Dishevelled-2 maps to human chromosome 17 and distal to Wnt3a and vestigial tail (vt) on mouse chromosome 11

Study of microRNAs targeted Dvl2 on the osteoblasts differentiation of rat BMSCs in hyperlipidemia environment

Dishevelled 2 (Dvl-2), a key mediator of the wnt/β-catenin signaling pathway, plays critical roles in osteoblasts differentiation in hyperlipidemia environment. In our previous study, we observed a strong correlation between increased dvl2 expression and decreased new bone formation around implants in a rat hyperlipidemia implant surgery model. However, transcriptional regulation of Dvl2 by microRNAs in this process remains unknown. In the current study, we searched in online database and identified four significantly up-regulated miRNAs, miR-21-5p, miR-29c-3p, miR-138-5p, and miR-351-5p that could potentially regulate Dvl2. Using Western blot and dual-luciferase assays, we confirmed that miR29c-3p suppresses Dvl2 expression by binding to its 3'-UTR. Our results suggest a novel transcriptional regulation mechanism of Dvl2 by miR-29c-3p in osteoblasts differentiation of BMSCs.

The dopamine D2 receptor regulates Akt and GSK-3 via Dvl-3

The dopamine D2 receptor (D2DR) regulates Akt and may also target the Wnt pathway, two signalling cascades that inhibit glycogen synthase kinase-3 (GSK-3). This study examined whether the Wnt pathway is regulated by D2DR and the role of Akt and dishevelled-3 (Dvl-3) in regulating GSK-3 and the transcription factor β-catenin in the rat brain. Western blotting showed that subchronic treatment of raclopride (D2DR antagonist) increase phosphorylated Akt, Dvl-3, GSK-3, phosphorylated GSK-3 and β-catenin, whereas subchronic treatment of quinpirole (D2DR agonist) induced the opposite response. Co-immunopreciptations revealed an association between GSK-3 and the D2DR complex that was altered following raclopride and quinpirole, albeit in opposite directions. SCH23390 (D1DR antagonist) and nafadotride (D3DR antagonist) were also used to determine if the response was specific to the D2DR. Neither subchronic treatment affected Dvl-3, GSK-3, Akt nor β-catenin protein levels, although nafadotride altered the phosphorylation state of Akt and GSK-3. In addition, in-vitro experiments were conducted to manipulate Akt and Dvl-3 activity in SH-SY5Y cells to elucidate how the pattern of change observed following manipulation of D2DR developed. Results indicate that Akt affects the phosphorylation state of GSK-3 but has no effect on β-catenin levels. However, altering Dvl-3 levels resulted in changes in Akt and the Wnt pathway similar to what was observed following raclopride or quinpirole treatment. Collectively, the data suggests that the D2DR very specifically regulates Wnt and Akt signalling via Dvl-3.

Perturbation of zebrafish swimbladder development by enhancing Wnt signaling in Wif1 morphants

Wnt signaling plays critical roles in development of both tetrapod lung and fish swimbladder, which are the two evolutionary homologous organs. Our previous data reveal that down-regulation of Wnt signaling leads to defective swimbladder development. However, the effects of up-regulation of Wnt signaling on swimbladder development remain unclear. By knockdown of the Wnt protein inhibitory gene wif1, we demonstrated that up-regulation of Wnt signaling also resulted in perturbed development of the swimbladder. Specifically, the growth of epithelium and mesenchyme was greatly inhibited, the smooth muscle differentiation was abolished, and the organization of mesothelium was disturbed. Furthermore, our data reveal that it is the reduced cell proliferation, but not enhanced apoptosis, that contributes to the disturbance of swimbladder development in wif1 morphants. Blocking Wnt signaling by the Wnt antagonist IWR-1 did not affect wif1 expression in the swimbladder, but complete suppression of Hedgehog signaling in smo-/- mutants abolished wif expression, consistent with our earlier report of a negative feedback regulation of Wnt signaling in the swimbladder by the Hedgehog signaling. Our works established the importance of proper level of Wnt signaling for normal development of swimbladder in zebrafish.

Regulation of Akt and Wnt signaling by the group II metabotropic glutamate receptor antagonist LY341495 and agonist LY379268

Metabotropic glutamate receptors 2/3 (mGlu(2/3)) have been implicated in schizophrenia and as a novel treatment target for schizophrenia. The current study examined whether mGlu(2/3) regulates Akt (protein kinase B) and Wnt (Wingless/Int-1) signaling, two cascades associated with schizophrenia and modified by antipsychotics. Western blotting revealed increases in phosphorylated Akt (pAkt) and phosphorylated glycogen synthase kinase-3 (pGSK-3) following acute and repeated treatment of LY379268 (mGlu(2/3) agonist), whereas increases in dishevelled-2 (Dvl-2), dishevelled-3 (Dvl-3), GSK-3 and β-catenin were only observed following repeated treatment. LY341495 (mGlu(2/3) antagonist) induced the opposite response compared with LY379268. Co-immunoprecipitation experiments showed an association between the mGlu(2/3) complex and Dvl-2 providing a possible mechanism to explain how the mGlu(2/3) can mediate changes in Wnt signaling. However, there was no association between the mGlu(2/3) complex and Akt suggesting that changes in Akt signaling following LY341495 and LY379268 treatments may not be directly mediated by the mGlu(2/3) . Finally, an increase in locomotor activity induced by LY341495 treatment correlated with increased pAkt and pGSK-3 levels and was attenuated by the administration of the GSK-3 inhibitor, SB216763. Overall, the results suggest that mGlu(2/3) regulates Akt and Wnt signaling and LY379268 treatment has overlapping effects with D(2) dopamine receptor antagonists (antipsychotic drugs).

Molecular basis of Wnt activation via the DIX domain protein Ccd1

The Wnt signaling plays pivotal roles in embryogenesis and cancer, and the three DIX domain-containing proteins, Dvl, Axin, and Ccd1, play distinct roles in the initiation and regulation of canonical Wnt signaling. Overexpressed Dvl has a tendency to form large polymers in a cytoplasmic punctate pattern, whereas the biologically active Dvl in fact forms low molecular weight oligomers. The molecular basis for how the polymeric sizes of Dvl proteins are controlled upon Wnt signaling remains unclear. Here we show that Ccd1 up-regulates canonical Wnt signaling via acting synergistically with Dvl. We determined the crystal structures of wild type Ccd1-DIX and mutant Dvl1-DIX(Y17D), which pack into "head-to-tail" helical filaments. Structural analyses reveal two sites crucial for intra-filament homo- and hetero-interaction and a third site for inter-filament homo-assembly. Systematic mutagenesis studies identified critical residues from all three sites required for Dvl homo-oligomerization, puncta formation, and stimulation of Wnt signaling. Remarkably, Ccd1 forms a hetero-complex with Dvl through the "head" of Dvl-DIX and the "tail" of Ccd1-DIX, depolymerizes Dvl homo-assembly, and thereby controls the size of Dvl polymer. These data together suggest a molecular mechanism for Ccd1-mediated Wnt activation in that Ccd1 converts latent polymeric Dvl to a biologically active oligomer(s).

Protease-activated receptor-1 (PAR1) acts via a novel Galpha13-dishevelled axis to stabilize beta-catenin levels

We have previously shown a novel link between hPar-1 (human protease-activated receptor-1) and beta-catenin stabilization. Although it is well recognized that Wnt signaling leads to beta-catenin accumulation, the role of PAR1 in the process is unknown. We provide here evidence that PAR1 induces beta-catenin stabilization independent of Wnt, Fz (Frizzled), and the co-receptor LRP5/6 (low density lipoprotein-related protein 5/6) and identify selective mediators of the PAR1-beta-catenin axis. Immunohistological analyses of hPar1-transgenic (TG) mouse mammary tissues show the expression of both Galpha(12) and Galpha(13) compared with age-matched control counterparts. However, only Galpha(13) was found to be actively involved in PAR1-induced beta-catenin stabilization. Indeed, a dominant negative form of Galpha(13) inhibited both PAR1-induced Matrigel invasion and Lef/Tcf (lymphoid enhancer factor/T cell factor) transcription activity. PAR1-Galpha(13) association is followed by the recruitment of DVL (Dishevelled), an upstream Wnt signaling protein via the DIX domain. Small interfering RNA-Dvl silencing leads to a reduction in PAR1-induced Matrigel invasion, inhibition of Lef/Tcf transcription activity, and decreased beta-catenin accumulation. It is of note that PAR1 also promotes the binding of beta-arrestin-2 to DVL, suggesting a role for beta-arrestin-2 in PAR1-induced DVL phosphorylation dynamics. Although infection of small interfering RNA-LRP5/6 or the use of the Wnt antagonists, SFRP2 (soluble Frizzled-related protein 2) or SFRP5 potently reduced Wnt3A-mediated beta-catenin accumulation, no effect was observed on PAR1-induced beta-catenin stabilization. Collectively, our data show that PAR1 mediates beta-catenin stabilization independent of Wnt. We propose here a novel cascade of PAR1-induced Galpha(13)-DVL axis in cancer and beta-catenin stabilization.

Dishevelled family proteins are expressed in non-small cell lung cancer and function differentially on tumor progression

BACKGROUND

Dishevelled (Dvl) family proteins are cytoplasmic mediators of the Wnt/beta-catenin signaling pathway and have recently been linked to cancers. However, the roles of individual Dvls and their expression in human cancers are poorly defined. This work aimed to characterize the expression of Dvls and their correlation to clinicopathological factors and beta-catenin expression in non-small cell lung cancer (NSCLC).

METHODS

We used immunohistochemistry to assess the presence of the three Dvl family proteins in 113 individual NSCLC specimens. Thirty-nine of the 113 cases were examined further for Dvl and beta-catenin protein expression in matched primary growths and autologous nodal metastases. We also examined the effect of Dvl-1 and Dvl-3 overexpression on beta-catenin expression and the invasive ability of A549 and QG56 lung cancer cells.

RESULTS

The positive expression rate in primary tumors was 53.1% (60/113) for total Dvl, 36.3% (41/113) for Dvl-1, 36.3% (41/113) for Dvl-2 and 41.6% (47/113) for Dvl-3, while normal adult bronchial and alveolar epithelia showed negative expression of all these proteins. The expression levels of all three Dvl proteins were significantly higher in adenocarcinomas than in squamous carcinomas, and were associated with poor tumor differentiation. The positive expression of Dvl-1 and Dvl-2 proteins was correlated to advanced pTNM stages (III-IV vs. I-II). In addition, the expression levels of Dvl-1 and Dvl-3 were significantly higher in nodal metastases than in primary growths, with the Dvl-1 expression correlating to beta-catenin expression in the metastases. Exogenous expression of Dvl-1 and Dvl-3 both enhanced the invasive ability of A549 and QG56 cells, but had differential effects on beta-catenin protein expression in either cell line, without influencing beta-catenin mRNA levels.

CONCLUSIONS

Expression of Dvl family proteins, Dvl-1, Dvl-2 and Dvl-3, is common in NSCLCs. They may contribute to the progression of NSCLCs, but Dvl-1 and Dvl-3 may function on this process through different signaling pathways.

Analysis of dishevelled localization and function in the early sea urchin embryo

Dishevelled (Dsh) is a key signaling molecule in the canonical Wnt pathway. Although the mechanism by which Dsh transduces a Wnt signal remains elusive, the subcellular localization of Dsh may be critical for its function. In the early sea urchin embryo, Dsh is concentrated in punctate structures within the cytoplasm of vegetal blastomeres. In these cells, Dsh stabilizes beta-catenin and causes it to accumulate in nuclei, resulting in the activation of transcriptional gene regulatory networks that drive mesoderm and endoderm formation. Here, we present a systematic mutational analysis of Lytechinus variegatus Dsh (LvDsh) that identifies motifs required for its vegetal cortical localization (VCL). In addition to a previously identified lipid-binding motif near the N-terminus of Dsh (Weitzel, H.E., Illies, M.R., Byrum, C.A., Xu, R., Wikramanayake, A.H., Ettensohn, C.A., 2004. Differential stability of beta-catenin along the animal-vegetal axis of the sea urchin embryo mediated by dishevelled. Development 131, 2947-56), we identify a short (21 amino acid) motif between the PDZ and DEP domains that is required for VCL. Phosphorylation of threonine residues in this region regulates both the targeting and stability of LvDsh. We also identify functional nuclear import and export signals within LvDsh. We provide additional evidence that LvDsh is active locally in the vegetal region of the embryo but is inactive in animal blastomeres and show that the inability of LvDsh to function in animal cells is not a consequence of impaired nuclear import. The DIX domain of LvDsh functions as a potent dominant negative when overexpressed (Weitzel, H.E., Illies, M.R., Byrum, C.A., Xu, R., Wikramanayake, A.H., Ettensohn, C.A., 2004. Differential stability of beta-catenin along the animal-vegetal axis of the sea urchin embryo mediated by dishevelled. Development 131, 2947-56). Here, we show that the dominant negative effect of DIX is dependent on a highly conserved, lipid-binding motif that includes residues K57 and E58. The dominant negative effect of DIX is not a consequence of blocking VCL or the nuclear import of LvDsh. We provide evidence that isolated DIX domains interact with full-length LvDsh in vivo. In addition, we show that the K57/E58 lipid-binding motif of DIX is essential for this interaction. We propose that binding of the isolated DIX domain to full-length Dsh may be facilitated by interactions with lipids, and that this interaction may inhibit signaling by a) preventing endogenous Dsh from interacting with Axin, or b) blocking the ability of Dsh to recruit other proteins, such as GBP/Frat1, to the beta-catenin degradation complex.

Genetic analysis of molecular oscillators in mammalian somitogenesis: Clues for studies of human vertebral disorders

The repeating pattern of the human vertebral column is shaped early in development, by a process called somitogenesis. In this embryonic process, pairs of mesodermal segments called somites are serially laid down along the developing neural tube. Somitogenesis is an iterative process, repeating at regular time intervals until the last somite is formed. This process lays down the vertebrate body axis from head to tail, making for a progression of developmental steps along the rostral-caudal axis. In this review, the roles of the Notch, Wnt, fibroblast growth factor, retinoic acid and other pathways are described during the following key steps in somitogenesis: formation of the presomitic mesoderm (PSM) and establishment of molecular gradients; prepatterning of the PSM by molecular oscillators; patterning of rostral-caudal polarity within the somite; formation of somite borders; and maturation and resegmentation of somites to form musculoskeletal tissues. Disruption of somitogenesis can lead to severe vertebral birth defects such as spondylocostal dysostosis (SCD). Genetic studies in the mouse have been instrumental in finding mutations in this disorder, and ongoing mouse studies should provide functional insights and additional candidate genes to help in efforts to identify genes causing human spinal birth defects.

The development of cortical connections

The cortex receives its major sensory input from the thalamus via thalamocortical axons, and cortical neurons are interconnected in complex networks by corticocortical and callosal axons. Our understanding of the mechanisms generating the circuitry that confers functional properties on cortical neurons and networks, although poor, has been advanced significantly by recent research on the molecular mechanisms of thalamocortical axonal guidance and ordering. Here we review recent advances in knowledge of how thalamocortical axons are guided and how they maintain order during that process. Several studies have shown the importance in this process of guidance molecules including Eph receptors and ephrins, members of the Wnt signalling pathway and members of a novel planar cell polarity pathway. Signalling molecules and transcription factors expressed with graded concentrations across the cortex are important in establishing cortical maps of the topography of sensory surfaces. Neural activity, both spontaneous and evoked, plays a role in refining thalamocortical connections but recent work has indicated that neural activity is less important than was previously thought for the development of some early maps. A strategy used widely in the development of corticocortical and callosal connections is the early overproduction of projections followed by selection after contact with the target structure. Here we discuss recent work in primates indicating that elimination of juvenile projections is not a major mechanism in the development of pathways feeding information forward to higher levels of cortical processing, although its use is common to developing feedback pathways.

Expression of planar cell polarity genes during development of the mouse CNS

Atypical cadherin (Celsr3) and the receptor Frizzled3 (Fzd3) are crucial for the development of axonal tracts in the mouse CNS. Celsr3 and Fzd3 are orthologues of the Drosophila'planar cell polarity' (PCP) genes flamingo/starry night (fmi/stan) and frizzled, respectively. Reasoning that Celsr3 and Fzd3 might interact with PCP orthologues in mammals like they do in flies, we used mRNA in situ hybridization to compare the expression of Celsr3 and Fzd3 with that of dishevelled 1, 2 and 3 (Dvl1-3), van gogh-like 1 and 2 (Vangl1, 2), and prickle-like 1 and 2 (Prickle1, 2), during mouse CNS development, from embryonic day 10.5 to postnatal day 21. With the relative exception of Vangl1, all genes were expressed in the developing CNS. Although Celsr3- and Fzd3-deficient mice have similar phenotypes, Fzd3 expression was more widespread than that of Celsr3. Vangl2 and Dvl2 were preferentially expressed in ventricular zones, in keeping with their role during neural tube closure, where they could be partners of Celsr1. Dvl1 had a broad expression, reminiscent of that of Celsr2, and may be involved in neural maintenance. A large overlap in the expression territories of Dvl genes suggested redundancy. Vangl1 and Prickle1 had expression canvases different from each other and from other candidates, indicating unrelated function. Like Celsr3, Dvl3 and Prickle2 were expressed more strongly in postmitotic neurons than in precursors. Thus, the analogy between the PCP and Celsr3-Fzd3 genetic networks is limited, but may include Dvl3 and/or Prickle2.

Conservation of dishevelled structure and function between flies and mice: isolation and characterization of Dvl2

The segment polarity gene dishevelled (dsh) of Drosophila is required for pattern formation of the embryonic segments and the adult imaginal discs. dsh encodes the earliest-acting and most specific known component of the signal transduction pathway of Wingless, an extracellular signal homologous to Wnt1 in mice. We have previously described the isolation and characterization of the Dvl1 mouse dsh homolog. We report here the isolation of a second mouse dsh homolog, Dvl2, which maps to chromosome 11. The Dvl2 amino acid sequence is equally related to the dsh sequence as is that of Dvl1, but Dvl2 is most similar to the Xenopus homolog Xdsh. However, unlike the other vertebrate dsh homologs. Like the other genes, Dvl2 is ubiquitously expressed throughout most of embryogenesis and is expressed in many adult organs. We have developed an assay for dsh function in fly embryos, and show that Dvl2 can partially rescue the segmentation defects of embryos devoid of dsh. Thus, Dvl2 encodes a mammalian homolog of dsh which can transduce the Wingless signal.