Postsynaptic glutamate receptors regulate local BMP signaling at theDrosophilaneuromuscular junction

Abstract

Effective communication between pre-and postsynaptic compartments is required for proper synapse development and function. At the Drosophila neuromuscular junction (NMJ), a retrograde BMP signal functions to promote synapse growth, stability and homeostasis and coordinates the growth of synaptic structures. Retrograde BMP signaling triggers accumulation of the pathway effector pMad in motoneuron nuclei and at synaptic termini. Nuclear pMad, in conjunction with transcription factors, modulates the expression of target genes and instructs synaptic growth; a role for synaptic pMad remains to be determined. Here, we report that pMad signals are selectively lost at NMJ synapses with reduced postsynaptic sensitivities. Despite this loss of synaptic pMad, nuclear pMad persisted in motoneuron nuclei, and expression of BMP target genes was unaffected, indicating a specific impairment in pMad production/maintenance at synaptic termini. During development, synaptic pMad accumulation followed the arrival and clustering of ionotropic glutamate receptors (iGluRs) at NMJ synapses. Synaptic pMad was lost at NMJ synapses developing at suboptimal levels of iGluRs and Neto, an auxiliary subunit required for functional iGluRs. Genetic manipulations of non-essential iGluR subunits revealed that synaptic pMad signals specifically correlated with the postsynaptic type-A glutamate receptors. Altering type-A receptor activities via protein kinase A (PKA) revealed that synaptic pMad depends on the activity and not the net levels of postsynaptic type-A receptors. Thus, synaptic pMad functions as a local sensor for NMJ synapse activity and has the potential to coordinate synaptic activity with a BMP retrograde signal required for synapse growth and homeostasis.

Prodomain Removal Enables Neto to Stabilize Glutamate Receptors at the Drosophila Neuromuscular Junction

“…1A, B and [23,33]). Interestingly, neto overexpression in the muscle also induced abnormal synapse development.…”

Adipocyte amino acid sensing controls adult germline stem cell number via the amino acid response pathway and independently of Target of Rapamycin signaling in Drosophila

“…Tissues were incubated overnight at 4°C in the following primary antibodies diluted in blocking solution: rabbit anti-GFP (Torrey Pines; 1:2500, TP401); mouse monoclonal anti-Hts (1B1) (DSHB; 1:10); mouse anti-α-spectrin (3A9) (DSHB; 1:50); mouse monoclonal anti-Lamin C (LC28.26) (DSHB; 1:100); rat monoclonal anti-E-cadherin (DCAD2) (DSHB; 1:100); and rabbit anti-pMad (Smad3) (Epitomics; 1:100, #1880). [This particular Smad3 antibody is widely used in Drosophila to detect pMad specifically (Hayashi et al, 2009;Ables and Drummond-Barbosa, 2010;Issigonis and Matunis, 2012;Matsuoka et al, 2013;Ma et al, 2014;Sulkowski et al, 2014).] Tissues were washed in PBT, and incubated for 2 h at room temperature in 1:200 Alexa Fluor 488-or 568-conjugated secondary antibodies (Molecular Probes).…”

Regulation of neuromuscular junction organization by Rab2 and its effector ICA69 in Drosophila

“…A tight correlation exists between the amount of synaptic glutamate receptors and the NMJ morphology. Downregulation of iGluRs in muscles has been shown to reduce the number of boutons (Sulkowski et al, 2014). Similarly, hypomorphic mutants of GluRIII or GluRIIA have reduced bouton numbers (Sulkowski Fig.…”

“…For instance, neto and filamin (cheerio) mutants show reduced iGluR levels and bouton numbers (Kim et al, 2012;Lee and Schwarz, 2016). One of the possible mechanisms by which glutamate receptors can alter the NMJ morphology is through regulation of synaptic phospho-MAD levels (Sulkowski et al, 2014). As the iGluRs (for instance, GluRIID) have also been shown to localize in central neuropil (Featherstone et al, 2005), it remains a possibility that the endogenous pattern of central electrical activity could also play crucial roles in sculpting the NMJ during development.…”