Smad7 Protein Interacts with Receptor-regulated Smads (R-Smads) to Inhibit Transforming Growth Factor-β (TGF-β)/Smad Signaling

TGF-β is a pleiotropic cytokine that regulates a wide range of cellular actions and pathophysiological processes. TGF-β signaling is spatiotemporally fine-tuned. As a key negative regulator of TGF-β signaling, Smad7 exerts its inhibitory effects by blocking receptor activity, inducing receptor degradation or interfering with Smad-DNA binding. However, the functions and the molecular mechanisms underlying the actions of Smad7 in TGF-β signaling are still not fully understood. In this study we report a novel mechanism whereby Smad7 antagonizes TGF-β signaling at the Smad level. Smad7 oligomerized with R-Smad proteins upon TGF-β signaling and directly inhibited R-Smad activity, as assessed by Gal4-luciferase reporter assays. Mechanistically, Smad7 competes with Smad4 to associate with R-Smads and recruits the E3 ubiquitin ligase NEDD4L to activated R-Smads, leading to their polyubiquitination and proteasomal degradation. Similar to the R-Smad-Smad4 oligomerization, the interaction between R-Smads and Smad7 is mediated by their mad homology 2 (MH2) domains. A positive-charged basic region including the L3/β8 loop-strand module and adjacent amino acids in the MH2 domain of Smad7 is essential for the interaction. These results shed new light on the regulation of TGF-β signaling by Smad7.

Activin Regulates Self-renewal and Differentiation of Trophoblast Stem Cells by Down-regulating the X Chromosome Gene Bcor

The development of a functional placenta is largely dependent upon proper proliferation and differentiation of trophoblast stem cells (TSCs). Activin signaling has long been regarded to play important roles during this process, but the exact mechanism is largely unknown. Here, we demonstrate that the X chromosome gene BCL-6 corepressor (Bcor) is a critical downstream effector of activin to fine-tune mouse TSC fate decision. Bcor was specifically down-regulated by activin A in TSCs in a dose-dependent manner, and immediately up-regulated upon TSC differentiation. Knockdown of Bcor partially compensated for the absence of activin A in maintaining the self-renewal of TSCs together with FGF4, while promoting syncytiotrophoblast differentiation in the absence of FGF4. Moreover, the impaired trophoblast giant cell and spongiotrophoblast differentiation upon Bcor knockdown also resembled the function of activin. Reporter analysis showed that BCOR inhibited the expression of the key trophoblast regulator genes Eomes and Cebpa by binding to their promoter regions. Our findings provide us with a better understanding of placental development and placenta-related diseases.

Small C-terminal Domain Phosphatase 3 Dephosphorylates the Linker Sites of Receptor-regulated Smads (R-Smads) to Ensure Transforming Growth Factor β (TGFβ)-mediated Germ Layer Induction in Xenopus Embryos

Germ layer induction is one of the earliest events shortly after fertilization that initiates body formation of vertebrate embryos. In Xenopus, the maternally deposited transcriptional factor VegT promotes the expression of zygotic Nodal/Activin ligands that further form a morphogen gradient along the vegetal-animal axis and trigger the induction of the three germ layers. Here we found that SCP3 (small C-terminal domain phosphatase 3) is maternally expressed and vegetally enriched in Xenopus embryos and is essential for the timely induction of germ layers. SCP3 is required for the full activation of Nodal/Activin and bone morphogenetic protein signals and functions via dephosphorylation in the linker regions of receptor-regulated Smads. Consistently, the linker regions of receptor-regulated Smads are heavily phosphorylated in fertilized eggs, and this phosphorylation is gradually removed when embryos approach the midblastula transition. Knockdown of maternal SCP3 attenuates these dephosphorylation events and the activation of Nodal/Activin and bone morphogenetic protein signals after midblastula transition. This study thus suggested that the maternal SCP3 serves as a vegetally enriched, intrinsic factor to ensure a prepared status of Smads for their activation by the upcoming ligands during germ layer induction of Xenopus embryos.

Internalization of the TGF-β type I receptor into caveolin-1 and EEA1 double-positive early endosomes

Endocytosis and intracellular sorting of transforming growth factor-β (TGF-β) receptors play an important regulatory role in TGF-β signaling. Two major endocytic pathways, clathrin- and caveolae-mediated endocytosis, have been reported to independently mediate the internalization of TGF-β receptors. In this study, we demonstrate that the clathrin- and caveolae-mediated endocytic pathways can converge during TGF-β receptor endocytic trafficking. By tracking the intracellular dynamics of fluorescently-labeled TGF-β type I receptor (TβRI), we found that after mediating TβRI internalization, certain clathrin-coated vesicles and caveolar vesicles are fused underneath the plasma membrane, forming a novel type of caveolin-1 and clathrin double-positive vesicles. Under the regulation of Rab5, the fused vesicles are targeted to early endosomes and thus deliver the internalized TβRI to the caveolin-1 and EEA1 double-positive early endosomes (caveolin-1-positive early endosomes). We further showed that the caveolin-1-positive early endosomes are positive for Smad3/SARA, Rab11 and Smad7/Smurf2, and may act as a multifunctional device for TGF-β signaling and TGF-β receptor recycling and degradation. Therefore, these findings uncover a novel scenario of endocytosis, the direct fusion of clathrin-coated and caveolae vesicles during TGF-β receptor endocytic trafficking, which leads to the formation of the multifunctional sorting device, caveolin-1-positive early endosomes, for TGF-β receptors.

The non-muscle-myosin-II heavy chain Myh9 mediates colitis-induced epithelium injury by restricting Lgr5+ stem cells

Lgr5+ stem cells are crucial to gut epithelium homeostasis, and therapies targeting these cells hold promise for treatment of gastrointestinal diseases. Here we report that the non-muscle-myosin-II (NMII) heavy chain Myh9 accumulates at epithelial injury sites in mice distal colon treated with dextran sulphate sodium (DSS). Gut-epithelium-specific Myh9 monoallelic deletion alleviates DSS-induced colonic crypt damage and acute colitis. Consistently, the NMII inhibitor blebbistatin can improve the survival of Lgr5+ stem cells and the growth of Lgr5 organoids. Mechanistically, inhibition of NMII by blebbistatin or Myh9 monoallelic deletion activates Akt through Rac1 and PAK1, which is essential for the survival and pluripotency of Lgr5+ cells. These results establish a critical role of the Myh9-Rac1-PAK1-Akt pathway in the maintenance of Lgr5+ stem cells. As blebbistatin can mitigate DSS-induced colitis and preserve Lgr5+ colonic stem cells in vivo, our findings provide a potential therapeutic intervention of gastrointestinal epithelium injury and degenerative diseases.

Regulation of intestinal stem cell fate specification

The remarkable ability of rapid self-renewal makes the intestinal epithelium an ideal model for the study of adult stem cells. The intestinal epithelium is organized into villus and crypt, and a group of intestinal stem cells located at the base of crypt are responsible for this constant self-renewal throughout the life. Identification of the intestinal stem cell marker Lgr5, isolation and in vitro culture of Lgr5+ intestinal stem cells and the use of transgenic mouse models have significantly facilitated the studies of intestinal stem cell homeostasis and differentiation, therefore greatly expanding our knowledge of the regulatory mechanisms underlying the intestinal stem cell fate determination. In this review, we summarize the current understanding of how signals of Wnt, BMP, Notch and EGF in the stem cell niche modulate the intestinal stem cell fate.

The Wnt Signaling Antagonist Dapper1 Accelerates Dishevelled2 Degradation via Promoting Its Ubiquitination and Aggregate-induced Autophagy

Autophagy is a regulated process that sequesters and transports cytoplasmic materials such as protein aggregates via autophagosomes to lysosomes for degradation. Dapper1 (Dpr1), an interacting protein of Dishevelled (Dvl), antagonizes Wnt signaling by promoting Dishevelled degradation via lysosomes. However, the mechanism is unclear. Here, we show that Dpr1 promotes the von Hippel-Lindau tumor suppressor (VHL)-mediated ubiquitination of Dvl2 and its autophagic degradation. Knockdown of Dpr1 decreases the interaction between Dvl2 and pVHL, resulting in reduced ubiquitination of Dvl2. Dpr1-mediated autophagic degradation of Dvl2 depends on Dvl2 aggregation. Moreover, the aggregate-prone proteins Dvl2, p62, and the huntingtin mutant Htt103Q promote autophagy in a Dpr1-dependent manner. These protein aggregates enhance the Beclin1-Vps34 interaction and Atg14L puncta formation, indicating that aggregated proteins stimulate autophagy initiation. Ubiquitination is not essential for the aggregate-induced autophagy initiation as inhibition of the ubiquitin-activation E1 enzyme activity did not block the aggregate-induced Atg14L puncta formation. Our findings suggest that Dpr1 promotes the ubiquitination of Dvl2 by pVHL and mediates the protein aggregate-elicited autophagy initiation.

Carbon nanotube-assisted optical activation of TGF-β signalling by near-infrared light

Receptor-mediated signal transduction modulates complex cellular behaviours such as cell growth, migration and differentiation. Although photoactivatable proteins have emerged as a powerful tool for controlling molecular interactions and signalling cascades at precise times and spaces using light, many of these light-sensitive proteins are activated by ultraviolent or visible light, which has limited tissue penetration. Here, we report a single-walled carbon nanotube (SWCNT)-assisted approach that enables near-infrared light-triggered activation of transforming growth factor β (TGF-β) signal transduction, an important signalling pathway in embryonic development and cancer progression. The protein complex of TGF-β and its latency-associated peptide is conjugated onto SWCNTs, where TGF-β is inactive. Upon near-infrared irradiation, TGF-β is released through the photothermal effect of SWCNTs and becomes active. The released TGF-β activates downstream signal transduction in live cells and modulates cellular behaviours. Furthermore, preliminary studies show that the method can be used to mediate TGF-β signalling in living mice.

Dynamic Sialylation in Transforming Growth Factor-β (TGF-β)-induced Epithelial to Mesenchymal Transition

Epithelial-mesenchymal transition (EMT) is a fundamental process in embryonic development and organ formation. Aberrant regulation of EMT often leads to tumor progression. Changes in cell surface sialylation have recently been implicated in mediating EMT. Herein we report the visualization of dynamic changes of sialylation and glycoproteomic analysis of newly synthesized sialylated proteins in EMT by metabolic labeling of sialylated glycans with azides, followed by click labeling with fluorophores or affinity tags. We discovered that sialylation was down-regulated during EMT but then reverted and up-regulated in the mesenchymal state after EMT, accompanied by mRNA expression level changes of genes involved in the sialic acid biosynthesis. Quantitative proteomic analysis identified a list of sialylated proteins whose biosynthesis was dynamically regulated during EMT. Sialylation of cell surface adherent receptor integrin β4 was found to be down-regulated, which may regulate integrin functions during EMT. Furthermore, a global sialylation inhibitor was used to probe the functional role of sialylation during EMT. We found that inhibition of sialylation promoted EMT. Taken together, our findings suggest the important role of sialylation in regulating EMT and imply its possible function in related pathophysiological events, such as cancer metastasis.

Neural oscillatory correlates of duration maintenance in working memory

Working memory (WM) is a core element of temporal information processing, but little is known about the internal representation and neuronal underpinnings of the duration maintenance in WM. The neural oscillations during maintenance of duration in WM were examined using electroencephalogram (EEG) recordings. The EEG results showed that theta amplitude was not modulated by the length of duration retained in WM, while alpha amplitude decreased in a 4-s duration condition compared with 1-s, 2-s, and 3-s duration conditions. The amplitude of alpha power positively correlated with accuracy for the 3-s duration condition. The results suggest that alpha activity is involved in duration maintenance in WM. Our study provides electrophysiological evidence that different internal representations are retained in WM for durations below and above about 3s.

Visualization of the post-Golgi vesicle-mediated transportation of TGF-β receptor II by quasi-TIRFM

Transforming growth factor β receptor II (Tβ RII) is synthesized in the cytoplasm and then transported to the plasma membrane of cells to fulfil its signalling duty. Here, we applied live-cell fluorescence imaging techniques, in particular quasi-total internal reflection fluorescence microscopy, to imaging fluorescent protein-tagged Tβ RII and monitoring its secretion process. We observed punctuate-like Tβ RII-containing post-Golgi vesicles formed in MCF7 cells. Single-particle tracking showed that these vesicles travelled along the microtubules at an average speed of 0.51 μm/s. When stimulated by TGF-β ligand, these receptor-containing vesicles intended to move towards the plasma membrane. We also identified several factors that could inhibit the formation of such post-Golgi vesicles. Although the inhibitory mechanisms still remain unknown, the observed characteristics of Tβ RII-containing vesicles provide new information on intracellular Tβ RII transportation. It also renders Tβ RII a good model system for studying post-Golgi vesicle-trafficking and protein transportation.

Regulation of TGF-β Signal Transduction

Transforming growth factor-β (TGF-β) signaling regulates diverse cellular processes, including cell proliferation, differentiation, apoptosis, cell plasticity, and migration. TGF-β signaling can be mediated by Smad proteins or other signaling proteins such as MAP kinases and Akt. TGF-β signaling is tightly regulated at different levels along the pathways to ensure its proper physiological functions in different cells and tissues. Deregulation of TGF-β signaling has been associated with various kinds of diseases, such as cancer and tissue fibrosis. This paper focuses on our recent work on regulation of TGF-β signaling.

Enrichment of the β-catenin-TCF complex at the S and G2 phases ensures cell survival and cell cycle progression

Wnt-β-catenin (β-catenin is also known as CTNNB1 in human) signaling through the β-catenin-TCF complex plays crucial roles in tissue homeostasis. Wnt-stimulated β-catenin-TCF complex accumulation in the nucleus regulates cell survival, proliferation and differentiation through the transcription of target genes. Compared with their levels in G1, activation of the receptor LRP6 and cytosolic β-catenin are both upregulated in G2 cells. However, accumulation of the Wnt pathway negative regulator AXIN2 also occurs in this phase. Therefore, it is unclear whether Wnt signaling is active in G2 phase cells. Here, we established a bimolecular fluorescence complementation (BiFC) biosensor system for the direct visualization of the β-catenin-TCF interaction in living cells. Using the BiFC biosensor and co-immunoprecipitation experiments, we demonstrate that levels of the nucleus-localized β-catenin-TCF complex increase during the S and G2 phases, and declines in the next G1 phase. Accordingly, a subset of Wnt target genes is transcribed by the β-catenin-TCF complex during both the S and G2 phases. By contrast, transient inhibition of this complex disturbs both cell survival and G2/M progression. Our results suggest that in S and G2 phase cells, Wnt-β-catenin signaling is highly active and functions to ensure cell survival and cell cycle progression.

Dapper1 promotes autophagy by enhancing the Beclin1-Vps34-Atg14L complex formation

Autophagy is an intracellular degradation process to clear up aggregated proteins or aged and damaged organelles. The Beclin1-Vps34-Atg14L complex is essential for autophagosome formation. However, how the complex formation is regulated is unclear. Here, we show that Dapper1 (Dpr1) acts as a critical regulator of the Beclin1-Vps34-Atg14L complex to promote autophagy. Dpr1 ablation in the central nervous system results in motor coordination defect and accumulation of p62 and ubiquitinated proteins. Dpr1 increases autophagosome formation as indicated by elevated puncta formation of LC3, Atg14L and DFCP1 (Double FYVE-containing protein 1). Conversely, loss of Dpr1 impairs LC3 lipidation and causes p62/SQSTM1 accumulation. Dpr1 directly interacts with Beclin1 and Atg14L and enhances the Beclin1-Vps34 interaction and Vps34 activity. Together, our findings suggest that Dpr1 enhances the Atg14L-Beclin1-Vps34 complex formation to drive autophagy.

Correlation and interventional embolization therapy of posterior intercostal arteries-induced hemoptysis

The incidence of posterior intercostal arteries-induced hemoptysis, its correlation with primary diseases, and the value of interventional embolization therapy were investigated. Clinical data, multislice spiral computed tomography (MSCT), digital subtraction angiography (DSA), and other imaging data of 143 cases of hemoptysis were retrospectively analyzed. After the offending vessels were subjected to interventional embolization therapy, patients were followed-up for observations of clinical efficacies and complications. Thirty-one patients (21.7%) showed 65 branches of posterior intercostal arteries as the non-bronchial systemic arteries involved in hemoptysis; pleural thickening was evident in 25 (80.6%) cases. Posterior intercostal arteries-induced hemoptysis was observed in 16 of the 27 (59.3%) patients with pulmonary tuberculosis, and in 9 of the 10 (90.0%) patients with pulmonary tuberculosis and pulmonary damage. Posterior intercostal arteries-induced hemoptysis was correlated to pleural thickening (P<0.05), which differed significantly among different underlying diseases (P<0.05). Twenty-eight cases of 58 branches of posterior intercostal arteries were found to be involved in hemoptysis by preoperative chest CT angiogram (CTA); the intraoperative matching rates were 90.3% (28/31) and 89.2% (58/65), respectively. Thirty-one patients received transcatheter arterial embolization (TAE), of which 29 (93.5%) showed immediate hemostasis; 1 case had surgical treatment for ineffectuality, and 2 cases showed recurrence without serious complications. The posterior intercostal arteries were commonly involved in hemoptysis, and were closely associated with pleural thickening and pulmonary tuberculosis, especially when accompanied by pulmonary damage. Complete TAE could improve the treatment effect of hemoptysis and preoperative chest CTA was helpful for interventional embolization therapy.

NEDD4L regulates convergent extension movements in Xenopus embryos via Disheveled-mediated non-canonical Wnt signaling

During the early vertebrate body plan formation, convergent extension (CE) of dorsal mesoderm and neurectoderm is coordinated by the evolutionarily conserved non-canonical Wnt/PCP signaling. Disheveled (Dvl), a key mediator of Wnt/PCP signaling, is essential for the medial-lateral polarity formation in the cells undergoing convergent extension movements. NEDD4L, a highly conserved HECT type E3 ligase, has been reported to regulate the stability of multiple substrates including Dvl2. Here we demonstrate that NEDD4L is required for the cellular polarity formation and convergent extension in the early Xenopus embryos. Depletion of NEDD4L in early Xenopus embryos results in the loss of mediolateral polarity of the convergent-extending mesoderm cells and the shortened body axis, resembling those defects caused by the disruption of non-canonical Wnt signaling. Depletion of xNEDD4L also blocks the elongation of the animal explants in response to endogenous mesoderm inducing signals and partially compromises the expression of Brachyury. Importantly, reducing Dvl2 expression can largely rescue the cellular polarity and convergent extension defects in NEDD4L-depleted embryos and explants. Together with the data that NEDD4L reduces Dvl2 protein expression in the frog embryos, our findings suggest that regulation of Dvl protein levels by NEDD4L is essential for convergent extension during early Xenopus embryogenesis.

Four amino acids within a tandem QxVx repeat in a predicted extended α-helix of the Smad-binding domain of Sip1 are necessary for binding to activated Smad proteins

The zinc finger transcription factor Smad-interacting protein-1 (Sip1; Zeb2, Zfhx1b) plays an important role during vertebrate embryogenesis in various tissues and differentiating cell types, and during tumorigenesis. Previous biochemical analysis suggests that interactions with several partner proteins, including TGFβ family receptor-activated Smads, regulate the activities of Sip1 in the nucleus both as a DNA-binding transcriptional repressor and activator. Using a peptide aptamer approach we mapped in Sip1 its Smad-binding domain (SBD), initially defined as a segment of 51 amino acids, to a shorter stretch of 14 amino acids within this SBD. Modelling suggests that this short SBD stretch is part of an extended α-helix that may fit the binding to a hydrophobic corridor within the MH2 domain of activated Smads. Four amino acids (two polar Q residues and two non-polar V residues) that form the tandem repeat (QxVx)₂ in this 14-residue stretch were found to be crucial for binding to both TGFβ/Nodal/Activin-Smads and BMP-Smads. A full-length Sip1 with collective mutation of these Q and V residues (to A) no longer binds to Smads, while it retains its binding activity to its cognate bipartite target DNA sequence. This missense mutant Sip1(AxAx)₂ provides a new molecular tool to identify SBD (in)dependent target genes in Sip1-controlled TGFβ and/or BMP (de)regulated cellular, developmental and pathological processes.

Temporal induction of immunoregulatory processes coincides with age-dependent resistance to viral-induced type 1 diabetes

The dilute plasma cytokine milieu associated with type 1 diabetes (T1D), while difficult to measure directly, is sufficient to drive transcription in a bioassay that uses healthy leukocytes as reporters. Previously, we reported disease-associated, partially IL-1 dependent, transcriptional signatures in both T1D patients and the BioBreeding (BB) rat model. Here, we examine temporal signatures in congenic BBDR.lyp/lyp rats that develop spontaneous T1D, and BBDR rats where T1D progresses only after immunological perturbation in young animals. After weaning, the BBDR temporal signature showed early coincident induction of transcription related to innate inflammation as well as IL-10- and TGF-β-mediated regulation. BBDR plasma cytokine levels mirrored the signatures showing early inflammation, followed by induction of a regulated state that correlated with failure of virus to induce T1D in older rats. In contrast, the BBDR.lyp/lyp temporal signature exhibited asynchronous dynamics, with delayed induction of inflammatory transcription and later, weaker induction of regulatory transcription, consistent with their deficiency in regulatory T cells. Through longitudinal analyses of plasma-induced signatures in BB rats and a human T1D progressor, we have identified changes in immunoregulatory processes that attenuate a preexisting innate inflammatory state in BBDR rats, suggesting a mechanism underlying the decline in T1D susceptibility with age.

Hybrid phase-change plasmonic crystals for active tuning of lattice resonances

Tunable lattice resonances are demonstrated in a hybrid plasmonic crystal incorporating the phase-change material Ge2Sb2Te5 (GST) as a 20-nm-thick layer sandwiched between a gold nanodisk array and a quartz substrate. Non-volatile tuning of lattice resonances over a range Δλ of about 500 nm (1.89 µm to 2.27 µm) is achieved experimentally via intermediate phase states of the GST layer. This work demonstrates the efficacy and ease of resonance tuning via GST in the near infrared, suggesting the possibility to design broadband non-volatile tunable devices for optical modulation, switching, sensing and nonlinear optical devices.

Disruption of the Dapper3 gene aggravates ureteral obstruction-mediated renal fibrosis by amplifying Wnt/β-catenin signaling

Wnt/β-catenin signaling plays key roles in embryonic development and tissue homeostasis. Dapper3/Dact3, one of the three members of the Dapper gene family, is transcriptionally repressed in colorectal cancer and may function as a negative regulator of Wnt/β-catenin signaling. To investigate its physiological functions, we generated a mouse strain harboring conditional null alleles of Dapper3 (Dapper3(flox/flox)), and homozygous Dapper3-deficient (Dapper3(-/-)) mice were produced after crossing with EIIa-cre transgenic mice. We found that Dapper3 is not essential for mouse embryogenesis, postnatal survival, and reproduction. However, adult Dapper3(-/-) mice exhibited a mild reduction in body weight compared with their wild-type littermates, suggesting a functional role of Dapper3 in postnatal growth. To investigate the role of Dapper3 in renal fibrosis, we employed the unilateral ureteral obstruction model. Dapper3 mRNA expression was up-regulated in kidney after unilateral ureteral obstruction. Loss of the Dapper3 gene enhanced myofibroblast activation and extracellular matrix overproduction in the obstructed kidney. Moreover, this aggravated fibrotic phenotype was accompanied with accumulation of Dishevelled2 and β-catenin proteins and activation of Wnt-targeted fibrotic genes. In primary renal tubular cells, Dapper3 inhibits Wnt-induced epithelial-to-mesenchymal transition. Consistently, Dapper3 interacted with and down-regulated Dishevelled2 protein and attenuated the Wnt-responsive Topflash reporter expression. These findings together suggest that Dapper3 antagonizes the fibrotic actions of Wnt signaling in kidney.

HECT domain-containing E3 ubiquitin ligase NEDD4L negatively regulates Wnt signaling by targeting dishevelled for proteasomal degradation

Wnt signaling plays a pivotal role in embryogenesis and tissue homeostasis. Dishevelled (Dvl) is a central mediator for both Wnt/β-catenin and Wnt/planar cell polarity pathways. NEDD4L, an E3 ubiquitin ligase, has been shown to regulate ion channel activity, cell signaling, and cell polarity. Here, we report a novel role of NEDD4L in the regulation of Wnt signaling. NEDD4L induces Dvl2 polyubiquitination and targets Dvl2 for proteasomal degradation. Interestingly, the NEDD4L-mediated ubiquitination of Dvl2 is Lys-6, Lys-27, and Lys-29 linked but not typical Lys-48-linked ubiquitination. Consistent with the role of Dvl in both Wnt/β-catenin and Wnt/planar cell polarity signaling, NEDD4L regulates the cellular β-catenin level and Rac1, RhoA, and JNK activities. We have further identified a hierarchical regulation that Wnt5a induces JNK-mediated phosphorylation of NEDD4L, which in turn promotes its ability to degrade Dvl2. Finally, we show that NEDD4L inhibits Dvl2-induced axis duplication in Xenopus embryos. Our work thus demonstrates that NEDD4L is a negative feedback regulator of Wnt signaling.