Differential Localization of Glutamate Receptor Subunits at theDrosophilaNeuromuscular Junction

Abstract

The subunit composition of postsynaptic neurotransmitter receptors is a key determinant of synaptic physiology. Two glutamate receptor subunits, Drosophila glutamate receptor IIA (DGluRIIA) and DGluRIIB, are expressed at the Drosophila neuromuscular junction and are redundant for viability, yet differ in their physiological properties. We now identify a third glutamate receptor subunit at the Drosophila neuromuscular junction, DGluRIII, which is essential for viability. DGluRIII is required for the synaptic localization of DGluRIIA and DGluRIIB and for synaptic transmission. Either DGluRIIA or DGluRIIB, but not both, is required for the synaptic localization of DGluRIII. DGluRIIA and DGluRIIB compete with each other for access to DGluRIII and subsequent localization to the synapse. These results are consistent with a model of a multimeric receptor in which DGluRIII is an essential component. At single postsynaptic cells that receive innervation from multiple motoneurons, DGluRIII is abundant at all synapses. However, DGluRIIA and DGluRIIB are differentially localized at the postsynaptic density opposite distinct motoneurons. Hence, innervating motoneurons may regulate the subunit composition of their receptor fields within a shared postsynaptic cell. The capacity of presynaptic inputs to shape the subunit composition of postsynaptic receptors could be an important mechanism for synapse-specific regulation of synaptic function and plasticity.

The atypical cadherin flamingo regulates synaptogenesis and helps prevent axonal and synaptic degeneration in Drosophila

“…These varicosities were found randomly at a low rate (â3-5 per larva) throughout all segments; there was no particular preference for one segment. These âen passantâ varicosities also had presynaptic active zones (marked by the nc82 antibody, Wagh et al, 2005) and postsynaptic receptors (Marrus et al, 2004) and functioned normally in response to nerve stimulation (Fig. 5).…”

“…Following one hour incubation with a blocker solution (2-5% bovine serum albumin, 0.2% Tween-20 in PBS, PBT), the preparation was stained overnight at 4 ÂC using primary antisera, followed by one hour washes with PBT and 1-2 hours incubation with secondary antibodies at room temperature, and visualized using a Nikon fluorescence microscope. The following primary antibodies were used: rat anti-Syb (1:300, Wu et al, 1999), mAb anti-CSP (ab49, 1:20, Zinsmaier et al, 1994), rabbit anti-Syt (1:300, Mackler et al, 2002), mAb anti-Futsch (22C10, 1:100, Developmental Studies Hybridoma Bank), mAb anti-Hiw (6H4, 1:3, Wan et al, 2000), rabbit anti-DAP 160 (1:300, Roos and Kelly, 1999), mAb nc82 (1:20; Wagh et al, 2005), a polyclonal antibody to clathrin heavy chain (1:50) and to LAP (1:200, Zhang et al, 1998), a polyclonal antibody to glutamate receptor III (Marrus et al, 2004), a polyclonal antibody to the Drosophila vesicular glutamate transporter (VGluT, 1:500, Daniels et al, 2004), and a polyclonal antibody to HRP (Jan and Jan, 1982). Fluorescence-conjugated secondary antibodies were used 1:100 (Jackson Immunology Labs).…”

DrosophilaFragile X Mental Retardation Protein and Metabotropic Glutamate Receptor A Convergently Regulate the Synaptic Ratio of Ionotropic Glutamate Receptor Subclasses

“…This glutamatergic NMJ contains five AMPA-like GluR subunits, GluRIIA-GluRIIE. Three subunits (GluRIIC, GluRIID, and GluRIIE) are essential for all GluRs, whereas the other two subunits define two GluR classes: A-class (GluRIIA) and B-class (GluRIIB), which are differentially regulated, subsynaptically localized, and possess distinct functional properties, including differential conductance and opening kinetics (Schuster et al, 1991;Petersen et al, 1997;DiAntonio et al, 1999;Sigrist et al, 2002;Marrus et al, 2004;Featherstone et al, 2005;.…”

The ubiquitin–proteasome system postsynaptically regulates glutamatergic synaptic function

“…If B-class receptor desensitization is regulated through a calcium-dependent mechanism, this could explain the increased EJC amplitudes in lower calcium with no amplitude changes in higher calcium. Another possibility may reflect the fact that A-class and B-class receptors localize to separate postsynaptic domains (Marrus et al, 2004), with B-class domains potentially more active at lower calcium concentrations. Further characterization of the biophysical properties and synaptic localization of A-class and B-class receptors will be necessary to test these possibilities.…”

“…Postsynaptically, five GluR subunits (GluRIIA-E) share homology to mammalian AMPA/kainate ionotropic GluRs in mammals (Petersen et al, 1997;Marrus et al, 2004). Recent evidence has demonstrated the presence of two spatially and functionally distinct GluR classes, composed of common GluRIII (IIC), IID, and IIE subunits and either GluRIIA (Aclass) or GluRIIB (B-class) (Marrus et al, 2004;Qin et al, 2005;Featherstone et al, 2005). These two GluR classes are known to be regulated by separable mechanisms , but possible differential regulation by the UPS has not been investigated.…”