciculated nerve halts further growth then after a pause, the nerve later initiates branching to muscles. This transition point is potentially an intermediate target or guidepost to present specific cellular and molecular signals for navigation. Here we describe the navigation of the oculomotor nerve and its association with developing muscles in mouse embryos. We found that the oculomotor nerve initially grew to the eye three days prior to the appearance of any extraocular muscles. The oculomotor axons spread to form a plexus within a mass of cells, which included precursors of extraocular muscles and other orbital tissues and expressed the transcription factor Pitx2. The nerve growth paused in the plexus for more than two days, persisting during primary extraocular myogenesis, with a subsequent phase in which the nerve branched out to specific muscles. To test the functional significance of the nerve contact with Pitx2+ cells in the plexus, we used two strategies to genetically ablate Pitx2+ cells or muscle precursors early in nerve development. The first strategy used Myf5-Cre-mediated expression of diphtheria toxin A to ablate muscle precursors, leading to loss of extraocular muscles. The oculomotor axons navigated to the eye to form the main nerve, but subsequently largely failed to initiate terminal branches. The second strategy studied Pitx2 homozygous mutants, which have early apoptosis of Pitx2-expressing precursor cells, including precursors for extraocular muscles and other orbital tissues. Oculomotor nerve fibers also grew to the eye, but failed to stop to form the plexus, instead grew long ectopic projections. These results show that neither Pitx2 function nor Myf5-expressing cells are required for oculomotor nerve navigation to the eye. However, Pitx2 function is required for oculomotor axons to pause growth in the plexus, while Myf5-expressing cells are required for terminal branch initiation.
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Affiliation(s)
- Brielle Bjorke
- Department of Biology, University of Nevada, Reno, NV, 89557, USA
| | | | - Lauren E Jones
- Department of Biology, University of Nevada, Reno, NV, 89557, USA
| | - G Eric Robinson
- Department of Biology, University of Nevada, Reno, NV, 89557, USA
| | - Michelle Vesser
- Department of Biology, University of Nevada, Reno, NV, 89557, USA
| | - Lisheng Chen
- Department of Ophthalmology & Visual Science, University of Michigan Medical School, Ann Arbor, MI, 48105, USA
| | - Philip J Gage
- Department of Ophthalmology & Visual Science, University of Michigan Medical School, Ann Arbor, MI, 48105, USA
| | - Thomas W Gould
- Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, United States
| | - Grant S Mastick
- Department of Biology, University of Nevada, Reno, NV, 89557, USA.
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8
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Structural and Functional Synaptic Plasticity Induced by Convergent Synapse Loss in the Drosophila Neuromuscular Circuit. J Neurosci 2021; 41:1401-1417. [PMID: 33402422 DOI: 10.1523/jneurosci.1492-20.2020] [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] [Received: 06/11/2020] [Revised: 11/28/2020] [Accepted: 12/17/2020] [Indexed: 12/22/2022] Open
Abstract
Throughout the nervous system, the convergence of two or more presynaptic inputs on a target cell is commonly observed. The question we ask here is to what extent converging inputs influence each other's structural and functional synaptic plasticity. In complex circuits, isolating individual inputs is difficult because postsynaptic cells can receive thousands of inputs. An ideal model to address this question is the Drosophila larval neuromuscular junction (NMJ) where each postsynaptic muscle cell receives inputs from two glutamatergic types of motor neurons (MNs), known as 1b and 1s MNs. Notably, each muscle is unique and receives input from a different combination of 1b and 1s MNs; we surveyed multiple muscles for this reason. Here, we identified a cell-specific promoter that allows ablation of 1s MNs postinnervation and measured structural and functional responses of convergent 1b NMJs using microscopy and electrophysiology. For all muscles examined in both sexes, ablation of 1s MNs resulted in NMJ expansion and increased spontaneous neurotransmitter release at corresponding 1b NMJs. This demonstrates that 1b NMJs can compensate for the loss of convergent 1s MNs. However, only a subset of 1b NMJs showed compensatory evoked neurotransmission, suggesting target-specific plasticity. Silencing 1s MNs led to similar plasticity at 1b NMJs, suggesting that evoked neurotransmission from 1s MNs contributes to 1b synaptic plasticity. Finally, we genetically blocked 1s innervation in male larvae and robust 1b synaptic plasticity was eliminated, raising the possibility that 1s NMJ formation is required to set up a reference for subsequent synaptic perturbations.SIGNIFICANCE STATEMENT In complex neural circuits, multiple convergent inputs contribute to the activity of the target cell, but whether synaptic plasticity exists among these inputs has not been thoroughly explored. In this study, we examined synaptic plasticity in the structurally and functionally tractable Drosophila larval neuromuscular system. In this convergent circuit, each muscle is innervated by a unique pair of motor neurons. Removal of one neuron after innervation causes the adjacent neuron to increase neuromuscular junction outgrowth and functional output. However, this is not a general feature as each motor neuron differentially compensates. Further, robust compensation requires initial coinnervation by both neurons. Understanding how neurons respond to perturbations in adjacent neurons will provide insight into nervous system plasticity in both healthy and disease states.
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9
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Rizalar FS, Roosen DA, Haucke V. A Presynaptic Perspective on Transport and Assembly Mechanisms for Synapse Formation. Neuron 2020; 109:27-41. [PMID: 33098763 DOI: 10.1016/j.neuron.2020.09.038] [Citation(s) in RCA: 36] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2020] [Revised: 08/26/2020] [Accepted: 09/25/2020] [Indexed: 01/01/2023]
Abstract
Neurons are highly polarized cells with a single axon and multiple dendrites derived from the cell body to form tightly associated pre- and postsynaptic compartments. As the biosynthetic machinery is largely restricted to the somatodendritic domain, the vast majority of presynaptic components are synthesized in the neuronal soma, packaged into synaptic precursor vesicles, and actively transported along the axon to sites of presynaptic biogenesis. In contrast with the significant progress that has been made in understanding synaptic transmission and processing of information at the post-synapse, comparably little is known about the formation and dynamic remodeling of the presynaptic compartment. We review here our current understanding of the mechanisms that govern the biogenesis, transport, and assembly of the key components for presynaptic neurotransmission, discuss how alterations in presynaptic assembly may impact nervous system function or lead to disease, and outline key open questions for future research.
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Affiliation(s)
- Filiz Sila Rizalar
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Dorien A Roosen
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany
| | - Volker Haucke
- Leibniz-Forschungsinstitut für Molekulare Pharmakologie (FMP), Berlin, Germany; Faculty of Biology, Chemistry, Pharmacy, Freie Universität Berlin, 14195 Berlin, Germany.
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10
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Poovathumkadavil P, Jagla K. Genetic Control of Muscle Diversification and Homeostasis: Insights from Drosophila. Cells 2020; 9:cells9061543. [PMID: 32630420 PMCID: PMC7349286 DOI: 10.3390/cells9061543] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 06/19/2020] [Accepted: 06/23/2020] [Indexed: 12/13/2022] Open
Abstract
In the fruit fly, Drosophila melanogaster, the larval somatic muscles or the adult thoracic flight and leg muscles are the major voluntary locomotory organs. They share several developmental and structural similarities with vertebrate skeletal muscles. To ensure appropriate activity levels for their functions such as hatching in the embryo, crawling in the larva, and jumping and flying in adult flies all muscle components need to be maintained in a functionally stable or homeostatic state despite constant strain. This requires that the muscles develop in a coordinated manner with appropriate connections to other cell types they communicate with. Various signaling pathways as well as extrinsic and intrinsic factors are known to play a role during Drosophila muscle development, diversification, and homeostasis. In this review, we discuss genetic control mechanisms of muscle contraction, development, and homeostasis with particular emphasis on the contractile unit of the muscle, the sarcomere.
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11
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Guangming G, Junhua G, Chenchen Z, Yang M, Wei X. Neurexin and Neuroligins Maintain the Balance of Ghost and Satellite Boutons at the Drosophila Neuromuscular Junction. Front Neuroanat 2020; 14:19. [PMID: 32581727 PMCID: PMC7296126 DOI: 10.3389/fnana.2020.00019] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Accepted: 03/26/2020] [Indexed: 11/22/2022] Open
Abstract
Neurexins and neuroligins are common synaptic adhesion molecules that are associated with autism and interact with each other in the synaptic cleft. The Drosophila neuromuscular junction (NMJ) bouton is a well-known model system in neuroscience, and ghost and satellite boutons, respectively, indicate the poor development and overgrowth of the NMJ boutons. However, the Drosophila neurexin (DNrx) and Drosophila neuroligins (DNlgs) are mainly observed in type Ib boutons, indicating the ultrastructural and developmental phenotypes of the Drosophila NMJ. Here, we identified the ultrastructural and developmental features of ghost and satellite boutons by utilizing dneurexin (dnrx) and dneuroligins (dnlgs) fly mutants and other associated fly strains. Ghost boutons contain synaptic vesicles with multiple diameters but very rarely contain T-bar structures and swollen or thin subsynaptic reticulum (SSR) membranes. The muscle cell membrane is invaginated at different sites, stretches to the ghost bouton from different directions, forms several layers that enwrap the ghost bouton, and then branches into the complex SSR. Satellite boutons share a common SSR membrane and present either a typical profile in which a main bouton is encircled by small boutons or two atypical profiles in which the small boutons are grouped together or distributed in beads without a main bouton. Electron and confocal microscopy data showed that dnrx, dnlg1, dnlg2, dnlg3, and dnlg4 mutations led to ghost boutons; the overexpression of dnrx, dnlg1, dnlg2, dnlg3, and dnlg4 led to satellite boutons; and the dnlg2;dnlg3 double mutation also led to satellite boutons. These results suggested that DNrx and DNlgs jointly maintain the development and function of NMJ boutons by regulating the balance of ghost and satellite boutons in Drosophila.
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Affiliation(s)
- Gan Guangming
- School of Medicine, Southeast University, Nanjing, China.,The Key Laboratory of Developmental Genes and Human Disease, Institute of Life Sciences, Southeast University, Nanjing, China
| | - Geng Junhua
- The Key Laboratory of Developmental Genes and Human Disease, Institute of Life Sciences, Southeast University, Nanjing, China
| | - Zhang Chenchen
- School of Medicine, Southeast University, Nanjing, China.,The Key Laboratory of Developmental Genes and Human Disease, Institute of Life Sciences, Southeast University, Nanjing, China
| | - Mou Yang
- School of Medicine, Southeast University, Nanjing, China
| | - Xie Wei
- The Key Laboratory of Developmental Genes and Human Disease, Institute of Life Sciences, Southeast University, Nanjing, China.,Institute of Life Sciences, The Collaborative Innovation Center for Brain Science, Southeast University, Nanjing, China
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12
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Brown JR, Phongthachit C, Sulkowski MJ. Immunofluorescence and image analysis pipeline for Drosophila motor neurons. Biol Methods Protoc 2019; 4:bpz010. [PMID: 31403085 PMCID: PMC6676502 DOI: 10.1093/biomethods/bpz010] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 07/03/2019] [Accepted: 07/09/2019] [Indexed: 11/23/2022] Open
Abstract
The neuromuscular junction (NMJ) of larval Drosophila is widely used as a genetic model for basic neuroscience research. The presynaptic side of the NMJ is formed by axon terminals of motor neurons, the soma of which reside in the ventral ganglion of the central nervous system (CNS). Here we describe a streamlined protocol for dissection and immunostaining of the Drosophila CNS and NMJ that allows processing of multiple genotypes within a single staining tube. We also present a computer script called Automated Image Analysis with Background Subtraction which facilitates identification of motor nuclei, quantification of pixel intensity, and background subtraction. Together, these techniques provide a pipeline for neuroscientists to compare levels of different biomolecules in motor nuclei. We conclude that these methods should be adaptable to a variety of different cell and tissue types for the improvement of efficiency, reproducibility, and throughput during data quantification.
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Affiliation(s)
- Jeremy R Brown
- Biology Department, Southern Arkansas University, Magnolia, AR, USA
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, CO, USA
| | | | - Mikolaj J Sulkowski
- Biology Department, Southern Connecticut State University, New Haven, CT, USA
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13
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Kurshan PT, Shen K. Synaptogenic pathways. Curr Opin Neurobiol 2019; 57:156-162. [PMID: 30986749 DOI: 10.1016/j.conb.2019.03.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2019] [Revised: 03/11/2019] [Accepted: 03/13/2019] [Indexed: 11/30/2022]
Abstract
During synaptogenesis, presynaptic and postsynaptic assembly are driven by diverse molecular mechanisms, mediated by intrinsic as well as extrinsic factors. How these processes are initiated and coordinated are open questions. Synapse specificity, or synaptic partner selection, is widely understood to be determined by the trans-synaptic binding of cell adhesion molecules. However, in vivo evidence that cell adhesion molecules subsequently function to initiate synapse assembly, as initially proposed, is lacking. Here, we present a summary of our current understanding of synaptogenic pathways that mediate presynaptic and postsynaptic assembly and the coordination of these processes.
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Affiliation(s)
| | - Kang Shen
- Stanford University, Department of Biology, United States; Howard Hughes Medical Institute, United States
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14
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Stocker B, Bochow C, Damrau C, Mathejczyk T, Wolfenberg H, Colomb J, Weber C, Ramesh N, Duch C, Biserova NM, Sigrist S, Pflüger HJ. Structural and Molecular Properties of Insect Type II Motor Axon Terminals. Front Syst Neurosci 2018; 12:5. [PMID: 29615874 PMCID: PMC5867341 DOI: 10.3389/fnsys.2018.00005] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 02/26/2018] [Indexed: 11/25/2022] Open
Abstract
A comparison between the axon terminals of octopaminergic efferent dorsal or ventral unpaired median neurons in either desert locusts (Schistocerca gregaria) or fruit flies (Drosophila melanogaster) across skeletal muscles reveals many similarities. In both species the octopaminergic axon forms beaded fibers where the boutons or varicosities form type II terminals in contrast to the neuromuscular junction (NMJ) or type I terminals. These type II terminals are immunopositive for both tyramine and octopamine and, in contrast to the type I terminals, which possess clear synaptic vesicles, only contain dense core vesicles. These dense core vesicles contain octopamine as shown by immunogold methods. With respect to the cytomatrix and active zone peptides the type II terminals exhibit active zone-like accumulations of the scaffold protein Bruchpilot (BRP) only sparsely in contrast to the many accumulations of BRP identifying active zones of NMJ type I terminals. In the fruit fly larva marked dynamic changes of octopaminergic fibers have been reported after short starvation which not only affects the formation of new branches (“synaptopods”) but also affects the type I terminals or NMJs via octopamine-signaling (Koon et al., 2011). Our starvation experiments of Drosophila-larvae revealed a time-dependency of the formation of additional branches. Whereas after 2 h of starvation we find a decrease in “synaptopods”, the increase is significant after 6 h of starvation. In addition, we provide evidence that the release of octopamine from dendritic and/or axonal type II terminals uses a similar synaptic machinery to glutamate release from type I terminals of excitatory motor neurons. Indeed, blocking this canonical synaptic release machinery via RNAi induced downregulation of BRP in neurons with type II terminals leads to flight performance deficits similar to those observed for octopamine mutants or flies lacking this class of neurons (Brembs et al., 2007).
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Affiliation(s)
- Bettina Stocker
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Christina Bochow
- Institute of Biology, Genetics, Freie Universität Berlin, Berlin, Germany
| | - Christine Damrau
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Thomas Mathejczyk
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Heike Wolfenberg
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Julien Colomb
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Claudia Weber
- Institute of Biology, Genetics, Freie Universität Berlin, Berlin, Germany
| | - Niraja Ramesh
- Institute of Biology, Genetics, Freie Universität Berlin, Berlin, Germany
| | - Carsten Duch
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Natalia M Biserova
- Institute of Biology, Neurobiology, Freie Universität Berlin, Berlin, Germany
| | - Stephan Sigrist
- Institute of Biology, Genetics, Freie Universität Berlin, Berlin, Germany
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15
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Yadav R, Nisha, Sarkar S. Drosophila globin1 is required for maintenance of the integrity of F-actin based cytoskeleton during development. Exp Cell Res 2018. [PMID: 29524391 DOI: 10.1016/j.yexcr.2018.03.005] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Hemoglobins (Hbs) are evolutionarily conserved small globular proteins with characteristic 3-over-3 α-helical sandwich structure that is typically known as "globin fold". Hbs have been found to be involved in diverse biological functions and the characteristic property of oxygen transportation is relatively a recent adaptation. Drosophila genome possesses three globin genes (glob1, glob2, and glob3) and it was previously reported that adequate expression of glob1 is required for various aspects of development, and also to regulate the cellular level of reactive oxygen species (ROS). The present study illustrates the explicit role of glob1 gene in Drosophila development. We demonstrate a dynamic expression pattern of glob1 in larval tissues which largely concentrate around F-actin rich structures and also co-precipitate. Reduced expression of glob1 leads to developmental abnormalities which appeared to be largely mediated by inappropriately formed F-actin based cytoskeletal structures. Our subsequent analysis in FLP/FRT mediated somatic clones establishes specific role of Drosophila glob1 in maintenance of the integrity of F-actin based cytoskeleton during development. For the first time, we report interaction between Glob1 and actin, and propose a novel role of glob1 in maintenance of F-actin based cytoskeleton in Drosophila.
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Affiliation(s)
- Renu Yadav
- Department of Genetics, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi 110021, India
| | - Nisha
- Department of Genetics, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi 110021, India
| | - Surajit Sarkar
- Department of Genetics, University of Delhi South Campus, Benito Juarez Road, Dhaula Kuan, New Delhi 110021, India.
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16
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mRNA expression characteristics are different in irreversibly atrophic intrinsic muscles of the forepaw compared with reversibly atrophic biceps in a rat model of obstetric brachial plexus palsy (OBPP). J Muscle Res Cell Motil 2016; 37:17-25. [PMID: 26902607 DOI: 10.1007/s10974-016-9442-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 02/16/2016] [Indexed: 10/22/2022]
Abstract
In obstetric brachial plexus palsy (OBPP), irreversible muscle atrophy occurs much faster in intrinsic muscles of the hand than in the biceps. To elucidate the mechanisms involved, mRNA expression profiles of denervated intrinsic muscles of the forepaw (IMF) and denervated biceps were determined by microarray using the rat model of OBPP where atrophy of IMF is irreversible while atrophy of biceps is reversible. Relative to contralateral control, 446 dysregulated mRNAs were detected in denervated IMF and mapped to 51 KEGG pathways, and 830 dysregulated mRNAs were detected in denervated biceps and mapped to 52 KEGG pathways. In denervated IMF, 10 of the pathways were related to muscle regulation; six with down-regulated and one with up-regulated mRNAs. The remaining three pathways had both up- and down-regulated mRNAs. In denervated biceps, 13 of the pathways were related to muscle regulation, six with up-regulated and seven with down-regulated mRNAs. Five of the pathways with up-regulated mRNAs were related to regrowth and differentiation of muscle cells. Among the 23 pathways with dysregulated mRNAs, 13 were involved in regulation of neuromuscular junctions. Our results demonstrated that mRNAs expression characteristics in irreversibly atrophic denervated IMF were different from those in reversibly atrophic denervated biceps; dysregulated mRNAs in IMF were associated with inactive pathways of muscle regulation, and in biceps they were associated with active pathways of regrowth and differentiation. Lack of self-repair potential in IMF may be a major reason why atrophy of IMF becomes irreversible much faster than atrophy of biceps after denervation.
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17
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Hara Y, Yuk F, Puri R, Janssen WGM, Rapp PR, Morrison JH. Estrogen Restores Multisynaptic Boutons in the Dorsolateral Prefrontal Cortex while Promoting Working Memory in Aged Rhesus Monkeys. J Neurosci 2016; 36:901-10. [PMID: 26791219 PMCID: PMC4719022 DOI: 10.1523/jneurosci.3480-13.2016] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2013] [Revised: 12/02/2015] [Accepted: 12/08/2015] [Indexed: 02/07/2023] Open
Abstract
Humans and nonhuman primates are vulnerable to age- and menopause- related decline in working memory, a cognitive function reliant on area 46 of the dorsolateral prefrontal cortex (dlPFC). We showed previously that presynaptic mitochondrial number and morphology in monkey dlPFC neurons correlate with working memory performance. The current study tested the hypothesis that the types of synaptic connections these boutons form are altered with aging and menopause in rhesus monkeys and that these metrics may be coupled with mitochondrial measures and working memory. Using serial section electron microscopy, we examined the frequencies and characteristics of nonsynaptic, single-synaptic, and multisynaptic boutons (MSBs) in the dlPFC. In contrast to our previous observations in the monkey hippocampal dentate gyrus, where MSBs comprised ∼40% of boutons, the vast majority of dlPFC boutons were single-synaptic, whereas MSBs constituted a mere 10%. The frequency of MSBs was not altered by normal aging, but decreased by over 50% with surgical menopause induced by ovariectomy in aged monkeys. Cyclic estradiol treatment in aged ovariectomized animals restored MSB frequencies to levels comparable to young and aged premenopausal monkeys. Notably, the frequency of MSBs positively correlated with working memory scores, as measured by the average accuracy on the delayed response (DR) test. Furthermore, MSB incidence positively correlated with the number of healthy straight mitochondria in dlPFC boutons and inversely correlated with the number of pathological donut-shaped mitochondria. Together, our data suggest that MSBs are coupled to cognitive function and mitochondrial health and are sensitive to estrogen. Significance statement: Many aged menopausal individuals experience deficits in working memory, an executive function reliant on recurrent firing of prefrontal cortex (PFC) neurons. However, little is known about the organization of presynaptic inputs to these neurons and how they may be altered with aging and menopause. Multisynaptic boutons (MSBs) were of particular interest, because they form multiple synapses and can enhance coupling between presynaptic and postsynaptic neurons. We found that higher MSB frequency correlated with better working memory performance in rhesus monkeys. Additionally, aged surgically menopausal monkeys experienced a 50% loss of MSBs that was restored with cyclic estradiol treatment. Together, our findings suggest that hormone replacement therapy benefits cognitive aging, in part by retaining complex synaptic organizations in the PFC.
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Affiliation(s)
- Yuko Hara
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories, Friedman Brain Institute
| | - Frank Yuk
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories, Friedman Brain Institute
| | - Rishi Puri
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories, Friedman Brain Institute
| | - William G M Janssen
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories, Friedman Brain Institute
| | - Peter R Rapp
- National Institute on Aging, Laboratory of Behavioral Neuroscience, Baltimore, Maryland 21224
| | - John H Morrison
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories, Friedman Brain Institute, Department of Geriatrics and Palliative Medicine, and Graduate School of Biomedical Sciences, Icahn School of Medicine at Mount Sinai, New York, New York 10029, California National Primate Research Center, Davis, California 95616, and Department of Neurology, School of Medicine, University of California, Davis, California 95616
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18
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Slater CR. The functional organization of motor nerve terminals. Prog Neurobiol 2015; 134:55-103. [DOI: 10.1016/j.pneurobio.2015.09.004] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2015] [Revised: 08/28/2015] [Accepted: 09/05/2015] [Indexed: 12/19/2022]
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19
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Gan G, Lv H, Xie W. Morphological identification and development of neurite in Drosophila ventral nerve cord neuropil. PLoS One 2014; 9:e105497. [PMID: 25166897 PMCID: PMC4148333 DOI: 10.1371/journal.pone.0105497] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2013] [Accepted: 07/24/2014] [Indexed: 12/02/2022] Open
Abstract
In Drosophila, ventral nerve cord (VNC) occupies most of the larval central nervous system (CNS). However, there is little literature elaborating upon the specific types and growth of neurites as defined by their structural appearance in Drosophila larval VNC neuropil. Here we report the ultrastructural development of different types VNC neurites in ten selected time points in embryonic and larval stages utilizing transmission electron microscopy. There are four types of axonal neurites as classified by the type of vesicular content: clear vesicle (CV) neurites have clear vesicles and some T-bar structures; Dense-core vesicle (DV) neurites have dense-core vesicles and without T-bar structures; Mixed vesicle (MV) neurites have mixed vesicles and some T-bar structures; Large vesicle (LV) neurites are dominated by large, translucent spherical vesicles but rarely display T-bar structures. We found dramatic remodeling in CV neurites which can be divided into five developmental phases. The neurite is vacuolated in primary (P) phase, they have mitochondria, microtubules or big dark vesicles in the second (S) phase, and they contain immature synaptic features in the third (T) phase. The subsequent bifurcate (B) phase appears to undergo major remodeling with the appearance of the bifurcation or dendritic growth. In the final mature (M) phase, high density of commensurate synaptic vesicles are distributed around T-bar structures. There are four kinds of morphological elaboration of the CVI neurite sub-types. First, new neurite produces at the end of axon. Second, new neurite bubbles along the axon. Third, the preexisting neurite buds and develops into several neurites. The last, the bundled axons form irregularly shape neurites. Most CVI neurites in M phase have about 1.5–3 µm diameter, they could be suitable to analyze their morphology and subcellular localization of specific proteins by light microscopy, and they could serve as a potential model in CNS in vivo development.
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Affiliation(s)
- Guangming Gan
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China
- School of Medicine, Southeast University, Nanjing, China
- * E-mail:
| | - Huihui Lv
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China
| | - Wei Xie
- The Key Laboratory of Development Genes and Human Diseases, Ministry of Education, Institute of Life Sciences, Southeast University, Nanjing, China
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20
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Transcriptional networks regulating the costamere, sarcomere, and other cytoskeletal structures in striated muscle. Cell Mol Life Sci 2013; 71:1641-56. [PMID: 24218011 DOI: 10.1007/s00018-013-1512-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2013] [Revised: 10/27/2013] [Accepted: 10/30/2013] [Indexed: 10/26/2022]
Abstract
Structural abnormalities in striated muscle have been observed in numerous transcription factor gain- and loss-of-function phenotypes in animal and cell culture model systems, indicating that transcription is important in regulating the cytoarchitecture. While most characterized cytoarchitectural defects are largely indistinguishable by histological and ultrastructural criteria, analysis of dysregulated gene expression in each mutant phenotype has yielded valuable information regarding specific structural gene programs that may be uniquely controlled by each of these transcription factors. Linking the formation and maintenance of each subcellular structure or subset of proteins within a cytoskeletal compartment to an overlapping but distinct transcription factor cohort may enable striated muscle to control cytoarchitectural function in an efficient and specific manner. Here we summarize the available evidence that connects transcription factors, those with established roles in striated muscle such as MEF2 and SRF, as well as other non-muscle transcription factors, to the regulation of a defined cytoskeletal structure. The notion that genes encoding proteins localized to the same subcellular compartment are coordinately transcriptionally regulated may prompt rationally designed approaches that target specific transcription factor pathways to correct structural defects in muscle disease.
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21
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Randlett O, MacDonald RB, Yoshimatsu T, Almeida AD, Suzuki SC, Wong RO, Harris WA. Cellular requirements for building a retinal neuropil. Cell Rep 2013; 3:282-90. [PMID: 23416047 PMCID: PMC3607253 DOI: 10.1016/j.celrep.2013.01.020] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2012] [Revised: 11/21/2012] [Accepted: 01/16/2013] [Indexed: 01/14/2023] Open
Abstract
How synaptic neuropil is formed within the CNS is poorly understood. The retinal inner plexiform layer (IPL) is positioned between the cell bodies of amacrine cells (ACs) and retinal ganglion cells (RGCs). It consists of bipolar cell (BC) axon terminals that synapse on the dendrites of ACs and RGCs intermingled with projections from Müller glia (MG). We examined whether any of these cellular processes are specifically required for the formation of the IPL. Using genetic and pharmacological strategies, we eliminated RGCs, ACs, and MG individually or in combination. Even in the absence of all of these partner cells, an IPL-like neuropil consisting of only BC axon terminals still forms, complete with presynaptic specializations and sublaminar organization. Previous studies have shown that an IPL can form in the complete absence of BCs; therefore, we conclude that neither presynaptic nor postsynaptic processes are individually essential for the formation of this synaptic neuropil.
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Affiliation(s)
- Owen Randlett
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3DY, UK
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22
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Synaptic functions of invertebrate varicosities: what molecular mechanisms lie beneath. Neural Plast 2012; 2012:670821. [PMID: 22655209 PMCID: PMC3359714 DOI: 10.1155/2012/670821] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2011] [Accepted: 02/27/2012] [Indexed: 11/26/2022] Open
Abstract
In mammalian brain, the cellular and molecular events occurring in both synapse formation and plasticity are difficult to study due to the large number of factors involved in these processes and because the contribution of each component is not well defined. Invertebrates, such as Drosophila, Aplysia, Helix, Lymnaea, and Helisoma, have proven to be useful models for studying synaptic assembly and elementary forms of learning. Simple nervous system, cellular accessibility, and genetic simplicity are some examples of the invertebrate advantages that allowed to improve our knowledge about evolutionary neuronal conserved mechanisms. In this paper, we present an overview of progresses that elucidates cellular and molecular mechanisms underlying synaptogenesis and synapse plasticity in invertebrate varicosities and their validation in vertebrates. In particular, the role of invertebrate synapsin in the formation of presynaptic terminals and the cell-to-cell interactions that induce specific structural and functional changes in their respective targets will be analyzed.
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23
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Koper A, Schenck A, Prokop A. Analysis of adhesion molecules and basement membrane contributions to synaptic adhesion at the Drosophila embryonic NMJ. PLoS One 2012; 7:e36339. [PMID: 22558441 PMCID: PMC3340374 DOI: 10.1371/journal.pone.0036339] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2012] [Accepted: 03/30/2012] [Indexed: 12/12/2022] Open
Abstract
Synapse formation and maintenance crucially underlie brain function in health and disease. Both processes are believed to depend on cell adhesion molecules (CAMs). Many different classes of CAMs localise to synapses, including cadherins, protocadherins, neuroligins, neurexins, integrins, and immunoglobulin adhesion proteins, and further contributions come from the extracellular matrix and its receptors. Most of these factors have been scrutinised by loss-of-function analyses in animal models. However, which adhesion factors establish the essential physical links across synaptic clefts and allow the assembly of synaptic machineries at the contact site in vivo is still unclear. To investigate these key questions, we have used the neuromuscular junction (NMJ) of Drosophila embryos as a genetically amenable model synapse. Our ultrastructural analyses of NMJs lacking different classes of CAMs revealed that loss of all neurexins, all classical cadherins or all glutamate receptors, as well as combinations between these or with a Laminin deficiency, failed to reveal structural phenotypes. These results are compatible with a view that these CAMs might have no structural role at this model synapse. However, we consider it far more likely that they operate in a redundant or well buffered context. We propose a model based on a multi-adaptor principle to explain this phenomenon. Furthermore, we report a new CAM-independent adhesion mechanism that involves the basement membranes (BM) covering neuromuscular terminals. Thus, motorneuronal terminals show strong partial detachment of the junction when BM-to-cell surface attachment is impaired by removing Laminin A, or when BMs lose their structural integrity upon loss of type IV collagens. We conclude that BMs are essential to tie embryonic motorneuronal terminals to the muscle surface, lending CAM-independent structural support to their adhesion. Therefore, future developmental studies of these synaptic junctions in Drosophila need to consider the important contribution made by BM-dependent mechanisms, in addition to CAM-dependent adhesion.
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Affiliation(s)
- Andre Koper
- Faculty of Life Sciences, Wellcome Trust Centre for Cell-Matrix Research, Manchester, United Kingdom
| | - Annette Schenck
- Department of Human Genetics, Nijmegen Centre for Molecular Life Sciences, Donders Institute for Brain, Cognition and Behaviour, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands
| | - Andreas Prokop
- Faculty of Life Sciences, Wellcome Trust Centre for Cell-Matrix Research, Manchester, United Kingdom
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24
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Glutamate receptors in synaptic assembly and plasticity: case studies on fly NMJs. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 970:3-28. [PMID: 22351049 DOI: 10.1007/978-3-7091-0932-8_1] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The molecular and cellular mechanisms that control the composition and functionality of ionotropic glutamate receptors may be considered as most important "set screws" for adjusting excitatory transmission in the course of developmental and experience-dependent changes within neural networks. The Drosophila larval neuromuscular junction has emerged as one important invertebrate model system to study the formation, maintenance, and plasticity-related remodeling of glutamatergic synapses in vivo. By exploiting the unique genetic accessibility of this organism combined with diverse tools for manipulation and analysis including electrophysiology and state of the art imaging, considerable progress has been made to characterize the role of glutamate receptors during the orchestration of junctional development, synaptic activity, and synaptogenesis. Following an introduction to basic features of this model system, we will mainly focus on conceptually important findings such as the selective impact of glutamate receptor subtypes on the formation of new synapses, the coordination of presynaptic maturation and receptor subtype composition, the role of nonvesicularly released glutamate on the synaptic localization of receptors, or the homeostatic feedback of receptor functionality on presynaptic transmitter release.
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25
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SULKOWSKI MIKOLAJJ, KUROSAWA MATHIEUS, OX DANIELN. Growing pains: development of the larval nocifensive response in Drosophila. THE BIOLOGICAL BULLETIN 2011; 221:300-306. [PMID: 22186918 PMCID: PMC4209481 DOI: 10.1086/bblv221n3p300] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/31/2023]
Abstract
The ability to perceive and avoid harmful substances or stimuli is key to an organism's survival. The neuronal cognate of the perception of pain is known as nociception, and the reflexive motion to avoid pain is termed the nocifensive response. As the nocifensive response is an ancient and evolutionarily conserved behavioral response to nociceptive stimuli, it is amenable to study in relatively simple and genetically tractable model systems such as Drosophila. Recent studies have taken advantage of the useful properties of Drosophila larvae to begin elucidating the neuronal connectivity and molecular machinery underlying the nocifensive response. However, these studies have primarily utilized the third-instar larval stage, and many mutations that potentially influence nociception survive only until earlier larval stages. Here we characterize the nocifensive responses of Drosophila throughout larval development and find dramatic changes in the nature of the behavior. Notably, we find that prior to the third instar, larvae are unable to perform the characteristic "corkscrew-like roll" behavior. Also, we identify an avoidance behavior consistent with a nocifensive response that is present immediately after larval hatching, representing a paradigm that may be useful in examining mutations with an early lethal phenotype.
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Affiliation(s)
- MIKOLAJ J. SULKOWSKI
- School of Systems Biology, George Mason University, Manassas, Virginia 20120
- Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia 22030
| | - MATHIEU S. KUROSAWA
- School of Systems Biology, George Mason University, Manassas, Virginia 20120
- Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia 22030
| | - DANIEL N. OX
- School of Systems Biology, George Mason University, Manassas, Virginia 20120
- Krasnow Institute for Advanced Study, George Mason University, Fairfax, Virginia 22030
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26
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Hara Y, Park CS, Janssen WGM, Punsoni M, Rapp PR, Morrison JH. Synaptic characteristics of dentate gyrus axonal boutons and their relationships with aging, menopause, and memory in female rhesus monkeys. J Neurosci 2011; 31:7737-44. [PMID: 21613486 PMCID: PMC3103072 DOI: 10.1523/jneurosci.0822-11.2011] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2011] [Revised: 04/12/2011] [Accepted: 04/13/2011] [Indexed: 11/21/2022] Open
Abstract
Age-related memory impairment occurs in many mammalian species, including humans. Moreover, women undergoing the menopausal transition often complain of problems with memory. We recently reported that rhesus monkeys display age- and menopause-related recognition memory impairment on a hippocampus-reliant test [delayed nonmatching-to-sample (DNMS)]. In the same monkeys, perforated synapse densities in the dentate gyrus outer molecular layer (OML) correlated with DNMS recognition accuracy, while total axospinous synapse density was similar across age and menses groups. The current study examined whether synaptic characteristics of OML axonal boutons are coupled with age- or menopause-related memory deficits. Using serial section electron microscopy, we measured the frequencies of single-synapse boutons (SSBs), multiple-synapse boutons (MSBs), and boutons with no apparent synaptic contacts [nonsynaptic boutons (NSBs)] in the OML. Aged females had double the percentage of NSBs compared with young females, and this measure correlated positively and inversely with DNMS acquisition (number of trials to criterion) and delay performance (average accuracy), respectively. Aged compared with young females also had a lower frequency of MSBs and a lower number of synaptic contacts per MSB, and the latter variable inversely correlated with DNMS acquisition. Although proportions of NSBs, SSBs, and MSBs were similar across menses groups, compared with premenopausal monkeys, peri/postmenopausal monkeys had fewer MSBs contacting one or more segmented perforated synapses, and the abundance of this bouton subtype positively correlated with DNMS performance. These results suggest that age- and menopause-related shifts in OML synaptic subtypes may be coupled with deficits in task acquisition and recognition memory.
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Affiliation(s)
- Yuko Hara
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories
| | - C. Sehwan Park
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories
| | | | - Michael Punsoni
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories
| | - Peter R. Rapp
- Laboratory of Experimental Gerontology, National Institute on Aging, Baltimore, Maryland 21224
| | - John H. Morrison
- Fishberg Department of Neuroscience and Kastor Neurobiology of Aging Laboratories
- Department of Geriatrics and Palliative Medicine, and
- Computational Neurobiology and Imaging Center, Mount Sinai School of Medicine, New York, New York 10029, and
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27
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Soria Van Hoeve JS, Borst JGG. Delayed appearance of the scaffolding proteins PSD-95 and Homer-1 at the developing rat calyx of Held synapse. J Comp Neurol 2011; 518:4581-90. [PMID: 20886623 DOI: 10.1002/cne.22479] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The calyx of Held synapse is a giant axosomatic synapse that acts as a fast relay in the sound localization circuit of the brainstem. In rodents it forms within a relatively brief period starting around the second postnatal day (P2). The relative timing of the formation of its pre- and the postsynaptic compartment are not yet known. By means of fluorescent immunohistochemistry in neonatal rats we therefore compared the developmental expression patterns of the vesicular glutamate transporter (VGLUT)-1 and the postsynaptic density scaffolding proteins Homer-1 and PSD-95 in the medial nucleus of the trapezoid body (MNTB). Before its formation, colocalized punctate staining of VGLUT-1 and Homer-1 or PSD-95 was observed on principal neurons, in agreement with earlier work showing that they are already innervated by fibers from the cochlear nucleus before the calyx forms. The expression of VGLUT-1 clusters within the nascent calyx of Held synapse preceded the expression of Homer-1 and PSD-95 clusters, as indicated by the presence of principal neurons with only a large contiguous cluster (LCC) of VGLUT-1 at P2-3, whereas no neurons with only an LCC for Homer-1 or PSD-95 were seen. At P3 the first principal neurons with both a pre- and a postsynaptic LCC were observed, and at P12 all principal neurons had both a pre- and a postsynaptic LCC. The relatively late appearance of Homer-1 and PSD-95 within the developing calyx of Held synapse suggests that they play a role in its stabilization and the recruitment of additional receptors to its postsynaptic density.
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Affiliation(s)
- John S Soria Van Hoeve
- Department of Neuroscience, Erasmus MC, University Medical Center Rotterdam, 3015 GE Rotterdam, The Netherlands
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29
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Betley JN, Wright CVE, Kawaguchi Y, Erdélyi F, Szabó G, Jessell TM, Kaltschmidt JA. Stringent specificity in the construction of a GABAergic presynaptic inhibitory circuit. Cell 2009; 139:161-74. [PMID: 19804761 DOI: 10.1016/j.cell.2009.08.027] [Citation(s) in RCA: 162] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2009] [Revised: 06/12/2009] [Accepted: 08/12/2009] [Indexed: 11/25/2022]
Abstract
GABAergic interneurons are key elements in neural coding, but the mechanisms that assemble inhibitory circuits remain unclear. In the spinal cord, the transfer of sensory signals to motor neurons is filtered by GABAergic interneurons that act presynaptically to inhibit sensory transmitter release and postsynaptically to inhibit motor neuron excitability. We show here that the connectivity and synaptic differentiation of GABAergic interneurons that mediate presynaptic inhibition is directed by their sensory targets. In the absence of sensory terminals these GABAergic neurons shun other available targets, fail to undergo presynaptic differentiation, and withdraw axons from the ventral spinal cord. A sensory-specific source of brain derived neurotrophic factor induces synaptic expression of the GABA synthetic enzyme GAD65--a defining biochemical feature of this set of interneurons. The organization of a GABAergic circuit that mediates presynaptic inhibition in the mammalian CNS is therefore controlled by a stringent program of sensory recognition and signaling.
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Affiliation(s)
- J Nicholas Betley
- Howard Hughes Medical Institute, Kavli Institute of Brain Science, Departments of Neuroscience, Biochemistry and Molecular Biophysics, Columbia University, New York, NY 10032, USA
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30
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Owald D, Sigrist SJ. Assembling the presynaptic active zone. Curr Opin Neurobiol 2009; 19:311-8. [PMID: 19395253 DOI: 10.1016/j.conb.2009.03.003] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2009] [Revised: 03/08/2009] [Accepted: 03/17/2009] [Indexed: 12/28/2022]
Abstract
Rapid neurotransmission depends on the structural and functional integrity of synaptic connections. How synapses assemble is currently being intensely investigated to help our understanding of neuronal development and synaptic plasticity. Here we focus on the assembly of the presynaptic active zone, which regulates the synaptic vesicle exo/endo-cycle and is characterized by ultrastructural specializations and large scaffold proteins. While genetic and biochemical studies from rodents, Caenorhabditis elegans and Drosophila have started to identify proteins organizing active zone assembly, drawing a coherent picture remains challenging, with genetically established hierarchies and protein-protein interactions still to be placed into spatio-temporal and functional context. Recent advances in light and electron microscopy, together with in vivo imaging of protein traffic, will help to tackle this challenge.
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Affiliation(s)
- David Owald
- NeuroCure Cluster of Excellence, Charité Berlin, Berlin, Germany.
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31
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Abstract
Information processing in the nervous system relies on properly localized and organized synaptic structures at the correct locations. The formation of synapses is a long and intricate process involving multiple interrelated steps. Decades of research have identified a large number of molecular components of the presynaptic compartment. In addition to neurotransmitter-containing synaptic vesicles, presynaptic terminals are defined by cytoskeletal and membrane specializations that allow highly regulated exo- and endocytosis of synaptic vesicles and that maintain precise registration with postsynaptic targets. Functional studies at multiple levels have revealed complex interactions between the transport of vesicular intermediates, the presynaptic cytoskeleton, growth cone navigation, and synaptic targets. With the advent of finer anatomical, physiological, and molecular tools, great insights have been gained toward the mechanistic dissection of functionally redundant processes controlling the specificity and dynamics of synapses. This review highlights the recent findings pertaining to the cellular and molecular regulation of presynaptic differentiation.
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Affiliation(s)
- Yishi Jin
- Division of Biological Sciences, Section of Neurobiology, Howard Hughes Medical Institute, University of California, San Diego, La Jolla, California 92093, USA.
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32
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Oh HW, Campusano JM, Hilgenberg LGW, Sun X, Smith MA, O'Dowd DK. Ultrastructural analysis of chemical synapses and gap junctions between Drosophila brain neurons in culture. Dev Neurobiol 2008; 68:281-94. [PMID: 18044733 DOI: 10.1002/dneu.20575] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Dissociated cultures from many species have been important tools for exploring factors that regulate structure and function of central neuronal synapses. We have previously shown that cells harvested from brains of late stage Drosophila pupae can regenerate their processes in vitro. Electrophysiological recordings demonstrate the formation of functional synaptic connections as early as 3 days in vitro (DIV), but no information about synapse structure is available. Here, we report that antibodies against pre-synaptic proteins Synapsin and Bruchpilot result in punctate staining of regenerating neurites. Puncta density increases as neuritic plexuses develop over the first 4 DIV. Electron microscopy reveals that closely apposed neurites can form chemical synapses with both pre- and postsynaptic specializations characteristic of many inter-neuronal synapses in the adult brain. Chemical synapses in culture are restricted to neuritic processes and some neurite pairs form reciprocal synapses. GABAergic synapses have a significantly higher percentage of clear core versus granular vesicles than non-GABA synapses. Gap junction profiles, some adjacent to chemical synapses, suggest that neurons in culture can form purely electrical as well as mixed synapses, as they do in the brain. However, unlike adult brain, gap junctions in culture form between neuronal somata as well as neurites, suggesting soma ensheathing glia, largely absent in culture, regulate gap junction location in vivo. Thus pupal brain cultures, which support formation of interneuronal synapses with structural features similar to synapses in adult brain, are a useful model system for identifying intrinsic and extrinsic regulators of central synapse structure as well as function.
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Affiliation(s)
- Hyun-Woo Oh
- Department of Anatomy and Neurobiology, University of California, Irvine, California 92697-1280, USA
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33
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Liebl FLW, Wu Y, Featherstone DE, Noordermeer JN, Fradkin L, Hing H. Derailed regulates development of the Drosophila neuromuscular junction. Dev Neurobiol 2008; 68:152-65. [PMID: 17963254 PMCID: PMC2279185 DOI: 10.1002/dneu.20562] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Neural function is dependent upon the proper formation and development of synapses. We show here that Wnt5 regulates the growth of the Drosophila neuromuscular junction (NMJ) by signaling through the Derailed receptor. Mutations in both wnt5 and drl result in a significant reduction in the number of synaptic boutons. Cell-type specific rescue experiments show that wnt5 functions in the presynaptic motor neuron while drl likely functions in the postsynaptic muscle cell. Epistatic analyses indicate that drl acts downstream of wnt5 to promote synaptic growth. Structure-function analyses of the Drl protein indicate that normal synaptic growth requires the extracellular Wnt inhibitory factor domain and the intracellular domain, which includes an atypical kinase. Our findings reveal a novel signaling mechanism that regulates morphology of the Drosophila NMJ.
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Affiliation(s)
- Faith L W Liebl
- Cell and Developmental Biology Program, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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34
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Potthoff MJ, Olson EN. MEF2: a central regulator of diverse developmental programs. Development 2007; 134:4131-40. [PMID: 17959722 DOI: 10.1242/dev.008367] [Citation(s) in RCA: 630] [Impact Index Per Article: 37.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The myocyte enhancer factor 2 (MEF2) transcription factor acts as a lynchpin in the transcriptional circuits that control cell differentiation and organogenesis. The spectrum of genes activated by MEF2 in different cell types depends on extracellular signaling and on co-factor interactions that modulate MEF2 activity. Recent studies have revealed MEF2 to form an intimate partnership with class IIa histone deacetylases, which together function as a point of convergence of multiple epigenetic regulatory mechanisms. We review the myriad roles of MEF2 in development and the mechanisms through which it couples developmental, physiological and pathological signals with programs of cell-specific transcription.
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Affiliation(s)
- Matthew J Potthoff
- Department of Molecular Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9148, USA
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35
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Abstract
During skeletal muscle differentiation, the actomyosin motor is assembled into myofibrils, multiprotein machines that generate and transmit force to cell ends. How expression of muscle proteins is coordinated to build the myofibril is unknown. Here we show that zebrafish Mef2d and Mef2c proteins are required redundantly for assembly of myosin-containing thick filaments in nascent muscle fibres, but not for the earlier steps of skeletal muscle fibre differentiation, elongation, fusion or thin filament gene expression. mef2d mRNA and protein is present in myoblasts, whereas mef2c expression commences in muscle fibres. Knockdown of both Mef2s with antisense morpholino oligonucleotides or in mutant fish blocks muscle function and prevents sarcomere assembly. Cell transplantation and heat-shock-driven rescue reveal a cell-autonomous requirement for Mef2 within fibres. In nascent fibres, Mef2 drives expression of genes encoding thick, but not thin, filament proteins. Among genes analysed, myosin heavy and light chains and myosin-binding protein C require Mef2 for normal expression, whereas actin, tropomyosin and troponin do not. Our findings show that Mef2 controls skeletal muscle formation after terminal differentiation and define a new maturation step in vertebrate skeletal muscle development at which thick filament gene expression is controlled.
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Affiliation(s)
| | - Simon M. Hughes
- Corresponding author: Simon M. Hughes, MRC Centre for Developmental Neurobiology, 4th floor south, New Hunt's House, Guy's Campus, King's College London, London SE1 1UL, UK. Tel.: +44 20 7848 6445; fax: +44 20 7848 6550;
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36
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Schmid A, Qin G, Wichmann C, Kittel RJ, Mertel S, Fouquet W, Schmidt M, Heckmann M, Sigrist SJ. Non-NMDA-type glutamate receptors are essential for maturation but not for initial assembly of synapses at Drosophila neuromuscular junctions. J Neurosci 2006; 26:11267-77. [PMID: 17079654 PMCID: PMC6674544 DOI: 10.1523/jneurosci.2722-06.2006] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The assembly of glutamatergic postsynaptic densities (PSDs) seems to involve the gradual recruitment of molecular components from diffuse cellular pools. Whether the glutamate receptors themselves are needed to instruct the structural and molecular assembly of the PSD has hardly been addressed. Here, we engineered Drosophila neuromuscular junctions (NMJs) to express none or only drastically reduced amounts of their postsynaptic non-NMDA-type glutamate receptors. At such NMJs, principal synapse formation proceeded and presynaptic active zones showed normal composition and ultrastructure as well as proper glutamate release. At the postsynaptic site, initial steps of molecular and structural assembly took place as well. However, growth of the nascent PSDs to mature size was inhibited, and proteins normally excluded from PSD membranes remained at these apparently immature sites. Intriguingly, synaptic transmission as well as glutamate binding to glutamate receptors appeared dispensable for synapse maturation. Thus, our data suggest that incorporation of non-NMDA-type glutamate receptors and likely their protein-protein interactions with additional PSD components triggers a conversion from an initial to a mature stage of PSD assembly.
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Affiliation(s)
- Andreas Schmid
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | - Gang Qin
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | - Carolin Wichmann
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
- Institut für Klinische Neurobiologie, Universität Würzburg, and
| | - Robert J. Kittel
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | - Sara Mertel
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | - Wernher Fouquet
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | - Manuela Schmidt
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
| | | | - Stephan J. Sigrist
- European Neuroscience Institute Göttingen, 37077 Göttingen, Germany, and
- Institut für Klinische Neurobiologie, Rudolf-Virchow Zentrum, Universität Würzburg, 97080 Würzburg, Germany
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37
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Sandmann T, Jensen LJ, Jakobsen JS, Karzynski MM, Eichenlaub MP, Bork P, Furlong EEM. A Temporal Map of Transcription Factor Activity: Mef2 Directly Regulates Target Genes at All Stages of Muscle Development. Dev Cell 2006; 10:797-807. [PMID: 16740481 DOI: 10.1016/j.devcel.2006.04.009] [Citation(s) in RCA: 188] [Impact Index Per Article: 10.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2006] [Revised: 03/27/2006] [Accepted: 04/05/2006] [Indexed: 01/10/2023]
Abstract
Dissecting components of key transcriptional networks is essential for understanding complex developmental processes and phenotypes. Genetic studies have highlighted the role of members of the Mef2 family of transcription factors as essential regulators in myogenesis from flies to man. To understand how these transcription factors control diverse processes in muscle development, we have combined chromatin immunoprecipitation analysis with gene expression profiling to obtain a temporal map of Mef2 activity during Drosophila embryonic development. This global approach revealed three temporal patterns of Mef2 enhancer binding, providing a glimpse of dynamic enhancer use within the context of a developing embryo. Our results provide mechanistic insight into the regulation of Mef2's activity at the level of DNA binding and suggest cooperativity with the bHLH protein Twist. The number and diversity of new direct target genes indicates a much broader role for Mef2, at all stages of myogenesis, than previously anticipated.
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Affiliation(s)
- Thomas Sandmann
- European Molecular Biology Laboratory, D-69117 Heidelberg, Germany
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38
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Layden MJ, Odden JP, Schmid A, Garces A, Thor S, Doe CQ. Zfh1, a somatic motor neuron transcription factor, regulates axon exit from the CNS. Dev Biol 2006; 291:253-63. [PMID: 16458285 DOI: 10.1016/j.ydbio.2005.12.009] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2005] [Revised: 12/01/2005] [Accepted: 12/05/2005] [Indexed: 11/23/2022]
Abstract
Motor neurons are defined by their axon projections, which exit the CNS to innervate somatic or visceral musculature, yet remarkably little is known about how motor axons are programmed to exit the CNS. Here, we describe the role of the Drosophila Zfh1 transcription factor in promoting axon exit from the CNS. Zfh1 is detected in all embryonic somatic motor neurons, glia associated with the CNS surface and motor axons, and one identified interneuron. In zfh1 mutants, ventral projecting motor axons often stall at the edge of the CNS, failing to enter the muscle field, despite having normal motor neuron identity. Conversely, ectopic Zfh1 induces a subset of interneurons--all normally expressing two or more "ventral motor neuron transcription factors" (e.g. Islet, Hb9, Nkx6, Lim3)--to project laterally and exit the CNS. We conclude that Zfh1 is required for ventral motor axon exit from the CNS.
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Affiliation(s)
- Michael J Layden
- Institute of Neuroscience, Institute of Molecular Biology, Howard Hughes Medical Institute 1254 University of Oregon, Eugene, OR 97403, USA
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39
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Ruiz-Cañada C, Budnik V. Introduction on the use of the Drosophila embryonic/larval neuromuscular junction as a model system to study synapse development and function, and a brief summary of pathfinding and target recognition. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2006; 75:1-31. [PMID: 17137921 DOI: 10.1016/s0074-7742(06)75001-2] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- Catalina Ruiz-Cañada
- Department of Biochemistry and Molecular Pharmacology, University of Massachusetts, Medical School, Massachusetts 01605, USA
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40
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Prokop A. Organization of the Efferent System and Structure of Neuromuscular Junctions In Drosophila. INTERNATIONAL REVIEW OF NEUROBIOLOGY 2006; 75:71-90. [PMID: 17137924 DOI: 10.1016/s0074-7742(06)75004-8] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Affiliation(s)
- Andreas Prokop
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, United Kingdom
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41
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Abstract
Structural synapses are key regulators of information flow in neuronal networks. To understand the function and formation of neuronal circuits, the development and function of synapses have therefore been intensely studied in both vertebrate and invertebrate species. Precise descriptions of synapses and their amenability to genetic analysis in the model organism Drosophila provide an efficient platform from which to explore mechanisms and principles of synapse formation, which find many counterparts in other animals. Here we summarise our knowledge of the structure of Drosophila synapses. Focussing on neuromuscular junctions and photoreceptor synapses, we provide an overview of mechanisms underlying the development of synaptic structure in Drosophila.
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Affiliation(s)
- Andreas Prokop
- The University of Manchester, Michael Smith Building, Oxford Road, Manchester M13 9PT, UK.
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42
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Junion G, Jagla T, Duplant S, Tapin R, Da Ponte JP, Jagla K. Mapping Dmef2-binding regulatory modules by using a ChIP-enriched in silico targets approach. Proc Natl Acad Sci U S A 2005; 102:18479-84. [PMID: 16339902 PMCID: PMC1317932 DOI: 10.1073/pnas.0507030102] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2005] [Accepted: 10/27/2005] [Indexed: 11/18/2022] Open
Abstract
Mapping the regulatory modules to which transcription factors bind in vivo is a key step toward understanding of global gene expression programs. We have developed a chromatin immunoprecipitation (ChIP)-chip strategy for identifying factor-specific regulatory regions acting in vivo. This method, called the ChIP-enriched in silico targets (ChEST) approach, combines immunoprecipitation of cross-linked protein-DNA complexes (X-ChIP) with in silico prediction of targets and generation of computed DNA microarrays. We report the use of ChEST in Drosophila to identify several previously unknown targets of myocyte enhancer factor 2 (MEF2), a key regulator of myogenic differentiation. Our approach was validated by demonstrating that the identified sequences act as enhancers in vivo and are able to drive reporter gene expression specifically in MEF2-positive muscle cells. Presented here, the ChEST strategy was originally designed to identify regulatory modules in Drosophila, but it can be adapted for any sequenced and annotated genome.
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Affiliation(s)
- Guillaume Junion
- Institut National de la Santé et de la Recherche Médicale Unité 384, Faculté de Médecine, 28 Place Henri Dunant, 63000 Clermont-Ferrand, France
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43
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Liebl FLW, Chen K, Karr J, Sheng Q, Featherstone DE. Increased synaptic microtubules and altered synapse development in Drosophila sec8 mutants. BMC Biol 2005; 3:27. [PMID: 16351720 PMCID: PMC1326216 DOI: 10.1186/1741-7007-3-27] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2005] [Accepted: 12/13/2005] [Indexed: 02/02/2023] Open
Abstract
Background Sec8 is highly expressed in mammalian nervous systems and has been proposed to play a role in several aspects of neural development and function, including neurite outgrowth, calcium-dependent neurotransmitter secretion, trafficking of ionotropic glutamate receptors and regulation of neuronal microtubule assembly. However, these models have never been tested in vivo. Nervous system development and function have not been described after mutation of sec8 in any organism. Results We identified lethal sec8 mutants in an unbiased forward genetic screen for mutations causing defects in development of glutamatergic Drosophila neuromuscular junctions (NMJs). The Drosophila NMJ is genetically malleable and accessible throughout development to electrophysiology and immunocytochemistry, making it ideal for examination of the sec8 mutant synaptic phenotype. We developed antibodies to Drosophila Sec8 and showed that Sec8 is abundant at the NMJ. In our sec8 null mutants, in which the sec8 gene is specifically deleted, Sec8 immunoreactivity at the NMJ is eliminated but immunoblots reveal substantial maternal contribution in the rest of the animal. Contrary to the hypothesis that Sec8 is required for neurite outgrowth or synaptic terminal growth, immunocytochemical examination revealed that sec8 mutant NMJs developed more branches and presynaptic terminals during larval development, compared to controls. Synaptic electrophysiology showed no evidence that Sec8 is required for basal neurotransmission, though glutamate receptor trafficking was mildly disrupted in sec8 mutants. The most dramatic NMJ phenotype in sec8 mutants was an increase in synaptic microtubule density, which was approximately doubled compared to controls. Conclusion Sec8 is abundant in the Drosophila NMJ. Sec8 is required in vivo for regulation of synaptic microtubule formation, and (probably secondarily) regulation of synaptic growth and glutamate receptor trafficking. We did not find any evidence that Sec8 is required for basal neurotransmission.
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Affiliation(s)
- Faith LW Liebl
- Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, 601 South Goodwin Avenue, C626, Urbana, IL 61801 USA
| | - Kaiyun Chen
- Department of Biological Sciences, University of Illinois at Chicago, 840 W. Taylor St. (M/C 067), Chicago, IL 60607 USA
| | - Julie Karr
- Department of Biological Sciences, University of Illinois at Chicago, 840 W. Taylor St. (M/C 067), Chicago, IL 60607 USA
| | - Qi Sheng
- Department of Biological Sciences, University of Illinois at Chicago, 840 W. Taylor St. (M/C 067), Chicago, IL 60607 USA
| | - David E Featherstone
- Department of Biological Sciences, University of Illinois at Chicago, 840 W. Taylor St. (M/C 067), Chicago, IL 60607 USA
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44
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Craig AM, Graf ER, Linhoff MW. How to build a central synapse: clues from cell culture. Trends Neurosci 2005; 29:8-20. [PMID: 16337695 PMCID: PMC2820512 DOI: 10.1016/j.tins.2005.11.002] [Citation(s) in RCA: 144] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2005] [Revised: 08/31/2005] [Accepted: 11/10/2005] [Indexed: 01/10/2023]
Abstract
Central neurons develop and maintain molecularly distinct synaptic specializations for excitatory and inhibitory transmitters, often only microns apart on their dendritic arbor. Progress towards understanding the molecular basis of synaptogenesis has come from several recent studies using a coculture system of non-neuronal cells expressing molecules that generate presynaptic or postsynaptic "hemi-synapses" on contacting neurons. Together with molecular properties of these protein families, such studies have yielded interesting clues to how glutamatergic and GABAergic synapses are assembled. Other clues come from heterochronic cultures, manipulations of activity in subsets of neurons in a network, and of course many in vivo studies. Taking into account these data, we consider here how basic parameters of synapses--competence, placement, composition, size and longevity--might be determined.
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Affiliation(s)
- Ann Marie Craig
- Brain Research Centre and Department of Psychiatry, University of British Columbia, Vancouver, Canada V6T 2B5.
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45
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Barallobre MJ, Pascual M, Del Río JA, Soriano E. The Netrin family of guidance factors: emphasis on Netrin-1 signalling. ACTA ACUST UNITED AC 2005; 49:22-47. [PMID: 15960985 DOI: 10.1016/j.brainresrev.2004.11.003] [Citation(s) in RCA: 166] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2004] [Revised: 10/14/2004] [Accepted: 11/29/2004] [Indexed: 12/13/2022]
Abstract
During the development of the nervous system, neurons respond to the coordinated action of a variety of attractive and repulsive signals from the embryonic environment. Netrins form a family of extracellular proteins that regulate the migration of neurons and axonal growth cones. These proteins are bifunctional signals that are chemoattractive for some neurons and chemorepellent for others. Netrins mainly interact with the specific receptors DCC and UNC-5 family. To date, several Netrins have been described in mouse and humans: Netrin-1, -3/NTL2, -4/beta and G-Netrins. Netrin-1 is the most studied member of the family. It is involved in the development many projections of the nervous system. When Netrin-1 interacts with its specific receptors, a cascade of local cytoplasmic events is triggered. Several signal transduction pathways and effector molecules have been implicated in the response to Netrin-1: small Rho-GTPases, MAP-Kinases, second messengers and the Microtubule Associated Protein 1B (MAP1B).
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Affiliation(s)
- María J Barallobre
- Department of Cell Biology and IRBB-Barcelona Science Park, University of Barcelona, Barcelona E-08028, Spain.
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46
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de Jong S, Cavallo JA, Rios CD, Dworak HA, Sink H. Target recognition and synaptogenesis by motor axons: responses to the sidestep protein. Int J Dev Neurosci 2004; 23:397-410. [PMID: 15927764 DOI: 10.1016/j.ijdevneu.2004.10.002] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2004] [Revised: 10/08/2004] [Accepted: 10/11/2004] [Indexed: 10/26/2022] Open
Abstract
Sidestep (Side) is a pivotal molecular player in embryonic motor axon pathfinding. But questions about its functional repertoire remain: (i) can Side permanently overturn targeting preferences? (ii) does it promote synaptogenesis, and (iii) can Side facilitate synaptic stabilization? To address these questions, Side was temporally and spatially misexpressed and the visible consequences for neuromuscular junction morphology were assessed. When Side was misexpressed either broadly or selectively in muscles during targeting in a wildtype background motor axon targeting preferences were permanently overturned. However the misexpression of Side in all muscles post-targeting neither changed synapse morphology, nor compensated for a lack of the synapse-stabilizing protein Fasciclin II (FasII). Rather Side appears to be dependent on FasII, instead of on intrinsic ability, for sustaining targeting changes. We propose that Side helps to bring motor axons to their correct muscle targets and promotes synaptogenesis, then FasII serves to stabilize the synaptic contacts.
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Affiliation(s)
- Samanta de Jong
- Skirball Institute of Biomolecular Medicine, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA
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47
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Küppers-Munther B, Letzkus JJ, Lüer K, Technau G, Schmidt H, Prokop A. A new culturing strategy optimises Drosophila primary cell cultures for structural and functional analyses. Dev Biol 2004; 269:459-78. [PMID: 15110713 DOI: 10.1016/j.ydbio.2004.01.038] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2003] [Revised: 12/08/2003] [Accepted: 01/28/2004] [Indexed: 11/24/2022]
Abstract
Neurons in primary cell cultures provide important experimental possibilities complementing or substituting those in the nervous system. However, Drosophila primary cell cultures have unfortunate limitations: they lack either a range of naturally occurring cell types, or of mature physiological properties. Here, we demonstrate a strategy which supports both aspects integrated in one culture: Initial culturing in conventional serum-supplemented Schneider's medium (SM(20K)) guarantees acquisition of all properties known from 30 years of work on cell type-specific differentiation in this medium. Through subsequent shift to newly developed active Schneider's medium (SM(active)), neurons adopt additional mature properties like the ability to carry out plastic morphological changes, neurotransmitter expression and electrical activity. We introduce long-term FM-dye measurements as a tool for Drosophila primary cell cultures demonstrating the presence of increased, action potential-dependent synaptic activity in SM(active). This is confirmed by patch-clamp recordings, which in addition show that SM(active)-cultured neurons display different spiking patterns. Furthermore, we demonstrate that transmission can be evoked in SM(active) cultures, revealing the existence of synaptic plasticity. Thus, these culture conditions support developmental, structural and physiological properties known or expected from the nervous system, enhancing possibilities for future experiments complementing or substituting those in nervous systems of Drosophila.
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48
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Abmayr SM, Balagopalan L, Galletta BJ, Hong SJ. Cell and molecular biology of myoblast fusion. INTERNATIONAL REVIEW OF CYTOLOGY 2003; 225:33-89. [PMID: 12696590 DOI: 10.1016/s0074-7696(05)25002-7] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
In organisms from Drosophila to mammals, the musculature is comprised of an elaborate array of distinct fibers that are generated by the fusion of committed myoblasts. These muscle fibers differ from each other in features that include location, pattern of innervation, site of attachment, and size. The sizes of the newly formed muscles of an embryo are controlled in large part by the number of cells that form the syncitial fiber. Over the past few decades, an extensive body of literature has described the process of myoblast fusion in vertebrates, relying primarily on the strengths of tissue culture model systems. More recently, genetic studies in Drosophila embryos have provided new insights into the process. Together, these studies define the steps necessary for myoblast differentiation, the acquisition of fusion competence, the recognition and adhesion between myoblasts, and the fusion of two lipid bilayers into one. In this review, we have attempted to combine insights from both Drosophila and vertebrate studies to trace the processes and molecules involved in myoblast fusion. Implicit in this approach is the assumption that fundamental aspects of myoblast fusion will be similar, independent of the organism in which it is occurring.
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MESH Headings
- Animals
- Cell Adhesion/physiology
- Cell Differentiation/physiology
- Cell Membrane/metabolism
- Drosophila melanogaster/embryology
- Drosophila melanogaster/metabolism
- Drosophila melanogaster/ultrastructure
- Embryo, Nonmammalian/embryology
- Embryo, Nonmammalian/metabolism
- Embryo, Nonmammalian/ultrastructure
- Humans
- Membrane Fusion/physiology
- Muscle Fibers, Skeletal/metabolism
- Muscle Fibers, Skeletal/ultrastructure
- Muscle, Skeletal/embryology
- Muscle, Skeletal/metabolism
- Muscle, Skeletal/ultrastructure
- Myoblasts, Skeletal/metabolism
- Myoblasts, Skeletal/ultrastructure
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Affiliation(s)
- Susan M Abmayr
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, Pennsylvania 16802, USA
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Landgraf M, Jeffrey V, Fujioka M, Jaynes JB, Bate M. Embryonic origins of a motor system: motor dendrites form a myotopic map in Drosophila. PLoS Biol 2003; 1:E41. [PMID: 14624243 PMCID: PMC261881 DOI: 10.1371/journal.pbio.0000041] [Citation(s) in RCA: 111] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2003] [Accepted: 08/25/2003] [Indexed: 11/19/2022] Open
Abstract
The organisational principles of locomotor networks are less well understood than those of many sensory systems, where in-growing axon terminals form a central map of peripheral characteristics. Using the neuromuscular system of the Drosophila embryo as a model and retrograde tracing and genetic methods, we have uncovered principles underlying the organisation of the motor system. We find that dendritic arbors of motor neurons, rather than their cell bodies, are partitioned into domains to form a myotopic map, which represents centrally the distribution of body wall muscles peripherally. While muscles are segmental, the myotopic map is parasegmental in organisation. It forms by an active process of dendritic growth independent of the presence of target muscles, proper differentiation of glial cells, or (in its initial partitioning) competitive interactions between adjacent dendritic domains. The arrangement of motor neuron dendrites into a myotopic map represents a first layer of organisation in the motor system. This is likely to be mirrored, at least in part, by endings of higher-order neurons from central pattern-generating circuits, which converge onto the motor neuron dendrites. These findings will greatly simplify the task of understanding how a locomotor system is assembled. Our results suggest that the cues that organise the myotopic map may be laid down early in development as the embryo subdivides into parasegmental units.
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Affiliation(s)
- Matthias Landgraf
- Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
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Abstract
Coordinated motor behaviors rely on a maze-like network of axonal connections between motoneurons and the body musculature. Since the time of the Renaissance, scientists have been fascinated by the question of how such complex, yet stereotypic, connectivity arises during embryogenesis. Here, we review the long journey of motor axons, which traverse diverse territories along predetermined routes riddled with a wealth of divergent pathway options. We conclude that motor axon migration occurs in a stepwise manner, with each step being controlled by local guidance cues, that motor axons rely on some of the same cues that also control axon migration within the CNS, and that, due to species-specific anatomical variations, the cell types providing such local cues may vary. Although studies of motor axon migration have not yet resulted in a complete understanding of the cellular and molecular mechanisms regulating this process, we have come a long way since the days of da Vinci.
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Affiliation(s)
- Valerie A Schneider
- Department of Cell and Developmental Biology, University of Pennsylvania, 421 Curie Boulevard, Philadelphia, PA 19104, USA
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