Probing Motoneuron Function with Targeted Genetic Manipulation in Drosophila
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1
Arizona State University, School of Life Sciences, United States
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2
Johannes Gutenberg University of Mainz, Department of Neurobiology, Germany
Brain function relies on the coordinated activity of a large number of neurons assembled into neural circuitry. However, the individual network components, single neurons, are amazingly complex cells, and each neuron may carry out behaviorally relevant computations. Different types of neurons display different molecular identities, which manifest in specific morphologies and membrane properties. In addition, individual neuron properties may change as a function of experience and developmental plasticity. Our research addresses both the developmental mechanisms underlying single neuron morphology and membrane currents as well as the functions of morphology and ionic currents for behavior in mature animals.
We employ a combination of electrophysiological, imaging, genetic, and molecular biological tools to test how dendritic morphology and the ion channel bouquet of individually identified Drosophila motoneurons, the output elements of motor circuitry, are tuned toward their specific behavioral functions. We compare larval and adult Drosophila motoneurons because they participate in the generation of very different motor behaviors, slow larval crawling versus fast adult flight with stretch activated flight muscles.
To address the role of dendritic structure for motoneuron function we utilize genetic tools to specifically manipulate dendritic structure in selected motoneurons and test the resulting consequences on motoneuron firing patterns and behavior. We have unraveled a critical role of the transcription factor AP-1 in activity-dependent dendritic growth, which now allows for manipulation of dendritic structure in selected neurons to test for the resulting consequences for motoneuron function.
With regard to ion channels the strategy is to first identify the genes underlying each membrane current, manipulate these genes selectively in identified motoneurons without affecting the rest of the network to then test the resulting consequences for neuronal input-output operations and ultimately for behavior. The Drosophila genome contains three genes for voltage-gated calcium channels (VGCCs; Dmca1A, Dmca1D, DmαG), each of which resembles one vertebrate gene family (Cav1, Cav2, Cav3). Larval crawling and adult flight motoneurons express different VGCCs. Dual patch clamp recordings of control and knock-down motoneurons during restrained crawling indicate that larval motoneurons display somatodendritic L-type-like HVA (high voltage-activated) calcium currents mediated by Dmca1D channels, which serve to boost synaptic drive to motoneuron dendrites during crawling. By contrast adult flight motoneurons contain N-type-like HVA and t-type-like LVA (low voltage- activated) calcium currents encoded by Dcma1A and DmαG. Surprisingly, genetic and pharmacological data prove that Dmca1A encodes at least three calcium currents in one flight motoneuron, somatodendritic LVA and HVA calcium currents as well as presynaptic HVA calcium current. DmαG underlies activity-dependent regulation of Dmca1A based LVA and HVA currents during development. The Dmca1A gene contains multiple alternative splice and RNA editing sites. The role of alternative splicing is addressed by targeted expression of different splice variants in a Dmca1A null background. In situ voltage- and current-clamp recordings reveal distinct roles for splicing and RNA editing of Dmca1A for dendritically and presynaptically localized HVA and LVA calcium currents and their roles in motoneuron excitability. Extracellular in vivo recordings during flight reveal specific roles of somatodendritic LVA and HVA calcium currents for flight behavior.
Acknowledgements
Support by the NIH (5R01NS072128) to C Duch and by the NSF (IOS- 0949051) to C Duch and RB Levine is gratefully acknowledged.
Keywords:
calcium current,
Dendrite,
development,
Drosophila,
ion channel,
motoneuron,
motor behavior,
transcription
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Plenary Address (including special lectures) (Note, these individuals have already been invited)
Topic:
Cellular Properties
Citation:
Duch
C
(2012). Probing Motoneuron Function with Targeted Genetic Manipulation in Drosophila.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00057
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Received:
03 May 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Prof. Carsten Duch, Arizona State University, School of Life Sciences, Tempe, Arizona, 85287, United States, carsten.duch@asu.edu