The Glypican proteoglycans show intrinsic interactions with Wnt-3a in human prostate cancer cells that are not always associated with cascade activation.

BACKGROUND: Prostate cancer occurs through multiple steps until advanced metastasis. Signaling pathways studies can result in the identification of targets to interrupt cancer progression. Glypicans are cell surface proteoglycans linked to the membrane through glycosylphosphatidylinositol. Their interaction with specific ligands has been reported to trigger diverse signaling, including Wnt. In this study, prostate cancer cell lines PC-3, DU-145, and LNCaP were compared to normal prostate RWPE-1 cell line to investigate glypican family members and the activation of the Wnt signaling pathway. RESULTS: Glypican-1 (GPC1) was highly expressed in all the examined cell lines, except for LNCaP, which expressed glypican-5 (GPC5). The subcellular localization of GPC1 was detected on the cell surface of RWPE-1, PC-3, and DU-145 cell lines, while GPC5 suggested cytoplasm localization in LNCaP cells. Besides glypican, flow cytometry analysis in these prostate cell lines confirmed the expression of Wnt-3a and unphosphorylated ß-catenin. The co-immunoprecipitation assay revealed increased levels of binding between Wnt-3a and glypicans in cancer cells, suggesting a relationship between these proteoglycans in this pathway. A marked increase in nuclear ß-catenin was observed in tumor cells. However, only PC-3 cells demonstrated activation of canonical Wnt signaling, according to the TOPFLASH assay. CONCLUSIONS: GPC1 was the majorly expressed gene in all the studied cell lines, except for LNCaP, which expressed GPC5. We assessed by co-immunoprecipitation that these GPCs could interact with Wnt-3a. However, even though nuclear ß-catenin was found increased in the prostate cancer cells (i.e., PC-3, DU-145 and LNCaP), activation of Wnt pathway was only found in PC-3 cells. In these PC-3 cells, GPC1 and Wnt-3a revealed high levels of colocalization, as assessed by confocal microscopy studies. This suggests a localization at the cellular surface, where Frizzled receptor is required for downstream activation. The interaction of Wnt-3a with GPCs in DU-145 and LNCaP cells, which occurs in absence of Wnt signaling activation, requires further studies. Once non-TCF-LEF proteins can also bind ß-catenin, another signaling pathway may be involved in these cells with regulatory function.

LGR5/R-Spo1/Wnt3a axis promotes stemness and aggressive phenotype in hepatoblast-like hepatocellular carcinoma cell lines.

Leucine-rich repeat-containing G protein-coupled receptor 5 (LGR5) is a newly defined stem cell marker in endoderm-derived organs such as the small intestine, colon and pancreas. Recently, LGR5 was demonstrated to be an important factor in liver regeneration and stem cell maintenance. Moreover, LGR5 expression is highly up-regulated in various cancers including hepatocellular carcinoma. Herein, we demonstrate that LGR5 expression is specifically observed in certain subset of HCC cell lines with "hepatoblast-like" appearance, characterized by the expression of liver fetal/progenitor markers. Notably, the activation of the canonical Wnt pathway significantly increases the expression of LGR5 in this subset of cell lines, whereas it does not cause any induction of LGR5 expression in mesenchymal like cell lines SNU-475 and SNU-449. Furthermore, we showed that treatment of the hepatoblast-like HCC cell lines HuH-7 and Hep3B with LGR5 ligand R-Spo1 significantly amplifies the induction of LGR5 expression, the phosphorylation of LRP6 and ß-catenin resulting in enhanced TCF/LEF activity either alone or in combination with Wnt3a. Consistently, the silencing of the LGR5 gene attenuates the co-stimulatory effect of R-Spo1/Wnt3a on TCF/LEF activity while overexpression of LGR5 enhances it. On the contrary, overexpression of LGR5 does not change TCF/LEF activity induced by R-Spo1/Wnt3a in mesenchymal-like HCC line, SNU-449. Importantly, LGR5-overexpressing cells have increased expression of several Wnt target genes and stemness-related genes including EpCAM and CK19 upon R-Spo1/Wnt3a treatment. LGR5-overexpressing cells also have increased spheroid forming, migration and invasion abilities and stimulation with R-Spo1/Wnt3a augments these abilities of LGR5-overexpressing cells. In addition, ectopic overexpression of LGR5 significantly increases cell proliferation rate independent of R-Spo1/Wnt3a stimulation. Moreover, in vitro tubulogenesis assay demonstrates that treatment with R-Spo1/Wnt3a enhances the sprouting of capillary tubules in only LGR5-overexpressing cells. Finally, R-Spo1/Wnt3a significantly promotes dissemination of LGR5-overexpressing cells in vivo in a zebrafish xenograft model. Our study unravels a tumor-promoting role for LGR5 through activation of canonical Wnt/ß-catenin signaling in the hepatoblast-like HCCs. In conclusion, our results suggest that LGR5/R-Spo1/Wnt3a generates an axis that mediates the acquisition of aggressive phenotype specifically in hepatoblast-like subset of HCCs and might represent a valuable target for treatment of HCC tumors with aberrant activation of Wnt/ß-catenin pathway.

Role of Wnt3a in the pathogenesis of cancer, current status and prospective.

The Wnt signaling pathway plays a critical role in initiation, progression, invasion and metastasis of cancer. Wnt3a as a canonical Wnt ligand is strongly implicated in the etiology and pathology of a number of diseases including cancer. Depending on cancer type, Wnt3a enhances or suppresses metastasis, cell proliferation and apoptosis of cancer cells. This review summarizes the role of Wnt3a in the pathogenesis of different cancers including colorectal, prostate, hepatocellular, lung and leukemia, for promoting greater understanding and clinical management of these diseases.

A model of neocortical area patterning in the lissencephalic mouse may hold for larger gyrencephalic brains.

In the mouse, two telencephalic signaling centers orchestrate embryonic patterning of the cerebral cortex. From the rostral patterning center in the telencephalon, the Fibroblast Growth Factor, FGF8, disperses as a morphogen to establish the rostral to caudal axis of the neocortical area map. FGF8 coordinates with Wnt3a from the cortical hem to regulate graded expression of transcription factors that position neocortical areas, and control hippocampal development. Whether similar signaling centers pattern the much larger cortices of carnivore and primate species, however, is unclear. The limited dispersion range of FGF8 and Wnt3a is inconsistent with patterning larger cortical primordia. Yet the implication that different mechanisms organize cortex in different mammals flies in the face of the tenet that developmental patterning mechanisms are conserved across vertebrate species. In the present study, both signaling centers were identified in the ferret telencephalon, as were expression gradients of the patterning transcription factor genes regulated by FGF8 and Wnt3a. Notably, at the stage corresponding to the peak period of FGF8 signaling in the mouse neocortical primordium (NP), the NP was the same size in ferret and mouse, which would allow morphogen patterning of the ferret NP. Subsequently, the size of ferret neocortex shot past that of the mouse. Images from online databases further suggest that NP growth in humans, too, is slowed in early cortical development. We propose that if early growth in larger brains is held back, mechanisms that pattern the neocortical area map in the mouse could be conserved across mammalian species.

Interaction of LEF1 with TAZ is necessary for the osteoblastogenic activity of Wnt3a.

Canonical Wnt signalling plays an important role in osteoblast differentiation and bone formation. However, the molecular mechanisms by which canonical Wnt signalling exerts its osteoblastogenic effect remain elusive. Here, we investigated the relationship between lymphoid enhancer-binding factor 1 (LEF1) and transcriptional co-activator with PDZ-binding motif (TAZ), both of which are transcriptional regulators that mediate canonical Wnt signalling during osteoblast differentiation. Reporter assay and co-immunoprecipitation experiments revealed functional and physical interaction between LEF1 and TAZ. Overexpression of dominant-negative forms of either LEF1 or TAZ markedly inhibited Wnt3a-dependent osteoblast differentiation. Moreover, we found that LEF1 and TAZ formed a transcriptional complex with runt-related transcription factor 2 (Runx2) and that inhibition of LEF1 or TAZ by their dominant-negative forms dramatically suppressed the osteoblastogenic activity of Ruxn2. Additionally, Wnt3a enhanced osteoblast differentiation induced by bone morphogenetic protein 2 (BMP2), which stimulates osteoblast differentiation by regulating Runx2. Collectively, these findings suggest that interaction between LEF1 and TAZ is crucial for the osteoblastogenic activity of Wnt3a and that LEF1 and TAZ contribute to the cooperative effect of Wnt3a and BMP2 on osteoblast differentiation through association with Runx2.

Dickkopf-1 inhibits Wnt3a-induced migration and epithelial-mesenchymal transition of human lens epithelial cells.

Posterior capsular opacification (PCO) is a major post-operative complication of cataract surgery. Epithelial-mesenchymal transition (EMT) contributes to PCO. We previously indicated that Wnt3a induces the EMT of human lens epithelial cells (LECs) and plays an important role in the development of PCO. The present study aimed to test the potential effect of Dickkopf-1 (Dkk1) on Wnt3a-induced cell migration and the EMT of LECs and to explore possible cellular mechanisms. The secretion of Dkk1 was reduced in the rabbit PCO model, and Dkk1 injected into the eyes post-surgical manipulation prevented PCO formation. Cultured HLE-B3 cells were then transfected with Wnt3a in the presence or absence of Dkk1. Dkk1 treatment restored the epithelial phenotype and reversed the expression of EMT-associated proteins induced by Wnt3a. Dkk1 suppressed LEC migration and the expression of matrix metalloproteinase-1 (MMP-1), and the activity of MMP-2 and MMP-9. Dkk1 inhibited the nuclear accumulation of ß-catenin, which is the key regulator of the canonical Wnt signaling. Our results indicate that Dkk1 inhibits Wnt3a-induced migration and the EMT of human LECs.The results contribute to the prevention of PCO formation and development.

SRI36160 is a specific inhibitor of Wnt/ß-catenin signaling in human pancreatic and colorectal cancer cells.

Activation of Wnt/ß-catenin signaling is associated with pancreatic and colorectal cancer, among others. To-date, there are no FDA-approved small molecule Wnt/ß-catenin inhibitors and many past efforts resulted in compounds with undesirable off-target effects. We recently identified a series of benzimidazole analogs as potent inhibitors of Wnt/ß-catenin signaling. Here, we show that the lead compound SRI36160 displayed selective Wnt inhibition and potent antiproliferative activity in pancreatic and colorectal cancer cells. Moreover, SRI36160 had no effect on STAT3 and mTORC1 signaling in pancreatic and colorectal cancer cells, and was not effective in inhibiting proliferation of non-cancerous cells. Our findings suggest that this series of benzimidazole analogs presents a novel approach for the treatment of Wnt-dependent cancers such as colorectal and pancreatic cancer.

Effect of Wnt3a delivery on early healing events during guided bone regeneration.

OBJECTIVE: To evaluate the effect of recombinant Wnt3a delivery on the bone regeneration potential following application of the guided bone regeneration (GBR) principle. MATERIALS AND METHODS: A critical-size calvarial defect was created on each parietal bone of 14 Wistar strain rats. One defect was used as the test side and was treated with a collagen sponge carrying 2.0 µg of recombinant Wnt3a protein, whereas the contralateral side served as sham-operated control. Both defects were covered at both the extracranial and intracranial aspects with ePTFE non-resorbable membranes, according to the GBR principle. Following healing periods of 4 and 7 days, qualitative histological and histomorphometric evaluation of undecalcified sections was performed in subgroups of seven animals. The primary outcome parameter was the mean percentage of defect closure in the test and control defects. RESULTS: At 4 days of healing, a network of coagulum and fibrin was observed and initial signs of granulation tissue formation were evident with no apparent differences between the test and control groups. At 7 days of healing, the test group presented newly formed woven bone, originating from the borders of the defect, as opposed to the control group, whereby woven bone formation was not observed in any of the specimens. CONCLUSIONS: The delivery of mouse recombinant Wnt-3a protein in combination with GBR may promote woven bone formation in critical-size calvarial defects at 7 days of healing.

Wnt Signaling Promotes Breast Cancer by Blocking ITCH-Mediated Degradation of YAP/TAZ Transcriptional Coactivator WBP2.

Cross-talk between the Hippo and Wnt pathways has been implicated recently in breast cancer development, but key intersections have yet to be fully defined. Here we report that WBP2, a transcription coactivator that binds the Hippo pathway transcription factor YAP/TAZ, contributes to Wnt signaling and breast cancer pathogenesis. Clinically, overexpression of WBP2 in breast cancer specimens correlated with malignant progression and poor patient survival. In breast cancer cells, nuclear entry and interaction of WBP2 with ß-catenin was stimulated by Wnt3A, thereby activating TCF-mediated transcription and driving malignant invasive character. Mechanistic investigations showed WBP2 levels were controlled by the E3 ligase ITCH, which bound and target WBP2 for ubiquitin-dependent proteasomal degradation. Accordingly, ITCH silencing could elevate WBP2 levels. Wnt signaling upregulated WBP2 by disrupting ITCH-WBP2 interactions via EGFR-mediated tyrosine phosphorylation of WBP2 and TAZ/YAP competitive binding. Conversely, ITCH-mediated downregulation of WBP2 inhibited TCF/ß-catenin transcription, in vitro transformation, and in vivo tumorigenesis. We identified somatic mutations in ITCH, which impaired its ability to degrade WBP2 and to block its function in cancer, even while retaining binding capacity to WBP2. Thus, the Wnt pathway appeared to engage WBP2 primarily by affecting its protein stability. Our findings show how WBP2/ITCH signaling functions to link the intricate Wnt and Hippo signaling networks in breast cancer. Cancer Res; 76(21); 6278-89. ©2016 AACR.

Crosstalk between TGFß and Wnt signaling pathways in the human trabecular meshwork.

Primary Open Angle Glaucoma (POAG) is an irreversible, vision-threatening disease that affects millions worldwide. The principal risk factor of POAG is increased intraocular pressure (IOP) due to pathological changes in the trabecular meshwork (TM). The TGFß signaling pathway activator TGFß2 and the Wnt signaling pathway inhibitor secreted frizzled-related protein 1 (sFRP1) are elevated in the POAG TM. In this study, we determined whether there is a crosstalk between the TGFß/Smad pathway and the canonical Wnt pathway using luciferase reporter assays. Lentiviral luciferase reporter vectors for studying the TGFß/Smad pathway or the canonical Wnt pathway were transduced into primary human non-glaucomatous TM (NTM) cells. Cells were treated with or without a combination of 5 µg/ml TGFß2 and/or 100 ng/ml Wnt3a recombinant proteins, and luciferase levels were measured using a plate reader. We found that TGFß2 inhibited Wnt3a-induced canonical Wnt pathway activation, while Wnt3a inhibited TGFß2-induced TGFß/Smad pathway activation (n = 6, p < 0.05) in 3 NTM cell strains. We also found that knocking down of Smad4 or ß-catenin using siRNA in HTM5 cells transfected with similar luciferase reporter plasmids abolished the inhibitory effect of TGFß2 and/or Wnt3a on the other pathway (n = 6). Our results suggest the existence of a cross-inhibition between the TGFß/Smad and canonical Wnt pathways in the TM, and this cross-inhibition may be mediated by Smad4 and ß-catenin.

Wnt Protein Signaling Reduces Nuclear Acetyl-CoA Levels to Suppress Gene Expression during Osteoblast Differentiation.

Developmental signals in metazoans play critical roles in inducing cell differentiation from multipotent progenitors. The existing paradigm posits that the signals operate directly through their downstream transcription factors to activate expression of cell type-specific genes, which are the hallmark of cell identity. We have investigated the mechanism through which Wnt signaling induces osteoblast differentiation in an osteoblast-adipocyte bipotent progenitor cell line. Unexpectedly, Wnt3a acutely suppresses the expression of a large number of genes while inducing osteoblast differentiation. The suppressed genes include Pparg and Cebpa, which encode adipocyte-specifying transcription factors and suppression of which is sufficient to induce osteoblast differentiation. The large scale gene suppression induced by Wnt3a corresponds to a global decrease in histone acetylation, an epigenetic modification that is associated with gene activation. Mechanistically, Wnt3a does not alter histone acetyltransferase or deacetylase activities but, rather, decreases the level of acetyl-CoA in the nucleus. The Wnt-induced decrease in histone acetylation is independent of ß-catenin signaling but, rather, correlates with suppression of glucose metabolism in the tricarboxylic acid cycle. Functionally, preventing histone deacetylation by increasing nucleocytoplasmic acetyl-CoA levels impairs Wnt3a-induced osteoblast differentiation. Thus, Wnt signaling induces osteoblast differentiation in part through histone deacetylation and epigenetic suppression of an alternative cell fate.

Wnt3a suppresses Pseudomonas aeruginosa-induced inflammation and promotes bacterial killing in macrophages.

Pseudomonas aeruginosa (PA) is a common Gram­negative bacterium and can cause serious infections, including hospital­acquired pneumonia, suppurative bacterial keratitis and acute burn wound infection. The pathogenesis of PA infections is closely associated with excessive inflammatory responses and bacterial virulence factors. Wingless­type MMTV integration site family, member 3A (Wnt3a), an upstream mediator in the canonical Wnt signaling pathway, has been implicated as a regulator of inflammation. However, its role in PA­induced inflammation and bacterial clearance remains unknown. In the present study, the efficacy of Wnt3a conditioned media (Wnt3a­CM) was assessed using western blotting and immunofluorescence, which showed that ß­catenin, a downstream molecule of Wnt3a, was upregulated and translocated to the nucleus following exposure to 50% Wnt3a­CM for 6 h. To explore the role of Wnt3a in PA­induced inflammation, the mRNA levels of pro­inflammatory cytokines and apoptosis in macrophages were measured using reverse transcription­quantitative polymerase chain reaction and flow cytometry, respectively. This indicated that Wnt3a suppressed inflammation by reducing the production of pro­inflammatory cytokines and by promoting apoptosis in macrophages. Furthermore, the mechanism of macrophage­mediated bacterial killing was investigated, and the results indicated that Wnt3a enhanced macrophage­mediated intracellular bacterial killing via the induction of the production of cathelicidin­related antimicrobial peptide and ß­defensins 1. Taken together, the current study explored the role of Wnt3a in inflammation and bacterial invasion, which may provide an improved understanding of host resistance to PA infection.

Wnt3a: functions and implications in cancer.

Wnt3a, one of Wnt family members, plays key roles in regulating pleiotropic cellular functions, including self-renewal, proliferation, differentiation, and motility. Accumulating evidence has suggested that Wnt3a promotes or suppresses tumor progression via the canonical Wnt signaling pathway depending on cancer type. In addition, the roles of Wnt3a signaling can be inhibited by multiple proteins or chemicals. Herein, we summarize the latest findings on Wnt3a as an important therapeutic target in cancer.

RBMY, a novel inhibitor of glycogen synthase kinase 3ß, increases tumor stemness and predicts poor prognosis of hepatocellular carcinoma.

UNLABELLED: Male predominance of hepatocellular carcinoma (HCC) occurs particularly among young children aged 6-9 years, indicative of a possible role of the Y chromosome-encoded oncogene in addition to an androgenic effect. The discovery of oncogenic activation of RBMY (RNA-binding motif on Y chromosome), which is absent in normal hepatocytes but present in male HCC tissues, sheds light on this issue. Herein, we report on a critical hepatocarcinogenic role of RBMY and its ontogenic origin. During liver development, the Ser/Thr phosphorylated RBMY is expressed in the cytoplasm of human and rodent fetal livers. It is then silenced in mature hepatocytes and restricted to scarce expression in the bile ductular cells. Upon hepatocarcinogenesis, a noteworthy increase of cytoplasmic and nuclear RBMY is observed in HCC tissues; however, only the former is expressed dominantly in hepatic cancer stem cells and correlates significantly to a poor prognosis and decreased survival rate in HCC patients. Cytoplasmic expression of RBMY, which is mediated by binding to nuclear exporter chromosome region maintenance 1 and further enriched upon Wnt-3a stimulation, confers upon tumor cells the traits of cancer stem cell by augmenting self-renewal, chemoresistance, cell-cycle progression, proliferation, and xenograft tumor growth. This is achieved mechanistically through increasing Ser9 phosphorylation-inactivation of glycogen synthase kinase 3ß by RBMY, thereby impeding the glycogen synthase kinase 3ß-dependent degradation of ß-catenin and eventually inducing the nuclear entry of ß-catenin for the transcription of downstream oncogenes. CONCLUSION: RBMY is a novel oncofetal protein that plays a key role in attenuating glycogen synthase kinase 3ß activity, leading to aberrant activation of Wnt/ß-catenin signaling, which facilitates malignant hepatic stemness; because of its absence from normal human tissues except the testis, RBMY represents a feasible therapeutic target for the selective eradication of HCC cells in male patients.

Wnt3a Mediates the Inhibitory Effect of Hyperoxia on the Transdifferentiation of AECIIs to AECIs.

The aim of this study is to investigate the effect of Wnt3a in the transdifferentiation of type II alveolar epithelial cells (AECIIs) to type I alveolar epithelial cells (AECIs) under hyperoxia condition. In the in vivo study, preterm rats were exposed in hyperoxia for 21 days. In the in vitro study, primary rat AECIIs were subjected to a hyperoxia and normoxia exposure alternatively every 24 hr for 7 days. siRNA-mediated knockout of Wnt3a and exogenous Wnt3a were used to investigate the effect of Wnt3a on transdifferentiation of AECIIs to AECIs. Wnt5a-overexpressed AECIIs were also used to investigate whether Wnt3a could counteract the effect of Wnt5a. The results showed that hyperoxia induced alveolar damage in the lung of preterm born rats, as well as an increased expression of Wnt3a and nuclear accumulation of ß-catenin. In addition, Wnt3a/ß-catenin signaling was activated in isolated AECIIs after hyperoxia exposure. Wnt3a knockout blocked the inhibition of the transdifferentiation induced by hyperoxia, and Wnt3a addition exacerbated this inhibition. Furthermore, Wnt3a addition blocked the transdifferentiation-promoting effect of Wnt5a in hyperoxia-exposed Wnt5a-overexpressed AECIIs. In conclusion, our results demonstrate that the activated Wnt3a/ß-catenin signal may be involved in the hyperoxia-induced inhibition of AECIIs' transdifferentiation to AECIs.

Number and brightness analysis of sFRP4 domains in live cells demonstrates vesicle association signal of the NLD domain and dynamic intracellular responses to Wnt3a.

The Wnts are secreted, lipidated glycoproteins that play a role in cellular processes of differentiation, proliferation, migration, survival, polarity and stem cell self-renewal. The majority of Wnts biological effects are through binding to specific frizzled (Fzd) receptor complexes leading to activation of downstream pathways. Secreted frizzled-related proteins (sFRPs) were first identified as antagonists of Wnt signalling by binding directly to Wnts. They comprise two domains, a Fzd-like cysteine rich domain (CRD) and a netrin-like domain (NLD). Subsequently sFRPs have been shown to also interact with Fzd receptors and more diverse functions have been identified, including potentiation of Wnt signalling. Many aspects of the biology of this family remain to be elucidated. We used the number and brightness (N&B) method, a technique based on fluorescence fluctuation analysis, to characterise the intracellular aggregation and trafficking of sFRP4 domains. We expressed sFRP4 and its' domains as EGFP fusions and then characterised the effect of endogenous Wnt3a by fluorescence confocal imaging. We observed vesicular trafficking of sFRP4 and that the NLD domain has a vesicular association signal. We found that sFRP4 and the CRD formed oligomeric aggregates in the perinuclear region while the NLD was distributed evenly throughout the cell with a larger proportion of aggregates. Most significantly we observed intracellular redistribution of sFRP4 in response to Wnt3a suggesting that Wnt3a can modulate intracellular localisation and secretion of sFRP4. Our results reveal a number of novel findings regarding sFRP4 which are likely to have relevance to this wider family.

Wnt8a and Wnt3a cooperate in the axial stem cell niche to promote mammalian body axis extension.

BACKGROUND: Vertebrate body axis extension occurs in a head-to-tail direction from a caudal progenitor zone that responds to interacting signals. Wnt/ß-catenin signaling is critical for generation of paraxial mesoderm, somite formation, and maintenance of the axial stem cell pool. Body axis extension requires Wnt8a in lower vertebrates, but in mammals Wnt3a is required, although the anterior trunk develops in the absence of Wnt3a. RESULTS: We examined mouse Wnt8a(-/-) and Wnt3a(-/-) single and double mutants to explore whether mammalian Wnt8a contributes to body axis extension and to determine whether a posterior growth function for Wnt8a is conserved throughout the vertebrate lineage. We find that caudal Wnt8a is expressed only during early somite stages and is required for normal development of the anterior trunk in the absence of Wnt3a. During this time, we show that Wnt8a and Wnt3a cooperate to maintain Fgf8 expression and prevent premature Sox2 up-regulation in the axial stem cell niche, critical for posterior growth. Similar to Fgf8, Wnt8a requires retinoic acid (RA) signaling to restrict its caudal expression boundary and possesses an upstream RA response element that binds RA receptors. CONCLUSIONS: These findings provide new insight into interaction of caudal Wnt-FGF-RA signals required for body axis extension.