A divergent canonical WNT-signaling pathway regulates microtubule dynamics: Dishevelled signals locally to stabilize microtubules

Dishevelled (DVL) is associated with axonal microtubules and regulates microtubule stability through the inhibition of the serine/threonine kinase, glycogen synthase kinase 3β (GSK-3β). In the canonical WNT pathway, the negative regulator Axin forms a complex with β-catenin and GSK-3β, resulting in β-catenin degradation. Inhibition of GSK-3β by DVL increases β-catenin stability and TCF transcriptional activation. Here, we show that Axin associates with microtubules and unexpectedly stabilizes microtubules through DVL. In turn, DVL stabilizes microtubules by inhibiting GSK-3β through a transcription- and β-catenin–independent pathway. More importantly, axonal microtubules are stabilized after DVL localizes to axons. Increased microtubule stability is correlated with a decrease in GSK-3β–mediated phosphorylation of MAP-1B. We propose a model in which Axin, through DVL, stabilizes microtubules by inhibiting a pool of GSK-3β, resulting in local changes in the phosphorylation of cellular targets. Our data indicate a bifurcation in the so-called canonical WNT-signaling pathway to regulate microtubule stability

Signaling across the synapse: a role for Wnt and Dishevelled in presynaptic assembly and neurotransmitter release

Proper dialogue between presynaptic neurons and their targets is essential for correct synaptic assembly and function. At central synapses, Wnt proteins function as retrograde signals to regulate axon remodeling and the accumulation of presynaptic proteins. Loss of Wnt7a function leads to defects in the localization of presynaptic markers and in the morphology of the presynaptic axons. We show that loss of function of Dishevelled-1 (Dvl1) mimics and enhances the Wnt7a phenotype in the cerebellum. Although active zones appear normal, electrophysiological recordings in cerebellar slices from Wnt7a/Dvl1 double mutant mice reveal a defect in neurotransmitter release at mossy fiber–granule cell synapses. Deficiency in Dvl1 decreases, whereas exposure to Wnt increases, synaptic vesicle recycling in mossy fibers. Dvl increases the number of Bassoon clusters, and like other components of the Wnt pathway, it localizes to synaptic sites. These findings demonstrate that Wnts signal across the synapse on Dvl-expressing presynaptic terminals to regulate synaptic assembly and suggest a potential novel function for Wnts in neurotransmitter release

Wnt signalling tunes neurotransmitter release by directly targeting Synaptotagmin-1

The functional assembly of the synaptic release machinery is well understood; however, how signalling factors modulate this process remains unknown. Recent studies suggest that Wnts play a role in presynaptic function. To examine the mechanisms involved, we investigated the interaction of release machinery proteins with Dishevelled-1 (Dvl1), a scaffold protein that determines the cellular locale of Wnt action. Here we show that Dvl1 directly interacts with Synaptotagmin-1 (Syt-1) and indirectly with the SNARE proteins SNAP25 and Syntaxin (Stx-1). Importantly, the interaction of Dvl1 with Syt-1, which is regulated by Wnts, modulates neurotransmitter release. Moreover, presynaptic terminals from Wnt signalling-deficient mice exhibit reduced release probability and are unable to sustain high-frequency release. Consistently, the readily releasable pool size and formation of SNARE complexes are reduced. Our studies demonstrate that Wnt signalling tunes neurotransmitter release and identify Syt-1 as a target for modulation by secreted signalling proteins.Fil: Ciani, Lorenza. University College London; Estados UnidosFil: Marzo, Aude. University College London; Estados UnidosFil: Boyle, Kieran. University College London; Estados UnidosFil: Stamatakou, Eleanna. University College London; Estados UnidosFil: Lopes, Douglas M.. University College London; Estados UnidosFil: Anane, Derek. University College London; Estados UnidosFil: McLeod, Faye. University College London; Estados UnidosFil: Rosso, Silvana Beatriz. University College London; Estados Unidos. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Gibb, Alasdair. University College London; Estados UnidosFil: Salinas, Patricia C.. University College London; Estados Unido

Reversal of Synapse Degeneration by Restoring Wnt Signaling in the Adult Hippocampus

Synapse degeneration occurs early in neurodegenerative diseases and correlates strongly with cognitive decline in Alzheimer's disease (AD). The molecular mechanisms that trigger synapse vulnerability and those that promote synapse regeneration after substantial synaptic failure remain poorly understood. Increasing evidence suggests a link between a deficiency in Wnt signaling and AD. The secreted Wnt antagonist Dickkopf-1 (Dkk1), which is elevated in AD, contributes to amyloid-β-mediated synaptic failure. However, the impact of Dkk1 at the circuit level and the mechanism by which synapses disassemble have not yet been explored. Using a transgenic mouse model that inducibly expresses Dkk1 in the hippocampus, we demonstrate that Dkk1 triggers synapse loss, impairs long-term potentiation, enhances long-term depression, and induces learning and memory deficits. We decipher the mechanism involved in synapse loss induced by Dkk1 as it can be prevented by combined inhibition of the Gsk3 and RhoA-Rock pathways. Notably, after loss of synaptic connectivity, reactivation of the Wnt pathway by cessation of Dkk1 expression completely restores synapse number, synaptic plasticity, and long-term memory. These findings demonstrate the remarkable capacity of adult neurons to regenerate functional circuits and highlight Wnt signaling as a targetable pathway for neuronal circuit recovery after synapse degeneration

Complete Issue 42(1)

Complete digitized issue (volume 42, issue 1, November 1959) of The Gavel of Delta Sigma Rho

C-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability-5

<p><b>Copyright information:</b></p><p>Taken from "c-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability"</p><p>http://www.biomedcentral.com/1471-2121/8/27</p><p>BMC Cell Biology 2007;8():27-27.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1940000.</p><p></p>with neurons expressing Dvl and Gsk3β. Scale bar 15 μm. Quantification shows that neurons expressing Dvl and Gsk3β and treated with JNK inhibitor have a decreased level of MTs stability than untreated neurons expressing Dvl and Gsk3β. Quantification shows that neurons expressing Dvl together with Gsk3β and treated with Anisomicin have comparable level of MT stability as untreated neurons. Inhibition of JNK by expression of JBD does not affect the level of phosphorylated MAP1B in granule cell neurons expressing Dvl when compared to control neurons expressing Dvl alone (arrow). Scale bar 10 μm. Two asterisks, < 0.01; Three asterisks, < 0.001

C-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability-4

<p><b>Copyright information:</b></p><p>Taken from "c-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability"</p><p>http://www.biomedcentral.com/1471-2121/8/27</p><p>BMC Cell Biology 2007;8():27-27.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1940000.</p><p></p>ated with or without the JNK inhibitor SP600125 and MT stability was examined after Nocodazole treatment. Quantification shows that neurons expressing ΔDIX or ΔPDZ mutants and treated with SP600125 exhibit the same low level of MT stability as untreated neurons. Conversely, neurons expressing ΔDEP-Dvl mutant and treated with SP600125 show lower level of MT stability than control untreated neurons. C) Full length Dvl and ΔDEP-Dvl bind to MTs along the axon whereas low levels of ΔPDZ-Dvl mutant remains associated to MTs after detergent fixation. Scale bar 15 μm. Three asterisks, < 0.001

C-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability-1

<p><b>Copyright information:</b></p><p>Taken from "c-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability"</p><p>http://www.biomedcentral.com/1471-2121/8/27</p><p>BMC Cell Biology 2007;8():27-27.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1940000.</p><p></p>g neurons. Expression of dominant negative Rho (RhoN19), dominant negative Rac (RacN17), and dominant negative Ccd42 (Cdc42 N17) do not alter the ability of Dvl to stabilise microtubules. In addition, neurons expressing Dvl and treated with the ROCK inhibitor Y27632 exhibit comparable level of microtubule stability as untreated Dvl-expressing neurons. All neurons were treated with Nocodazole to test MT stability Quantification shows that coexpression of Dvl together with dominant negative Rac Rho, or Cdc42 or the ROCK inhibitor does not change the ability of Dvl to stabilise MTs. Scale bar: 15 μm

C-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability-3

<p><b>Copyright information:</b></p><p>Taken from "c-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability"</p><p>http://www.biomedcentral.com/1471-2121/8/27</p><p>BMC Cell Biology 2007;8():27-27.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1940000.</p><p></p>of endogenous JNK activity, when compared to controls. Low levels of Anisomicin also increase the level of p-c-Jun when compared with control untreated EGFP-expressing neurons or neurons exposed to β-estradiol for three hrs. However, the levels of total c-Jun remain unchanged. Quantification of three independent experiments shows that induction of Dvl-ER expression induces a 40% increase in p-c-Jun levels compare to control. Expression of Dvl increases the level of p-JNK decorating the MT network along neurites when compared to EGFP-expressing control neurons. Pseudocolor panels show Dvl increases the level of p-JNK associated with microtubules. Scale bar 5 μm. Two asterisks, < 0.01

C-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability-2

<p><b>Copyright information:</b></p><p>Taken from "c-Jun N-terminal kinase (JNK) cooperates with Gsk3β to regulate Dishevelled-mediated microtubule stability"</p><p>http://www.biomedcentral.com/1471-2121/8/27</p><p>BMC Cell Biology 2007;8():27-27.</p><p>Published online 3 Jul 2007</p><p>PMCID:PMC1940000.</p><p></p>e stability when compared to EGFP-expressing neurons. Neurons expressing JNK alone reveals a level of stability comparable to that one obtained after exposure of neurons to Anisomicin. Quantification shows that Anisomicin treatment and JNK expression increase the level of MT stability in neurons Dvl-expressing neurons treated with the JNK inhibitor SP600125 or expressing the dominant negative JNK (JBD) show decreased MT stability when compared to control Dvl-expressing neurons. Quantification shows that treatment of Dvl expressing neurons with JNK inhibitor SP 600125 or expression of JBD reduces the level of MT stability. Scale bar 15 μm. Three asterisks, < 0.001; For asterisks, < 0.0001