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Zhai RG. The Architecture of the Presynaptic Release Site. ADVANCES IN NEUROBIOLOGY 2023; 33:1-21. [PMID: 37615861 DOI: 10.1007/978-3-031-34229-5_1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/25/2023]
Abstract
The architecture of the presynaptic release site is exquisitely designed to facilitate and regulate synaptic vesicle exocytosis. With the identification of some of the building blocks of the active zone and the advent of super resolution imaging techniques, we are beginning to understand the morphological and functional properties of synapses in great detail. Presynaptic release sites consist of the plasma membrane, the cytomatrix, and dense projections. These three components are morphologically distinct but intimately connected with each other and with postsynaptic specializations, ensuring the fidelity of synaptic vesicle tethering, docking, and fusion, as well as signal detection. Although the morphology and molecular compositions of active zones may vary among species, tissues, and cells, global architectural design of the release sites is highly conserved.
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Affiliation(s)
- R Grace Zhai
- Department of Molecular and Cellular Pharmacology, Leonard M. Miller School of Medicine, University of Miami, Miami, FL, USA.
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2
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Hartsock MJ, Spencer RL. Memory and the circadian system: Identifying candidate mechanisms by which local clocks in the brain may regulate synaptic plasticity. Neurosci Biobehav Rev 2020; 118:134-162. [PMID: 32712278 DOI: 10.1016/j.neubiorev.2020.07.023] [Citation(s) in RCA: 25] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2019] [Revised: 07/14/2020] [Accepted: 07/18/2020] [Indexed: 12/11/2022]
Abstract
The circadian system is an endogenous biological network responsible for coordinating near-24-h cycles in behavior and physiology with daily timing cues from the external environment. In this review, we explore how the circadian system regulates memory formation, retention, and recall. Circadian rhythms in these memory processes may arise through several endogenous pathways, and recent work highlights the importance of genetic timekeepers found locally within tissues, called local clocks. We evaluate the circadian memory literature for evidence of local clock involvement in memory, identifying potential nodes for direct interactions between local clock components and mechanisms of synaptic plasticity. Our discussion illustrates how local clocks may pervasively modulate neuronal plastic capacity, a phenomenon that we designate here as circadian metaplasticity. We suggest that this function of local clocks supports the temporal optimization of memory processes, illuminating the potential for circadian therapeutic strategies in the prevention and treatment of memory impairment.
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Affiliation(s)
- Matthew J Hartsock
- Department of Psychology and Neuroscience, University of Colorado Boulder, Boulder, Colorado 80309, United States.
| | - Robert L Spencer
- Department of Psychology and Neuroscience, University of Colorado Boulder, Boulder, Colorado 80309, United States.
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3
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Sugie A, Marchetti G, Tavosanis G. Structural aspects of plasticity in the nervous system of Drosophila. Neural Dev 2018; 13:14. [PMID: 29960596 PMCID: PMC6026517 DOI: 10.1186/s13064-018-0111-z] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 06/12/2018] [Indexed: 12/15/2022] Open
Abstract
Neurons extend and retract dynamically their neurites during development to form complex morphologies and to reach out to their appropriate synaptic partners. Their capacity to undergo structural rearrangements is in part maintained during adult life when it supports the animal's ability to adapt to a changing environment or to form lasting memories. Nonetheless, the signals triggering structural plasticity and the mechanisms that support it are not yet fully understood at the molecular level. Here, we focus on the nervous system of the fruit fly to ask to which extent activity modulates neuronal morphology and connectivity during development. Further, we summarize the evidence indicating that the adult nervous system of flies retains some capacity for structural plasticity at the synaptic or circuit level. For simplicity, we selected examples mostly derived from studies on the visual system and on the mushroom body, two regions of the fly brain with extensively studied neuroanatomy.
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Affiliation(s)
- Atsushi Sugie
- Center for Transdisciplinary Research, Niigata University, Niigata, 951-8585 Japan
- Brain Research Institute, Niigata University, Niigata, 951-8585 Japan
| | | | - Gaia Tavosanis
- Center for Neurodegenerative Diseases (DZNE), 53127 Bonn, Germany
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4
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Gruber L, Rybak J, Hansson BS, Cantera R. Synaptic Spinules in the Olfactory Circuit of Drosophila melanogaster. Front Cell Neurosci 2018; 12:86. [PMID: 29636666 PMCID: PMC5880883 DOI: 10.3389/fncel.2018.00086] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2018] [Accepted: 03/12/2018] [Indexed: 11/14/2022] Open
Abstract
Here we report on ultrastructural features of brain synapses in the fly Drosophila melanogaster and outline a perspective for the study of their functional significance. Images taken with the aid of focused ion beam-scanning electron microscopy (EM) at 20 nm intervals across olfactory glomerulus DA2 revealed that some synaptic boutons are penetrated by protrusions emanating from other neurons. Similar structures in the brain of mammals are known as synaptic spinules. A survey with transmission EM (TEM) disclosed that these structures are frequent throughout the antennal lobe. Detailed neuronal tracings revealed that spinules are formed by all three major types of neurons innervating glomerulus DA2 but the olfactory sensory neurons (OSNs) receive significantly more spinules than other olfactory neurons. Double-membrane vesicles (DMVs) that appear to represent material that has pinched-off from spinules are also most abundant in presynaptic boutons of OSNs. Inside the host neuron, a close association was observed between spinules, the endoplasmic reticulum (ER) and mitochondria. We propose that by releasing material into the host neuron, through a process triggered by synaptic activity and analogous to axonal pruning, synaptic spinules could function as a mechanism for synapse tagging, synaptic remodeling and neural plasticity. Future directions of experimental work to investigate this theory are proposed.
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Affiliation(s)
- Lydia Gruber
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology (MPG)Jena, Germany
| | - Jürgen Rybak
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology (MPG)Jena, Germany
| | - Bill S Hansson
- Department of Evolutionary Neuroethology, Max Planck Institute for Chemical Ecology (MPG)Jena, Germany
| | - Rafael Cantera
- Departamento de Biología del Neurodesarrollo, Instituto de Investigaciones Biológicas Clemente Estable (IIBCE)Montevideo, Uruguay.,Zoology Department, Stockholm UniversityStockholm, Sweden
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5
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Ehmann N, Owald D, Kittel RJ. Drosophila active zones: From molecules to behaviour. Neurosci Res 2018; 127:14-24. [DOI: 10.1016/j.neures.2017.11.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/2017] [Revised: 11/30/2017] [Accepted: 11/30/2017] [Indexed: 11/15/2022]
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6
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Abstract
The brain is a network of neurons, one that generates behaviour, and knowing the former is crucial to understanding the latter. Identifying the exact network of synaptic connections, or connectome, of the fly's central nervous system is now a major objective in Drosophila neurobiology, one that has been initiated in several laboratories, especially the Janelia Research Campus of the Howard Hughes Medical Institute. Progress is most advanced in the optic neuropiles of the visual system. The effort to derive a connectome from these and other neuropile regions is proceeding by various methods of electron microscopy, especially focused-ion beam milling scanning electron microscopy, and relies upon - but is to be carefully distinguished from - published light microscopic methods that reveal the projections of genetically labelled cell types. The latter reveal those neurons that come into close proximity and are therefore candidate synaptic partners. Synaptic partnerships are not in fact reliably revealed by such candidate pairs, anatomical connections often revealing unexpected pathways. Synaptic partnerships identified from ultrastructural features provide a strong heuristic basis to interpret not only functional interactions between identified neurons, but also a powerful means to predict such interactions, and suggest functional pathways not readily predicted from existing experimental evidence. The analysis of circuit function may proceed cell by cell, by examining the behavioural outcome of either interrupting or restoring function to any one element in an anatomically defined circuit, but can be foiled by degeneracy in pathway elements. Circuit information can also be used to identify and analyse circuit motifs, and their role in higher-order network properties. These attempts in Drosophila anticipate parallel attempts in other systems, notably the inner plexiform layer of the vertebrate retina, and augment the one complete connectome already available to us, that available for 30 years in the nematode Caenorhabditis elegans.
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Affiliation(s)
- Ian A Meinertzhagen
- a Department of Psychology and Neuroscience, Life Sciences Centre , Dalhousie University , Halifax , Canada ;,b Janelia Research Campus of Howard Hughes Medical Institute , Ashburn , VA , USA
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7
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Rybak J, Talarico G, Ruiz S, Arnold C, Cantera R, Hansson BS. Synaptic circuitry of identified neurons in the antennal lobe of Drosophila melanogaster. J Comp Neurol 2016; 524:1920-56. [PMID: 26780543 PMCID: PMC6680330 DOI: 10.1002/cne.23966] [Citation(s) in RCA: 46] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2015] [Revised: 01/05/2016] [Accepted: 01/13/2016] [Indexed: 11/09/2022]
Abstract
In Drosophila melanogaster olfactory sensory neurons (OSNs) establish synapses with projection neurons (PNs) and local interneurons within antennal lobe (AL) glomeruli. Substantial knowledge regarding this circuitry has been obtained by functional studies, whereas ultrastructural evidence of synaptic contacts is scarce. To fill this gap, we studied serial sections of three glomeruli using electron microscopy. Ectopic expression of a membrane-bound peroxidase allowed us to map synaptic sites along PN dendrites. Our data prove for the first time that each of the three major types of AL neurons is both pre- and postsynaptic to the other two types, as previously indicated by functional studies. PN dendrites carry a large proportion of output synapses, with approximately one output per every three input synapses. Detailed reconstructions of PN dendrites showed that these synapses are distributed unevenly, with input and output sites partially segregated along a proximal-distal gradient and the thinnest branches carrying solely input synapses. Moreover, our data indicate synapse clustering, as we found evidence of dendritic tiling of PN dendrites. PN output synapses exhibited T-shaped presynaptic densities, mostly arranged as tetrads. In contrast, output synapses from putative OSNs showed elongated presynaptic densities in which the T-bar platform was supported by several pedestals and contacted as many as 20 postsynaptic profiles. We also discovered synaptic contacts between the putative OSNs. The average synaptic density in the glomerular neuropil was about two synapses/µm(3) . These results are discussed with regard to current models of olfactory glomerular microcircuits across species.
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Affiliation(s)
- Jürgen Rybak
- Department of Evolutionary NeuroethologyMax Planck Institute for Chemical Ecology07745JenaGermany
| | - Giovanni Talarico
- Department of Evolutionary NeuroethologyMax Planck Institute for Chemical Ecology07745JenaGermany
| | - Santiago Ruiz
- Clemente Estable Institute of Biological Research11600 MontevideoUruguay
| | - Christopher Arnold
- Department of Evolutionary NeuroethologyMax Planck Institute for Chemical Ecology07745JenaGermany
| | - Rafael Cantera
- Clemente Estable Institute of Biological Research11600 MontevideoUruguay
- Zoology DepartmentStockholm University10691StockholmSweden
| | - Bill S. Hansson
- Department of Evolutionary NeuroethologyMax Planck Institute for Chemical Ecology07745JenaGermany
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8
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Becker N, Kucharski R, Rössler W, Maleszka R. Age-dependent transcriptional and epigenomic responses to light exposure in the honey bee brain. FEBS Open Bio 2016; 6:622-39. [PMID: 27398303 PMCID: PMC4932443 DOI: 10.1002/2211-5463.12084] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2016] [Revised: 05/02/2016] [Accepted: 05/09/2016] [Indexed: 01/21/2023] Open
Abstract
Light is a powerful environmental stimulus of special importance in social honey bees that undergo a behavioral transition from in-hive to outdoor foraging duties. Our previous work has shown that light exposure induces structural neuronal plasticity in the mushroom bodies (MBs), a brain center implicated in processing inputs from sensory modalities. Here, we extended these analyses to the molecular level to unravel light-induced transcriptomic and epigenomic changes in the honey bee brain. We have compared gene expression in brain compartments of 1- and 7-day-old light-exposed honey bees with age-matched dark-kept individuals. We have found a number of differentially expressed genes (DEGs), both novel and conserved, including several genes with reported roles in neuronal plasticity. Most of the DEGs show age-related changes in the amplitude of light-induced expression and are likely to be both developmentally and environmentally regulated. Some of the DEGs are either known to be methylated or are implicated in epigenetic processes suggesting that responses to light exposure are at least partly regulated at the epigenome level. Consistent with this idea light alters the DNA methylation pattern of bgm, one of the DEGs affected by light exposure, and the expression of microRNA miR-932. This confirms the usefulness of our approach to identify candidate genes for neuronal plasticity and provides evidence for the role of epigenetic processes in driving the molecular responses to visual stimulation.
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Affiliation(s)
- Nils Becker
- Behavioral Physiology and Sociobiology Biozentrum University of Würzburg Germany
| | - Robert Kucharski
- Research School of Biology The Australian National University Acton Australia
| | - Wolfgang Rössler
- Behavioral Physiology and Sociobiology Biozentrum University of Würzburg Germany
| | - Ryszard Maleszka
- Research School of Biology The Australian National University Acton Australia
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9
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Kittel RJ, Heckmann M. Synaptic Vesicle Proteins and Active Zone Plasticity. Front Synaptic Neurosci 2016; 8:8. [PMID: 27148040 PMCID: PMC4834300 DOI: 10.3389/fnsyn.2016.00008] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2016] [Accepted: 03/31/2016] [Indexed: 11/13/2022] Open
Abstract
Neurotransmitter is released from synaptic vesicles at the highly specialized presynaptic active zone (AZ). The complex molecular architecture of AZs mediates the speed, precision and plasticity of synaptic transmission. Importantly, structural and functional properties of AZs vary significantly, even for a given connection. Thus, there appear to be distinct AZ states, which fundamentally influence neuronal communication by controlling the positioning and release of synaptic vesicles. Vice versa, recent evidence has revealed that synaptic vesicle components also modulate organizational states of the AZ. The protein-rich cytomatrix at the active zone (CAZ) provides a structural platform for molecular interactions guiding vesicle exocytosis. Studies in Drosophila have now demonstrated that the vesicle proteins Synaptotagmin-1 (Syt1) and Rab3 also regulate glutamate release by shaping differentiation of the CAZ ultrastructure. We review these unexpected findings and discuss mechanistic interpretations of the reciprocal relationship between synaptic vesicles and AZ states, which has heretofore received little attention.
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Affiliation(s)
- Robert J Kittel
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
| | - Manfred Heckmann
- Department of Neurophysiology, Institute of Physiology, Julius-Maximilians-University Würzburg Würzburg, Germany
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10
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Abstract
Neuronal response or adaption to a changing environment relies on the modulation of synaptic function. How this modulation is achieved remains controversial. In this issue of Neuron, Sugie et al. (2015) now report that active zones of Drosophila photoreceptors undergo activity-dependent changes in their molecular composition.
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Affiliation(s)
- Mathias A Böhme
- Freie Universität Berlin, Institute for Biology/Genetics, Takustrasse 6, 14195 Berlin, Germany; NeuroCure, Charité, Charitéplatz 1, 10117 Berlin, Germany
| | - Stephan J Sigrist
- Freie Universität Berlin, Institute for Biology/Genetics, Takustrasse 6, 14195 Berlin, Germany; NeuroCure, Charité, Charitéplatz 1, 10117 Berlin, Germany.
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11
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Sugie A, Hakeda-Suzuki S, Suzuki E, Silies M, Shimozono M, Möhl C, Suzuki T, Tavosanis G. Molecular Remodeling of the Presynaptic Active Zone of Drosophila Photoreceptors via Activity-Dependent Feedback. Neuron 2015; 86:711-25. [PMID: 25892303 DOI: 10.1016/j.neuron.2015.03.046] [Citation(s) in RCA: 60] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2014] [Revised: 02/10/2015] [Accepted: 03/18/2015] [Indexed: 11/27/2022]
Abstract
Neural activity contributes to the regulation of the properties of synapses in sensory systems, allowing for adjustment to a changing environment. Little is known about how synaptic molecular components are regulated to achieve activity-dependent plasticity at central synapses. Here, we found that after prolonged exposure to natural ambient light the presynaptic active zone in Drosophila photoreceptors undergoes reversible remodeling, including loss of Bruchpilot, DLiprin-α, and DRBP, but not of DSyd-1 or Cacophony. The level of depolarization of the postsynaptic neurons is critical for the light-induced changes in active zone composition in the photoreceptors, indicating the existence of a feedback signal. In search of this signal, we have identified a crucial role of microtubule meshwork organization downstream of the divergent canonical Wnt pathway, potentially via Kinesin-3 Imac. These data reveal that active zone composition can be regulated in vivo and identify the underlying molecular machinery.
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Affiliation(s)
- Atsushi Sugie
- Dendrite Differentiation, German Center for Neurodegenerative Diseases (DZNE), Bonn 53175, Germany
| | - Satoko Hakeda-Suzuki
- Core Division of Advanced Research, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology (Titech), Yokohama 226-8501, Japan
| | - Emiko Suzuki
- Gene Network Laboratory, National Institute of Genetics and Department of Genetics, SOKENDAI, Mishima 411-8540, Japan
| | - Marion Silies
- European Neuroscience Institute (ENI), 37077 Göttingen, Germany
| | - Mai Shimozono
- Core Division of Advanced Research, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology (Titech), Yokohama 226-8501, Japan
| | - Christoph Möhl
- Image and Data Analysis Facility, German Center for Neurodegenerative Diseases (DZNE), Bonn 53175, Germany
| | - Takashi Suzuki
- Core Division of Advanced Research, Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology (Titech), Yokohama 226-8501, Japan.
| | - Gaia Tavosanis
- Dendrite Differentiation, German Center for Neurodegenerative Diseases (DZNE), Bonn 53175, Germany.
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12
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Agi E, Langen M, Altschuler SJ, Wu LF, Zimmermann T, Hiesinger PR. The evolution and development of neural superposition. J Neurogenet 2014; 28:216-32. [PMID: 24912630 PMCID: PMC4245170 DOI: 10.3109/01677063.2014.922557] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Visual systems have a rich history as model systems for the discovery and understanding of basic principles underlying neuronal connectivity. The compound eyes of insects consist of up to thousands of small unit eyes that are connected by photoreceptor axons to set up a visual map in the brain. The photoreceptor axon terminals thereby represent neighboring points seen in the environment in neighboring synaptic units in the brain. Neural superposition is a special case of such a wiring principle, where photoreceptors from different unit eyes that receive the same input converge upon the same synaptic units in the brain. This wiring principle is remarkable, because each photoreceptor in a single unit eye receives different input and each individual axon, among thousands others in the brain, must be sorted together with those few axons that have the same input. Key aspects of neural superposition have been described as early as 1907. Since then neuroscientists, evolutionary and developmental biologists have been fascinated by how such a complicated wiring principle could evolve, how it is genetically encoded, and how it is developmentally realized. In this review article, we will discuss current ideas about the evolutionary origin and developmental program of neural superposition. Our goal is to identify in what way the special case of neural superposition can help us answer more general questions about the evolution and development of genetically “hard-wired” synaptic connectivity in the brain.
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Affiliation(s)
- Egemen Agi
- Green Center for Systems Biology, University of Texas Southwestern Medical Center , Dallas, TX , USA
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13
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Sztarker J, Rind FC. A look into the cockpit of the developing locust: looming detectors and predator avoidance. Dev Neurobiol 2014; 74:1078-95. [PMID: 24753464 DOI: 10.1002/dneu.22184] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2013] [Accepted: 04/16/2014] [Indexed: 11/12/2022]
Abstract
For many animals, the visual detection of looming stimuli is crucial at any stage of their lives. For example, human babies of only 6 days old display evasive responses to looming stimuli (Bower et al. [1971]: Percept Psychophys 9: 193-196). This means the neuronal pathways involved in looming detection should mature early in life. Locusts have been used extensively to examine the neural circuits and mechanisms involved in sensing looming stimuli and triggering visually evoked evasive actions, making them ideal subjects in which to investigate the development of looming sensitivity. Two lobula giant movement detectors (LGMD) neurons have been identified in the lobula region of the locust visual system: the LGMD1 neuron responds selectively to looming stimuli and provides information that contributes to evasive responses such as jumping and emergency glides. The LGMD2 responds to looming stimuli and shares many response properties with the LGMD1. Both neurons have only been described in the adult. In this study, we describe a practical method combining classical staining techniques and 3D neuronal reconstructions that can be used, even in small insects, to reveal detailed anatomy of individual neurons. We have used it to analyze the anatomy of the fan-shaped dendritic tree of the LGMD1 and the LGMD2 neurons in all stages of the post-embryonic development of Locusta migratoria. We also analyze changes seen during the ontogeny of escape behaviors triggered by looming stimuli, specially the hiding response.
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Affiliation(s)
- Julieta Sztarker
- Institute of Neuroscience, Newcastle University, Newcastle upon Tyne NE1 7RU, United Kingdom; Departamento de Fisiología, Biología Molecular y Celular, FCEN, Universidad de Buenos Aires, IFIBYNE-CONICET, Pabellón 2 Ciudad Universitaria, Intendente Güiraldes 2160, Buenos Aires, 1428, Argentina
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14
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Chen Y, Akin O, Nern A, Tsui CYK, Pecot MY, Zipursky SL. Cell-type-specific labeling of synapses in vivo through synaptic tagging with recombination. Neuron 2014; 81:280-93. [PMID: 24462095 PMCID: PMC4025979 DOI: 10.1016/j.neuron.2013.12.021] [Citation(s) in RCA: 120] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/27/2013] [Indexed: 11/19/2022]
Abstract
The study of synaptic specificity and plasticity in the CNS is limited by the inability to efficiently visualize synapses in identified neurons using light microscopy. Here, we describe synaptic tagging with recombination (STaR), a method for labeling endogenous presynaptic and postsynaptic proteins in a cell-type-specific fashion. We modified genomic loci encoding synaptic proteins within bacterial artificial chromosomes such that these proteins, expressed at endogenous levels and with normal spatiotemporal patterns, were labeled in an inducible fashion in specific neurons through targeted expression of site-specific recombinases. Within the Drosophila visual system, the number and distribution of synapses correlate with electron microscopy studies. Using two different recombination systems, presynaptic and postsynaptic specializations of synaptic pairs can be colabeled. STaR also allows synapses within the CNS to be studied in live animals noninvasively. In principle, STaR can be adapted to the mammalian nervous system.
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Affiliation(s)
- Yi Chen
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Orkun Akin
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Aljoscha Nern
- Janelia Farm Research Campus, Howard Hughes Medical Institute, Ashburn, VA 20147-2408, USA
| | - C Y Kimberly Tsui
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - Matthew Y Pecot
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA
| | - S Lawrence Zipursky
- Department of Biological Chemistry, Howard Hughes Medical Institute, David Geffen School of Medicine, University of California, Los Angeles, Los Angeles, CA 90095, USA.
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15
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Ruiz S, Ferreiro MJ, Menhert KI, Casanova G, Olivera A, Cantera R. Rhythmic changes in synapse numbers in Drosophila melanogaster motor terminals. PLoS One 2013; 8:e67161. [PMID: 23840613 PMCID: PMC3695982 DOI: 10.1371/journal.pone.0067161] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Accepted: 05/15/2013] [Indexed: 11/18/2022] Open
Abstract
Previous studies have shown that the morphology of the neuromuscular junction of the flight motor neuron MN5 in Drosophila melanogaster undergoes daily rhythmical changes, with smaller synaptic boutons during the night, when the fly is resting, than during the day, when the fly is active. With electron microscopy and laser confocal microscopy, we searched for a rhythmic change in synapse numbers in this neuron, both under light:darkness (LD) cycles and constant darkness (DD). We expected the number of synapses to increase during the morning, when the fly has an intense phase of locomotion activity under LD and DD. Surprisingly, only our DD data were consistent with this hypothesis. In LD, we found more synapses at midnight than at midday. We propose that under LD conditions, there is a daily rhythm of formation of new synapses in the dark phase, when the fly is resting, and disassembly over the light phase, when the fly is active. Several parameters appeared to be light dependent, since they were affected differently under LD or DD. The great majority of boutons containing synapses had only one and very few had either two or more, with a 70∶25∶5 ratio (one, two and three or more synapses) in LD and 75∶20∶5 in DD. Given the maintenance of this proportion even when both bouton and synapse numbers changed with time, we suggest that there is a homeostatic mechanism regulating synapse distribution among MN5 boutons.
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Affiliation(s)
- Santiago Ruiz
- Departamento de Biología del Neurodesarrollo, Instituto de Investigaciones Biológicas Clemente
- Estable, Montevideo, Uruguay
| | - Maria Jose Ferreiro
- Departamento de Biología del Neurodesarrollo, Instituto de Investigaciones Biológicas Clemente
- Estable, Montevideo, Uruguay
| | | | - Gabriela Casanova
- Unidad de Microscopía Electrónica de Transmisión, Facultad de Ciencias, UdelaR, Montevideo, Uruguay
| | - Alvaro Olivera
- Unidad de Microscopía Electrónica de Transmisión, Facultad de Ciencias, UdelaR, Montevideo, Uruguay
| | - Rafael Cantera
- Departamento de Biología del Neurodesarrollo, Instituto de Investigaciones Biológicas Clemente
- Estable, Montevideo, Uruguay
- Zoology Department, Stockholm University, Stockholm, Sweden
- * E-mail:
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16
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Butcher NJ, Friedrich AB, Lu Z, Tanimoto H, Meinertzhagen IA. Different classes of input and output neurons reveal new features in microglomeruli of the adult Drosophila mushroom body calyx. J Comp Neurol 2012; 520:2185-201. [DOI: 10.1002/cne.23037] [Citation(s) in RCA: 73] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
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17
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Borst A, Euler T. Seeing Things in Motion: Models, Circuits, and Mechanisms. Neuron 2011; 71:974-94. [PMID: 21943597 DOI: 10.1016/j.neuron.2011.08.031] [Citation(s) in RCA: 154] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2011] [Indexed: 12/31/2022]
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18
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Abstract
The synaptic active zone, the site where Ca(2+)-triggered fusion of synaptic vesicles takes place, is commonly associated with protein-rich, electron-dense cytomatrices. The molecular composition and functional role of active zones, especially in the context of vesicular exo- and endocytosis, are under intense investigation. Per se, Drosophila synapses, which display so-called T-bars as electron-dense specializations, should be a highly suitable model system, as they allow for a combination of efficient genetics with ultrastructural and electrophysiological analyses. However, it needed a biochemical approach of the Buchner laboratory to "molecularly" access the T-bar by identification of the CAST/ERC-family member Bruchpilot as the first T-bar-residing protein. Genetic elimination of Bruchpilot revealed that the protein is essential for T-bar formation, calcium channel clustering, and hence proper vesicle fusion and patterned synaptic plasticity. Recently, Bruchpilot was shown to directly shape the T-bar, likely by adopting an elongated conformation. Moreover, first mechanisms that control the availability of Bruchpilot for T-bar assembly were described. This review seeks to summarize the information on T-bar structure, as well as on functional aspects, formulating the hypothesis that T-bars are genuine "plasticity modules."
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Affiliation(s)
- Carolin Wichmann
- NeuroCure Cluster of Excellence, Charité Berlin, Berlin, Germany
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Circadian rhythms in the morphology of neurons in Drosophila. Cell Tissue Res 2011; 344:381-9. [DOI: 10.1007/s00441-011-1174-x] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2010] [Accepted: 04/13/2011] [Indexed: 12/13/2022]
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Sigrist SJ, Schmitz D. Structural and functional plasticity of the cytoplasmic active zone. Curr Opin Neurobiol 2010; 21:144-50. [PMID: 20832284 DOI: 10.1016/j.conb.2010.08.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2010] [Revised: 08/02/2010] [Accepted: 08/15/2010] [Indexed: 12/30/2022]
Abstract
The presynaptic active zone (AZ) membrane is the site where vesicle fusion mediates information transfer between connected neurons. Reaching into the cytoplasm, an electron-dense cytomatrix (CAZ) is found to decorate the AZ membranes. CAZ architectures are meant not only to regulate the synaptic vesicle exocycle/endocycle, but also to structurally stabilize the presynaptic site. The CAZ is composed of a set of large scaffold proteins, many of which are evolutionarily conserved. Recently, several signaling factors controlling the developmental assembly of CAZs were found by unbiased genetics in Drosophila and Caenorhabditis elegans. At the same time, post-translational modification of CAZ proteins was implicated in changing the strength of mammalian brain synapses. Studying how processes of structural and functional CAZ plasticity get integrated within circuit remodeling remains an important challenge.
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Affiliation(s)
- Stephan J Sigrist
- Genetics Institute of Biology, Freie Universität Berlin, Takustr. 6, 14195 Berlin, Germany.
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Barth M, Schultze M, Schuster CM, Strauss R. Circadian plasticity in photoreceptor cells controls visual coding efficiency in Drosophila melanogaster. PLoS One 2010; 5:e9217. [PMID: 20169158 PMCID: PMC2821403 DOI: 10.1371/journal.pone.0009217] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2009] [Accepted: 01/20/2010] [Indexed: 12/05/2022] Open
Abstract
In the fly Drosophila melanogaster, neuronal plasticity of synaptic terminals in the first optic neuropil, or lamina, depends on early visual experience within a critical period after eclosion [1]. The current study revealed two additional and parallel mechanisms involved in this type of synaptic terminal plasticity. First, an endogenous circadian rhythm causes daily oscillations in the volume of photoreceptor cell terminals. Second, daily visual experience precisely modulates the circadian time course and amplitude of the volume oscillations that the photoreceptor-cell terminals undergo. Both mechanisms are separable in their molecular basis. We suggest that the described neuronal plasticity in Drosophila ensures continuous optimal performance of the visual system over the course of a 24 h-day. Moreover, the sensory system of Drosophila cannot only account for predictable, but also for acute, environmental changes. The volumetric changes in the synaptic terminals of photoreceptor cells are accompanied by circadian and light-induced changes of presynaptic ribbons as well as extensions of epithelial glial cells into the photoreceptor terminals, suggesting that the architecture of the lamina is altered by both visual exposure and the circadian clock. Clock-mutant analysis and the rescue of PER protein rhythmicity exclusively in all R1-6 cells revealed that photoreceptor-cell plasticity is autonomous and sufficient to control visual behavior. The strength of a visually guided behavior, the optomotor turning response, co-varies with synaptic-terminal volume oscillations of photoreceptor cells when elicited at low light levels. Our results show that behaviorally relevant adaptive processing of visual information is performed, in part, at the level of visual input level.
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Affiliation(s)
- Martin Barth
- Friedrich-Miescher-Laboratory of the Max-Planck Society (MPG), Tuebingen, Germany
| | - Michael Schultze
- Friedrich-Miescher-Laboratory of the Max-Planck Society (MPG), Tuebingen, Germany
| | | | - Roland Strauss
- Friedrich-Miescher-Laboratory of the Max-Planck Society (MPG), Tuebingen, Germany
- * E-mail:
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22
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Edwards TN, Meinertzhagen IA. The functional organisation of glia in the adult brain of Drosophila and other insects. Prog Neurobiol 2010; 90:471-97. [PMID: 20109517 DOI: 10.1016/j.pneurobio.2010.01.001] [Citation(s) in RCA: 148] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/10/2009] [Revised: 01/14/2010] [Accepted: 01/14/2010] [Indexed: 12/24/2022]
Abstract
This review annotates and categorises the glia of adult Drosophila and other model insects and analyses the developmental origins of these in the Drosophila optic lobe. The functions of glia in the adult vary depending upon their sub-type and location in the brain. The task of annotating glia is essentially complete only for the glia of the fly's lamina, which comprise: two types of surface glia-the pseudocartridge and fenestrated glia; two types of cortex glia-the distal and proximal satellite glia; and two types of neuropile glia-the epithelial and marginal glia. We advocate that the term subretinal glia, as used to refer to both pseudocartridge and fenestrated glia, be abandoned. Other neuropiles contain similar glial subtypes, but other than the antennal lobes these have not been described in detail. Surface glia form the blood brain barrier, regulating the flow of substances into and out of the nervous system, both for the brain as a whole and the optic neuropiles in particular. Cortex glia provide a second level of barrier, wrapping axon fascicles and isolating neuronal cell bodies both from neighbouring brain regions and from their underlying neuropiles. Neuropile glia can be generated in the adult and a subtype, ensheathing glia, are responsible for cleaning up cellular debris during Wallerian degeneration. Both the neuropile ensheathing and astrocyte-like glia may be involved in clearing neurotransmitters from the extracellular space, thus modifying the levels of histamine, glutamate and possibly dopamine at the synapse to ultimately affect behaviour.
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Affiliation(s)
- Tara N Edwards
- Department of Biology, Life Sciences Centre, Dalhousie University, Halifax, NS, Canada, B3H 4J1.
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Groh C, Meinertzhagen IA. Brain plasticity in Diptera and Hymenoptera. Front Biosci (Schol Ed) 2010; 2:268-88. [PMID: 20036946 DOI: 10.2741/s63] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
To mediate different types of behaviour, nervous systems need to coordinate the proper operation of their neural circuits as well as short- and long-term alterations that occur within those circuits. The latter ultimately devolve upon specific changes in neuronal structures, membrane properties and synaptic connections that are all examples of plasticity. This reorganization of the adult nervous system is shaped by internal and external influences both during development and adult maturation. In adults, behavioural experience is a major driving force of neuronal plasticity studied particularly in sensory systems. The range of adaptation depends on features that are important to a particular species, and is therefore specific, so that learning is essential for foraging in honeybees, while regenerative capacities are important in hemimetabolous insects with long appendages. Experience is usually effective during a critical period in early adult life, when neural function becomes tuned to future conditions in an insect's life. Tuning occur at all levels, in synaptic circuits, neuropile volumes, and behaviour. There are many examples, and this review incorporates only a select few, mainly those from Diptera and Hymenoptera.
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Affiliation(s)
- Claudia Groh
- Life Sciences Centre, Dalhousie University, Halifax, NS, Canada B3H 4J1
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Fouquet W, Owald D, Wichmann C, Mertel S, Depner H, Dyba M, Hallermann S, Kittel RJ, Eimer S, Sigrist SJ. Maturation of active zone assembly by Drosophila Bruchpilot. ACTA ACUST UNITED AC 2009; 186:129-45. [PMID: 19596851 PMCID: PMC2712991 DOI: 10.1083/jcb.200812150] [Citation(s) in RCA: 301] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Synaptic vesicles fuse at active zone (AZ) membranes where Ca2+ channels are clustered and that are typically decorated by electron-dense projections. Recently, mutants of the Drosophilamelanogaster ERC/CAST family protein Bruchpilot (BRP) were shown to lack dense projections (T-bars) and to suffer from Ca2+ channel–clustering defects. In this study, we used high resolution light microscopy, electron microscopy, and intravital imaging to analyze the function of BRP in AZ assembly. Consistent with truncated BRP variants forming shortened T-bars, we identify BRP as a direct T-bar component at the AZ center with its N terminus closer to the AZ membrane than its C terminus. In contrast, Drosophila Liprin-α, another AZ-organizing protein, precedes BRP during the assembly of newly forming AZs by several hours and surrounds the AZ center in few discrete punctae. BRP seems responsible for effectively clustering Ca2+ channels beneath the T-bar density late in a protracted AZ formation process, potentially through a direct molecular interaction with intracellular Ca2+ channel domains.
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Affiliation(s)
- Wernher Fouquet
- Institute for Biology/Genetics, Free University Berlin, Berlin, Germany
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25
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Hiesinger PR, Zhai RG, Zhou Y, Koh TW, Mehta SQ, Schulze KL, Cao Y, Verstreken P, Clandinin TR, Fischbach KF, Meinertzhagen IA, Bellen HJ. Activity-independent prespecification of synaptic partners in the visual map of Drosophila. Curr Biol 2006; 16:1835-43. [PMID: 16979562 PMCID: PMC3351197 DOI: 10.1016/j.cub.2006.07.047] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/26/2006] [Revised: 07/12/2006] [Accepted: 07/13/2006] [Indexed: 01/27/2023]
Abstract
Specifying synaptic partners and regulating synaptic numbers are at least partly activity-dependent processes during visual map formation in all systems investigated to date . In Drosophila, six photoreceptors that view the same point in visual space have to be sorted into synaptic modules called cartridges in order to form a visuotopically correct map . Synapse numbers per photoreceptor terminal and cartridge are both precisely regulated . However, it is unknown whether an activity-dependent mechanism or a genetically encoded developmental program regulates synapse numbers. We performed a large-scale quantitative ultrastructural analysis of photoreceptor synapses in mutants affecting the generation of electrical potentials (norpA, trp;trpl), neurotransmitter release (hdc, syt), vesicle endocytosis (synj), the trafficking of specific guidance molecules during photoreceptor targeting (sec15), a specific guidance receptor required for visual map formation (Dlar), and 57 other novel synaptic mutants affecting 43 genes. Remarkably, in all these mutants, individual photoreceptors form the correct number of synapses per presynaptic terminal independently of cartridge composition. Hence, our data show that each photoreceptor forms a precise and constant number of afferent synapses independently of neuronal activity and partner accuracy. Our data suggest cell-autonomous control of synapse numbers as part of a developmental program of activity-independent steps that lead to a "hard-wired" visual map in the fly brain.
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Affiliation(s)
- P. Robin Hiesinger
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
- Correspondence: (P.R.H.); (H.J.B.)
| | - R. Grace Zhai
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
| | - Yi Zhou
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
| | - Tong-Wey Koh
- Program in Developmental Biology, Baylor College of Medicine Houston, Texas 77030
| | - Sunil Q. Mehta
- Program in Developmental Biology, Baylor College of Medicine Houston, Texas 77030
| | - Karen L. Schulze
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
| | - Yu Cao
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
| | - Patrik Verstreken
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
| | | | | | - Ian A. Meinertzhagen
- Neuroscience Institute and Department of Psychology, Life Sciences Centre, Dalhousie University, Halifax, Nova Scotia B3H 4J1, Canada
| | - Hugo J. Bellen
- Howard Hughes Medical Institute, Baylor College of Medicine Houston, Texas 77030
- Department of Molecular and Human Genetics, Baylor College of Medicine Houston, Texas 77030
- Program in Developmental Biology, Baylor College of Medicine Houston, Texas 77030
- Department of Neuroscience, Baylor College of Medicine Houston, Texas 77030
- Correspondence: (P.R.H.); (H.J.B.)
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26
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Takemura SY, Arikawa K. Ommatidial type-specific interphotoreceptor connections in the lamina of the swallowtail butterfly, Papilio xuthus. J Comp Neurol 2006; 494:663-72. [PMID: 16374804 DOI: 10.1002/cne.20830] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
The eye of the butterfly Papilio xuthus contains a random array of three types of ommatidia (types I-III), each bearing nine photoreceptors, R1-R9. Of the six spectral classes of photoreceptors identified, types I, II, and III ommatidia contain four, three, and two classes, respectively: the ommatidia are thus spectrally heterogeneous. The photoreceptors send their axons to the lamina where, together with some large monopolar cells (LMCs), the nine from a single ommatidium contribute to a module called a lamina cartridge. We recently reported that among different photoreceptor axon terminals visualized by confocal microscopy, the number and length of axon collaterals differ for different spectral receptors, suggesting that lamina circuits are specific for each ommatidial type. Here we studied the distribution of synapse-like structures in the cartridges, first characterizing a photoreceptor by measuring its spectral sensitivity and then injecting Lucifer yellow (LY). We subsequently histologically identified the type of ommatidium to which the injected photoreceptor belonged, cut serial ultrathin sections of the entire lamina, labeled these with anti-LY immunocytochemistry, and then localized synapse-like structures. We found numerous interphotoreceptor contacts both within and between cartridges, the combination of which was again specific for the ommatidial type. R3 and R4, which are green-sensitive photoreceptors in all ommatidia, have thick axons lacking collaterals. We found that these cells exclusively make contacts with LMCs and not with photoreceptors. We therefore presume that R3 and R4 construct a system for motion vision, whereas other randomly distributed spectral types provide inputs for color vision.
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Affiliation(s)
- Shin-Ya Takemura
- Graduate School of Integrated Science, Yokohama City University, Yokohama 236-0027, Japan
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27
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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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28
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Zhai RG, Bellen HJ. The Architecture of the Active Zone in the Presynaptic Nerve Terminal. Physiology (Bethesda) 2004; 19:262-70. [PMID: 15381754 DOI: 10.1152/physiol.00014.2004] [Citation(s) in RCA: 194] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Active zones are highly specialized sites for release of neurotransmitter from presynaptic nerve terminals. The architecture of the active zone is exquisitely designed to facilitate the regulated tethering, docking, and fusing of the synaptic vesicles with the plasma membrane. Here we present our view of the structural and molecular organization of active zones across species and propose that all active zones are organized according to a common principle in which the structural differences correlate with the kinetics of transmitter release.
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Affiliation(s)
- R Grace Zhai
- Howard Hughes Medical Institute and Department of Molecular and Human Genetics, Division of Neuroscience, Program In Developmental Biology, Baylor College of Medicine, Houston, Texas 77030, USA.
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29
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Abstract
Retrieval of synaptic vesicles from the membrane of neurons is crucial to maintain normal rates of neurotransmitter release. Photoreceptor terminals of the fly's eye release neurotransmitter in a tonic manner. They therefore rely heavily on vesicle regeneration. Null mutations in endophilin (endo) block clathrin-mediated endocytosis at the Drosophila neuromuscular junction, where previous analysis of hypomorphic mutations has suggested a function for Endophilin (Endo) before vesicle fission, during membrane bending. Here, at fly photoreceptor synapses, we show that Endo is localized to synaptic vesicles at sites of endocytosis that are glial invaginations called capitate projections, and that when the photoreceptor synapses lack Endo they are impaired in their ability to release neurotransmitter. Detailed ultrastructural analysis of endo null mutant photoreceptor synapses fails to reveal a defect at early stages of vesicle reformation but, instead, reveals an accumulation of clusters of electron-dense, apparently nonfunctional, late endocytotic vesicles. Using dynamin;endo double-mutant photoreceptors, we provide further evidence that ultimately the function of Endophilin is required late in endocytosis, allowing vesicles to progress through the synaptic vesicle cycle.
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30
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Pyza E, Meinertzhagen IA. The regulation of circadian rhythms in the fly's visual system: involvement of FMRFamide-like neuropeptides and their relationship to pigment dispersing factor in Musca domestica and Drosophila melanogaster. Neuropeptides 2003; 37:277-89. [PMID: 14607105 DOI: 10.1016/j.npep.2003.06.001] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The cross-sectional area of axon profiles in two classes of interneuron, L1 and L2, in the fly's lamina, exhibits a circadian rhythm of swelling and shrinking; axon caliber also changes after microinjecting putative lamina neurotransmitters. Among these, the neuropeptide pigment-dispersing factor, PDF, is proposed to transmit circadian information from the housefly's (Musca domestica) clock to L1 and L2, increasing axon caliber during the day. Testing whether other neurotransmitters may modulate this effect we have: (1) examined optic lobe cell immunoreactivity to FMRFamide peptides and its co-immunolocalization to PDF in M. domestica and Drosophila melanogaster, and to the product of the circadian clock gene PER in D. melanogaster; and (2) made microinjections of FMRFamide and related neuropeptides into the second neuropil, or medulla. In M. domestica, nine groups of optic lobe cells, several cells in the lateral and dorsal protocerebrum, and in the subesophageal ganglion, together contribute dense FMRFamide immunoreactive arborizations in almost all central brain and optic lobe neuropils. In D. melanogaster a similar pattern of labeling arises from fewer cells. Daytime microinjections show that another neuropeptide, similar to molluscan FMRFamide, shrinks M. domestica's L1 and L2 axons, thus opposing the action of PDF. We discuss evidence for a medulla site of action for a released FMRFamide-like peptide, either from: MeRF2 cells, acting directly on L1 and L2's medulla terminals; or MeRF1 cells, acting indirectly via medulla centrifugal cells C2 and C3.
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Affiliation(s)
- E Pyza
- Department of Cytology and Histology, Institute of Zoology, Jagiellonian University, Ingardena 6, 30-060, Kraków, Poland.
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31
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Pyza E. Dynamic structural changes of synaptic contacts in the visual system of insects. Microsc Res Tech 2002; 58:335-44. [PMID: 12214300 DOI: 10.1002/jemt.10141] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
The visual system of insects provides an excellent model to study processes of transduction and transmission of photic information, synaptogenesis, synaptic plasticity, and wiring between photoreceptors and their visual interneurons in the optic lobe. This review describes synaptic contacts between photoreceptors and other neurons in the visual system of insects, especially in the fly's first optic neuropile (the lamina), and summarizes changes observed in the synapses of visual cells that have been reported both in phylogeny and ontogeny, and also examples of synaptic plasticity in adult insects that have been evoked by intrinsic and extrinsic factors. Plasticity observed in synapses of the insect's visual system seems to exemplify not only synaptic contacts in insects but, given that similar examples of plasticity have been found in other animal groups, may also be a general phenomenon in the nervous system.
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Affiliation(s)
- Elzbieta Pyza
- Department of Cytology and Histology, Institute of Zoology, Jagiellonian University, Kraków, Poland.
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Leitinger G, Simmons PJ. The organization of synaptic vesicles at tonically transmitting connections of locust visual interneurons. JOURNAL OF NEUROBIOLOGY 2002; 50:93-105. [PMID: 11793357 DOI: 10.1002/neu.10018] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Large, second-order neurons of locust ocelli, or L-neurons, make some output connections that transmit small changes in membrane potential and can sustain transmission tonically. The synaptic connections are made from the axons of L-neurons in the lateral ocellar tracts, and are characterized by bar-shaped presynaptic densities and densely packed clouds of vesicles near to the cell membrane. A cloud of vesicles can extend much of the length of this synaptic zone, and there is no border between the vesicles that are associated with neighboring presynaptic densities. In some axons, presynaptic densities are associated with discrete small clusters of vesicles. Up to 6% of the volume of a length of axon in a synaptic zone can be occupied with a vesicle cloud, packed with 4.5 to 5.5 thousand vesicles per microm(3). Presynaptic densities vary in length, from less than 70 nm to 1.5 microm, with shorter presynaptic densities being most frequent. The distribution of vesicles around short presynaptic densities was indistinguishable from that around long presynaptic densities, and vesicles were distributed in a similar way right along the length of a presynaptic density. Within the cytoplasm, vesicles are homogeneously distributed within a cloud. We found no differences in the distribution of vesicles in clouds between locusts that had been dark-adapted and locusts that had been light-adapted before fixation.
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Affiliation(s)
- Gerd Leitinger
- Department of Neuroscience, University of Newcastle upon Tyne, The Medical School, Framlington Place, Newcastle Upon Tyne, NE2 4HH, UK
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Meinertzhagen IA, Piper ST, Sun XJ, Fröhlich A. Neurite morphogenesis of identified visual interneurons and its relationship to photoreceptor synaptogenesis in the flies, Musca domestica and Drosophila melanogaster. Eur J Neurosci 2000; 12:1342-56. [PMID: 10762363 DOI: 10.1046/j.1460-9568.2000.00033.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The first neuropile, or lamina, of the fly's optic lobe comprises a model set of identified neurons that are arrayed in cylindrical modules, called cartridges. The cartridge acquires adult form only in the second half of the fly's pupal life. All cells are by then correctly located within each of the lamina's cartridges (Drosophila, Musca), becoming invested by glial cells after 75% of pupal development (P + 75%). In adult cartridges, two lamina cells, L1 and L2, receive input from photoreceptor terminals R1-R6, at so-called tetrad synapses that form in the pupa when these cells' dendrites contact R1-R6. Single-section electron microscopy (EM, Drosophila) and serial-EM reconstructions of L1 and L2 (Musca) reveal relationships between the morphogenesis of L1/L2 dendrites and the formation of tetrads. Neurite outgrowth is initially (P + 55%) random and neurites are unbranched; many neurites invaginate surrounding terminals of R1-R6 but, later, embrace the outer surfaces of these. The maximum profusion of neurites at P + 74% coincides with peak numbers of nascent tetrads; neurites then branch vertically, in the lamina's depth. Later, neurites failing to reach R1-R6's outer surfaces regress. Down the length of their axons, L1 and L2's neurites initially form a random sequence, L1 partnering L1 as often as L2, etc., but beginning at P + 74%, L1 partners L2, and L2 partners L1, with progressive strictness. L1 has more neurites overall than L2. These observations are consistent with the following hypotheses: a neurite only survives if it contacts a presynaptic site; a synapse only survives if it progressively acquires the appropriate number and combination of postsynaptic neurites, culminating in a tetrad; an interaction exists between the neurites of L1 and L2, so that the growth of one respects the pattern of growth of the other.
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Affiliation(s)
- I A Meinertzhagen
- Life Sciences Centre, Dalhousie University, Halifax, Nova Scotia, Canada.
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35
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Pyza E, Meinertzhagen IA. Daily rhythmic changes of cell size and shape in the first optic neuropil in Drosophila melanogaster. JOURNAL OF NEUROBIOLOGY 1999; 40:77-88. [PMID: 10398073 DOI: 10.1002/(sici)1097-4695(199907)40:1<77::aid-neu7>3.0.co;2-0] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Daily rhythms of changes in axon size and shape are seen in two types of monopolar cell-L1 and L2-that are unique cells within each of the modules or cartridges of the first optic neuropil or lamina in the fly's optic lobe. In the fruit fly Drosophila, L1 and L2's axons swell at the beginning of both day and night, with larger size increases occurring at the beginning of night. Later, they shrink during the day and night, respectively. Simultaneously, they change shape from an inverted conical form during the day to a cylindrical one at night. This is because the axonal cross section of L1 increases during the night, especially at proximal depths of the lamina, closest to the brain, whereas the axon of L2 increases in size at distal lamina depths. The cross-sectional areas of the L1 cell and of an individual cartridge both change under constant darkness (DD), indicating the circadian origin of changes observed under day/night (LD) conditions. We sought to see whether such changes impart a net change to the entire lamina's volume or shape that is visible by light microscopy, but oscillations in the volume or the curvature of the whole lamina neuropil are found neither in LD nor in DD. These size changes are discussed in relation to previous findings in the housefly Musca, with respect to differences in L1 and L2 between the two species, and to differences in the time course of their circadian changes.
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Affiliation(s)
- E Pyza
- Zoological Museum, Institute of Zoology, Jagiellonian University, Ingardena 6, 30-060 Kraków, Poland
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36
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Abstract
The visual system of the fly's compound eye undergoes a number of cyclical day/night changes that have a circadian basis. Such responses are seen in the synaptic terminals of the photoreceptors and in their large monopolar-cell interneurons in the first optic neuropile, or lamina. These changes include, in the photoreceptor terminals, rhythms in the numbers of synapses and the vertical migration of screening pigment; and, in the monopolar cells L1 and L2, a rhythm in the transients of the electroretinogram and in the cyclical swelling of L1 and L2 lamina axons, as well as of the epithelial glia that surround these. Some of these changes are seen in both the housefly and the fruit fly, but the time-course of such changes differs between the two species. Many of the changes are influenced by the injection of various transmitter candidates, in a direction that can be reconciled with the possibility of normal endogenous release of two substances, 5HT from the neurites of 5HT-immunoreactive neurons, and pigment dispersing factor peptide from the neurites of PDH cells. Consistent with this interpretation, the immunoreactive varicosities of PDH cells exhibit size changes attributable to their cyclical release of peptide, or to its cyclical synthesis and/or transport from the PDH cell somata. Thus, neurotransmitter substances not only have rapid electrophysiological actions in the optic lobe, but also longer-lasting, presumably indirect, neuromodulatory actions, which are manifest as structural changes among the lamina's neurons and synapses. These actions involve an interplay between aminergic and peptidergic systems, but the exact role and especially the site of action of each has still to be elucidated.
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Affiliation(s)
- I A Meinertzhagen
- Neuroscience Institute, Dalhousie University, Halifax, Nova Scotia, Canada.
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37
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Meinertzhagen IA, Govind CK, Stewart BA, Carter JM, Atwood HL. Regulated spacing of synapses and presynaptic active zones at larval neuromuscular junctions in different genotypes of the flies Drosophila and Sarcophaga. J Comp Neurol 1998; 393:482-92. [PMID: 9550153 DOI: 10.1002/(sici)1096-9861(19980420)393:4<482::aid-cne7>3.0.co;2-x] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Synapses at larval neuromuscular junctions of the flies Drosophila melanogaster and Sarcophaga bullata are not distributed randomly. They have been studied in serial electron micrographs of two identified axons (axons 1 and 2) that innervate ventral longitudinal muscles 6 and 7 of the larval body wall. The following fly larvae were examined: axon 1--wild-type Sarcophaga and Drosophila and Drosophila mutants dunce(m14) and fasII(e76), a hypomorphic allele of the fasciclin II gene; and axon 2--drosophila wild-type, dunce(m14), and fasII(e76). These lines were selected to provide a wide range of nerve terminal phenotypes in which to study the distribution and spacing of synapses. Each terminal varicosity is applied closely to the underlying subsynaptic reticulum of the muscle fiber and has 15-40 synapses. Each synapse usually bears one or more active zones, characterized by dense bodies that are T-shaped in cross section; they are located at the presumed sites of transmitter release. The distribution of synapses was characterized from the center-to-center distance of each synapse to its nearest neighbor. The mean spacing between nearest-neighbor pairs ranged from 0.84 microm to 1.05 microm for axon 1, showing no significant difference regardless of genotype. The corresponding values for axon 2, 0.58 microm to 0.75 microm, were also statistically indistinguishable from one another in terminals of different genotype but differed significantly from the values for axon 1. Thus, the functional class of the axon provides a clear prediction of the spacing of its synapses, suggesting that spacing may be determined by the functional properties of transmission at the two types of terminals. Individual dense bodies were situated mostly at least 0.4 microm away from one another, suggesting that an interaction between neighboring active zones could prevent their final positions from being located more closely.
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Affiliation(s)
- I A Meinertzhagen
- Neuroscience Institute, Life Sciences Centre, Dalhousie University, Halifax, Nova Scotia, Canada.
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Shimohigashi M, Meinertzhagen IA. The shaking B gene in Drosophila regulates the number of gap junctions between photoreceptor terminals in the lamina. JOURNAL OF NEUROBIOLOGY 1998; 35:105-17. [PMID: 9552170 DOI: 10.1002/(sici)1097-4695(199804)35:1<105::aid-neu9>3.0.co;2-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The molecular structure of insect gap junctions differs from that in vertebrates, and in Drosophila is possibly encoded by the shaking B (= Passover) locus. shaking B2 is a null allele that acts in the nervous system. In the shakB2 mutant, one site of action are gap junctions between photoreceptor terminals in the cartridges of the lamina, beneath the compound eye, which we assayed from the number of close-apposition profiles in thin-section EM. The number of profiles in the Canton-S (C-S) wild type is about 0.5 per cartridge per section in distal and mid-lamina depths, and significantly less, about one quarter this value, closer to the brain, in the proximal lamina. In shakB2, there are fewer profiles, approximately one quarter the number of appositions in distal and mid-lamina depths as in C-S, and their number does not differ significantly from those at the proximal depth in either the mutant or wild type. Thus mutant action is associated with a reduced number of appositions at distal and mid-lamina depths. We propose that R1-R6 gap junctions are partitioned into at least two strata, proximal and distal, and that two populations of gap junctions exist, one extending throughout the lamina that does not require shakB, and a second at distal and mid-depth levels, which does. The number of gap junctions is reduced in mutant shakB2, and surviving appositions at distal and middle lamina depths possibly have wider clefts than in C-S. Gap junctions are reduced equally between all R1-R6 terminals, so the two different types of junction proposed, shakB2- and non-shakB2-dependent, can apparently express in a single receptor terminal.
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Affiliation(s)
- M Shimohigashi
- Neuroscience Institute, Life Sciences Centre, Dalhousie University, Halifax, Nova Scotia, Canada
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Pyza E, Meinertzhagen IA. Circadian rhythms in screening pigment and invaginating organelles in photoreceptor terminals of the housefly's first optic neuropile. ACTA ACUST UNITED AC 1997. [DOI: 10.1002/(sici)1097-4695(199705)32:5<517::aid-neu6>3.0.co;2-8] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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