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Ishida IG, Sethi S, Mohren TL, Abbott L, Maimon G. Neuronal calcium spikes enable vector inversion in the Drosophila brain. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.24.568537. [PMID: 38077032 PMCID: PMC10705278 DOI: 10.1101/2023.11.24.568537] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/23/2023]
Abstract
A typical neuron signals to downstream cells when it is depolarized and firing sodium spikes. Some neurons, however, also fire calcium spikes when hyperpolarized. The function of such bidirectional signaling remains unclear in most circuits. Here we show how a neuron class that participates in vector computation in the fly central complex employs hyperpolarization-elicited calcium spikes to invert two-dimensional mathematical vectors. When cells switch from firing sodium to calcium spikes, this leads to a ~180° realignment between the vector encoded in the neuronal population and the fly's internal heading signal, thus inverting the vector. We show that the calcium spikes rely on the T-type calcium channel Ca-α1T, and argue, via analytical and experimental approaches, that these spikes enable vector computations in portions of angular space that would otherwise be inaccessible. These results reveal a seamless interaction between molecular, cellular and circuit properties for implementing vector math in the brain.
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Affiliation(s)
- Itzel G. Ishida
- Laboratory of Integrative Brain Function and Howard Hughes Medical Institute, The Rockefeller University, New York NY, USA
| | - Sachin Sethi
- Laboratory of Integrative Brain Function and Howard Hughes Medical Institute, The Rockefeller University, New York NY, USA
| | - Thomas L. Mohren
- Laboratory of Integrative Brain Function and Howard Hughes Medical Institute, The Rockefeller University, New York NY, USA
| | - L.F. Abbott
- Mortimer B. Zuckerman Mind Brain Behavior Institute, Department of Neuroscience, Columbia University, New York NY, USA
| | - Gaby Maimon
- Laboratory of Integrative Brain Function and Howard Hughes Medical Institute, The Rockefeller University, New York NY, USA
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2
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Mishra A, Serbe-Kamp E, Borst A, Haag J. Voltage to Calcium Transformation Enhances Direction Selectivity in Drosophila T4 Neurons. J Neurosci 2023; 43:2497-2514. [PMID: 36849417 PMCID: PMC10082464 DOI: 10.1523/jneurosci.2297-22.2023] [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: 12/16/2022] [Revised: 02/03/2023] [Accepted: 02/08/2023] [Indexed: 03/01/2023] Open
Abstract
An important step in neural information processing is the transformation of membrane voltage into calcium signals leading to transmitter release. However, the effect of voltage to calcium transformation on neural responses to different sensory stimuli is not well understood. Here, we use in vivo two-photon imaging of genetically encoded voltage and calcium indicators, ArcLight and GCaMP6f, respectively, to measure responses in direction-selective T4 neurons of female Drosophila Comparison between ArcLight and GCaMP6f signals reveals calcium signals to have a significantly higher direction selectivity compared with voltage signals. Using these recordings, we build a model which transforms T4 voltage responses into calcium responses. Using a cascade of thresholding, temporal filtering and a stationary nonlinearity, the model reproduces experimentally measured calcium responses across different visual stimuli. These findings provide a mechanistic underpinning of the voltage to calcium transformation and show how this processing step, in addition to synaptic mechanisms on the dendrites of T4 cells, enhances direction selectivity in the output signal of T4 neurons. Measuring the directional tuning of postsynaptic vertical system (VS)-cells with inputs from other cells blocked, we found that, indeed, it matches the one of the calcium signal in presynaptic T4 cells.SIGNIFICANCE STATEMENT The transformation of voltage to calcium influx is an important step in the signaling cascade within a nerve cell. While this process has been intensely studied in the context of transmitter release mechanism, its consequences for information transmission and neural computation are unclear. Here, we measured both membrane voltage and cytosolic calcium levels in direction-selective cells of Drosophila in response to a large set of visual stimuli. We found direction selectivity in the calcium signal to be significantly enhanced compared with membrane voltage through a nonlinear transformation of voltage to calcium. Our findings highlight the importance of an additional step in the signaling cascade for information processing within single nerve cells.
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Affiliation(s)
- Abhishek Mishra
- Max Planck Institute for Biological Intelligence, 82152 Martinsried, Germany
- Graduate School of Systemic Neurosciences, Ludwig Maximilian University of Munich, 82152 Martinsried, Germany
| | - Etienne Serbe-Kamp
- Max Planck Institute for Biological Intelligence, 82152 Martinsried, Germany
| | - Alexander Borst
- Max Planck Institute for Biological Intelligence, 82152 Martinsried, Germany
- Graduate School of Systemic Neurosciences, Ludwig Maximilian University of Munich, 82152 Martinsried, Germany
| | - Juergen Haag
- Max Planck Institute for Biological Intelligence, 82152 Martinsried, Germany
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3
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Seizure Phenotype and Underlying Cellular Defects in Drosophila Knock-In Models of DS (R1648C) and GEFS+ (R1648H) SCN1A Epilepsy. eNeuro 2021; 8:ENEURO.0002-21.2021. [PMID: 34475263 PMCID: PMC8454921 DOI: 10.1523/eneuro.0002-21.2021] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/01/2021] [Revised: 08/05/2021] [Accepted: 08/14/2021] [Indexed: 11/21/2022] Open
Abstract
Mutations in the voltage-gated sodium channel gene SCN1A are associated with human epilepsy disorders, but how most of these mutations alter channel properties and result in seizures is unknown. This study focuses on two different mutations occurring at one position within SCN1A. R1648C (R-C) is associated with the severe disorder Dravet syndrome, and R1648H (R-H), with the milder disorder GEFS+. To explore how these different mutations contribute to distinct seizure disorders, Drosophila lines with the R-C or R-H mutation, or R1648R (R-R) control substitution in the fly sodium channel gene para were generated by CRISPR-Cas9 gene editing. The R-C and R-H mutations are homozygous lethal. Animals heterozygous for R-C or R-H mutations displayed reduced life spans and spontaneous and temperature-induced seizures not observed in R-R controls. Electrophysiological recordings from adult GABAergic neurons in R-C and R-H mutants revealed the appearance of sustained neuronal depolarizations and altered firing frequency that were exacerbated at elevated temperature. The only significant change observed in underlying sodium currents in both R-C and R-H mutants was a hyperpolarized deactivation threshold at room and elevated temperature compared with R-R controls. Since this change is constitutive, it is likely to interact with heat-induced changes in other cellular properties to result in the heat-induced increase in sustained depolarizations and seizure activity. Further, the similarity of the behavioral and cellular phenotypes in the R-C and R-H fly lines, suggests that disease symptoms of different severity associated with these mutations in humans could be due in large part to differences in genetic background.
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Vesicular neurotransmitter transporters in Drosophila melanogaster. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2020; 1862:183308. [PMID: 32305263 DOI: 10.1016/j.bbamem.2020.183308] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/23/2020] [Revised: 04/09/2020] [Accepted: 04/10/2020] [Indexed: 12/11/2022]
Abstract
Drosophila melanogaster express vesicular transporters for the storage of neurotransmitters acetylcholine, biogenic amines, GABA, and glutamate. The large array of powerful molecular-genetic tools available in Drosophila enhances the use of this model organism for studying transporter function and regulation.
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Martelli C, Fiala A. Slow presynaptic mechanisms that mediate adaptation in the olfactory pathway of Drosophila. eLife 2019; 8:43735. [PMID: 31169499 PMCID: PMC6581506 DOI: 10.7554/elife.43735] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2018] [Accepted: 06/05/2019] [Indexed: 12/14/2022] Open
Abstract
The olfactory system encodes odor stimuli as combinatorial activity of populations of neurons whose response depends on stimulus history. How and on which timescales previous stimuli affect these combinatorial representations remains unclear. We use in vivo optical imaging in Drosophila to analyze sensory adaptation at the first synaptic step along the olfactory pathway. We show that calcium signals in the axon terminals of olfactory receptor neurons (ORNs) do not follow the same adaptive properties as the firing activity measured at the antenna. While ORNs calcium responses are sustained on long timescales, calcium signals in the postsynaptic projection neurons (PNs) adapt within tens of seconds. We propose that this slow component of the postsynaptic response is mediated by a slow presynaptic depression of vesicle release and enables the combinatorial population activity of PNs to adjust to the mean and variance of fluctuating odor stimuli.
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Affiliation(s)
- Carlotta Martelli
- Molecular Neurobiology of Behavior, Johann-Friedrich-Blumenbach-Institute for Zoology and Anthropology, University of Goettingen, Goettingen, Germany.,Department of Biology, Neurobiology, University of Konstanz, Konstanz, Germany
| | - André Fiala
- Molecular Neurobiology of Behavior, Johann-Friedrich-Blumenbach-Institute for Zoology and Anthropology, University of Goettingen, Goettingen, Germany
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6
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Lam A, Karekar P, Shah K, Hariharan G, Fleyshman M, Kaur H, Singh H, Gururaja Rao S. Drosophila Voltage-Gated Calcium Channel α1-Subunits Regulate Cardiac Function in the Aging Heart. Sci Rep 2018; 8:6910. [PMID: 29720608 PMCID: PMC5932002 DOI: 10.1038/s41598-018-25195-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2017] [Accepted: 04/17/2018] [Indexed: 12/20/2022] Open
Abstract
Ion channels maintain numerous physiological functions and regulate signaling pathways. They are the key targets for cellular reactive oxygen species (ROS), acting as signaling switches between ROS and ionic homeostasis. We have carried out a paraquat (PQ) screen in Drosophila to identify ion channels regulating the ROS handling and survival in Drosophila melanogaster. Our screen has revealed that α1-subunits (D-type, T-type, and cacophony) of voltage-gated calcium channels (VGCCs) handle PQ-mediated ROS stress differentially in a gender-based manner. Since ROS are also involved in determining the lifespan, we discovered that the absence of T-type and cacophony decreased the lifespan while the absence of D-type maintained a similar lifespan to that of the wild-type strain. VGCCs are also responsible for electrical signaling in cardiac cells. The cardiac function of each mutant was evaluated through optical coherence tomography (OCT), which revealed that α1-subunits of VGCCs are essential in maintaining cardiac rhythmicity and cardiac function in an age-dependent manner. Our results establish specific roles of α1-subunits of VGCCs in the functioning of the aging heart.
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Affiliation(s)
- Alexander Lam
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Priyanka Karekar
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Kajol Shah
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Girija Hariharan
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Michelle Fleyshman
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Harmehak Kaur
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA
| | - Harpreet Singh
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA. .,Division of Cardiology, Department of Medicine, Drexel University College of Medicine, Philadelphia, PA, 19102, USA.
| | - Shubha Gururaja Rao
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, PA, 19102, USA.
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7
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Limpitikul WB, Viswanathan MC, O'Rourke B, Yue DT, Cammarato A. Conservation of cardiac L-type Ca 2+ channels and their regulation in Drosophila: A novel genetically-pliable channelopathic model. J Mol Cell Cardiol 2018; 119:64-74. [PMID: 29684406 DOI: 10.1016/j.yjmcc.2018.04.010] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/10/2017] [Revised: 04/08/2018] [Accepted: 04/11/2018] [Indexed: 01/28/2023]
Abstract
Dysregulation of L-type Ca2+ channels (LTCCs) underlies numerous cardiac pathologies. Understanding their modulation with high fidelity relies on investigating LTCCs in their native environment with intact interacting proteins. Such studies benefit from genetic manipulation of endogenous channels in cardiomyocytes, which often proves cumbersome in mammalian models. Drosophila melanogaster, however, offers a potentially efficient alternative as it possesses a relatively simple heart, is genetically pliable, and expresses well-conserved genes. Fluorescence in situ hybridization confirmed an abundance of Ca-α1D and Ca-α1T mRNA in fly myocardium, which encode subunits that specify hetero-oligomeric channels homologous to mammalian LTCCs and T-type Ca2+ channels, respectively. Cardiac-specific knockdown of Ca-α1D via interfering RNA abolished cardiac contraction, suggesting Ca-α1D (i.e. A1D) represents the primary functioning Ca2+ channel in Drosophila hearts. Moreover, we successfully isolated viable single cardiomyocytes and recorded Ca2+ currents via patch clamping, a feat never before accomplished with the fly model. The profile of Ca2+ currents recorded in individual cells when Ca2+ channels were hypomorphic, absent, or under selective LTCC blockage by nifedipine, additionally confirmed the predominance of A1D current across all activation voltages. T-type current, activated at more negative voltages, was also detected. Lastly, A1D channels displayed Ca2+-dependent inactivation, a critical negative feedback mechanism of LTCCs, and the current through them was augmented by forskolin, an activator of the protein kinase A pathway. In sum, the Drosophila heart possesses a conserved compendium of Ca2+ channels, suggesting that the fly may serve as a robust and effective platform for studying cardiac channelopathies.
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Affiliation(s)
- Worawan B Limpitikul
- Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States
| | - Meera C Viswanathan
- Institute of CardioScience, Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States
| | - Brian O'Rourke
- Institute of CardioScience, Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States
| | - David T Yue
- Calcium Signals Laboratory, Department of Biomedical Engineering, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States
| | - Anthony Cammarato
- Institute of CardioScience, Division of Cardiology, Department of Medicine, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States; Department of Physiology, The Johns Hopkins University School of Medicine, Ross Research Building, 720 Rutland Avenue, Baltimore, MD 21205, United States.
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8
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Chakraborty S, Hasan G. Spontaneous Ca 2+ Influx in Drosophila Pupal Neurons Is Modulated by IP 3-Receptor Function and Influences Maturation of the Flight Circuit. Front Mol Neurosci 2017; 10:111. [PMID: 28473752 PMCID: PMC5398029 DOI: 10.3389/fnmol.2017.00111] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2017] [Accepted: 04/04/2017] [Indexed: 11/14/2022] Open
Abstract
Inositol 1,4,5-trisphosphate receptors (IP3R) are Ca2+ channels on the neuronal endoplasmic reticulum (ER) membrane. They are gated by IP3, produced upon external stimulation and activation of G protein-coupled receptors on the plasma membrane (PM). IP3-mediated Ca2+ release, and the resulting depletion of the ER store, triggers entry of extracellular Ca2+ by store-operated Ca2+ entry (SOCE). Mutations in IP3R attenuate SOCE. Compromised IP3R function and SOCE during pupal development of Drosophila leads to flight deficits and mimics suppression of neuronal activity during pupal or adult development. To understand the effect of compromised IP3R function on pupal neuronal calcium signaling, we examined the effects of mutations in the IP3R gene (itpr) on Ca2+ signals in cultured neurons derived from Drosophila pupae. We observed increased spontaneous Ca2+ influx across the PM of isolated pupal neurons with mutant IP3R and also a loss of SOCE. Both spontaneous Ca2+ influx and reduced SOCE were reversed by over-expression of dOrai and dSTIM, which encode the SOCE Ca2+ channel and the ER Ca2+-sensor that regulates it, respectively. Expression of voltage-gated Ca2+ channels (cac, Ca-α1D and Ca-αT) was significantly reduced in itpr mutant neurons. However, expression of trp mRNAs and transient receptor potential (TRP) protein were increased, suggesting that TRP channels might contribute to the increased spontaneous Ca2+ influx in neurons with mutant IP3R. Thus, IP3R/SOCE modulates spontaneous Ca2+ influx and expression of PM Ca2+ channels in Drosophila pupal neurons. Spontaneous Ca2+ influx compensates for the loss of SOCE in Drosophilaitpr mutant neurons.
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Affiliation(s)
- Sumita Chakraborty
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBangalore, India
| | - Gaiti Hasan
- National Centre for Biological Sciences, Tata Institute of Fundamental ResearchBangalore, India
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9
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Fisher YE, Yang HH, Isaacman-Beck J, Xie M, Gohl DM, Clandinin TR. FlpStop, a tool for conditional gene control in Drosophila. eLife 2017; 6. [PMID: 28211790 PMCID: PMC5342825 DOI: 10.7554/elife.22279] [Citation(s) in RCA: 39] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2016] [Accepted: 02/13/2017] [Indexed: 12/15/2022] Open
Abstract
Manipulating gene function cell type-specifically is a common experimental goal in Drosophila research and has been central to studies of neural development, circuit computation, and behavior. However, current cell type-specific gene disruption techniques in flies often reduce gene activity incompletely or rely on cell division. Here we describe FlpStop, a generalizable tool for conditional gene disruption and rescue in post-mitotic cells. In proof-of-principle experiments, we manipulated apterous, a regulator of wing development. Next, we produced conditional null alleles of Glutamic acid decarboxylase 1 (Gad1) and Resistant to dieldrin (Rdl), genes vital for GABAergic neurotransmission, as well as cacophony (cac) and paralytic (para), voltage-gated ion channels central to neuronal excitability. To demonstrate the utility of this approach, we manipulated cac in a specific visual interneuron type and discovered differential regulation of calcium signals across subcellular compartments. Thus, FlpStop will facilitate investigations into the interactions between genes, circuits, and computation. DOI:http://dx.doi.org/10.7554/eLife.22279.001
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Affiliation(s)
- Yvette E Fisher
- Department of Neurobiology, Stanford University, Stanford, United States
| | - Helen H Yang
- Department of Neurobiology, Stanford University, Stanford, United States
| | | | - Marjorie Xie
- Department of Neurobiology, Stanford University, Stanford, United States
| | - Daryl M Gohl
- Department of Neurobiology, Stanford University, Stanford, United States
| | - Thomas R Clandinin
- Department of Neurobiology, Stanford University, Stanford, United States
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10
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Honeybee locomotion is impaired by Am-Ca V3 low voltage-activated Ca 2+ channel antagonist. Sci Rep 2017; 7:41782. [PMID: 28145504 PMCID: PMC5286435 DOI: 10.1038/srep41782] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2016] [Accepted: 12/29/2016] [Indexed: 11/17/2022] Open
Abstract
Voltage‐gated Ca2+ channels are key transducers of cellular excitability and participate in several crucial physiological responses. In vertebrates, 10 Ca2+ channel genes, grouped in 3 families (CaV1, CaV2 and CaV3), have been described and characterized. Insects possess only one member of each family. These genes have been isolated in a limited number of species and very few have been characterized although, in addition to their crucial role, they may represent a collateral target for neurotoxic insecticides. We have isolated the 3 genes coding for the 3 Ca2+ channels expressed in Apis mellifera. This work provides the first detailed characterization of the honeybee T-type CaV3 Ca2+ channel and demonstrates the low toxicity of inhibiting this channel. Comparing Ca2+ currents recorded in bee neurons and myocytes with Ca2+ currents recorded in Xenopus oocytes expressing the honeybee CaV3 gene suggests native expression in bee muscle cells only. High‐voltage activated Ca2+ channels could be recorded in the somata of different cultured bee neurons. These functional data were confirmed by in situ hybridization, immunolocalization and in vivo analysis of the effects of a CaV3 inhibitor. The biophysical and pharmacological characterization and the tissue distribution of CaV3 suggest a role in honeybee muscle function.
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11
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Subcellular Imaging of Voltage and Calcium Signals Reveals Neural Processing In Vivo. Cell 2016; 166:245-57. [PMID: 27264607 DOI: 10.1016/j.cell.2016.05.031] [Citation(s) in RCA: 173] [Impact Index Per Article: 21.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 04/19/2016] [Accepted: 05/06/2016] [Indexed: 11/23/2022]
Abstract
A mechanistic understanding of neural computation requires determining how information is processed as it passes through neurons and across synapses. However, it has been challenging to measure membrane potential changes in axons and dendrites in vivo. We use in vivo, two-photon imaging of novel genetically encoded voltage indicators, as well as calcium imaging, to measure sensory stimulus-evoked signals in the Drosophila visual system with subcellular resolution. Across synapses, we find major transformations in the kinetics, amplitude, and sign of voltage responses to light. We also describe distinct relationships between voltage and calcium signals in different neuronal compartments, a substrate for local computation. Finally, we demonstrate that ON and OFF selectivity, a key feature of visual processing across species, emerges through the transformation of membrane potential into intracellular calcium concentration. By imaging voltage and calcium signals to map information flow with subcellular resolution, we illuminate where and how critical computations arise.
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12
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Guven-Ozkan T, Busto GU, Schutte SS, Cervantes-Sandoval I, O'Dowd DK, Davis RL. MiR-980 Is a Memory Suppressor MicroRNA that Regulates the Autism-Susceptibility Gene A2bp1. Cell Rep 2016; 14:1698-1709. [PMID: 26876166 DOI: 10.1016/j.celrep.2016.01.040] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2015] [Revised: 10/26/2015] [Accepted: 01/09/2016] [Indexed: 01/07/2023] Open
Abstract
MicroRNAs have been associated with many different biological functions, but little is known about their roles in conditioned behavior. We demonstrate that Drosophila miR-980 is a memory suppressor gene functioning in multiple regions of the adult brain. Memory acquisition and stability were both increased by miR-980 inhibition. Whole cell recordings and functional imaging experiments indicated that miR-980 regulates neuronal excitability. We identified the autism susceptibility gene, A2bp1, as an mRNA target for miR-980. A2bp1 levels varied inversely with miR-980 expression; memory performance was directly related to A2bp1 levels. In addition, A2bp1 knockdown reversed the memory gains produced by miR-980 inhibition, consistent with A2bp1 being a downstream target of miR-980 responsible for the memory phenotypes. Our results indicate that miR-980 represses A2bp1 expression to tune the excitable state of neurons, and the overall state of excitability translates to memory impairment or improvement.
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Affiliation(s)
- Tugba Guven-Ozkan
- Department of Neuroscience, The Scripps Research Institute Florida, Jupiter, FL 33458, USA
| | - Germain U Busto
- Department of Neuroscience, The Scripps Research Institute Florida, Jupiter, FL 33458, USA
| | - Soleil S Schutte
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697, USA; Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, CA 92697, USA
| | | | - Diane K O'Dowd
- Department of Developmental and Cell Biology, University of California, Irvine, Irvine, CA 92697, USA; Department of Anatomy and Neurobiology, University of California, Irvine, Irvine, CA 92697, USA
| | - Ronald L Davis
- Department of Neuroscience, The Scripps Research Institute Florida, Jupiter, FL 33458, USA.
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Neuron class-specific requirements for Fragile X Mental Retardation Protein in critical period development of calcium signaling in learning and memory circuitry. Neurobiol Dis 2016; 89:76-87. [PMID: 26851502 DOI: 10.1016/j.nbd.2016.02.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Revised: 01/27/2016] [Accepted: 02/02/2016] [Indexed: 01/22/2023] Open
Abstract
Neural circuit optimization occurs through sensory activity-dependent mechanisms that refine synaptic connectivity and information processing during early-use developmental critical periods. Fragile X Mental Retardation Protein (FMRP), the gene product lost in Fragile X syndrome (FXS), acts as an activity sensor during critical period development, both as an RNA-binding translation regulator and channel-binding excitability regulator. Here, we employ a Drosophila FXS disease model to assay calcium signaling dynamics with a targeted transgenic GCaMP reporter during critical period development of the mushroom body (MB) learning/memory circuit. We find FMRP regulates depolarization-induced calcium signaling in a neuron-specific manner within this circuit, suppressing activity-dependent calcium transients in excitatory cholinergic MB input projection neurons and enhancing calcium signals in inhibitory GABAergic MB output neurons. Both changes are restricted to the developmental critical period and rectified at maturity. Importantly, conditional genetic (dfmr1) rescue of null mutants during the critical period corrects calcium signaling defects in both neuron classes, indicating a temporally restricted FMRP requirement. Likewise, conditional dfmr1 knockdown (RNAi) during the critical period replicates constitutive null mutant defects in both neuron classes, confirming cell-autonomous requirements for FMRP in developmental regulation of calcium signaling dynamics. Optogenetic stimulation during the critical period enhances depolarization-induced calcium signaling in both neuron classes, but this developmental change is eliminated in dfmr1 null mutants, indicating the activity-dependent regulation requires FMRP. These results show FMRP shapes neuron class-specific calcium signaling in excitatory vs. inhibitory neurons in developing learning/memory circuitry, and that FMRP mediates activity-dependent regulation of calcium signaling specifically during the early-use critical period.
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14
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Ca-α1T, a fly T-type Ca2+ channel, negatively modulates sleep. Sci Rep 2015; 5:17893. [PMID: 26647714 PMCID: PMC4673464 DOI: 10.1038/srep17893] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2015] [Accepted: 11/06/2015] [Indexed: 01/14/2023] Open
Abstract
Mammalian T-type Ca2+ channels are encoded by three separate genes (Cav3.1, 3.2, 3.3). These channels are reported to be sleep stabilizers important in the generation of the delta rhythms of deep sleep, but controversy remains. The identification of precise physiological functions for the T-type channels has been hindered, at least in part, by the potential for compensation between the products of these three genes and a lack of specific pharmacological inhibitors. Invertebrates have only one T-type channel gene, but its functions are even less well-studied. We cloned Ca-α1T, the only Cav3 channel gene in Drosophila melanogaster, expressed it in Xenopus oocytes and HEK-293 cells, and confirmed it passes typical T-type currents. Voltage-clamp analysis revealed the biophysical properties of Ca-α1T show mixed similarity, sometimes falling closer to Cav3.1, sometimes to Cav3.2, and sometimes to Cav3.3. We found Ca-α1T is broadly expressed across the adult fly brain in a pattern vaguely reminiscent of mammalian T-type channels. In addition, flies lacking Ca-α1T show an abnormal increase in sleep duration most pronounced during subjective day under continuous dark conditions despite normal oscillations of the circadian clock. Thus, our study suggests invertebrate T-type Ca2+ channels promote wakefulness rather than stabilizing sleep.
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