The extracellular matrix component WIF-1 is expressed during, and can modulate, retinal development

WNT-inhibitory factor 1-mediated glycolysis protects photoreceptor cells in diabetic retinopathy

BACKGROUND

In diabetic retinopathy (DR), hypoxia-inducible factor (HIF-1α) induces oxidative stress by upregulating glycolysis. This process leads to neurodegeneration, particularly photoreceptor cell damage, which further contributes to retinal microvascular deterioration. Further, the regulation of Wnt-inhibitory factor 1 (WIF1), a secreted Wnt signaling antagonist, has not been fully characterized in neurodegenerative eye diseases. We aimed to explore the impact of WIF1 on photoreceptor function within the context of DR.

METHOD

Twelve-week-old C57BL/KsJ-db/db mice were intravitreally injected with WIF1 overexpression lentivirus. After 4 weeks, optical coherence tomography (OCT), transmission electron microscopy (TEM), H&E staining, and electroretinography (ERG) were used to assess the retinal tissue and function. The potential mechanism of action of WIF1 in photoreceptor cells was explored using single-cell RNA sequencing. Under high-glucose conditions, 661 W cells were used as an in vitro DR model. WIF1-mediated signaling pathway components were assessed using quantitative real-time PCR, immunostaining, and western blotting.

RESULT

Typical diabetic manifestations were observed in db/db mice. Notably, the expression of WIF1 was decreased at the mRNA and protein levels. These pathological manifestations and visual function improved after WIF1 overexpression in db/db mice. TEM demonstrated that WIF1 restored damaged mitochondria, the Golgi apparatus, and photoreceptor outer segments. Moreover, ERG indicated the recovery of a-wave potential amplitude. Single-cell RNA sequencing and in vitro experiments suggested that WIF1 overexpression prevented the expression of glycolytic enzymes and lactate production by inhibiting the canonical Wnt signaling pathway, HIF-1α, and Glut1, thereby reducing retinal and cellular reactive oxygen species levels and maintaining 661 W cell viability.

CONCLUSIONS

WIF1 exerts an inhibitory effect on the Wnt/β-catenin-HIF-1α-Glut1 glycolytic pathway, thereby alleviating oxidative stress levels and mitigating pathological structural characteristics in retinal photoreceptor cells. This mechanism helps preserve the function of photoreceptor cells in DR and indicates that WIF1 holds promise as a potential therapeutic candidate for DR and other neurodegenerative ocular disorders.

Wif1 Mediates Coordination of Bone Morphogenetic Protein and Wnt Signaling in Neural and Glioma Stem Cells

Wnts, bone morphogenetic protein (BMP), and fibroblast growth factor (FGF) are paracrine signaling pathways implicated in the niche control of stem cell fate decisions. BMP-on and Wnt-off are the dominant quiescent niche signaling pathways in many cell types, including neural stem cells (NSCs). However, among the multiple inhibitory family members of the Wnt pathway, those with direct action after BMP4 stimulation in NSCs remain unclear. We examined 11 Wnt inhibitors in NSCs after BMP4 treatment. Wnt inhibitory factor 1 (Wif1) has been identified as the main factor reacting to BMP4 stimuli. RNA sequencing confirmed that Wif1 was markedly upregulated after BMP4 treatment in different gene expression analyses. Similar to the functional role of BMP4, Wif1 significantly decreased the cell cycle of NSCs and significantly inhibited cell proliferation (P < 0.05). Combined treatment with BMP4 and Wif1 significantly enhanced the inhibition of cell growth compared with the single treatment (P < 0.05). Wif1 expression was clearly lower in glioblastoma and low-grade glioma samples than in normal samples (P < 0.05). A functional analysis revealed that both BMP4 and Wif1 could decrease glioma cell growth. These effects were abrogated by the BMP inhibitor Noggin. The collective findings demonstrate that Wif1 plays a key role in quiescent NSC homeostasis and glioma cell growth downstream of BMP-on signaling. The functional roles of Wif1/BMP4 in glioma cells may provide a technical basis for regenerative medicine, drug discovery, and personal molecular therapy in future clinical treatments.

Lmx1a-Dependent Activation of miR-204/211 Controls the Timing of Nurr1-Mediated Dopaminergic Differentiation

The development of midbrain dopaminergic (DA) neurons requires a fine temporal and spatial regulation of a very specific gene expression program. Here, we report that during mouse brain development, the microRNA (miR-) 204/211 is present at a high level in a subset of DA precursors expressing the transcription factor Lmx1a, an early determinant for DA-commitment, but not in more mature neurons expressing Th or Pitx3. By combining different in vitro model systems of DA differentiation, we show that the levels of Lmx1a influence the expression of miR-204/211. Using published transcriptomic data, we found a significant enrichment of miR-204/211 target genes in midbrain dopaminergic neurons where Lmx1a was selectively deleted at embryonic stages. We further demonstrated that miR-204/211 controls the timing of the DA differentiation by directly downregulating the expression of Nurr1, a late DA differentiation master gene. Thus, our data indicate the Lmx1a-miR-204/211-Nurr1 axis as a key component in the cascade of events that ultimately lead to mature midbrain dopaminergic neurons differentiation and point to miR-204/211 as the molecular switch regulating the timing of Nurr1 expression.

Wnt inhibitory 1 ameliorates neovascularization and attenuates photoreceptor injury in an oxygen-induced retinopathy mouse model

Retinal neovascularization (RNV) associated diseases typically exhibit pathological neovascularization and neurodegeneration. Wnt inhibitor factor 1 (WIF1) is a secreted Wnt antagonist that regulates angiogenesis. However, the significance of WIF1 in RNV associated disease has not been explicitly tested. In our study, we found that the WIF1 expressions were strongly downregulated in the vitreous of proliferative diabetic retinopathy (PDR) and retinopathy of prematurity (ROP). Similarly, retinal WIF1 expression was significantly downregulated in OIR mice, relative to normal mice at P17. After injection of WIF1 overexpression lentivirus into the vitreous of OIR mice, overexpressing WIF1 in OIR mice vitreous strongly reduced avascular areas and neovascular tufts, increased vessel branches, raised a-, b-waves and oscillatory potentials amplitudes on ERG, increased retinal thickness and the number of synapses in retina, normalized the Golgi, mitochondria, and outer segments of photoreceptors. Furthermore, overexpression WIF1 suppressed expressions of β-catenin, vascular endothelial growth factor (VEGF), p-AKT and p-ERK, reduced retinal reactive oxygen species (ROS) and 4-HNE levels, improved autophagic flux, and mitigated apoptosis. In summary, WIF1 plays a key role in alleviating angiogenesis and in improving visual function in OIR mice by suppressing the Wnt/β-catenin-VEGF signaling pathway and ROS levels. WIF1 is an excellent candidate for targeted therapy against RNV associated diseases.

Wnt antagonist as therapeutic targets in ovarian cancer

Ovarian cancer is a fatal malignancy in women with a low survival rate that demands new therapeutic paradigms. Cancer cells acquire various exclusive alterations to proliferate, invade, metastasize, and escape cell death, acting independently of growth-inducing or growth-inhibiting signals. The nature of cellular signaling in tumorigenesis is interwoven. Wnt signaling is an evolutionarily conserved signaling cascade that has been shown to regulate ovarian cancer pathogenesis. The molecular mechanism of Wnt signaling underlying the development of ovarian cancer, drug resistance, and relapse is not completely understood. Extracellularly secreted Wnt signaling inhibitors are crucial regulators of ovarian cancer tumorigenesis and malignant properties of cancer stem cells. Wnt inhibitors arbitrated modifications affecting Wnt pathway proteins on the cell membranes, in the cytoplasm, and in the nucleus have been shown to span essential contributions in the initiation, progression, and chemoresistance of ovarian cancer. Although many extrinsic inhibitors developed targeting the downstream components of the Wnt signaling pathway, investigating the molecular mechanisms of endogenous secreted inhibitors might substantiate prognostic or therapeutic biomarkers development. Given the importance of Wnt signaling in ovarian cancer, more systematic studies combined with clinical studies are requisite to probe the precise mechanistic interactions of Wnt antagonists in ovarian cancer. This review outlines the latest progress on the Wnt antagonists and ovarian cancer-specific regulators such as micro-RNAs, small molecules, and drugs regulating these Wnt antagonists in ovarian tumourigenesis.

Loss of Active Neurogenesis in the Adult Shark Retina

Neurogenesis is the process by which progenitor cells generate new neurons. As development progresses neurogenesis becomes restricted to discrete neurogenic niches, where it persists during postnatal life. The retina of teleost fishes is thought to proliferate and produce new cells throughout life. Whether this capacity may be an ancestral characteristic of gnathostome vertebrates is completely unknown. Cartilaginous fishes occupy a key phylogenetic position to infer ancestral states fixed prior to the gnathostome radiation. Previous work from our group revealed that the juvenile retina of the catshark Scyliorhinus canicula, a cartilaginous fish, shows active proliferation and neurogenesis. Here, we compared the morphology and proliferative status of the retina in catshark juveniles and adults. Histological and immunohistochemical analyses revealed an important reduction in the size of the peripheral retina (where progenitor cells are mainly located), a decrease in the thickness of the inner nuclear layer (INL), an increase in the thickness of the inner plexiform layer and a decrease in the cell density in the INL and in the ganglion cell layer in adults. Contrary to what has been reported in teleost fish, mitotic activity in the catshark retina was virtually absent after sexual maturation. Based on these results, we carried out RNA-Sequencing (RNA-Seq) analyses comparing the retinal transcriptome of juveniles and adults, which revealed a statistically significant decrease in the expression of many genes involved in cell proliferation and neurogenesis in adult catsharks. Our RNA-Seq data provides an excellent resource to identify new signaling pathways controlling neurogenesis in the vertebrate retina.

Negative regulators of Wnt signaling in non-small cell lung cancer: Theoretical basis and therapeutic potency

Significant advances in the treatment of non-small cell lung cancer (NSCLC) have been made over the past decade, and they predominantly involve molecular targets such as epidermal growth factor receptor (EGFR) mutations and anaplastic lymphoma kinase (ALK) rearrangements. However, despite the initial good response, drug resistance eventually develops. The Wnt signaling pathway has recently been considered important in embryonic development and tumorigenesis in many cancers, particularly NSCLC. Moreover, the aberrant Wnt pathway plays a significant role in NSCLC and is associated with cancer cell proliferation, metastasis, invasion and drug resistance, and the suppression of canonical or noncanonical Wnt signaling through various biological or pharmacological negative regulators has been proven to produce specific anticancer effects. Thus, blocking the Wnt pathway via its negative regulators may overcome the resistance of current treatment methods and lead to new treatment strategies for NSCLC. Therefore, in this review, we summarize recent studies on the role of negative regulators in Wnt signaling in NSCLC and the therapeutic potency of these molecules as agents and targets for NSCLC treatments.

An Eye on the Wnt Inhibitory Factor Wif1

The coordinated interplay between extrinsic activating and repressing cell signaling molecules is pivotal for embryonic development and subsequent tissue homeostasis. This is well exemplified by studies on the evolutionarily conserved Wnt signaling pathways. Tight temporal and spatial regulation of Wnt signaling activity is required throughout lifetime, from maternal stages before gastrulation until and throughout adulthood. Outside cells, the action of numerous Wnt ligands is counteracted and fine-tuned by only a handful of well characterized secreted inhibitors, such as for instance Dickkopf, secreted Frizzled Related Proteins and Cerberus. Here, we give an overview of our current understanding of another secreted Wnt signaling antagonist, the Wnt inhibitory factor Wif1. Wif1 can directly interact with various Wnt ligands and inhibits their binding to membrane bound receptors. Epigenetic promoter methylation of Wif1, leading to silencing of its transcription and concomitant up-regulation of Wnt signaling, is a common feature during cancer progression. Furthermore, an increasing number of reports describe Wif1 involvement in regulating processes during embryonic development, which so far has not received as much attention. We will summarize our knowledge on Wif1 function and its mode of action with a particular focus on the zebrafish (Danio rerio). In addition, we highlight the potential of Wif1 research to understand and possibly influence mechanisms underlying eye diseases and regeneration.

Transcriptome analysis reveals rod/cone photoreceptor specific signatures across mammalian retinas

A defined set of genetic instructions encodes functionality in complex organisms. Delineating these unique genetic signatures is essential to understanding the formation and functionality of specialized tissues. Vision, one of the five central senses of perception, is initiated by the retina and has evolved over time to produce rod and cone photoreceptors that vary in a species-specific manner, and in some cases by geographical region resulting in higher order visual acuity in humans. RNA-sequencing and use of existing and de novo transcriptome assemblies allowed ocular transcriptome mapping from a diverse set of rodent and primate species. Global genomic refinements along with systems-based comparative and co-expression analyses of these transcriptome maps identified gene modules that correlated with specific features of rod versus cone retinal cellular composition. Organization of the ocular transcriptome demonstrated herein defines the molecular basis of photoreceptor architecture and functionality, providing a new paradigm for neurogenetic analyses of the mammalian retina in health and disease.

Hedgehog Signaling Promotes the Proliferation and Subsequent Hair Cell Formation of Progenitor Cells in the Neonatal Mouse Cochlea

Hair cell (HC) loss is the major cause of permanent sensorineural hearing loss in mammals. Unlike lower vertebrates, mammalian cochlear HCs cannot regenerate spontaneously after damage, although the vestibular system does maintain limited HC regeneration capacity. Thus HC regeneration from the damaged sensory epithelium has been one of the main areas of research in the field of hearing restoration. Hedgehog signaling plays important roles during the embryonic development of the inner ear, and it is involved in progenitor cell proliferation and differentiation as well as the cell fate decision. In this study, we show that recombinant Sonic Hedgehog (Shh) protein effectively promotes sphere formation, proliferation, and differentiation of Lgr5+ progenitor cells isolated from the neonatal mouse cochlea. To further explore this, we determined the effect of Hedgehog signaling on cell proliferation and HC regeneration in cultured cochlear explant from transgenic R26-SmoM2 mice that constitutively activate Hedgehog signaling in the supporting cells of the cochlea. Without neomycin treatment, up-regulation of Hedgehog signaling did not significantly promote cell proliferation or new HC formation. However, after injury to the sensory epithelium by neomycin treatment, the over-activation of Hedgehog signaling led to significant supporting cell proliferation and HC regeneration in the cochlear epithelium explants. RNA sequencing and real-time PCR were used to compare the transcripts of the cochleae from control mice and R26-SmoM2 mice, and multiple genes involved in the proliferation and differentiation processes were identified. This study has important implications for the treatment of sensorineural hearing loss by manipulating the Hedgehog signaling pathway.

Loss of Axin2 Causes Ocular Defects During Mouse Eye Development

Purpose

The scaffold protein Axin2 is an antagonist and universal target of the Wnt/β-catenin pathway. Disruption of Axin2 may lead to developmental eye defects; however, this has not been examined. The purpose of this study was to investigate the role of Axin2 during ocular and extraocular development in mouse.

Methods

Animals heterozygous and homozygous for a Axin2^lacZ knock-in allele were analyzed at different developmental stages for reporter expression, morphology as well as for the presence of ocular and extraocular markers using histologic and immunohistochemical techniques.

Results

During early eye development, the Axin2^lacZ reporter was expressed in the periocular mesenchyme, RPE, and optic stalk. In the developing retina, Axin2^lacZ reporter expression was initiated in ganglion cells at late embryonic stages and robustly expressed in subpopulations of amacrine and horizontal cells postnatally. Activation of the Axin2^lacZ reporter overlapped with labeling of POU4F1, PAX6, and Calbindin. Germline deletion of Axin2 led to variable ocular phenotypes ranging from normal to severely defective eyes exhibiting microphthalmia, coloboma, lens defects, and expanded ciliary margin. These defects were correlated with abnormal tissue patterning in individual affected tissues, such as the optic fissure margins in the ventral optic cup and in the expanded ciliary margin.

Conclusions

Our results reveal a critical role for Axin2 during ocular development, likely by restricting the activity of the Wnt/β-catenin pathway.

WIF1 prevents Wnt5A mediated LIMK/CFL phosphorylation and adherens junction disruption in human vascular endothelial cells

Background

Wnt5A is released by activated macrophages and elevated levels have been detected in sepsis patients with severe systemic inflammation. However, the signalling and functional effects of Wnt5A in the vascular endothelial cells (VEC) remained unclear. Recently, we showed that Wnt5A affects barrier function in human VEC through Ryk interaction. Wnt5A/Ryk signalling activates LIMK to inactivate the actin depolymerisation factor CFL by phosphorylation, promotes actin polymerisation and disrupts endothelial adherens junctions.

Findings

Here, we investigate the antagonistic effect of the Ryk specific secreted Wnt antagonist Wnt inhibitory factor (WIF)-1 on Wnt5A-mediated activation/inactivation of LIMK/CFL, and adherens junction disruption in human VEC. In human coronary artery endothelial cells (HCAEC), treatment with Wnt5A enhanced the phosphorylation of LIMK and CFL that was significantly prevented by WIF1. The presence of WIF1 suppressed Wnt5A-mediated disruption of β-catenin and VE-cadherin adherens junctions in HCAEC, thereby preventing barrier dysfunction caused by Wnt5A.

Conclusion

We conclude that WIF1 or molecules with similar properties could be potent tools for the prevention of vascular leakage due to Wnt5A-mediated actin cytoskeleton remodeling in diseases associated with systemic inflammation.

Electronic supplementary material

The online version of this article (doi:10.1186/s12950-017-0157-4) contains supplementary material, which is available to authorized users.

WIF-1 gene inhibition and Wnt signal transduction pathway activation in NSCLC tumorigenesis

The aim of the present study is to explore the differential expression of key molecules associated with Wnt signaling in both clinical non-small cell lung cancer (NSCLC) tissue and adjacent normal lung tissue, and to discuss the tumorigenic role of the activation of Wnt signaling pathways in NSCLC. A total of 52 NSCLC patients were employed in the present study. Lung cancer tissue samples and paracarcinoma tissue samples were obtained from these patients, who had undergone surgical resection of their primary cancer. The cases were diagnosed by hematoxylin and eosin staining. Using reverse transcription-quantitative polymerase chain reaction and immunohistochemical straining, the messenger RNA (mRNA) and protein expression levels of Wnt inhibitory factor-1 (WIF-1) and important molecules associated with Wnt signaling pathways were detected. Compared with normal tissues, a marked decreased in the mRNA and protein expression levels of WIF-1, and an increase in β-catenin and cyclin D1 expression, were observed in tumor tissues. This suggests that the activation of the Wnt/β-catenin signaling pathway may be closely associated with lymph nodal metastasis and lower pathological classification. However, no obvious difference could be observed in adenomatous polyposis coli (APC) expression levels between lung cancer tissues and adjacent tissues to the carcinoma. The activation of the Wnt/β-catenin signaling pathway in NSCLC could be initiated by WIF-1 gene inhibition without APC expression changes, and this may be different to the mechanism in other tumors.

Wnt signaling promotes axonal regeneration following optic nerve injury in the mouse

Adult mammalian CNS axons generally do not regenerate, creating an obstacle to effective repair and recovery after neuronal injury. The canonical Wnt/β-catenin signaling pathway is an essential signal transduction cascade that regulates axon growth and neurite extension in the developing mammalian embryo. In this study, we investigated whether a Wnt/β-catenin signaling activator could be repurposed to induce regeneration in the adult CNS after axonal injury. We used a retinal ganglion cell (RGC) axon crush injury model in a transgenic Wnt reporter mouse, and intravitreal injections were used to deliver Wnt3a or saline to the RGC cell bodies within the retina. Our findings demonstrated that Wnt3a induced Wnt signaling in RGCs and resulted in significant axonal regrowth past the lesion site when measured at two and four weeks post-injury. Furthermore, Wnt3a-injected eyes showed increased survival of RGCs and significantly higher pattern electroretinography (PERG) amplitudes compared to the control. Additionally, Wnt3a-induced axonal regeneration and RGC survival were associated with elevated activation of the transcription factor Stat3, and reducing expression of Stat3 using a conditional Stat3 knock-out mouse line led to diminished Wnt3a-dependent axonal regeneration and RGC survival. Therefore, these findings reveal a novel role for retinal Wnt signaling in axonal regrowth and RGC survival following axonal injury, which may lead to the development of novel therapies for axonal regeneration.

Brg1 coordinates multiple processes during retinogenesis and is a tumor suppressor in retinoblastoma

Retinal development requires precise temporal and spatial coordination of cell cycle exit, cell fate specification, cell migration and differentiation. When this process is disrupted, retinoblastoma, a developmental tumor of the retina, can form. Epigenetic modulators are central to precisely coordinating developmental events, and many epigenetic processes have been implicated in cancer. Studying epigenetic mechanisms in development is challenging because they often regulate multiple cellular processes; therefore, elucidating the primary molecular mechanisms involved can be difficult. Here we explore the role of Brg1 (Smarca4) in retinal development and retinoblastoma in mice using molecular and cellular approaches. Brg1 was found to regulate retinal size by controlling cell cycle length, cell cycle exit and cell survival during development. Brg1 was not required for cell fate specification but was required for photoreceptor differentiation and cell adhesion/polarity programs that contribute to proper retinal lamination during development. The combination of defective cell differentiation and lamination led to retinal degeneration in Brg1-deficient retinae. Despite the hypocellularity, premature cell cycle exit, increased cell death and extended cell cycle length, retinal progenitor cells persisted in Brg1-deficient retinae, making them more susceptible to retinoblastoma. ChIP-Seq analysis suggests that Brg1 might regulate gene expression through multiple mechanisms.

Summary: The SWI/SNF protein Brg1 controls cell cycle length, cell cycle exit and cell survival, and is required for cell differentiation and retinal lamination, in the developing mouse retina.

Association between Wnt inhibitory factor-1 expression levels in articular cartilage and the disease severity of patients with osteoarthritis of the knee

Wnt inhibitory factor (WIF)-1 is a potent extracellular Wnt antagonist which may be used as a potential molecular therapy for the treatment of inflammatory and autoimmune diseases. Although previous studies have demonstrated that WIF-1 has a protective role in experimental studies of arthritis, its role in the various disease grades of osteoarthritis (OA) remains unclear. A total of 40 patients with various stages of primary OA of the knee and 10 control subjects were enrolled in the present study. Articular cartilage specimens were harvested from subjects following total knee arthroplasty or knee above amputation. Disease severity was determined according to Modified Mankin score and cartilage tissues were ascribed to four groups: Normal, mild, moderate and severe lesions. WIF-1 expression levels in articular cartilage were measured using immunohistochemical techniques. WIF-1 expression levels were detected in all cartilage tissues. As compared with the controls, patients with OA exhibited significantly decreased WIF-1 expression levels in the articular cartilage (0.19±0.05 vs. 0.26±0.04; P<0.01). Furthermore, articular cartilage WIF-1 expression levels in the moderate and severe lesion groups were significantly reduced, as compared with the controls (P<0.01) and mild lesion group (P<0.05). Subsequent analysis demonstrated that articular cartilage WIF-1 expression levels were negatively correlated with the severity of disease (r=-0.896, P<0.001). In conclusion, the results of the present study suggested that WIF-1 expression levels in articular cartilage may be negatively associated with progressive joint damage in patients with OA of the knee; therefore, WIF-1 expression may be a potential indictor for monitoring OA disease severity.

Wnt/β-catenin signaling plays an ever-expanding role in stem cell self-renewal, tumorigenesis and cancer chemoresistance

Wnt signaling transduces evolutionarily conserved pathways which play important roles in initiating and regulating a diverse range of cellular activities, including cell proliferation, calcium homeostasis, and cell polarity. The role of Wnt signaling in controlling cell proliferation and stem cell self-renewal is primarily carried out through the canonical pathway, which is the best-characterized the multiple Wnt signaling branches. The past 10 years has seen a rapid expansion in our understanding of the complexity of this pathway, as many new components of Wnt signaling have been identified and linked to signaling regulation, stem cell functions, and adult tissue homeostasis. Additionally, a substantial body of evidence links Wnt signaling to tumorigenesis of cancer types and implicates it in the development of cancer drug resistance. Thus, a better understanding of the mechanisms by which dysregulation of Wnt signaling precedes the development and progression of human cancer may hasten the development of pathway inhibitors to augment current therapy. This review summarizes and synthesizes our current knowledge of the canonical Wnt pathway in development and disease. We begin with an overview of the components of the canonical Wnt signaling pathway and delve into the role this pathway has been shown to play in stemness, tumorigenesis, and cancer drug resistance. Ultimately, we hope to present an organized collection of evidence implicating Wnt signaling in tumorigenesis and chemoresistance to facilitate the pursuit of Wnt pathway modulators that may improve outcomes of cancers in which Wnt signaling contributes to aggressive disease and/or treatment resistance.

Tocotrienol-rich fraction (TRF) suppresses the growth of human colon cancer xenografts in Balb/C nude mice by the Wnt pathway

Tocotrienols have been shown many biologic functions such as antioxidant, anti-cancer, maintaining fertility and regulating the immune system and so on. In this study, after feeding with tocotrienol-rich fraction from palm oil (TRF) for 2 weeks, Balb/c nude mice were inoculated human colon SW620 cancer cell and then continued to feed TRF for 4 weeks. At termination of experiments, xenografts were removed and determined the expression of Wnt-pathways related protein by immunohistochemistry or western blotting. Liver tissues were homogenated for determining the levels of antioxidative enzymes activity or malondialdehyde (MDA). The results showed that TRF significantly inhibited the growth of xenografts in nude mice. TRF also affected the activity of antioxidative enzymes in the liver tissue of mice. These changes were partly contributed to activation of wnt pathways or affecting their related protein. Thus, these finding suggested that the potent anticancer effect of TRF is associated with the regulation of Wnt signal pathways.

Activation of Wnt/β-catenin signaling in Muller glia protects photoreceptors in a mouse model of inherited retinal degeneration

The canonical Wnt/β-catenin ("Wnt") pathway is an essential signaling cascade in the embryonic central nervous system (CNS) that regulates neuronal differentiation and survival. Loss of Wnt signaling in developing and adult tissue has been implicated in numerous CNS diseases, but the precise role of Wnt in regulating neuronal survival, and how its absence could lead to disease, is not understood. In this study, we investigated the effect of Wnt activation on neuronal survival in the adult retina, and identified cellular and molecular mediators. Pan-retinal Wnt signaling activation using Wnt3a induced functional and morphological rescue of photoreceptor neurons in the rd10 mouse model of retinal degeneration. Furthermore, Wnt activation using constitutively active β-catenin specifically targeted to Muller glia increased photoreceptor survival and reduced markers of glial and neuronal remodeling. Wnt-induced photoreceptor protection was associated with elevated levels of the prosurvival protein Stat3, and was reduced by shRNA-mediated knock-down of Stat3, indicating cross-talk between survival pathways. Therefore, these data increase our understanding of the role of Wnt signaling in the retina, and identify radial Muller glia as important cellular mediators of Wnt activity.

Regulation of rod photoreceptor differentiation by STAT3 is controlled by a tyrosine phosphatase

Signal pathways that reduce the levels of tyrosine-phosphorylated STAT3 (pSTAT3) allow late retinal progenitors to exit the cell cycle and enter a terminal differentiation pathway into rod photoreceptors. In the mouse retina, we previously identified PKC-β1 and PKC-γ isoforms as essential components of a key signal pathway and IGF-1 as a major extrinsic factor regulating rod formation. In this manuscript, we demonstrate that PKC decreases phosphotyrosine but not phosphoserine on STAT3 in neonatal mouse retinas. Neither IGF-1 nor PMA induced a significant change in the levels of STAT3 or in the levels of the key proteins regulating STAT3 degradation, SOCS3, and PIAS3. Treatment of neonatal mouse retinal explants with sodium orthovanadate inhibited the PKC-mediated reduction in pSTAT3, indicating a role for a phosphatase. Addition of the PTEN inhibitor bpV(phen) to explant cultures treated with IGF-1 or PMA had no effect on the reduction in pSTAT3 levels, but the effect of both IGF-1 and PMA was blocked by a concentration of the inhibitor NSC87877 that is selective for the phosphatases Shp1 and Shp2. Inhibition of Shp1/2 phosphatases was also sufficient to abolish the IGF1-mediated induction of rod photoreceptor differentiation in the retina explant cultures. We conclude that one or both of these phosphatases are key components regulating the formation of rod photoreceptors in mouse retina.

WIF1 causes dysfunction of heart in transgenic mice

Wnt activity is a key regulator of cardiac progenitor cell self-renewal, differentiation and morphogenesis. However, Wnt inhibitory factor 1 (WIF1), a antagonists of Wnt signaling activity, its potential effects on heart development has not yet been approached by either in vivo or in vitro studies. Here, the expression of WIF1 was regulated in a different way in the dilated and hypertrophic cardiomyopathy heart from transgenic mice by mutations in cardiac troponin T, cTnT(R141W) and cTnT(R92Q). The heart tissue specific transgenic mice of WIF1 was studied using M-mode echocardiography and histologic analyses. Production levels of an array of effectors and transcription factors that impact cellular organization and tissue morphology were measured. The effects of WIF1 on β-catenin pathway could be reversed by LiCl regarding signaling pathways and effector and respondent molecules in H9c2 cells, consistent with the expression levels of c-myc, natriuretic peptide precursor type B and skeletal muscle actin α1. Among the most noteworthy findings were that WIF1 impaired the function and structure of heart, and the effects on β-catenin pathway maybe the course of the former. It is anticipated that our findings will contribute to expansion of our understanding of WIF1 biological function on heart development and possible modes of treatment of heart diseases.

Secreted and transmembrane wnt inhibitors and activators

Signaling by the Wnt family of secreted glycoproteins plays important roles in embryonic development and adult homeostasis. Wnt signaling is modulated by a number of evolutionarily conserved inhibitors and activators. Wnt inhibitors belong to small protein families, including sFRP, Dkk, WIF, Wise/SOST, Cerberus, IGFBP, Shisa, Waif1, APCDD1, and Tiki1. Their common feature is to antagonize Wnt signaling by preventing ligand-receptor interactions or Wnt receptor maturation. Conversely, the Wnt activators, R-spondin and Norrin, promote Wnt signaling by binding to Wnt receptors or releasing a Wnt-inhibitory step. With few exceptions, these antagonists and agonists are not pure Wnt modulators, but also affect additional signaling pathways, such as TGF-β and FGF signaling. Here we discuss their interactions with Wnt ligands and Wnt receptors, their role in developmental processes, as well as their implication in disease.

γ-Tocotrienol induces paraptosis-like cell death in human colon carcinoma SW620 cells

Colorectal cancer is one of the most serious illnesses among diagnosed cancer. As a new type of anti-cancer composition from tocotrienol-rich fraction of palm oil, γ-tocotrienol is widely used in anti-cancer research. The objectives of this study were to investigate the effects of γ-tocotrienol on human colon cancer SW620 and HCT-8 cells. We showed that treatment with different concentrations of γ-tocotrienol resulted in a dose dependent inhibition of cell growth. Cell death induced by γ-tocotrienol was mediated by a paraptosis-like cell death in SW620 and HCT-8 cells. Real-time RT-PCR and western blot analyses showed that γ-tocotrienol inhibited the expression level of β-catenin, cyclin D1 and c-jun. These data suggest that a paraptosis-like cell death induced by γ-tocotrienol in SW620 cells is associated with the suppression of the Wnt signaling pathway, which offers a novel tool for treating apoptosis-resistance colon cancer.

The Wnt/β-catenin pathway cross-talks with STAT3 signaling to regulate survival of retinal pigment epithelium cells

Wnt/β-catenin signaling is an essential pathway that regulates numerous cellular processes, including cell survival. The molecular mechanisms contributing to pro-survival Wnt signaling are mostly unknown. Signal transducer and activator of transcription proteins (STATs) are a well-described family of transcription factors. STAT3 induces expression of anti-apoptotic genes in many tissues and is a downstream mediator of protective growth factors and cytokines. In this study, we investigated whether pro-survival Wnt signaling is mediated by STAT3. The Wnt3a ligand activated Wnt signaling in the retinal pigment epithelium ARPE-19 cell line and significantly increased the viability of cells exposed to oxidative stress. Furthermore, Wnt3a increased STAT3 activation and nuclear translocation, as measured by an antibody against phosphorylated STAT3. Reducing STAT3 levels with siRNA eliminated Wnt3a-dependent protection from oxidative stress. Together, these data demonstrate a previously unknown link between Wnt3a-mediated activation of STAT3 and cell survival, and indicate cross-talk between two important pro-survival signaling pathways.

The WIF domain of the human and Drosophila Wif-1 secreted factors confers specificity for Wnt or Hedgehog

The Hedgehog (Hh) and Wnt signaling pathways are crucial for development as well as for adult stem cell maintenance in all organisms from Drosophila to humans. Aberrant activation of these pathways has been implicated in many types of human cancer. During evolution, organisms have developed numerous ways to fine-tune Wnt and Hh signaling. One way is through extracellular modulators that directly interact with Wnt or Hh, such as the Wnt inhibitory factor (Wif-1) family of secreted factors. Interestingly, Wif-1 family members have divergent functions in the Wnt and Hh pathways in different organisms. Whereas vertebrate Wif-1 blocks Wnt signaling, Drosophila Wif-1 [Shifted (Shf)] regulates only Hh distribution and spreading through the extracellular matrix. Here, we investigate which parts of the Shf and human Wif-1 (WIF1) proteins are responsible for functional divergence. We analyze the behavior of domain-swap (the Drosophila and human WIF domain and EGF repeats) chimeric constructs during wing development. We demonstrate that the WIF domain confers the specificity for Hh or Wg morphogen. The EGF repeats are important for the interaction of Wif-1 proteins with the extracellular matrix; Drosophila EGF repeats preferentially interact with the glypican Dally-like (Dlp) when the WIF domain belongs to human WIF1 and with Dally when the WIF domain comes from Shf. These results are important both from the evolutionary perspective and for understanding the mechanisms of morphogen distribution in a morphogenetic field.

The Wnt antagonist Wif-1 interacts with CTGF and inhibits CTGF activity

Wnt inhibitory factor 1 (Wif-1) is a secreted antagonist of Wnt signalling. We recently demonstrated that this molecule is expressed predominantly in superficial layers of epiphyseal cartilage but also in bone and tendon. Moreover, we showed that Wif-1 is capable of binding to several cartilage-related Wnt ligands and interferes with Wnt3a-dependent Wnt signalling in chondrogenic cells. Here we provide evidence that the biological function of Wif-1 may not be confined to the modulation of Wnt signalling but appears to include the regulation of other signalling pathways. Thus, we show that Wif-1 physically binds to connective tissue growth factor (CTGF/CCN2) in vitro, predominantly by interaction with the C-terminal cysteine knot domain of CTGF. In vivo such an interaction appears also likely since the expression patterns of these two secreted proteins overlap in peripheral zones of epiphyseal cartilage. In chondrocytes CTGF has been shown to induce the expression of cartilage matrix genes such as aggrecan (Acan) and collagen2a1 (Col2a1). In this study we demonstrate that Wif-1 is capable to interfere with CTGF-dependent induction of Acan and Col2a1 gene expression in primary murine chondrocytes. Conversely, CTGF does not interfere with Wif-1-dependent inhibition of Wnt signalling. These results indicate that Wif-1 may be a multifunctional modulator of signalling pathways in the cartilage compartment.

The role of glypicans in Wnt inhibitory factor-1 activity and the structural basis of Wif1's effects on Wnt and Hedgehog signaling

Proper assignment of cellular fates relies on correct interpretation of Wnt and Hedgehog (Hh) signals. Members of the Wnt Inhibitory Factor-1 (WIF1) family are secreted modulators of these extracellular signaling pathways. Vertebrate WIF1 binds Wnts and inhibits their signaling, but its Drosophila melanogaster ortholog Shifted (Shf) binds Hh and extends the range of Hh activity in the developing D. melanogaster wing. Shf activity is thought to depend on reinforcing interactions between Hh and glypican HSPGs. Using zebrafish embryos and the heterologous system provided by D. melanogaster wing, we report on the contribution of glypican HSPGs to the Wnt-inhibiting activity of zebrafish Wif1 and on the protein domains responsible for the differences in Wif1 and Shf specificity. We show that Wif1 strengthens interactions between Wnt and glypicans, modulating the biphasic action of glypicans towards Wnt inhibition; conversely, glypicans and the glypican-binding “EGF-like” domains of Wif1 are required for Wif1's full Wnt-inhibiting activity. Chimeric constructs between Wif1 and Shf were used to investigate their specificities for Wnt and Hh signaling. Full Wnt inhibition required the “WIF” domain of Wif1, and the HSPG-binding EGF-like domains of either Wif1 or Shf. Full promotion of Hh signaling requires both the EGF-like domains of Shf and the WIF domains of either Wif1 or Shf. That the Wif1 WIF domain can increase the Hh promoting activity of Shf's EGF domains suggests it is capable of interacting with Hh. In fact, full-length Wif1 affected distribution and signaling of Hh in D. melanogaster, albeit weakly, suggesting a possible role for Wif1 as a modulator of vertebrate Hh signaling.

In developing organisms, cells choose between alternative fates in order to make appropriately patterned tissues, and misregulation of those choices can underlie both developmental defects and cancers. Cells often make these decisions because of signals received from neighboring cells, such as those mediated by the secreted signaling proteins of the Wnt and Hedgehog (Hh) families. While signaling can be regulated by the levels of signaling or receptor proteins expressed by cells, another level of control is exerted by proteins that bind signaling proteins outside of cells and either inhibit or promote the signaling process. In the fruitfly Drosophilamelanogaster, the secreted Shifted protein has been shown to bind Hh and to increase Hh signaling, likely by reinforcing interactions between Hh and cell surface proteins of the glypican family. We provide evidence that the vertebrate homolog of Shifted, Wnt Inhibitory Factor-1 (Wif1), inhibits Wnt activity by a similar mechanism, reinforcing interactions between Wnts and glypicans in a manner that sequesters Wnts from their receptors. We also examine the structural basis for the specificities of Wif1 and Shifted for Wnt and Hh signaling, respectively, and provide evidence that Wif1, although a potent inhibitor of Wnt activity, influences D. melanogaster Hh signaling.

Distinct mechanism of small-for-size fatty liver graft injury--Wnt4 signaling activates hepatic stellate cells

In this study, we aimed to investigate the significance of hepatic stellate cells (HSCs) activation in small-for-size fatty liver graft injury and to explore the underlying molecular mechanism in a rat liver transplantation model. A rat orthotopic liver transplantation model using fatty grafts (40% of fatty changes) and cirrhotic recipients was applied. Intragraft gene expression profiles, ultrastructure features and HSCs activation were compared among the rats received different types of grafts (whole vs. small-for-size, normal vs. fatty). The distinct molecular signature of small-for-size fatty graft injury was identified by cDNA microarray screening and confirmed by RT-PCR detection. In vitro functional studies were further conducted to investigate the direct effect of specific molecular signature on HSCs activation. HSCs activation was predominantly present in small-for-size fatty grafts during the first 2 weeks after transplantation, and was strongly correlated with progressive hepatic sinusoidal damage and significant upregulation of intragraft Wnt4 signaling pathway. In vitro suppression of Wnt4 expression could inhibit HSC activation directly. In conclusion, upregulation of Wnt4 signaling led to direct HSC activation and subsequently induced small-for-size fatty liver grafts injury. Discovery of this distinct mechanism may lay the foundation for prophylactic treatment for marginal graft injury in living donor liver transplantation.

Stem cell paracrine actions and tissue regeneration

Stem cells have emerged as a key element of regenerative medicine therapies due to their inherent ability to differentiate into a variety of cell phenotypes, thereby providing numerous potential cell therapies to treat an array of degenerative diseases and traumatic injuries. A recent paradigm shift has emerged suggesting that the beneficial effects of stem cells may not be restricted to cell restoration alone, but also due to their transient paracrine actions. Stem cells can secrete potent combinations of trophic factors that modulate the molecular composition of the environment to evoke responses from resident cells. Based on this new insight, current research directions include efforts to elucidate, augment and harness stem cell paracrine mechanisms for tissue regeneration. This article discusses the existing studies on stem/progenitor cell trophic factor production, implications for tissue regeneration and cancer therapies, and development of novel strategies to use stem cell paracrine delivery for regenerative medicine.

Wnt inhibitory factor 1 decreases tumorigenesis and metastasis in osteosarcoma

It has been reported that the progression of osteosarcoma was closely associated with the aberrant activation of canonical Wnt signaling. Wnt inhibitory factor-1 (WIF-1) is a secreted Wnt inhibitor whose role in human osteosarcoma remains unknown. In this study, WIF-1 expression in NHOst and osteosarcoma cell lines was determined by real-time reverse transcription-PCR, methylation-specific PCR, and Western blotting analysis. In addition, tissue array from patient samples was examined for WIF-1 expression by immunohistochemistry. Compared with normal human osteoblasts, WIF-1 mRNA and protein levels were significantly downregulated in several osteosarcoma cell lines. The downregulation of WIF-1 mRNA expression is associated with its promoter hypermethylation in these tested cell lines. Importantly, WIF-1 expression was also downregulated in 76% of examined osteosarcoma cases. These results suggest that the downregulation of WIF-1 expression plays a role in osteosarcoma progression. To further study the potential tumor suppressor function of WIF-1 in osteosarcoma, we established stable 143B cell lines overexpressing WIF-1. WIF-1 overexpression significantly decreased tumor growth rate in nude mice as examined by the s.c. injection of 143B cells stably transfected with WIF-1 and vector control. WIF-1 overexpression also markedly reduced the number of lung metastasis in vivo in an orthotopic mouse model of osteosarcoma. Together, these data suggest that WIF-1 exerts potent antiosteosarcoma effect in vivo in mouse models. Therefore, the reexpression of WIF-1 in WIF-1-deficient osteosarcoma represents a potential novel treatment and preventive strategy.

Wif-1 is expressed at cartilage-mesenchyme interfaces and impedes Wnt3a-mediated inhibition of chondrogenesis

Wnt factors are involved in the regulation of all steps of cartilage development. The activity of Wnt factors is generally regulated at the extracellular level by factors like the Dkk family, sFRPs, Cerberus and Wnt inhibitory factor 1 (Wif-1). Here we report that Wif-1 is highly expressed at cartilage-mesenchyme interfaces of the early developing skeleton. In fetal and postnatal skeletal development, Wif-1 is expressed in a sharply restricted zone in the upper hyaline layer of epiphyseal and articular cartilage and in trabecular bone. Coimmunoprecipitation and pull-down assays using recombinant Wif-1 and Wnt factors show specific binding of Wif-1 to Wnt3a, Wnt4, Wnt5a, Wnt7a, Wnt9a and Wnt11. Moreover, Wif-1 was able to block Wnt3a-mediated activation of the canonical Wnt signalling pathway. Consequently, Wif-1 impaired growth of mesenchymal precursor cells and neutralised Wnt3a-mediated inhibition of chondrogenesis in micromass cultures of embryonic chick limb-bud cells. These results identify Wif-1 as a novel extracellular Wnt modulator in cartilage biology.

Zebrafish olfactomedin 1 regulates retinal axon elongation in vivo and is a modulator of Wnt signaling pathway

Olfactomedin 1 (Olfm1) is a secreted glycoprotein belonging to a family of olfactomedin domain-containing proteins. It is involved in the regulation of neural crest production in chicken and promotes neuronal differentiation in Xenopus. Here, we investigate the functions of Olfm1 in zebrafish eye development. Overexpression of full-length Olfm1, and especially its BMY form lacking the olfactomedin domain, increased the thickness of the optic nerve and produced a more extended projection field in the optic tectum compared with control embryos. In contrast, injection of olfm1-morpholino oligonucleotide (Olfm1-MO) reduced the eye size, inhibited optic nerve extension, and increased the number of apoptotic cells in the retinal ganglion cell and inner nuclear layers. Overexpression of full-length Olfm1 increased the lateral separation of the expression domains of eye-field markers, rx3 and six3. The Olfm1-MO had the opposite effect. These data suggest that zebrafish Olfm1 may play roles in the early eye determination, differentiation, optic nerve extension, and branching of the retinal ganglion cell axon terminals, with the N-terminal region of Olfm1 being critical for these effects. Injection of RNA encoding WIF-1, a secreted inhibitor of Wnt signaling, caused changes in the expression pattern of rx3 similar to those observed after Olfm1-MO injection. Simultaneous overexpression of WIF-1 and Olfm1 abolished the WIF-1 effect. Physical interaction of WIF-1 and Olfm1 was demonstrated by coimmunoprecipitation experiments. We concluded that Olfm1 serves as a modulator of Wnt signaling.

Expression pattern of Wnt inhibitor factor 1(Wif1) during the development in mouse CNS

Wnt inhibitor factor-1 (WIF-1) is an extracellular antagonist of Wnts secreted proteins. Here we describe the expression pattern of Wif1 throughout the development of the mouse central nervous system (CNS). Wif1 mRNA can be detected as early as the developmental stage E11, and expression persists to adulthood. In embryonic stages, the level of Wif1 expression was very prominent in several areas including the cerebral cortex, the diencephalon and the midbrain, with the strongest level in the hippocampal plate and the diencephalon. However, after birth, the expression level of Wif1 decreased in the cortex and diencephalon. By adulthood, Wif1 is mainly expressed in the medial habenular nucleus (MHb) in the epithalamus, the mitral layer cells in the olfactory bulb and a few nuclei in the hypothalamus. Our data shows that the expression of Wif1 was very strong during embryonic development of the CNS and suggests that Wif1 may play an essential role in the spatial and temporal regulation of Wnt signals.

Wnt signaling in eye organogenesis

The vertebrate eye consists of multiple tissues with distinct embryonic origins. To ensure formation of the eye as a functional organ, development of ocular tissues must be precisely coordinated. Besides intrinsic regulators, several extracellular pathways have been shown to participate in controlling critical steps during eye development. Many components of Wnt/Frizzled signaling pathways are expressed in developing ocular tissues, and substantial progress has been made in the past few years in understanding their function during vertebrate eye development. Here, I summarize recent work using functional experiments to elucidate the roles of Wnt/Frizzled pathways during development of ocular tissues in different vertebrates.

Docking of fatty acids into the WIF domain of the human Wnt inhibitory factor-1

Palmitoylated Wnt proteins comprise a conserved family of secreted signaling molecules associated with variety of human cancers. WIF domain of the human WIF (Wnt inhibitory factor)-1 is sufficient for Wnt binding and signaling inhibition. Detailed interactions between Wnt and WIF-1 are not known. Computational docking was employed to identify a possible fatty acid binding site in the WIF domain. A putative binding site was identified inside the domain. WIF domain exhibited the highest affinity for C16:0-C18:0 (-22 kJ/mol free energy of binding) fatty acids. The results suggest a role of the WIF domain as a palmitoyl binding domain required for WIF-1 binding to palmitoylated Wnt and signaling inhibition.

Characterization of Wnt signaling during photoreceptor degeneration

PURPOSE

The Wnt pathway is an essential signaling cascade that regulates multiple processes in developing and adult tissues, including differentiation, cellular survival, and stem cell proliferation. The authors recently demonstrated altered expression of Wnt pathway genes during photoreceptor death in rd1 mice, suggesting an involvement for Wnt signaling in the disease process. In this study, the authors investigated the role of Wnt signaling in retinal degeneration.

METHODS

The Wnt signaling reporter mouse line Tcf-LacZ was crossed with retinal degeneration rd1 mice, and beta-galactosidase expression was used to localize Wnt signaling during photoreceptor death. To analyze the role of Wnt signaling activation, primary mixed retinal cultures were prepared, and XTT and TUNEL assays were used to quantify cell death. Luciferase reporter assays were used to measure Wnt signaling.

RESULTS

The canonical Wnt signaling pathway was activated in Müller glia and the ganglion cell layer during rod photoreceptor degeneration in rd1/Tcf-LacZ mice. Wnt signaling was confirmed in cultured primary Müller glia. Furthermore, Wnt signaling activators protected photoreceptors in primary retinal cultures from H(2)O(2)-induced oxidative stress. The Wnt ligands Wnt5a, Wnt5b, Wnt10a, and Wnt13 were expressed in the degenerating retina and are candidate Wnt signaling activators in vivo.

CONCLUSIONS

This study is the first demonstration that Wnt signaling is activated in the degenerating retina and that it protects retinal cultures from oxidative stress. These data suggest that Wnt signaling is a component of the glial protective response during photoreceptor injury. Therefore, inducing Wnt activation, alone or in combination with growth factors, may increase the threshold for apoptosis and halt or delay further photoreceptor degeneration.

Familial cavitary optic disk anomalies: identification of a novel genetic locus

PURPOSE

To identify the chromosomal location of the gene involved in the pathogenesis of cavitary optic disk anomalies in a large pedigree with autosomal dominant inheritance of disease.

DESIGN

Linkage analysis of a pedigree affected with cavitary optic disk anomalies.

METHODS

Optic disk photographs were examined for the presence of cavitary optic disk anomalies. Sixteen affected family members and one obligate carrier were identified and studied with linkage analysis using both microarrays of single nucleotide polymorphisms (SNPs) and short tandem repeat polymorphism (STRP) markers.

RESULTS

Multipoint linkage analysis of SNP genotypes yielded a maximum nonparametric logarithm of the odds (LOD) score of 21.7 with markers located on chromosome 12q. Linkage was confirmed with 16 STRP markers in the 12q region. A maximum two-point LOD score of 4.06 (theta = 0) was obtained with marker D12S1700. The disease interval defined by observed recombinants is 9.1 cM, which corresponds to 13.5 Mbp. Three candidate genes (GDF-11, NEUROD4, and WIF1) in the chromosome 12q locus were evaluated as possible disease-causing genes. No mutations were detected in the coding sequence of these genes.

CONCLUSIONS

The discovery of the chromosomal location of a gene responsible for cavitary optic disk anomalies is a key step in identifying the genetic basis of this condition and ultimately may provide important insight into the pathogenesis of more common optic nerve diseases such as normal-tension glaucoma and primary open-angle glaucoma (POAG).

WIF1, an inhibitor of the Wnt pathway, is rearranged in salivary gland tumors

Chromosome rearrangements involving 12q13-15 are frequent among several tumors, including pleomorphic adenomas. The common molecular target for these aberrations is the HMGA2 gene, but various fusion partners of HMGA2 have been reported in tumors. Here we report the identification of the WNT inhibitory factor 1 (WIF1) gene as a novel HMGA2 fusion partner in a salivary gland pleomorphic adenoma. In normal salivary gland tissue WIF1 is expressed at a high level and HMGA2 is not expressed. However, in the pleomorphic adenoma expressing the HMGA2/WIF1 fusion transcript, we observed re-expression of HMGA2 wild-type transcripts and very low levels of WIF1 expression. These data suggest a possible synergistic effect between upregulation of HMGA2 and downregulation of WIF1. We screened 13 additional benign and malignant salivary gland tumors and detected WIF1 rearrangement in one out of two carcinomas ex-pleomorphic adenoma analyzed. In this malignant tumor, the rearrangement of one WIF1 allele coexists with loss of the other allele, a classic signature of a tumor suppressor gene. WIF1 is an antagonist of the Wnt signaling pathway, which plays a critical role in human cancer. In transgenic mouse models, Wnt activation leads to a high frequency of benign and malignant salivary gland tumors. To our knowledge, this is the first report suggesting that WIF1 is a recurrent target in human salivary gland oncogenesis and that downregulation of WIF1 plays a role in the development and/or progression of pleomorphic adenomas.

Beta-catenin is essential for lamination but not neurogenesis in mouse retinal development

During vertebrate retinal development, the seven retinal cell types differentiate sequentially from a single population of retinal progenitor cells (RPCs) and organize themselves into a distinct laminar structure. The purpose of this study was to determine whether beta-catenin, which functions both as a nuclear effector for the canonical Wnt signaling pathway and as a regulator of cell adhesion, is required for retinal neurogenesis or lamination. We used the Cre-loxP system to either eliminate beta-catenin or to express a constitutively active form during retinal neurogenesis. Eliminating beta-catenin did not affect cell differentiation, but did result in the loss of the radial arrangement of RPCs and caused abnormal migration of differentiated neurons. As a result, the laminar structure was massively disrupted in beta-catenin-null retinas, although all retinal cell types still formed. In contrast to other neural tissues, eliminating beta-catenin did not significantly reduce the proliferation rate of RPCs; likewise, activating beta-catenin ectopically in RPCs did not result in overproliferation, but loss of neural retinal identity. These results indicate that beta-catenin is essential during retinal neurogenesis as a regulator of cell adhesion but not as a nuclear effector of the canonical Wnt signaling pathway. The results further imply that retinal lamination and retinal cell differentiation are genetically separable processes.

Nok plays an essential role in maintaining the integrity of the outer nuclear layer in the zebrafish retina

Proper visual function of the vertebrate retina requires the maintenance of the integrity of the retinal outer nuclear layer (ONL), which is often affected in many blinding human retinal diseases. While the structural integrity of the ONL has long been considered to be maintained primarily through the outer limiting membrane (OLM), we have little knowledge on the development and maintenance of the OLM itself. Here, by analyzing the adhering properties of photoreceptors in zebrafish N-cad and nok mutants, we demonstrated for the first time that the nok gene is essential for the establishment and/or maintenance of the OLM. In addition, our results imply the possibility that Nok, Crumbs, and their associated proteins may constitute a type of photoreceptor-photoreceptor junctional complex that has not be described before. Thus, our study provides novel insights into the mechanisms by which the integrity of the ONL is maintained in the vertebrate retina.

Wnt inhibitory factor-1, a Wnt antagonist, is silenced by promoter hypermethylation in malignant pleural mesothelioma

Wnt inhibitory factor-1 (WIF-1) is a secreted protein that antagonizes Wnt signaling. We recently demonstrated the importance of aberrant activation of the Wnt signaling pathway in various cancers including malignant pleural mesothelioma. In this study, we revealed downregulated WIF-1 expression in cell lines and primary tissue when compared to normal mesothelial cell lines and adjacent pleura, respectively. We observed hypermethylation in four of four mesothelioma cell lines, but not in two normal mesothelial cell lines. In primary tissue samples, we observed methylation in three paired tumor specimens compared to their adjacent normal pleura and methylation in eight of nine unpaired tumor tissue samples. Taken together, our studies suggest that WIF-1 silencing due to its promoter hypermethylation is an important mechanism underlying the constitutively activated Wnt signaling in mesothelioma. New therapies toward inhibition of the Wnt pathway through WIF-1 might be promising for the future treatment of malignant mesothelioma.

NMR structure of the WIF domain of the human Wnt-inhibitory factor-1

The human Wnt-binding protein Wnt-inhibitory factor-1 (WIF-1) comprises an N-terminal WIF module followed by five EGF-like repeats. Here we report the three-dimensional structure of the WIF domain of WIF-1 determined by NMR spectroscopy. The fold consists of an eight-stranded beta-sandwich reminiscent of the immunoglobulin fold. Residual detergent (Brij-35) used in the refolding protocol was found to bind tightly to the WIF domain. The binding site was identified by intermolecular nuclear Overhauser effects observed between the WIF domain and the alkyl chain of the detergent. The results point to a possible role of WIF domains as a recognition motif of Wnt and Drosophila Hedgehog proteins that are activated by palmitoylation.

Challenges in the study of neuronal differentiation: a view from the embryonic eye

Progress in the study of the molecular mechanisms that regulate neuronal differentiation has been quite impressive in recent years, and promises to continue to an equally fast pace. This should not lead us into a sense of complacency, however, because there are still significant barriers that cannot be overcome by simply conducting the same type of experiments that we have been performing thus far. This article will describe some of these challenges, while highlighting the conceptual and methodological breakthroughs that will be necessary to overcome them.

PAX2 activates WNT4 expression during mammalian kidney development

The transcription factor PAX2 is expressed during normal kidney development and is thought to influence outgrowth and branching of the ureteric bud. Mice with homozygous null Pax2 mutations have developmental defects of the midbrain-hindbrain region, optic nerve, and ear and are anephric. During nephrogenesis, PAX2 is also expressed by mesenchymal cells as they cluster and reorganize to form proximal elements of each nephron, but the function of PAX2 in these cells is unknown. In this study we hypothesized that PAX2 activates expression of WNT4, a secreted glycoprotein known to be critical for successful nephrogenesis. PAX2 protein was identified in distal portions of the "S-shaped" body, and the protein persists in the emerging proximal tubules of murine fetal kidney. PAX2 activated WNT4 promoter activity 5-fold in co-transfection assays with JTC12 cells derived from the proximal tubule. Inspection of the 5'-flanking sequence of the human WNT4 gene identified three novel PAX2 recognition motifs; each exhibited specific PAX2 protein binding in electromobility shift assays. Two motifs were contained within a completely duplicated 0.66-kb cassette. Transfection of JTC12 cells with a PAX2 expression vector was associated with a 7-fold increase in endogenous WNT4 mRNA. In contrast, Wnt4 mRNA was decreased by 60% in mesenchymal cell condensates of fetal kidney from mice with a heterozygous Pax2 mutation. We speculated that a key function of PAX2 is to activate WNT4 gene expression in metanephric mesenchymal cells as they differentiate to form elements of the renal tubules.

The Wnt signaling pathway in retinal degenerations

The retina is a complex tissue composed of multiple interconnected cell layers, highly specialized for transforming light and color into electrical signals perceived by the brain. Damage or death of the primary light-sensing cells, the photoreceptors, results in devastating effects on vision. Despite the identification of numerous mutations that cause inherited retinal degenerations, the cellular and molecular mechanisms leading from the primary mutations to photoreceptor apoptosis are not understood. Wnt signaling has essential regulatory functions in a wide variety of critical developmental processes. Our research and others' have suggested that the Wnt pathway may be involved in retinal degeneration. Wnt ligands regulate developmental death of Drosophila photoreceptors, dysregulated Wnt signaling is involved in neuronal degeneration elsewhere in the central nervous system and Wnts control the expression of pro-survival growth factors in mammalian tissues. Additionally, altered expression of Wnt pathway genes, including the anti-apoptotic Wnt signaling regulator Dickkopf 3 (Dkk3), were observed during photoreceptor loss. This review examines the evidence and develops a model proposing a pro-survival role for Wnt signaling during photoreceptor injury. Because manipulating Wnt signaling has been demonstrated to have therapeutic potential for the treatment of Alzheimers disease, understanding the involvement of Wnts in photoreceptor death will determine whether targeting the Wnt pathway should also be considered as a possible therapeutic strategy for retinal degenerations.

Shifted, the Drosophila Ortholog of Wnt Inhibitory Factor-1, Controls the Distribution and Movement of Hedgehog

We here identify and characterize an extracellular modulator of Hedgehog signaling in Drosophila, Shifted. Shifted is required for high levels of long-range signaling in the developing wing imaginal disc. Surprisingly, shifted encodes the only Drosophila ortholog of the secreted vertebrate protein Wnt Inhibitory Factor-1 (WIF-1), whose known role is to bind to extracellular Wnts and inhibit their activity. However, Shifted does not regulate Hedgehog signaling by affecting Wingless or Wnt signaling. We show instead that Shifted is a secreted protein that acts over a long distance and is required for the normal accumulation of Hh protein and its movement in the wing. Our data further indicate that Shf interacts with Hh and the heparan sulfate proteoglycans. Therefore, we propose that Shf stabilizes the interaction between Hh and the proteoglycans, an unexpected role for a member of the WIF-1 family.