Presynaptic PI3K activity triggers the formation of glutamate receptors at neuromuscular terminals of Drosophila

Abstract

SummarySynapse transmission depends on the precise structural and functional assembly between pre-and postsynaptic elements. This tightly regulated interaction has been thoroughly characterised in vivo in the Drosophila glutamatergic larval neuromuscular junction (NMJ) synapse, a suitable model to explore synapse formation, dynamics and plasticity. Previous findings have demonstrated that presynaptic upregulation of phosphoinositide 3-kinase (PI3K) increases synapse number, generating new functional contacts and eliciting changes in behaviour. Here, we show that genetically driven overexpression of PI3K in the presynaptic element also leads to a correlated increase in the levels of glutamate receptor (GluRII) subunits and the number of postsynaptic densities (PSDs), without altering GluRII formation and assembly dynamics. In addition to GluRIIs, presynaptic PI3K activity also modifies the expression of the postsynaptic protein Discs large (Dlg). Remarkably, PI3K specifically overexpressed in the final larval stages is sufficient for the formation of NMJ synapses. No differences in the number of synapses and PSDs were detected when PI3K was selectively expressed in the postsynaptic compartment. Taken together, these results demonstrate that PI3K-dependent synaptogenesis plays an instructive role in PSD formation and growth from the presynaptic side.

Anterograde Activin Signaling Regulates Postsynaptic Membrane Potential and GluRIIA/B Abundance at the Drosophila Neuromuscular Junction

“…The only other known targets of Smox are InR, Pi3K and Akt, all of which are Insulin signaling components and are reduced in the Drosophila prothoracic gland in the absence of Actvin/TGF-β signaling [27]. Once again the effect may be indirect, but this finding is interesting since Insulin signaling components have been shown to control synaptic clustering of GluRs [58], [59].…”

Interference of the complex between NCS-1 and Ric8a with phenothiazines regulates synaptic function and is an approach for fragile X syndrome

“…Synapses were visualized under confocal microscopy by the mAb nc82 (DSHB Hybridoma Bank), which identifies the Bruch pilot protein, a constituent of the presynaptic active zone (49), located at the edge of the characteristic T-bar specialization of fly synapses (50). Also, presynaptic nc82 spots correlate with postsynaptic GluRII clusters (49,51). Throughout the text, we refer to nc82-positive spots as mature synapses.…”

Rhythmic Changes in Synapse Numbers in Drosophila melanogaster Motor Terminals

“…When the BRP immunostaining at the neuromuscular junction was observed with the electron microscope, it appeared exclusively at synapses [12]. Double staining for nc82 and antibodies specific for glutamate receptors defined that practically each BRP-spot (presynaptic side of a single synapse) correlated with a single cluster of glutamate receptors (postsynaptic side of the same synapse) reinforcing the view that anti-BRP alone can be used to obtain a good estimation of synapse numbers [12], [15], [36], [38], [39], [43], [46]–[48], [50].…”

“…antibodies against Horseradish peroxidase to outline the neuronal membrane [34] and antibodies against synaptic proteins), to study the preparation with laser confocal microscopy and to count the immunofluorescent “spots” (each representing a synapse). A monoclonal antibody (nc82, [35]) specific for the synaptic protein Bruchpilot (BRP, an ELK/CAST homologue, [15]) has became widely used to stain Drosophila neuromuscular synapses because of its many advantages [12], [15], [21], [36]–[46]. On one hand, antibody nc82 gives very consistent results with beautifully distinct, strongly fluorescent “spots” against a practically negative background, making very easy to count the stained structures [12], [21], [37], [39]–[42], [47]–[49].…”