Mutations in Wnt2 Alter Presynaptic Motor Neuron Morphology and Presynaptic Protein Localization at the Drosophila Neuromuscular Junction

Alain Chédotal,Faith L W Liebl,Ying Yao,Cassandra Mckeown,Huey K Hing

doi:10.1371/journal.pone.0012778

Alain Chédotal, Faith L W Liebl + Show 3 more

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https://doi.org/10.1371/journal.pone.0012778

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Abstract

Wnt proteins are secreted proteins involved in a number of developmental processes including neural development and synaptogenesis. We sought to determine the role of the Drosophila Wnt7b ortholog, Wnt2, using the neuromuscular junction (NMJ). Mutations in wnt2 produce an increase in the number of presynaptic branches and a reduction in immunolabeling of the active zone proteins, Bruchpilot and synaptobrevin, at the NMJ. There was no change, however, in immunolabeling for the presynaptic proteins cysteine-string protein (CSP) and synaptotagmin, nor the postsynaptic proteins GluRIIA and DLG at the NMJ. Consistent with the presynaptic defects, wnt2 mutants exhibit approximately a 50% reduction in evoked excitatory junctional currents. Rescue, RNAi, and tissue-specific qRT-PCR experiments indicate that Wnt2 is expressed by the postsynaptic cell where it may serve as a retrograde signal that regulates presynaptic morphology and the localization of presynaptic proteins.

Highlights

Synapses are specialized structures that allow neurons to communicate with one another
active zones (AZs) are made up of a dense protein matrix that collectively participates in synaptic vesicle exocytosis
Important components of this matrix include Ca2+ channels [3], proteins involved in vesicle fusion including SNAP-25, Synaptobrevin, and Syntaxin [4,5], scaffolding proteins including Bassoon [6], Piccolo [7], CAST/ ELKS/Bruchpilot [8,9,10], cell adhesion molecules including cadherins [11] and neuroligins [12,13]

Summary

Introduction

Synapses are specialized structures that allow neurons to communicate with one another. The mechanisms by which AZs are properly localized and maintained are largely unknown but likely involve transsynaptic signaling to coordinate the development of the presynaptic neuron with the postsynaptic cell. The mouse Wnt protein increases axon branching, growth cone size, and synapsin I clustering in presynaptic sensory neurons [24]. Drosophila Wnt positively regulates neuromuscular junction (NMJ) growth and the synaptic localization of active zone proteins [29]. The Drosophila larval NMJ is a well-established model system for dissecting the molecular basis of synapse formation, growth, and remodeling. These synapses are similar to mammalian central synapses in that they are glutamatergic and remodel in response to activity [41,42]. We postulate that Wnt may serve as a postsynaptic signal that regulates the development of the presynaptic neuron

Results

Discussion

Findings

Materials and Methods