PP2A and GSK-3β Act Antagonistically to Regulate Active Zone Development

Abstract

The synapse is composed of an active zone apposed to a postsynaptic cluster of neurotransmitter receptors. Each Drosophila neuromuscular junction comprises hundreds of such individual release sites apposed to clusters of glutamate receptors. Here, we show that protein phosphatase 2A (PP2A) is required for the development of structurally normal active zones opposite glutamate receptors. When PP2A is inhibited presynaptically, many glutamate receptor clusters are unapposed to Bruchpilot (Brp), an active zone protein required for normal transmitter release. These unapposed receptors are not due to presynaptic retraction of synaptic boutons, since other presynaptic components are still apposed to the entire postsynaptic specialization. Instead, these data suggest that Brp localization is regulated at the level of individual release sites. Live imaging of glutamate receptors demonstrates that this disruption to active zone development is accompanied by abnormal postsynaptic development, with decreased formation of glutamate receptor clusters. Remarkably, inhibition of the serine-threonine kinase GSK-3␤ completely suppresses the active zone defect, as well as other synaptic morphology phenotypes associated with inhibition of PP2A. These data suggest that PP2A and GSK-3␤ function antagonistically to control active zone development, providing a potential mechanism for regulating synaptic efficacy at a single release site.

Postsynaptic actin regulates active zone spacing and glutamate receptor apposition at the Drosophila neuromuscular junction

“…Changes in AZ size, distribution and postsynaptic DGluRIII apposition were easily identified at this synapse. Similar strategies have been previously used to successfully study active zone formation and alignment, as well as synaptic development (Graf et al, 2009; Viquez et al, 2009; Wairkar et al, 2009; Valakh et al, 2012; Enneking et al, 2013). We mutagenized males of an isogenized Canton-S line (hereafter referred to as control) and backcrossed single male progeny to a GFP balancer strain to generate homozygous lines for screening.…”

A TRPV Channel in Drosophila Motor Neurons Regulates Presynaptic Resting Ca2+ Levels, Synapse Growth, and Synaptic Transmission

“…However, expression of the constitutively active calcineurin does not suppress the synaptic growth defects in the futsch hypomorphs, indicating that futsch functions downstream of calcineurin . Previous studies have also implicated the other Ser/Thr protein phosphatase, PP2A, in regulating microtubule stability and NMJ development by antagonizing Sgg (Viquez et al, 2009; Viquez et al, 2006). Because PP2A is Ca 2+ -independent, these observations suggest that distinct signals can lead to similar alterations in NMJ synapse morphology via Futsch.…”

Rab3 Dynamically Controls Protein Composition at Active Zones

“…Mutations in synaptojanin (Dickman et al, 2006), liprin (Kaufmann et al, 2002), neurexin (Li et al, 2007), and spectrin (Pielage et al, 2006) affect the size and spacing of the entire array of active zones. Mutations in the Unc-51 kinase and the protein phosphatase PP2A have differential affects on active zones, resulting in a subset of glutamate receptors unapposed to Bruchpilot puncta as in the rab3 rup mutant (Viquez et al, 2009; Wairkar et al, 2009). However, in the unc-51 and PP2A mutants the remaining Brp puncta are not enlarged and there is no increase in the proportion of active zones with multiple T-bars.…”