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Mutations in Wnt2 alter presynaptic motor neuron morphology and presynaptic protein localization at the Drosophila neuromuscular junction.

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.

SUBMITTER: Liebl FL

PROVIDER: S-EPMC2939895 | biostudies-literature | 2010 Sep

REPOSITORIES: biostudies-literature

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Mutations in Wnt2 alter presynaptic motor neuron morphology and presynaptic protein localization at the Drosophila neuromuscular junction.

Liebl Faith L W FL McKeown Cassandra C Yao Ying Y Hing Huey K HK

PloS one 20100915 9

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 protein ...[more]

PMID: 20856675

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Project description:Retrograde growth factors regulating synaptic plasticity at the neuromuscular junction (NMJ) in Drosophila have long been predicted but their discovery has been scarce. In vertebrates, such retrograde factors produced by the muscle include GDNF and the neurotrophins (NT: NGF, BDNF, NT3 and NT4). NT superfamily members have been identified throughout the invertebrates, but so far no functional in vivo analysis has been carried out at the NMJ in invertebrates. The NT family of proteins in Drosophila is formed of DNT1, DNT2 and Spätzle (Spz), with sequence, structural and functional conservation relative to mammalian NTs. Here, we investigate the functions of Drosophila NTs (DNTs) at the larval NMJ. All three DNTs are expressed in larval body wall muscles, targets for motor-neurons. Over-expression of DNTs in neurons, or the activated form of the Spz receptor, Toll(10b), in neurons only, rescued the semi-lethality of spz(2) and DNT1(41), DNT2(e03444) double mutants, indicating retrograde functions in neurons. In spz(2) mutants, DNT1(41), DNT2(e03444) double mutants, and upon over-expression of the DNTs, NMJ size and bouton number increased. Boutons were morphologically abnormal. Mutations in spz and DNT1,DNT2 resulted in decreased number of active zones per bouton and decreased active zone density per terminal. Alterations in DNT function induced ghost boutons and synaptic debris. Evoked junction potentials were normal in spz(2) mutants and DNT1(41), DNT2(e03444) double mutants, but frequency and amplitude of spontaneous events were reduced in spz(2) mutants suggesting defective neurotransmission. Our data indicate that DNTs are produced in muscle and are required in neurons for synaptogenesis. Most likely alterations in DNT function and synapse formation induce NMJ plasticity leading to homeostatic adjustments that increase terminal size restoring overall synaptic transmission. Data suggest that Spz functions with neuron-type specificity at the muscle 4 NMJ, and DNT1 and DNT2 function together at the muscles 6,7 NMJ.

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Mutations in Wnt2 alter presynaptic motor neuron morphology and presynaptic protein localization at the Drosophila neuromuscular junction.

Publications

Mutations in Wnt2 alter presynaptic motor neuron morphology and presynaptic protein localization at the Drosophila neuromuscular junction.

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