Neto-α controls synapse organization and homeostasis at the Drosophila neuromuscular junction

Abstract

Glutamate receptor auxiliary proteins control receptor distribution and function, ultimately controlling synapse assembly, maturation and plasticity. At the Drosophila neuromuscular junction (NMJ), a synapse with both pre-and post-synaptic kainate-type glutamate receptors (KARs), we show that the auxiliary protein Neto evolved functionally distinct isoforms to modulate synapse development and homeostasis. Using genetics, cell biology and electrophysiology we demonstrate that Neto-α functions on both sides of the NMJ. In muscle, Neto-α limits the size of the postsynaptic receptors field. In motor neurons, Neto-α controls neurotransmitter release in a KAR-dependent manner. Furthermore, Neto-α is both required and sufficient for the presynaptic increase in neurotransmitter release in response to reduced postsynaptic sensitivity. This KARindependent function of Neto-α is involved in activity-induced cytomatrix remodeling. We propose that Drosophila ensured NMJ functionality by acquiring two Neto isoforms with differential expression patterns and activities.

Structure, Function, and Pharmacology of Glutamate Receptor Ion Channels

“…The C. elegans ortholog of Neto proteins, SOL-2, stabilizes synaptic localization and modified functional properties of the GLR-1 AMPA receptor (Wang et al, 2012). The Drosophila Neto proteins, Neto-a and Neto-b, are obligatory for synaptic accumulation of ionotropic glutamate receptors at neuromuscular junctions (Kim et al, 2012;Ramos et al, 2015) and, in the case of presynaptic Neto-a, for appropriate development of basal transmission and a form of homeostatic plasticity (Han et al, 2020).…”

Dynein acts to cluster glutamate receptors and traffic the PIP5 kinase, Skittles, to regulate postsynaptic membrane organization at the neuromuscular junction

“…To analyze the NMJs, we used the presynaptic membrane marker, horseradish peroxidase (HRP), and Discs Large (Dlg) which localizes postsynaptically. We quantified the number of synaptic boutons in third instar larvae, focusing on type 1b boutons at NMJ4 of abdominal segment A3 and at NMJ6/7 of abdominal segment A2, both well characterized NMJs that are commonly used for analysis of synaptic growth and function (Shen and Ganetzky, 2009;Xing et al, 2014;Han et al, 2020). To determine if there was a change in synaptic growth, we quantified the number of boutons per muscle area.…”