Presynaptic spinophilin tunes neurexin signalling to control active zone architecture and function

Abstract

Assembly and maturation of synapses at the Drosophila neuromuscular junction (NMJ) depend on trans-synaptic neurexin/neuroligin signalling, which is promoted by the scaffolding protein Syd-1 binding to neurexin. Here we report that the scaffold protein spinophilin binds to the C-terminal portion of neurexin and is needed to limit neurexin/neuroligin signalling by acting antagonistic to Syd-1. Loss of presynaptic spinophilin results in the formation of excess, but atypically small active zones. Neuroligin-1/neurexin-1/Syd-1 levels are increased at spinophilin mutant NMJs, and removal of single copies of the neurexin-1, Syd-1 or neuroligin-1 genes suppresses the spinophilin-active zone phenotype. Evoked transmission is strongly reduced at spinophilin terminals, owing to a severely reduced release probability at individual active zones. We conclude that presynaptic spinophilin fine-tunes neurexin/neuroligin signalling to control active zone number and functionality, thereby optimizing them for action potential-induced exocytosis.

Input-Specific Plasticity and Homeostasis at the Drosophila Larval Neuromuscular Junction

“…These are consistent with spontaneous quantal “miniature” events detected at the dissected larva in macropatch recordings (Karunanithi et al, 2002; Nguyen and Stewart, 2016) or imaging (Cho et al, 2015; Melom et al, 2013; Muhammad et al, 2015; Peled and Isacoff, 2011; Peled et al, 2014) as well as imaging in cultured neurons (Reese and Kavalali, 2015, 2016). These spontaneous events had larger amplitudes at Is synapses (Figure S2C–H), but were more frequent at Ib synapses (Figure 2L, S2C, F).…”

“…Quantal resolution measurement of excitatory transmission through Ca 2+ -permeant glutamate receptors (GluRs) has been achieved by imaging chemical or genetically-encoded Ca 2+ indicators (GECIs) in the postsynaptic cell (Cho et al, 2015; Guerrero et al, 2005; Lin and Schnitzer, 2016; Melom et al, 2013; Muhammad et al, 2015; Peled and Isacoff, 2011; Peled et al, 2014; Reese and Kavalali, 2015, 2016; Siegel and Lohmann, 2013). We generated a vastly improved postsynaptically targeted GECI based on GCaMP6f.…”

Presynaptic DLG regulates synaptic function through the localization of voltage-activated Ca2+ Channels

“…Surprisingly rim mutants, display low probability of release and altered responses to different calcium concentrations39. Recently it was shown that spinophilin mutants display a phenotype with bigger quantal size and GLUR fields size with a higher proportion of GLURIIA subtype of receptors as well as decreased EJCs and decreased pair pulse facilitation40. This is a phenotype very similar to the one described here for dlg mutants.…”

Regulation of synaptic release‐site Ca2+ channel coupling as a mechanism to control release probability and short‐term plasticity

“…An important function of spontaneous activity in early phases of synapse development is furthermore consistent with young axons of the rat hippocampal neurons preferentially undergoing spontaneous forms of vesicle cycling [144]. Recently, spontaneous and AP-evoked release events have been mapped with single synapse/AZ resolution [145][146][147][148]. This led to the conclusion that a subset of AZs at the Drosophila NMJ and at hippocampal synapses may be exclusively capable of spontaneous transmission [146,148,149].…”