Wls-mediated Wnts differentially regulate distal limb patterning and tissue morphogenesis

Lgr6-expressing functional nail stem-like cells differentiated from human-induced pluripotent stem cells

The nail matrix containing stem cell populations produces nails and may contribute to fingertip regeneration. Nails are important tissues that maintain the functions of the hand and foot for handling objects and locomotion. Tumor chemotherapy impairs nail growth and, in many cases, loses them, although not permanently. In this report, we have achieved the successful differentiation of nail stem (NS)-like cells from human-induced pluripotent stem cells (iPSCs) via digit organoids by stepwise stimulation, tracing the molecular processes involved in limb development. Comprehensive mRNA sequencing analysis revealed that the digit organoid global gene expression profile fits human finger development. The NS-like cells expressed Lgr6 mRNA and protein and produced type-I keratin, KRT17, and type-II keratin, KRT81, which are abundant in nails. Furthermore, we succeeded in producing functional Lgr6-reporter human iPSCs. The reporter iPSC-derived Lgr6-positive cells also produced KRT17 and KRT81 proteins in the percutaneously transplanted region. To the best of our knowledge, this is the first report of NS-like cell differentiation from human iPSCs. Our differentiation method and reporter construct enable the discovery of drugs for nail repair and possibly fingertip-regenerative therapy.

Overexpression of Wnt5a promoted the protective effect of mesenchymal stem cells on Lipopolysaccharide-induced endothelial cell injury via activating PI3K/AKT signaling pathway

BACKGROUND

Lung endothelial barrier injury plays an important role in the pathophysiology of acute lung injury/acute respiratory distress syndrome (ALI/ARDS). Mesenchymal stem cells (MSCs) therapy has shown promise in ARDS treatment and restoration of the impaired barrier function. It has been reported that Wnt5a shows protective effects on endothelial cells. Therefore, the study aimed to investigate whether overexpression of Wnt5a could promote the protective effects of MSCs on Lipopolysaccharide (LPS)-induced endothelial cell injury.

METHODS

To evaluate the protective effects of MSCs overexpressing Wnt5a, we assessed the migration, proliferation, apoptosis, and angiogenic ability of endothelial cells. We assessed the transcription of protective cellular factors using qPCR and determined the molecular mechanism using Western blot analysis.

RESULTS

Overexpression of Wnt5a upregulated the transcription of protective cellular factors in MSCs. Co-culture of MSCWnt5a promoted endothelial migration, proliferation and angiogenesis, and inhibited endothelial cell apoptosis through the PI3K/AKT pathway.

CONCLUSIONS

Overexpression of Wnt5a promoted the therapeutic effect of MSCs on endothelial cell injury through the PI3K/AKT signaling. Our study provides a novel approach for utilizing genetically modified MSCs in the transplantation therapy for ARDS.

Sirtuin 6 Overexpression Improves Rotator Cuff Tendon-to-Bone Healing in the Aged

Aging is an independent risk factor for recurrent tearing after surgical repair of rotator cuff ruptures around the tendon-to-bone area. However, aging signature factors and related mechanisms involved in the healing of the rotator cuff are still unknown. We hypothesized that differences in proteins involved in the rotator cuff according to age may affect tendon-to-bone healing. The proteome analysis performed to identify the signature aging proteins of the rotator cuff confirmed the sirtuin signal as an age-specific protein. In particular, the expression of SIRT6 was markedly down-regulated with age. Ingenuity pathway analysis of omics data from age-dependent rat rotator cuffs and linear regression from human rotator cuffs showed SIRT6 to be closely related to the Wnt/β-catenin signal. We confirmed that overexpression of SIRT6 in the rotator cuff and primary tenocyte regulated canonical Wnt signaling by inhibiting the transcriptional expression of sclerostin, a Wnt antagonist. Finally, SIRT6 overexpression promoted tendon-to-bone healing after tenotomy with reconstruction in elderly rats. This approach is considered an effective treatment method for recovery from recurrent rotator cuff tears, which frequently occur in the elderly.

Wnt/β-catenin signaling controls mouse eyelid growth by mediating epithelial-mesenchymal interactions

PURPOSE

To investigate the role of Wnt/β-catenin signaling in mouse eyelid development.

METHODS

Wnt/β-catenin signaling was disrupted by deleting supraorbital mesenchymal β-catenin or epithelial Wls. p63 was removed to determine whether the expression of Wnts is affected. The eyelid morphology was examined at different stages. Proliferation, apoptosis, and expression of Wnt ligands and their target genes were analyzed via immunofluorescence staining, TUNEL assay, and in situ hybridization.

RESULTS

Deletion of β-catenin in supraorbital mesenchyme abolishes eyelid growth by causing decreased proliferation in supraorbital epithelium and underlying mesenchyme. Inhibition of Wnt secretion by deleting Wls in supraorbital epithelium results in failure of eyelid development, similar to the effects of deleting mesenchymal β-catenin. Knockout of p63 results in formation of hypoplastic eyelids and reduced expression of several Wnt ligands in eyelid epithelium.

CONCLUSIONS

Epithelial Wnt ligands activate mesenchymal Wnt/β-catenin signaling to control eyelid growth and their expression is partially regulated by p63.

The role of Evi/Wntless in exporting Wnt proteins

Intercellular communication by Wnt proteins governs many essential processes during development, tissue homeostasis and disease in all metazoans. Many context-dependent effects are initiated in the Wnt-producing cells and depend on the export of lipidated Wnt proteins. Although much focus has been on understanding intracellular Wnt signal transduction, the cellular machinery responsible for Wnt secretion became better understood only recently. After lipid modification by the acyl-transferase Porcupine, Wnt proteins bind their dedicated cargo protein Evi/Wntless for transport and secretion. Evi/Wntless and Porcupine are conserved transmembrane proteins, and their 3D structures were recently determined. In this Review, we summarise studies and structural data highlighting how Wnts are transported from the ER to the plasma membrane, and the role of SNX3-retromer during the recycling of its cargo receptor Evi/Wntless. We also describe the regulation of Wnt export through a post-translational mechanism and review the importance of Wnt secretion for organ development and cancer, and as a future biomarker.

The WNT7A/WNT7B/GPR124/RECK signaling module plays an essential role in mammalian limb development

In central nervous system vascular endothelial cells, signaling via the partially redundant ligands WNT7A and WNT7B requires two co-activator proteins, GPR124 and RECK. WNT7A and RECK have been shown previously to play a role in limb development, but the mechanism of RECK action in this context is unknown. The roles of WNT7B and GPR124 in limb development have not been investigated. Using combinations of conventional and/or conditional loss-of-function alleles for mouse Wnt7a, Wnt7b, Gpr124 and Reck, including a Reck allele that codes for a protein that is specifically defective in WNT7A/WNT7B signaling, we show that reductions in ligand and/or co-activator function synergize to cause reduced and dysmorphic limb bone growth. Two additional limb phenotypes – loss of distal Lmx1b expression and ectopic growth of nail-like structures – occur with reduced Wnt7a/Wnt7b gene copy number and, respectively, with Reck mutations and with combined Reck and Gpr124 mutations. A third limb phenotype – bleeding into a digit – occurs with the most severe combinations of Wnt7a/Wnt7b, Reck and Gpr124 mutations. These data imply that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system functions as an integral unit in limb development.

Summary: Genetic analyses in mice show that the WNT7A/WNT7B-FRIZZLED-LRP5/LRP6-GPR124-RECK signaling system, first defined in the context of CNS angiogenesis and barrier development, also functions as an integral unit in limb development.

Mechanical feedback defines organizing centers to drive digit emergence

During embryonic development, digits gradually emerge in a periodic pattern. Although genetic evidence indicates that digit formation results from a self-organizing process, the underlying mechanisms are still unclear. Here, we find that convergent-extension tissue flows driven by active stresses underlie digit formation. These active stresses simultaneously shape cartilage condensations and lead to the emergence of a compressive stress region that promotes high activin/p-SMAD/SOX9 expression, thereby defining digit-organizing centers via a mechanical feedback. In Wnt5a mutants, such mechanical feedback is disrupted due to the loss of active stresses, organizing centers do not emerge, and digit formation is precluded. Thus, digit emergence does not result solely from molecular interactions, as was previously thought, but requires a mechanical feedback that ensures continuous coupling between phalanx specification and elongation. Our work, which links mechanical and molecular signals, provides a mechanistic context for the emergence of organizing centers that may underlie various developmental processes.

Promethazine Downregulates Wnt/β-Catenin Signaling and Increases the Biomechanical Forces of the Injured Achilles Tendon in the Early Stage of Healing

BACKGROUND

Wnt/β-catenin signaling suppresses the differentiation of cultured tenocytes, but its roles in tendon repair remain mostly elusive. No chemical compounds are currently available to treat tendon injury.

HYPOTHESIS

We hypothesized that the inhibition of Wnt/β-catenin signaling would accelerate tendon healing.

STUDY DESIGN

Controlled laboratory study.

METHODS

Tendon-derived cells (TDCs) were isolated from rat Achilles tendons. The right Achilles tendon was injured via a dermal punch, while the left tendon was sham operated. A Wnt/β-catenin inhibitor, IWR-1, and an antihistamine agent, promethazine (PH), were locally and intramuscularly injected, respectively, for 2 weeks after surgery. The healing tendons were histologically and biomechanically evaluated.

RESULTS

The amount of β-catenin protein was increased in the injured tendons from postoperative weeks 0.5 to 2. Inhibition of Wnt/β-catenin signaling by IWR-1 in healing tendons improved the histological abnormalities and decreased β-catenin, but it compromised the biomechanical properties. As we previously reported that antihistamine agents suppressed Wnt/β-catenin signaling in human chondrosarcoma cells, we examined the effects of antihistamines on TDCs. We found that a first-generation antihistamine agent, PH, increased the expression of the tendon marker genes Mkx and Tnmd in TDCs. Intramuscular injection of PH did not improve histological abnormalities, but it decreased β-catenin in healing tendons and increased the peak force and stiffness of the healing tendons on postoperative week 2. On postoperative week 8, however, the biomechanical properties of vehicle-treated tendons became similar to those of PH-treated tendons.

CONCLUSION

IWR-1 and PH suppressed Wnt/β-catenin signaling and improved the histological abnormalities of healing tendons. IWR-1, however, compromised the biomechanical properties of healing tendons, whereas PH improved them.

CLINICAL RELEVANCE

PH is a candidate repositioned drug that potentially accelerates tendon repair.

Comparison of Tendon Development Versus Tendon Healing and Regeneration

Tendon is a vital connective tissue in human skeletal muscle system, and tendon injury is very common and intractable in clinic. Tendon development and repair are two closely related but still not fully understood processes. Tendon development involves multiple germ layer, as well as the regulation of diversity transcription factors (Scx et al.), proteins (Tnmd et al.) and signaling pathways (TGFβ et al.). The nature process of tendon repair is roughly divided in three stages, which are dominated by various cells and cell factors. This review will describe the whole process of tendon development and compare it with the process of tendon repair, focusing on the understanding and recent advances in the regulation of tendon development and repair. The study and comparison of tendon development and repair process can thus provide references and guidelines for treatment of tendon injuries.

Endothelial Wnts control mammary epithelial patterning via fibroblast signaling

Endothelial and fibroblast niches are crucial for epithelial organs. How these heterotypic cells interact is of great interest. In this study, we reveal an axis of signaling in which fibroblasts relay Wnt signals from the endothelial niche to organize epithelial patterning. We generate an Axin2-membrane GFP (mGFP) reporter mouse and observe robust Wnt/β-catenin signaling activities in fibroblasts surrounding the mammary epithelium. To enable cell-type-specific gene manipulation in vitro, we establish an organoid system via coculture of endothelial cells (ECs), fibroblasts, and mammary epithelial cells. Deletion of β-catenin in fibroblasts impedes epithelium branching, and ECs are responsible for the activation of Wnt/β-catenin signaling in fibroblasts. In vivo, EC deletion of Wntless inhibits Wnt/β-catenin signaling activity in fibroblasts, rendering a reduction in epithelial branches. These findings highlight the significance of the endothelial niche in tissue patterning, shedding light on the interactive mechanisms in which distinct niche components orchestrate epithelial organogenesis and tissue homeostasis.

3D printing of chemical-empowered tendon stem/progenitor cells for functional tissue repair

Tendon injuries are the leading cause of chronic debilitation to patients. Tendon stem/progenitor cells (TSPCs) are potential seed cells for tendon tissue engineering and regeneration, but TSPCs are prone to lose their distinct phenotype in vitro and specific differentiation into the tenocyte lineage is challenging. Utilizing small molecules in an ex vivo culture system may be a promising solution and can significantly improve the therapeutic applications of these cells. Here, by using an image-based, high-throughput screening platform on small molecule libraries, this study established an effective stepwise culture strategy for TSPCs application. The study formulated a cocktail of small molecules which effected proliferation, tenogenesis initiation and maturation phases, and significantly upregulated expression of various tendon-related genes and proteins in TSPCs, which were demonstrated by high-throughput PCR, ScxGFP reporter assay and immunocytochemistry. Furthermore, by combining small molecule-based culture system with 3D printing technology, we embedded living, chemical-empowered TSPCs within a biocompatible hydrogel to engineer tendon grafts, and verified their enhanced ability in promoting functional tendon repair and regeneration both in vivo and in situ. The stepwise culture system for TSPCs and construction of engineered tendon grafts can not only serve as a platform for further studies of underlying molecular mechanisms of tenogenic differentiation, but also provide a new strategy for tissue engineering and development of novel therapeutics for clinical applications.

Activation of β-catenin by TGF-β1 promotes ligament-fibroblastic differentiation and inhibits cementoblastic differentiation of human periodontal ligament cells

TGF-β and Wnt/β-catenin signaling pathways are known to be essential for the development of periodontal tissue. In this study, we examined the crosstalk between TGF-β and Wnt/β-catenin signaling in ligament-fibroblastic differentiation of human periodontal ligament cells (hPDLCs). TGF-β1 treatment significantly increased the expression of ligament-fibroblastic markers, but such expression was preventing by treatment with SB431542, a TGF-β type I receptor inhibitor. As well as phosphorylation of Smad3, TGF-β1 increased β-catenin activation. The depletion of β-catenin reduced the expression of ligament-fibroblastic markers, suggesting that β-catenin is essential for ligament differentiation. The effect of TGF-β1 on β-catenin activation did not seem to be much correlated with Wnt stimuli, but endogenous DKK1 was suppressed by TGF-β1, indicating that β-catenin activation could be increased much more by TGF-β1. In addition to DKK1 suppression, Smad3 phosphorylation by TGF-β1 facilitated the nuclear translocation of cytoplasmic β-catenin. In contrast to ligament-fibroblastic differentiation, inhibition of TGF-β1 signaling was needed for cementoblastic differentiation of hPDLCs. BMP7 treatment accompanied by inhibition of TGF-β1 signaling had a synergistic effect on cementoblastic differentiation. In conclusion, β-catenin activation by TGF-β1 caused ligament-fibroblastic differentiation of hPDLCs, and the presence of TGF-β1 stimuli basically determined whether hPDLCs are differentiated into ligament progenitor or cementoblasts.

Wntless regulates lipogenic gene expression in adipocytes and protects against diet-induced metabolic dysfunction

OBJECTIVE

Obesity is a key risk factor for many secondary chronic illnesses, including type 2 diabetes and cardiovascular disease. Canonical Wnt/β-catenin signaling is established as an important endogenous inhibitor of adipogenesis. This pathway is operative in mature adipocytes; however, its roles in this context remain unclear due to complexities of Wnt signaling and differences in experimental models. In this study, we used novel cultured cell and mouse models to investigate functional roles of Wnts secreted from adipocytes.

METHODS

We generated adipocyte-specific Wntless (Wls) knockout mice and cultured cell models to investigate molecular and metabolic consequences of disrupting Wnt secretion from mature adipocytes. To characterize Wls-deficient cultured adipocytes, we evaluated the expression of Wnt target and lipogenic genes and the downstream functional effects on carbohydrate and lipid metabolism. We also investigated the impact of adipocyte-specific Wls deletion on adipose tissues and global glucose metabolism in mice fed normal chow or high-fat diets.

RESULTS

Many aspects of the Wnt signaling apparatus are expressed and operative in mature adipocytes, including the Wnt chaperone Wntless. Deletion of Wntless in cultured adipocytes results in the inhibition of de novo lipogenesis and lipid monounsaturation, likely through repression of Srebf1 (SREBP1c) and Mlxipl (ChREBP) and impaired cleavage of immature SREBP1c into its active form. Adipocyte-specific Wls knockout mice (Wls-/-) have lipogenic gene expression in adipose tissues and isolated adipocytes similar to that of controls when fed a normal chow diet. However, closer investigation reveals that a subset of Wnts and downstream signaling targets are upregulated within stromal-vascular cells of Wls-/- mice, suggesting that adipose tissues defend loss of Wnt secretion from adipocytes. Interestingly, this compensation is lost with long-term high-fat diet challenges. Thus, after six months of a high-fat diet, Wls-/- mice are characterized by decreased adipocyte lipogenic gene expression, reduced visceral adiposity, and improved glucose homeostasis.

CONCLUSIONS

Taken together, these studies demonstrate that adipocyte-derived Wnts regulate de novo lipogenesis and lipid desaturation and coordinate the expression of lipogenic genes in adipose tissues. In addition, we report that Wnt signaling within adipose tissues is defended, such that a loss of Wnt secretion from adipocytes is sensed and compensated for by neighboring stromal-vascular cells. With chronic overnutrition, this compensatory mechanism is lost, revealing that Wls-/- mice are resistant to diet-induced obesity, adipocyte hypertrophy, and metabolic dysfunction.

The Function of Wnt Ligands on Osteocyte and Bone Remodeling

Bone homeostasis is continually maintained by the process of bone remodeling throughout life. Recent studies have demonstrated that Wnt signaling pathways play a fundamental role in the process of bone homeostasis and remodeling. Intracellular Wnt signaling cascades are initially triggered by a Wnt ligand-receptor complex formation. In previous studies, the blocking of Wnt ligands from different osteoblastic differentiation stages could cause defective bone development at an early stage. Osteocytes, the most abundant and long-lived type of bone cell, are a crucial orchestrator of bone remodeling. However, the role of Wnt ligands on osteocyte and bone remodeling remains unclear. In our present study, we found that, besides osteoblasts, osteocytes also express multiple Wnt ligands in the bone environment. Then, we used a Dmp1-Cre mouse line, in which there is expression in a subset of osteoblasts but mainly osteocytes, to study the function of Wnt ligands on osteocyte and bone remodeling in vivo. Furthermore, we explored the role of Wnt ligands on osteocytic mineralization ability, as well as the regulatory function of osteocytes on the process of osteoblastic differentiation and osteoclastic migration and maturity in vitro. We concluded that Wnt proteins play an important regulatory role in 1) the process of perilacunar/canalicular remodeling, as mediated by osteocytes, and 2) the balance of osteogenesis and bone resorption at the bone surface, as mediated by osteoblasts and osteoclasts, at least partly through the canonical Wnt/β-catenin signaling pathway and the OPG/RANKL signaling pathway.

Deciphering the Proteome Dynamics during Development of Neurons Derived from Induced Pluripotent Stem Cells

Neuronal development is a complex multistep process that shapes neurons by progressing though several typical stages, including axon outgrowth, dendrite formation, and synaptogenesis. Knowledge of the mechanisms of neuronal development is mostly derived from the study of animal models. Advances in stem cell technology now enable us to generate neurons from human induced pluripotent stem cells (iPSCs). Here we provide a mass spectrometry-based quantitative proteomic signature of human iPSC-derived neurons, i.e., iPSC-derived induced glutamatergic neurons and iPSC-derived motor neurons, throughout neuronal differentiation. Tandem mass tag 10-plex labeling was carried out to perform proteomic profiling of cells at different time points. Our analysis reveals significant expression changes (FDR < 0.001) of several key proteins during the differentiation process, e.g., proteins involved in the Wnt and Notch signaling pathways. Overall, our data provide a rich resource of information on protein expression during human iPSC neuron differentiation.

Regulation of WNT5A and WNT11 during MSC in vitro chondrogenesis: WNT inhibition lowers BMP and hedgehog activity, and reduces hypertrophy

Re-directing mesenchymal stromal cell (MSC) chondrogenesis towards a non-hypertrophic articular chondrocyte-(AC)-like phenotype is important for improving articular cartilage neogenesis to enhance clinical cartilage repair strategies. This study is the first to demonstrate that high levels of non-canonical WNT5A followed by WNT11 and LEF1 discriminated MSC chondrogenesis from AC re-differentiation. Moreover, β-catenin seemed incompletely silenced in differentiating MSCs, which altogether suggested a role for WNT signaling in hypertrophic MSC differentiation. WNT inhibition with the small molecule IWP-2 supported MSC chondrogenesis according to elevated proteoglycan deposition and reduced the characteristic upregulation of BMP4, BMP7 and their target ID1, as well as IHH and its target GLI1 observed during endochondral differentiation. Along with the pro-hypertrophic transcription factor MEF2C, multiple hypertrophic downstream targets including IBSP and alkaline phosphatase activity were reduced by IWP-2, demonstrating that WNT activity drives BMP and hedgehog upregulation, and MSC hypertrophy. WNT inhibition almost matched the strong anti-hypertrophic capacity of pulsed parathyroid hormone-related protein application, and both outperformed suppression of BMP signaling with dorsomorphin, which also reduced cartilage matrix deposition. Yet, hypertrophic marker expression under IWP-2 remained above AC level, and in vivo mineralization and ectopic bone formation were reduced but not eliminated. Overall, the strong anti-hypertrophic effects of IWP-2 involved inhibition but not silencing of pro-hypertrophic BMP and IHH pathways, and more advanced silencing of WNT activity as well as combined application of IHH or BMP antagonists should next be considered to install articular cartilage neogenesis from human MSCs.

Regulation of WNT5A and WNT11 during MSC in vitro chondrogenesis: WNT inhibition lowers BMP and hedgehog activity, and reduces hypertrophy

Re-directing mesenchymal stromal cell (MSC) chondrogenesis towards a non-hypertrophic articular chondrocyte-(AC)-like phenotype is important for improving articular cartilage neogenesis to enhance clinical cartilage repair strategies. This study is the first to demonstrate that high levels of non-canonical WNT5A followed by WNT11 and LEF1 discriminated MSC chondrogenesis from AC re-differentiation. Moreover, β-catenin seemed incompletely silenced in differentiating MSCs, which altogether suggested a role for WNT signaling in hypertrophic MSC differentiation. WNT inhibition with the small molecule IWP-2 supported MSC chondrogenesis according to elevated proteoglycan deposition and reduced the characteristic upregulation of BMP4, BMP7 and their target ID1, as well as IHH and its target GLI1 observed during endochondral differentiation. Along with the pro-hypertrophic transcription factor MEF2C, multiple hypertrophic downstream targets including IBSP and alkaline phosphatase activity were reduced by IWP-2, demonstrating that WNT activity drives BMP and hedgehog upregulation, and MSC hypertrophy. WNT inhibition almost matched the strong anti-hypertrophic capacity of pulsed parathyroid hormone-related protein application, and both outperformed suppression of BMP signaling with dorsomorphin, which also reduced cartilage matrix deposition. Yet, hypertrophic marker expression under IWP-2 remained above AC level, and in vivo mineralization and ectopic bone formation were reduced but not eliminated. Overall, the strong anti-hypertrophic effects of IWP-2 involved inhibition but not silencing of pro-hypertrophic BMP and IHH pathways, and more advanced silencing of WNT activity as well as combined application of IHH or BMP antagonists should next be considered to install articular cartilage neogenesis from human MSCs.

Effect of Anacardic Acid against Thiram Induced Tibial Dyschondroplasia in Chickens via Regulation of Wnt4 Expression

Simple Summary

This study evaluated the ameliorating effect of anacardic acid (AA) in tibial dyschondroplasia (TD) chickens. Our results showed that AA can increase the feed conversion ratio, improve the weight, length and width of the tibia. AA administration restored the antioxidant parameters significantly (p < 0.05). The gene expression analysis revealed a decrease in wingless-type member 4 (Wnt4) expressions in TD chickens as compared to the control group, while AA treatment up-regulated the Wnt4 expression. The present study demonstrates that the AA plays an important role to prevent the lameness and restore the size of the tibial growth plate of chickens by regulating the expression of Wnt4.

Abstract

Tibial dyschondroplasia (TD) is a tibia bone problem in broilers. Anacardic acid (AA) is a traditional Chinese medicine, which is commonly used to treat arthritis in human. The purpose of the present study is to investigate the effect of AA against TD. A total of 300 day-old poultry birds were equally divided and distributed into three different groups: Control, TD and AA groups. The results showed that the feed conversion ratio was significantly lower in the TD group than control chickens. The tibia bone parameters including weight, length and width were of low quality in TD chickens, while the width of the tibial growth plate was enlarged remarkably. Whereas, in the AA treatment group, the tibia bone parameters showed improvement and tend to return to normal. The antioxidant parameters level of glutathione peroxidase (GSH-Px), superoxide dismutase (SOD), total and antioxidant capacity (T-AOC) was significantly decreased, while malondialdehyde (MDA) level was increased significantly in TD affected chickens. AA administration restored the antioxidant parameters significantly. The gene expression revealed a decrease in Wnt4 expression in TD chickens as compared to control chickens, while AA treatment up-regulated the Wnt4 expression. The present study demonstrates that the AA plays an important role to prevent the lameness and restore the size of tibial growth plate of chickens by regulating the expression of Wnt4.

Roles for HB-EGF in Mesenchymal Stromal Cell Proliferation and Differentiation During Skeletal Growth

HB-EGF, a member of the EGF superfamily, plays important roles in development and tissue regeneration. However, its functions in skeletal stem cells and skeleton development and growth remain poorly understood. Here, we used the Cre/LoxP system to ablate or express HB-EGF in Dermo1+ mesenchymal stromal cells and their progenies, including chondrocytes and osteoblast lineage cells, and bone marrow stromal cells (BMSCs). Dermo1-Cre; HB-EGF^f/f mice only showed a modest increase in bone mass, whereas Dermo1-HB-EGF mice developed progressive chondrodysplasia, chondroma, osteoarthritis-like joint defects, and loss of bone mass and density, which were alleviated by treatment with EGFR inhibitor AG1478. The cartilage defects were recapitulated in chondrocyte-specific HB-EGF overexpression (Col2-HB-EGF) mice with a lesser severity. Dermo1-HB-EGF mice showed an increase in proliferation but defects in differentiation of chondrocytes and osteoblasts. HB-EGF promoted BMSC proliferation via the Akt1 and Erk pathways but inhibited BMSC differentiation via restraining Smad1/5/8 activation. However, Dermo1-HB-EGF mice showed normal osteoclastogenesis and bone resorption. These results reveal an important function of autocrine or paracrine HB-EGF in mesenchymal stromal cell proliferation and differentiation and suggest that EGF signaling needs to be tightly controlled to maintain bone and articular cartilage integrity. © 2018 The Authors. Journal of Bone and Mineral Research Published by Wiley Periodicals Inc.

Impact of Wnt signals on human intervertebral disc cell regeneration

Although preconditioning strategies are growing areas of interest for therapies targeting intervertebral discs (IVDs), it is unknown whether the Wnt signals previously implicated in chondrogenesis, Wnt3A, Wnt5A, and Wnt11, play key roles in the promotion of human nucleus pulposus (NP) cell redifferentiation. In this study, NP cells isolated from herniated disc patients were transduced with lentiviral vectors to overexpress the WNT3A, WNT5A, or WNT11 genes, or CRISPR associated protein 9 (Cas9)/single-guide RNA (sgRNA) vectors to knock out these genes. Following expansion, transduced NP cells were induced for redifferentiation toward the NP phenotype. The overexpression of specific WNT factors led to increases in both glycosaminoglycan (GAG) deposition and expression of redifferentiation genes. These effects were attenuated by knockout of the same WNT genes. These results indicate that specific WNT signals can regulate the expression of redifferentiation genes, unequally impact GAG deposition, and contribute to the redifferentiation of human NP cells. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3196-3207, 2018.

β-catenin activation in hair follicle dermal stem cells induces ectopic hair outgrowth and skin fibrosis

Hair follicle dermal sheath (DS) harbors hair follicle dermal stem cells (hfDSCs), which can be recruited to replenish DS and dermal papilla (DP). Cultured DS cells can differentiate into various cell lineages in vitro. However, it is unclear how its plasticity is modulated in vivo. Wnt/β-catenin signaling plays an important role in maintaining stem cells of various lineages and is required for HF development and regeneration. Here we report that activation of β-catenin in DS generates ectopic HF outgrowth (EF) by reprogramming HF epidermal cells and DS cells themselves, and endows DS cells with hair inducing ability. Epidermal homeostasis of pre-existing HFs is disrupted. Additionally, cell-autonomous progressive skin fibrosis is prominent in dermis, where the excessive fibroblasts largely originate from DS. Gene expression analysis of purified DS cells with activated β-catenin revealed significantly increased expression of Bmp, Fgf, and Notch ligands and administration of Bmp, Fgf, or Notch signaling inhibitor attenuates EF formation. In summary, our findings advance the current knowledge of high plasticity of DS cells and provide an insight into understanding how Wnt/β-catenin signaling controls DS cell behaviors.

Coordinated directional outgrowth and pattern formation by integration of Wnt5a and Fgf signaling in planar cell polarity

Embryonic morphogenesis of a complex organism requires proper regulation of patterning and directional growth. Planar cell polarity (PCP) signaling is emerging as a crucial evolutionarily conserved mechanism whereby directional information is conveyed. PCP is thought to be established by global cues, and recent studies have revealed an instructive role of a Wnt signaling gradient in epithelial tissues of both invertebrates and vertebrates. However, it remains unclear whether Wnt/PCP signaling is regulated in a coordinated manner with embryonic patterning during morphogenesis. Here, in mouse developing limbs, we find that apical ectoderm ridge-derived Fgfs required for limb patterning regulate PCP along the proximal-distal axis in a Wnt5a-dependent manner. We demonstrate with genetic evidence that the Wnt5a gradient acts as a global cue that is instructive in establishing PCP in the limb mesenchyme, and that Wnt5a also plays a permissive role to allow Fgf signaling to orient PCP. Our results indicate that limb morphogenesis is regulated by coordination of directional growth and patterning through integration of Wnt5a and Fgf signaling.

Concise Review: Stem Cell Fate Guided By Bioactive Molecules for Tendon Regeneration

Tendon disorders, which are commonly presented in the clinical setting, disrupt the patients' normal work and life routines, and they damage the careers of athletes. However, there is still no effective treatment for tendon disorders. In the field of tissue engineering, the potential of the therapeutic application of exogenous stem cells to treat tendon pathology has been demonstrated to be promising. With the development of stem cell biology and chemical biology, strategies that use inductive tenogenic factors to program stem cell fate in situ are the most easily and readily translatable to clinical applications. In this review, we focus on bioactive molecules that can potentially induce tenogenesis in adult stem cells, and we summarize the various differentiation factors found in comparative studies. Moreover, we discuss the molecular regulatory mechanisms of tenogenesis, and we examine the various challenges in developing standardized protocols for achieving efficient and reproducible tenogenesis. Finally, we discuss and predict future directions for tendon regeneration. Stem Cells Translational Medicine 2018;7:404-414.

Wls Expression Correlates with Tumor Differentiation and TNM Stage in Hepatocellular Carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is an aggressive cancer with a poor prognosis. Effective biomarkers are necessary to predict the clinical course and outcome of patients with HCC. Wntless (Wls) is a key modulator of Wnt protein secretion and is overexpressed in various human cancers. However, the mechanism and alteration of Wls expression in HCC have not been clarified.

AIMS

The aim of this study was to evaluate expression level of Wls in HCC and its clinical significance.

METHODS

The levels of Wls expression were investigated in 84 HCC tissues using immunohistochemistry.

RESULTS

Wls was negatively expressed in normal liver tissue and was negatively or weakly (score 0) expressed in liver cirrhosis. Twenty-eight out of 84 samples (33.3%) were negative or weakly (score 0) expressed Wls, 38 out of 84 (45.2%) moderately (1+) expressed Wls, and 18 out of 84 (21.4%) strongly (2+) expressed Wls. Wls expression was positively associated with tumor size (P = 0.005, r = 0.302), tumor TNM stage (P = 0.017, r = 0.261), AFP (P = 0.051), and HBV infection (P = 0.009, r = 0.283), and was negatively associated with differentiation (P < 0.001, r = - 0.552). No significant relationship between Wls expression and liver cirrhosis, ALT, GGT, age, sex, or tumor focality was found.

CONCLUSIONS

Our data showed that Wls was differentially expressed in HCC. Statistical analysis results suggest that Wls expression might increase as HCC progresses.

Wnt/β-catenin signaling suppresses expressions of Scx, Mkx, and Tnmd in tendon-derived cells

After tendon injuries, biomechanical properties of the injured tendon are not fully recovered in most cases. Modulation of signaling pathways, which are involved in tendon development and tendon repair, is one of attractive modalities to facilitate proper regeneration of the injured tendon. The roles of TGF-β signaling in tendon homeostasis and tendon development have been elucidated. In contrast, the roles of Wnt/β-catenin signaling in tendon remain mostly elusive. We found that the number of β-catenin-positive cells was increased at the injured site, suggesting involvement of Wnt/β-catenin signaling in tendon healing. Activation of Wnt/β-catenin signaling suppressed expressions of tenogenic genes of Scx, Mkx, and Tnmd in rat tendon-derived cells (TDCs) isolated from the Achilles tendons of 6-week old rats. Additionally, activation of Wnt/β-catenin reduced the amounts of Smad2 and Smad3, which are intracellular mediators for TGF-β signaling, and antagonized upregulation of Scx induced by TGF-β signaling in TDCs. We found that Wnt/β-catenin decreased Mkx and Tnmd expressions without suppressing Scx expression in Scx-programmed tendon progenitors. Our studies suggest that Wnt/β-catenin signaling is a repressor for tenogenic gene expressions.

Wnt-Frizzled/planar cell polarity signaling: cellular orientation by facing the wind (Wnt)

The establishment of planar cell polarity (PCP) in epithelial and mesenchymal cells is a critical, evolutionarily conserved process during development and organogenesis. Analyses in Drosophila and several vertebrate model organisms have contributed a wealth of information on the regulation of PCP. A key conserved pathway regulating PCP, the so-called core Wnt-Frizzled PCP (Fz/PCP) signaling pathway, was initially identified through genetic studies of Drosophila. PCP studies in vertebrates, most notably mouse and zebrafish, have identified novel factors in PCP signaling and have also defined cellular features requiring PCP signaling input. These studies have shifted focus to the role of Van Gogh (Vang)/Vangl genes in this molecular system. This review focuses on new insights into the core Fz/Vangl/PCP pathway and recent advances in Drosophila and vertebrate PCP studies. We attempt to integrate these within the existing core Fz/Vangl/PCP signaling framework.

Does murine spermatogenesis require WNT signalling? A lesson from Gpr177 conditional knockout mouse models

Wingless-related MMTV integration site (WNT) proteins and several other components of the WNT signalling pathway are expressed in the murine testes. However, mice mutant for WNT signalling effector β-catenin using different Cre drivers have phenotypes that are inconsistent with each other. The complexity and overlapping expression of WNT signalling cascades have prevented researchers from dissecting their function in spermatogenesis. Depletion of the Gpr177 gene (the mouse orthologue of Drosophila Wntless), which is required for the secretion of various WNTs, makes it possible to genetically dissect the overall effect of WNTs in testis development. In this study, the Gpr177 gene was conditionally depleted in germ cells (Gpr177^flox/flox, Mvh-Cre; Gpr177^flox/flox, Stra8-Cre) and Sertoli cells (Gpr177^flox/flox, Amh-Cre). No obvious defects in fertility and spermatogenesis were observed in these three Gpr177 conditional knockout (cKO) mice at 8 weeks. However, late-onset testicular atrophy and fertility decline in two germ cell-specific Gpr177 deletion mice were noted at 8 months. In contrast, we did not observe any abnormalities of spermatogenesis and fertility, even in 8-month-old Gpr177^flox/flox, Amh-Cre mice. Elevation of reactive oxygen species (ROS) was detected in Gpr177 cKO germ cells and Sertoli cells and exhibited an age-dependent manner. However, significant increase in the activity of Caspase 3 was only observed in germ cells from 8-month-old germ cell-specific Gpr177 knockout mice. In conclusion, GPR177 in Sertoli cells had no apparent influence on spermatogenesis, whereas loss of GPR177 in germ cells disrupted spermatogenesis in an age-dependent manner via elevating ROS levels and triggering germ cell apoptosis.

Wnt signaling in cartilage development and diseases: lessons from animal studies

Cartilage not only plays essential roles in skeletal development and growth during pre- and postnatal stages but also serves to provide smooth movement of skeletons throughout life. Thus, dysfunction of cartilage causes a variety of skeletal disorders. Results from animal studies reveal that β-catenin-dependent canonical and independent non-canonical Wnt signaling pathways have multiple roles in regulation of cartilage development, growth, and maintenance. β-Catenin-dependent signaling is required for progression of endochondral ossification and growth of axial and appendicular skeletons, while excessive activation of this signaling can cause severe inhibition of initial cartilage formation and growth plate organization and function in mice. In contrast, non-canonical Wnt signaling is important in columnar organization of growth plate chondrocytes. Manipulation of Wnt signaling causes or ameliorates articular cartilage degeneration in rodent osteoarthritis models. Human genetic studies indicate that Wnt/β-catenin signaling is a risk factor for osteoarthritis. Accumulative findings from analysis of expression of Wnt signaling molecules and in vivo and in vitro functional experiments suggest that Wnt signaling is a therapeutic target for osteoarthritis. The target tissues of Wnt signaling may be not only articular cartilage but also synovium and subchondral bone.

The evolving roles of canonical WNT signaling in stem cells and tumorigenesis: implications in targeted cancer therapies

The canonical WNT/β-catenin signaling pathway governs a myriad of biological processes underlying the development and maintenance of adult tissue homeostasis, including regulation of stem cell self-renewal, cell proliferation, differentiation, and apoptosis. WNTs are secreted lipid-modified glycoproteins that act as short-range ligands to activate receptor-mediated signaling pathways. The hallmark of the canonical pathway is the activation of β-catenin-mediated transcriptional activity. Canonical WNTs control the β-catenin dynamics as the cytoplasmic level of β-catenin is tightly regulated via phosphorylation by the 'destruction complex', consisting of glycogen synthase kinase 3β (GSK3β), casein kinase 1α (CK1α), the scaffold protein AXIN, and the tumor suppressor adenomatous polyposis coli (APC). Aberrant regulation of this signaling cascade is associated with varieties of human diseases, especially cancers. Over the past decade, significant progress has been made in understanding the mechanisms of canonical WNT signaling. In this review, we focus on the current understanding of WNT signaling at the extracellular, cytoplasmic membrane, and intracellular/nuclear levels, including the emerging knowledge of cross-talk with other pathways. Recent progresses in developing novel WNT pathway-targeted therapies will also be reviewed. Thus, this review is intended to serve as a refresher of the current understanding about the physiologic and pathogenic roles of WNT/β-catenin signaling pathway, and to outline potential therapeutic opportunities by targeting the canonical WNT pathway.

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.

Distinct requirements for Wntless in habenular development

Secreted Wnt proteins play pivotal roles in development, including regulation of cell proliferation, differentiation, progenitor maintenance and tissue patterning. The transmembrane protein Wntless (Wls) is necessary for secretion of most Wnts and essential for effective Wnt signaling. During a mutagenesis screen to identify genes important for development of the habenular nuclei in the dorsal forebrain, we isolated a mutation in the sole wls gene of zebrafish and confirmed its identity with a second, independent allele. Early embryonic development appears normal in homozygous wls mutants, but they later lack the ventral habenular nuclei, form smaller dorsal habenulae and otic vesicles, have truncated jaw and fin cartilages and lack swim bladders. Activation of a reporter for β-catenin-dependent transcription is decreased in wls mutants, indicative of impaired signaling by the canonical Wnt pathway, and expression of Wnt-responsive genes is reduced in the dorsal diencephalon. Wnt signaling was previously implicated in patterning of the zebrafish brain and in the generation of left-right (L-R) differences between the bilaterally paired dorsal habenular nuclei. Outside of the epithalamic region, development of the brain is largely normal in wls mutants and, despite their reduced size, the dorsal habenulae retain L-R asymmetry. We find that homozygous wls mutants show a reduction in two cell populations that contribute to the presumptive dorsal habenulae. The results support distinct temporal requirements for Wls in habenular development and reveal a new role for Wnt signaling in the regulation of dorsal habenular progenitors.

Wntless spatially regulates bone development through β-catenin-dependent and independent mechanisms

BACKGROUND

Canonical and noncanonical Wnt signaling pathways both play pivotal roles in bone development. Wntless/GPR177 is a chaperone protein that is required for secretion of all Wnt ligands. We previously showed that deletion of Wntless within mature osteoblasts severely impaired postnatal bone homeostasis.

RESULTS

In this study, we systemically evaluated how deletion of Wntless in different stages of osteochondral differentiation affected embryonic bone development, by crossing Wntless (Wls)-flox/flox mice with strains expressing cre recombinase behind the following promoters: Osteocalcin, Collagen 2a1, or Dermo1. Ex vivo µCT and whole-mount skeletal staining were performed to examine skeletal mineralization. Histology and immunohistochemistry were used to evaluate cellular differentiation and alterations in Wnt signaling. In this work, we found that Wntless regulated chondrogenesis and osteogenesis through both canonical and noncanonical Wnt signaling.

CONCLUSIONS

These findings provide more insight into the requirements of different Wnt-secretion cell types critical for skeletal development.

Ablation of Wntless in endosteal niches impairs lymphopoiesis rather than HSCs maintenance

Osteoblasts and perivascular stromal cells constitute essential niches for HSC self-renewal and maintenance in the bone marrow. Wnt signaling is important to maintain HSC integrity. However, the paracrine role of Wnt proteins in osteoblasts-supported HSC maintenance and differentiation remains unclear. Here, we investigated hematopoiesis in mice with Wntless (Wls) deficiency in osteoblasts or Nestin-positive mesenchymal progenitor cells, which presumptively block Wnt secretion in osteoblasts. We detected defective B-cell lymphopoiesis and abnormal T-cell infiltration in the bone marrow of Wls mutant mice. Notably, no impact on HSC frequency and repopulation in the bone marrow was observed with the loss of osteoblastic Wls. Our findings revealed a supportive role of Wnts in osteoblasts-regulated B-cell lymphopoiesis. They also suggest a preferential niche role of osteoblastic Wnts for lymphoid cells rather than HSCs, providing new clues for the molecular nature of distinct niches occupied by different hematopoietic cells.

Involvement of epithelial Wntless in the regulation of postnatal hair follicle morphogenesis

The roles of the Wnt cargo receptor Wntless (Wls) during hair follicle (HF) induction and postnatal HF cycling in skin have been elucidated. However, whether Wls regulates postnatal HF morphogenesis remains unclear. In this study, we found that Wls is expressed in developing HF during the morphogenesis stage after birth. By knocking out Wls in mouse skin epithelia with hypomorphic K14-cre, we found that Wls is required for normal HF morphogenesis. Wls-deficient HFs prematurely regressed, which was possibly caused by abnormally activated TGF-β/JNK pathway. Although Wls was reported to be a direct target of the Wnt/β-catenin pathway, we found that epithelial β-catenin was not necessary to maintain Wls expression. Therefore, other signals are involved in regulating Wls transcription in mouse skin.

Molecular regulation of tendon cell fate during development

Although there have been several advances identifying novel mediators of tendon induction, differentiation, and patterning, much of the basic landscape of tendon biology from developmental stages onward remain almost completely undefined. During the New Frontiers in Tendon Research meeting, a group of developmental biologists with expertise across musculoskeletal disciplines identified key challenges for the tendon development field. The tools generated and the molecular regulators identified in developmental research have enhanced mechanistic studies in tendon injury and repair, both by defining benchmarks for success, as well as informing regenerative strategies. To address the needs of the orthopedic research community, this review will therefore focus on three key areas in tendon development that may have critical implications for the fields of tendon repair/regeneration and tendon tissue engineering, including functional markers of tendon cell identity, signaling regulators of tendon induction and differentiation, and in vitro culture models for tendon cell differentiation. Our goal is to provide a useful list of the currently known molecular players and their function in tendon differentiation within the context of development.

Wnts produced by Osterix-expressing osteolineage cells regulate their proliferation and differentiation

Wnt signaling is a critical regulator of bone development, but the identity and role of the Wnt-producing cells are still unclear. We addressed these questions through in situ hybridization, lineage tracing, and genetic experiments. First, we surveyed the expression of all 19 Wnt genes and Wnt target gene Axin2 in the neonatal mouse bone by in situ hybridization, and demonstrated--to our knowledge for the first time--that Osterix-expressing cells coexpress Wnt and Axin2. To track the behavior and cell fate of Axin2-expressing osteolineage cells, we performed lineage tracing and showed that they sustain bone formation over the long term. Finally, to examine the role of Wnts produced by Osterix-expressing cells, we inhibited Wnt secretion in vivo, and observed inappropriate differentiation, impaired proliferation, and diminished Wnt signaling response. Therefore, Osterix-expressing cells produce their own Wnts that in turn induce Wnt signaling response, thereby regulating their proliferation and differentiation.

Whole-genome expression profile in zebrafish embryos after chronic exposure to morphine: identification of new genes associated with neuronal function and mu opioid receptor expression

BACKGROUND

A great number of studies have investigated changes induced by morphine exposure in gene expression using several experimental models. In this study, we examined gene expression changes during chronic exposure to morphine during maturation and differentiation of zebrafish CNS.

RESULTS

Microarray analysis showed 254 genes whose expression was identified as different by at least 1.3 fold change following chronic morphine exposure as compared to controls. Of these, several novel genes (grb2, copb2, otpb, magi1b, grik-l, bnip4 and sox19b) have been detected for the first time in an experimental animal model treated with morphine. We have also identified a subset of genes (dao.1, wls, bnip4 and camk1γb) differentially expressed by chronic morphine exposure whose expression is related to mu opioid receptor gene expression. Altered expression of copb2, bnip4, sox19b, otpb, dao.1, grik-l and wls is indicative of modified neuronal development, CNS patterning processes, differentiation and dopaminergic neurotransmission, serotonergic signaling pathway, and glutamatergic neurotransmission. The deregulation of camk1γb signaling genes suggests an activation of axonogenesis and dendritogenesis.

CONCLUSIONS

Our study identified different functional classes of genes and individual candidates involved in the mechanisms underlying susceptibility to morphine actions related to CNS development. These results open new lines to study the treatment of pain and the molecular mechanisms involved in addiction. We also found a set of zebrafish-specific morphine-induced genes, which may be putative targets in human models for addiction and pain processes.

Modeling digits. Digit patterning is controlled by a Bmp-Sox9-Wnt Turing network modulated by morphogen gradients

During limb development, digits emerge from the undifferentiated mesenchymal tissue that constitutes the limb bud. It has been proposed that this process is controlled by a self-organizing Turing mechanism, whereby diffusible molecules interact to produce a periodic pattern of digital and interdigital fates. However, the identities of the molecules remain unknown. By combining experiments and modeling, we reveal evidence that a Turing network implemented by Bmp, Sox9, and Wnt drives digit specification. We develop a realistic two-dimensional simulation of digit patterning and show that this network, when modulated by morphogen gradients, recapitulates the expression patterns of Sox9 in the wild type and in perturbation experiments. Our systems biology approach reveals how a combination of growth, morphogen gradients, and a self-organizing Turing network can achieve robust and reproducible pattern formation.

Constitutive activation of ectodermal β-catenin induces ectopic outgrowths at various positions in mouse embryo and affects abdominal ventral body wall closure

Vertebrate limbs originate from the lateral plate mesoderm (LPM) and the overlying ectoderm. While normal limb formation in defined regions has been well studied, the question of whether other positions retain limb-forming potential has not been fully investigated in mice. By ectopically activating β-catenin in the ectoderm with Msx2-cre, we observed that local tissue outgrowths were induced, which either progressed into limb-like structure within the inter-limb flank or formed extra tissues in other parts of the mouse embryo. In the presumptive abdominal region of severely affected embryos, ectopic limb formation was coupled with impaired abdominal ventral body wall (AVBW) closure, which indicates the existence of a potential counterbalance of limb formation and AVBW closure. At the molecular level, constitutive β-catenin activation was sufficient to trigger, but insufficient to maintain the ectopic expression of a putative limb-inducing factor, Fgf8, in the ectoderm. These findings provide new insight into the mechanism of limb formation and AVBW closure, and the crosstalk between the Wnt/β-catenin pathway and Fgf signal.

Ectodermal Wnt signaling regulates abdominal myogenesis during ventral body wall development

Defects of the ventral body wall are prevalent birth anomalies marked by deficiencies in body wall closure, hypoplasia of the abdominal musculature and multiple malformations across a gamut of organs. However, the mechanisms underlying ventral body wall defects remain elusive. Here, we investigated the role of Wnt signaling in ventral body wall development by inactivating Wls or β-catenin in murine abdominal ectoderm. The loss of Wls in the ventral epithelium, which blocks the secretion of Wnt proteins, resulted in dysgenesis of ventral musculature and genito-urinary tract during embryonic development. Molecular analyses revealed that the dermis and myogenic differentiation in the underlying mesenchymal progenitor cells was perturbed by the loss of ectodermal Wls. The activity of the Wnt-Pitx2 axis was impaired in the ventral mesenchyme of the mutant body wall, which partially accounted for the defects in ventral musculature formation. In contrast, epithelial depletion of β-catenin or Wnt5a did not resemble the body wall defects in the ectodermal Wls mutant. These findings indicate that ectodermal Wnt signaling instructs the underlying mesodermal specification and abdominal musculature formation during ventral body wall development, adding evidence to the theory that ectoderm-mesenchyme signaling is a potential unifying mechanism for the origin of ventral body wall defects.

Distinct requirements for cranial ectoderm and mesenchyme-derived wnts in specification and differentiation of osteoblast and dermal progenitors

The cranial bones and dermis differentiate from mesenchyme beneath the surface ectoderm. Fate selection in cranial mesenchyme requires the canonical Wnt effector molecule β-catenin, but the relative contribution of Wnt ligand sources in this process remains unknown. Here we show Wnt ligands are expressed in cranial surface ectoderm and underlying supraorbital mesenchyme during dermal and osteoblast fate selection. Using conditional genetics, we eliminate secretion of all Wnt ligands from cranial surface ectoderm or undifferentiated mesenchyme, to uncover distinct roles for ectoderm- and mesenchyme-derived Wnts. Ectoderm Wnt ligands induce osteoblast and dermal fibroblast progenitor specification while initiating expression of a subset of mesenchymal Wnts. Mesenchyme Wnt ligands are subsequently essential during differentiation of dermal and osteoblast progenitors. Finally, ectoderm-derived Wnt ligands provide an inductive cue to the cranial mesenchyme for the fate selection of dermal fibroblast and osteoblast lineages. Thus two sources of Wnt ligands perform distinct functions during osteoblast and dermal fibroblast formation.

Craniofacial abnormalities are relatively common congenital birth defects, and the Wnt signaling pathway and its effectors have key roles in craniofacial development. Wntless/Gpr177 is required for the efficient secretion of all Wnt ligands and maps to a region that contains SNPs strongly associated with reduced bone mass, and heterozygous deletion is associated with facial dysmorphology. Here we test the role of specific sources of secreted Wnt proteins during early stages of craniofacial development and obtained dramatic craniofacial anomalies. We found that the overlying cranial surface ectoderm Wnts generate an instructive cue of Wnt signaling for skull bone and skin cell fate selection and transcription of additional Wnts in the underlying mesenchyme. Once initiated, mesenchymal Wnts may maintain Wnt signal transduction and function in an autocrine manner during differentiation of skull bones and skin. These results highlight how Wnt ligands from two specific tissue sources are integrated for normal craniofacial patterning and can contribute to complex craniofacial abnormalities.

Divergent differentiation of skeletal progenitors into cartilage and tendon: lessons from the embryonic limb

Repairing damaged cartilage and tendons is a major challenge of regenerative medicine. There has been great progress in the past decade toward obtaining stem cells for regenerative purposes from a variety of sources. However, the development of procedures to direct and maintain the differentiation of progenitors into cartilage or tendon is still a hurdle to overcome in regenerative medicine of the musculoskeletal system. This is because connective tissues often lack stable phenotypes and retain plasticity to return to the initial stages of differentiation or to transdifferentiate into another connective tissue cell lineage. This makes it necessary to unravel the molecular basis that is responsible for the differentiation of connective tissue cell lineages. In this review, we summarize the investigations performed in the past two decades to unravel the signals that regulate the differentiation of skeletal cell progenitors into cartilage and tendons during embryonic limb development. The data obtained in those studies demonstrate that Tgfβ, BMP, FGF, and Wnt establish a complex signaling network that directs the differentiation of skeletal cell progenitors. Remarkably, in the embryonic digit model, the divergent differentiation of progenitors depends on the temporal coordination of those signals, rather than being specified by an individual signaling pathway. Due to its potential medical relevance, we highlight the importance of the coordinate influence of the Tgfβ and BMP pathways in the differentiation of cell progenitors into tendon or cartilage.

Zygotic Porcn paternal allele deletion in mice to model human focal dermal hypoplasia

In mouse and humans, the X-chromosomal Porcupine homolog (Porcn) gene is required for the acylation and secretion of all 19 Wnt ligands, thus representing a bottleneck in the secretion of Wnt ligands. In humans, mutations in PORCN cause the X-linked dominant syndrome Focal Dermal Hypoplasia (FDH, OMIM#305600). This disorder is characterized by ecto-mesodermal dysplasias and shows a highly variable phenotype, potentially due to individual X chromosome inactivation patterns. To improve the understanding of human FDH, we have established a mouse model by generation of Porcn heterozygous animals carrying a zygotic deletion of the paternal allele. We show that heterozygous female fetuses display variable defects that do not significantly affect survival in the uterus, but lead to perinatal lethality in more than 95% of females. Rare survivors develop to adulthood and display variable skeletal and skin defects, representing an adult zygotic mouse model for human FDH. Although not frequently reported in humans, we also observed bronchopneumonia, rhinitis, and otitis media in these animals, suggesting a potential link between Porcn function and the normal development of ciliated cells in these tissues.

Osteoblastic Wnts differentially regulate bone remodeling and the maintenance of bone marrow mesenchymal stem cells

Wnt signaling has important roles in embryonic bone development and postnatal bone remodeling, but inconsistent impact on bone property is observed in different genetic alterations of Lrp5 and β-catenin. More importantly, it is still controversial whether Lrp5 regulate bone formation locally or globally through gut-derived serotonin. Here we explored the function of Wnt proteins in osteoblastic niche through inactivation of the Wntless (Wls) gene, which abrogates the secretion of Wnts. The depletion of Wls in osteoblast progenitor cells resulted in severe osteopenia with more profound defects in osteoblastogenesis, osteoclastogenesis and maintenance of bone marrow mesenchymal stem cells (BMSCs) compared to that observed in Lrp5 and β-catenin mutants. These findings support the point of view that Wnt/Lrp5 signaling locally regulates bone mass accrual through multiple effects of osteoblastic Wnts on osteoblastic bone formation and osteoclastic bone resorption. Moreover, osteoblastic Wnts confer a niche role for maintenance of BMSCs, providing novel cues for the definition of BMSCs niche in bone marrow.