Activation kinetics of Glutamate receptor channels from wild-type Drosophila muscle

Heckmann, Manfred; Parzefall, Franz; Dudél, J.

doi:10.1007/s004240050230

Cited by 16 publications

(17 citation statements)

References 28 publications

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“…Both GluRIIA and GluRIIB subtypes have a similar, low sensitivity to glutamate, EC 50 3 and 6 mM, respectively, which agrees well with the EC 50 of 2 mM obtained using singlechannel analysis for native Drosophila NMJ iGluRs (19). Similarly, in larval NMJ preparations, only L-glutamate mimicked the action of the natural neurotransmitter among many agonists tested, including aspartic acid (2), which also produced no response in our experiments.…”

Section: Discussionsupporting

confidence: 87%

Functional reconstitution ofDrosophila melanogasterNMJ glutamate receptors

Han

Dharkar

Mayer

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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The Drosophila larval neuromuscular junction (NMJ), at which glutamate acts as the excitatory neurotransmitter, is a widely used model for genetic analysis of synapse function and development. Despite decades of study, the inability to reconstitute NMJ glutamate receptor function using heterologous expression systems has complicated the analysis of receptor function, such that it is difficult to resolve the molecular basis for compound phenotypes observed in mutant flies. We find that Drosophila Neto functions as an essential component required for the function of NMJ glutamate receptors, permitting analysis of glutamate receptor responses in Xenopus oocytes. In combination with a crystallographic analysis of the GluRIIB ligand binding domain, we use this system to characterize the subunit dependence of assembly, channel block, and ligand selectivity for Drosophila NMJ glutamate receptors.T he amino acid L-glutamate is the major neurotransmitter at vertebrate excitatory central synapses and at the neuromuscular junction (NMJ) of insects and crustaceans (1-3). Many vertebrate AMPA and kainate receptors, as well as GluRI from the worm Caenorhabditis elegans and AvGluR1 from the rotifer Adineta vaga, can form functional homomeric ion channels (1, 4, 5). In contrast, genetic studies suggest that assembly of Drosophila NMJ type A and type B glutamate receptors requires four subunits: either GluRIIA or GluRIIB, plus GluRIIC, GluRIID, and GluRIIE (6-9); both subtypes desensitize rapidly, with time constants of 18.8 and 2.0 ms, respectively (6). In flies, lack of GluRIIA and GluRIIB or any other single subunit induces embryonic paralysis. Furthermore, in the absence of GluRIIA and GluRIIB, or any other subunit, none of the remaining iGluR subunits cluster at nascent synapses, suggesting that recruitment and stabilization of iGluRs at synaptic sites requires heterotetramers. Despite a decade of work, the molecular basis for this unique profile has remained obscure. In part, this is because the reconstitution of functional glutamate receptors (iGluRs) in heterologous systems, which has been a powerful tool for analysis of receptor function in other species, has not been achieved for the Drosophila NMJ (10).We recently demonstrated that the synaptic distribution of Drosophila NMJ iGluRs requires Neto (Neuropillin and Tolloidlike), a protein essential for NMJ function (11). Neto belongs to a family of highly conserved auxiliary proteins that modulate the function of vertebrate kainate receptors (12) and C. elegans AMPA receptors (13,14). In these species Neto plays a minor role in delivery and synaptic targeting, and instead modulates receptor gating properties. In contrast, in flies Neto is absolutely required for clustering of iGluRs at the NMJ and lack of Neto induces embryonic paralysis (11). This finding may reflect a role for Neto in receptor assembly, surface expression, synaptic trafficking and stabilization, or modulation of iGluR gating. To distinguish among these possibilities, a recombinant expression system for...

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Section: Discussionsupporting

confidence: 87%

Functional reconstitution ofDrosophila melanogasterNMJ glutamate receptors

Han

Dharkar

Mayer

et al. 2015

Proc. Natl. Acad. Sci. U.S.A.

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“…Our data suggest that constitutive desensitization is, on a longer time scale (hours), also associated with removal of receptors from the synapse. The EC 50 for activation of Drosophila larval muscle glutamate receptors is ϳ2 mM (Heckmann et al, 1996), and significant numbers of receptors can be desensitized at considerably lower concentrations (Heckmann and Dudel, 1997). Because 2 mM is near the concentration of glutamate bathing NMJ receptors in vivo (McDonald, 1975;Echalier, 1997;Pierce et al, 1999) (our unpublished results), we must conclude that one-half or more of Drosophila larval muscle glutamate receptors are constitutively desensitized, and therefore delocalized, in vivo.…”

Section: Discussionmentioning

confidence: 64%

Nonvesicular Release of Glutamate by Glial xCT Transporters Suppresses Glutamate Receptor ClusteringIn Vivo

Augustin¹,

Grosjean²,

Chen³

et al. 2007

J. Neurosci.

118

148

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We hypothesized that cystine/glutamate transporters (xCTs) might be critical regulators of ambient extracellular glutamate levels in the nervous system and that misregulation of this glutamate pool might have important neurophysiological and/or behavioral consequences. To test this idea, we identified and functionally characterized a novel Drosophila xCT gene, which we subsequently named "genderblind" ( gb). Genderblind is expressed in a previously overlooked subset of peripheral and central glia.

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“…Reminiscent to obvious expression of its mammalian homolog in border areas of the brain, Gb is expressed in surface glia of the CNS and within a particular glia cell (now termed Gb cell) associated with NMJs. Compared to ambient glutamate concentrations in the mammalian brain, which are normally in a low micromolar range (Featherstone and Shippy 2008), glutamate concentrations in the larval hemolymph are in a millimolar range, yet close to the level required for half-maximal activation of junctional receptors (Heckmann et al 1996). Loss of Gb causes an~50% reduction in hemolymph glutamate concentration.…”

Section: Control Of Synaptic Glurs By Ambient Glutamatementioning

confidence: 99%

Glutamate Receptors in Synaptic Assembly and Plasticity: Case Studies on Fly NMJs

Thomas

Sigrist

2012

Synaptic Plasticity

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The molecular and cellular mechanisms that control the composition and functionality of ionotropic glutamate receptors may be considered as most important "set screws" for adjusting excitatory transmission in the course of developmental and experience-dependent changes within neural networks. The Drosophila larval neuromuscular junction has emerged as one important invertebrate model system to study the formation, maintenance, and plasticity-related remodeling of glutamatergic synapses in vivo. By exploiting the unique genetic accessibility of this organism combined with diverse tools for manipulation and analysis including electrophysiology and state of the art imaging, considerable progress has been made to characterize the role of glutamate receptors during the orchestration of junctional development, synaptic activity, and synaptogenesis. Following an introduction to basic features of this model system, we will mainly focus on conceptually important findings such as the selective impact of glutamate receptor subtypes on the formation of new synapses, the coordination of presynaptic maturation and receptor subtype composition, the role of nonvesicularly released glutamate on the synaptic localization of receptors, or the homeostatic feedback of receptor functionality on presynaptic transmitter release.

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Activation kinetics of Glutamate receptor channels from wild-type Drosophila muscle

Cited by 16 publications

References 28 publications

Functional reconstitution ofDrosophila melanogasterNMJ glutamate receptors

Functional reconstitution ofDrosophila melanogasterNMJ glutamate receptors

Nonvesicular Release of Glutamate by Glial xCT Transporters Suppresses Glutamate Receptor ClusteringIn Vivo

Glutamate Receptors in Synaptic Assembly and Plasticity: Case Studies on Fly NMJs

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