Frizzled10 mediates WNT1 and WNT3A signaling in the dorsal spinal cord of the developing chick embryo

The Foxi3 transcription factor is necessary for the fate restriction of placodal lineages at the neural plate border

The Foxi3 transcription factor, expressed in the neural plate border at the end of gastrulation, is necessary for the formation of posterior placodes and is thus important for ectodermal patterning. We have created two knock-in mouse lines expressing GFP or a tamoxifen-inducible Cre recombinase to show that Foxi3 is one of the earliest genes to label the border between the neural tube and epidermis, and that Foxi3-expressing neural plate border progenitors contribute primarily to cranial placodes and epidermis from the onset of expression, but not to the neural crest or neural tube lineages. By simultaneously knocking out Foxi3 in neural plate border cells and following their fates, we show that neural plate border cells lacking Foxi3 contribute to all four lineages of the ectoderm - placodes, epidermis, crest and neural tube. We contrast Foxi3 with another neural plate border transcription factor, Zic5, the progenitors of which initially contribute broadly to all germ layers until gastrulation and gradually become restricted to the neural crest lineage and dorsal neural tube cells. Our study demonstrates that Foxi3 uniquely acts early at the neural plate border to restrict progenitors to a placodal and epidermal fate.

Exosomes: Emerging modulators of signal transduction in colorectal cancer from molecular understanding to clinical application

Exosomes are small cell derived membrane nano-vesicles that carry various components including lipids, proteins and nucleic acids. There is accumulating evidence that exosomes have a role in tumorigenesis, tumor invasiveness and metastasis. Furthermore, oncogene mutation may influence exosome release from tumor cells. Exosomes may induce colorectal cancer by altering signaling cascades such as the Wnt/β-catenin and KRAS pathways that are involved in cell proliferation, apoptosis, dissemination, angiogenesis, and drug resistance. The aim of this review was to overview recent findings evaluating the association between tumor cells-derived exosomes and their content in modulating signaling pathways in colorectal cancer.

Expression analysis of chick Frizzled receptors during spinal cord development

Frizzleds (Fzds) are transmembrane receptors that can transduce signals dependent upon binding of Wnts, a large family of secreted glycoproteins homologous to the Drosophila wingless gene. FZDs are critical for a wide variety of normal and pathological developmental processes. In the nervous system, Wnts and Frizzleds play an important role in anterior-posterior patterning, cell fate decisions, proliferation, and synaptogenesis. Here, we preformed a comprehensive expression profile of Wnt receptors (FZD) by using situ hybridization to identify FZDs that are expressed in dorsal-ventral regions of the neural tube development. Our data show specific expression for FZD1,2,3,7,9 and 10 in the chick developing spinal cord. This expression profile of cFZD receptors offers the basis for functional studies in the future to determine roles for the different FZD receptors and their interactions with Wnts during dorsal-ventral neural tube development in vivo. Furthermore, we also show that co-overexpression of Wnt1/3a by in vivo electroporation affects FZD7/10 expression in the neural tube. This illustrates an example of Wnts-FZDs interactions during spinal cord neurogenesis.

TBBPA, TBBPS, and TCBPA disrupt hESC hepatic differentiation and promote the proliferation of differentiated cells partly via up-regulation of the FGF10 signaling pathway

Halogenated flame retardants (HFRs), including Tetrabromobisphenol A (TBBPA), Tetrabromobisphenol S (TBBPS), and Tetrachlorobisphenol A (TCBPA), are widely applied in the manufacturing industry to improve fire safety and can be detected in pregnant women's serum at nanomolar levels. Thus, it is necessary to pay attention to the three HFR potential development toxicity, which has not been conclusively addressed yet. The liver is the main organ that detoxifies our body; TBBPA exposure may lead to increased liver weight in rodents. Therefore, in this study, we assessed the developmental hepatic toxicity of the three HFRs with a human embryonic stem cell hepatic differentiation-based system and transcriptomics analyses. We mostly evaluated lineage fate alterations and demonstrated the three HFRs may have common disruptive effects on hepatic differentiation, with TCBPA being significantly more potent. More specifically, the three HFRs up-regulated genes related to cell cycle and FGF10 signaling, at late stages of the hepatic differentiation. This indicates the three chemicals promoted hepatoblast proliferation likely via up-regulating the FGF10 cascade. At the same time, we also presented a powerful way to combine in vitro differentiation and in silico transcriptomic analyses, to efficiently evaluate hazardous materials' adverse effects on lineage fate decisions during early development.

FZD10 regulates cell proliferation and mediates Wnt1 induced neurogenesis in the developing spinal cord

Wnt/FZD signalling activity is required for spinal cord development, including the dorsal-ventral patterning of the neural tube, where it affects proliferation and specification of neurons. Wnt ligands initiate canonical, β -catenin-dependent, signaling by binding to Frizzled receptors. However, in many developmental contexts the cognate FZD receptor for a particular Wnt ligand remains to be identified. Here, we characterized FZD10 expression in the dorsal neural tube where it overlaps with both Wnt1 and Wnt3a, as well as markers of dorsal progenitors and interneurons. We show FZD10 expression is sensitive to Wnt1, but not Wnt3a expression, and FZD10 plays a role in neural tube patterning. Knockdown approaches show that Wnt1 induced ventral expansion of dorsal neural markes, Pax6 and Pax7, requires FZD10. In contrast, Wnt3a induced dorsalization of the neural tube is not affected by FZD10 knockdown. Gain of function experiments show that FZD10 is not sufficient on its own to mediate Wnt1 activity in vivo. Indeed excess FZD10 inhibits the dorsalizing activity of Wnt1. However, addition of the Lrp6 co-receptor dramatically enhances the Wnt1/FZD10 mediated activation of dorsal markers. This suggests that the mechanism by which Wnt1 regulates proliferation and patterning in the neural tube requires both FZD10 and Lrp6.

Transformation of the Transcriptomic Profile of Mouse Periocular Mesenchyme During Formation of the Embryonic Cornea

Purpose

Defects in neural crest development are a major contributing factor in corneal dysgenesis, but little is known about the genetic landscape during corneal development. The purpose of this study was to provide a detailed transcriptome profile and evaluate changes in gene expression during mouse corneal development.

Methods

RNA sequencing was used to uncover the transcriptomic profile of periocular mesenchyme (pNC) isolated at embryonic day (E) 10.5 and corneas isolated at E14.5 and E16.5. The spatiotemporal expression of several differentially expressed genes was validated by in situ hybridization.

Results

Analysis of the whole-transcriptome profile between pNC and embryonic corneas identified 3815 unique differentially expressed genes. Pathway analysis revealed an enrichment of differentially expressed genes involved in signal transduction (retinoic acid, transforming growth factor-β, and Wnt pathways) and transcriptional regulation.

Conclusions

Our analyses, for the first time, identify a large number of differentially expressed genes during progressive stages of mouse corneal development. Our data provide a comprehensive transcriptomic profile of the developing cornea. Combined, these data serve as a valuable resource for the identification of novel regulatory networks crucial for the advancement of studies in congenital defects, stem cell therapy, bioengineering, and adult corneal diseases.

Fatty acid recognition in the Frizzled receptor family

Wnt signaling regulates physiological processes ranging from cell differentiation to bone formation. Dysregulation of Wnt signaling is linked to several human ailments, including colorectal, pancreatic, and breast cancers. As such, modulation of this pathway has been an attractive strategy for therapeutic development of anticancer agents. Since the discovery of Wnt proteins more than 35 years ago, research efforts continue to focus on understanding the biochemistry of their molecular interactions and their biological functions. Wnt is a secreted glycoprotein covalently modified with a cis-unsaturated fatty acyl group at a conserved serine residue, and this modification is required for Wnt secretion and activity. To initiate signaling, Wnt proteins bind to cell-surface Frizzled (FZD) receptors, but the molecular basis for recognition of Wnt's fatty acyl moiety by the extracellular cysteine-rich domain of FZD has become clear only very recently. Here, we review the most recent developments in the field, focusing on structural and biochemical studies of the FZD receptor family and highlighting new insights into their molecular arrangement and mode of regulation by cis-unsaturated fatty acids. Additionally, we examine how other lipid-binding proteins recognize fatty acyl chains on Wnt proteins in the regulation of Wnt secretion and activities. Altogether, this perspective expands our understanding of fatty acid–protein interactions in the FZD system and provides a basis for guiding future research in the field.

Inhibition of canonical WNT/β-catenin signaling is involved in leflunomide (LEF)-mediated cytotoxic effects on renal carcinoma cells

Leflunomide (LEF), an inhibitor of dihydroorotate dehydrogenase (DHODH) in pyrimidine biosynthetic pathway, is an immunomodulatory agent approved for the treatment of rheumatoid arthritis. In this study, we show that LEF significantly reduced cell proliferation of renal carcinoma cells in a concentration-dependent manner. LEF at 50 μM induced S-phase arrest and autophagy. Higher doses of LEF (>50 μM) effectively induced cell apoptosis. Modulating the concentration of LEF resulted in distinct effects on the expression of regulatory proteins associated with cell cycle, apoptosis, and autophagy. In particular, high concentrations of LEF inhibited canonical WNT signaling by promoting nucleo-cytoplasmic shuttling and proteasome-dependent degradation of β-catenin. Mechanistic studies showed that the repression of AKT activation partly accounted for LEF-mediated WNT inhibition. Gene expression microarray revealed that LEF treatment greatly inhibited the expression of FZD10 gene, a receptor mediating WNT/β-catenin activation. In vivo xenograft study in NOD/SCID mice further validated the inhibitory effects of LEF on tumor growth and Wnt/β-catenin signaling. However, LEF treatment also triggered cell autophagy and elevated the expression of WNT3a, which ameliorated its cytotoxic effects. The combination of LEF with a WNT inhibitor IWP-2 or autophagy inhibitor HCQ could yield an enhanced anti-tumor outcome. Taken together, these results identify the potential utility and pharmacological feature of LEF in the chemotherapy of renal cell carcinoma (RCC).

The Use of Chick Embryos to Study Wnt Activity Gradients

The chick spinal cord provides a valuable model for assessing Wnt signaling activity. Loss or gain of function constructs that are transfected by electroporation can be directed to a single side of the spinal cord, thus leaving the contralateral side as an internal control. Here, we describe a method for measuring Wnt signaling via the use of BAT-Gal, a β-catenin dependent Wnt reporter.

The Onecut Transcription Factors Regulate Differentiation and Distribution of Dorsal Interneurons during Spinal Cord Development

During embryonic development, the dorsal spinal cord generates numerous interneuron populations eventually involved in motor circuits or in sensory networks that integrate and transmit sensory inputs from the periphery. The molecular mechanisms that regulate the specification of these multiple dorsal neuronal populations have been extensively characterized. In contrast, the factors that contribute to their diversification into smaller specialized subsets and those that control the specific distribution of each population in the developing spinal cord remain unknown. Here, we demonstrate that the Onecut transcription factors, namely Hepatocyte Nuclear Factor-6 (HNF-6) (or OC-1), OC-2 and OC-3, regulate the diversification and the distribution of spinal dorsal interneuron (dINs). Onecut proteins are dynamically and differentially distributed in spinal dINs during differentiation and migration. Analyzes of mutant embryos devoid of Onecut factors in the developing spinal cord evidenced a requirement in Onecut proteins for proper production of a specific subset of dI5 interneurons. In addition, the distribution of dI3, dI5 and dI6 interneuron populations was altered. Hence, Onecut transcription factors control genetic programs that contribute to the regulation of spinal dIN diversification and distribution during embryonic development.

Divergent effects of Porcupine and Wntless on WNT1 trafficking, secretion, and signaling

Loss-of-function studies have identified Porcupine (PORCN) and Wntless (WLS) as essential mediators of Wnt secretion and signaling. Whereas PORCN is thought to palmitoylate Wnt proteins, WLS is believed to transport palmitoylated Wnt proteins to the cell surface. However, little is known about how these two proteins cooperate to regulate Wnt palmitoylation, trafficking, secretion, and signaling. We first investigated possible interactions between PORCN, WLS, and WNT1, by carrying out co-immunoprecipitation studies. These studies demonstrate the existence of a complex containing PORCN and WLS. They further show that PORCN and WLS compete for binding to WNT1. Then, we used gain-of-function studies to investigate the cooperation between PORCN and WLS as well as possible biochemical interactions between PORCN, WLS, and WNT1. Consistent with the proposed roles for PORCN and WLS, we show that overexpression of PORCN promotes palmitoylation of WNT1 while overexpression of WLS does not. Overexpression of PORCN enhances the ability of WLS to promote WNT1 trafficking to the cell surface as well as secretion, but decreases the ability of WLS to activate WNT1 signaling in target cell. These observations suggest that the levels of WNT1 on the cell surface and in the media are not the sole determinants of the activation of Wnt signaling in target cells.

The Epigenetic Reprogramming Roadmap in Generation of iPSCs from Somatic Cells

Reprogramming of somatic cells to induced pluripotent stem cells (iPSCs) is a comprehensive epigenetic process involving genome-wide modifications of histones and DNA methylation. This process is often incomplete, which subsequently affects iPSC reprogramming, pluripotency, and differentiation capacity. Here, we review the epigenetic changes with a focus on histone modification (methylation and acetylation) and DNA modification (methylation) during iPSC induction. We look at changes in specific epigenetic signatures, aberrations and epigenetic memory during reprogramming and small molecules influencing the epigenetic reprogramming of somatic cells. Finally, we discuss how to improve iPSC generation and pluripotency through epigenetic manipulations.

microRNA regulation of Wnt signaling pathways in development and disease

Wnt signaling pathways and microRNAs (miRNAs) are critical regulators of development. Aberrant Wnt signaling pathways and miRNA levels lead to developmental defects and diverse human pathologies including but not limited to cancer. Wnt signaling pathways regulate a plethora of cellular processes during embryonic development and maintain homeostasis of adult tissues. A majority of Wnt signaling components are regulated by miRNAs which are small noncoding RNAs that are expressed in both animals and plants. In animal cells, miRNAs fine tune gene expression by pairing primarily to the 3'untranslated region of protein coding mRNAs to repress target mRNA translation and/or induce target degradation. miRNA-mediated regulation of signaling transduction pathways is important in modulating dose-sensitive response of cells to signaling molecules. This review discusses components of the Wnt signaling pathways that are regulated by miRNAs in the context of development and diseases. A fundamental understanding of miRNA functions in Wnt signaling transduction pathways may yield new insight into crosstalks of regulatory mechanisms essential for development and disease pathophysiology leading to novel therapeutics.

Concentration-dependent effects of WNTLESS on WNT1/3A signaling

BACKGROUND

WNTLESS (WLS) is a multi-transmembrane protein that transports Wnt ligands from the Golgi to the cell surface. Although WLS loss-of-function experiments in the developing central nervous system reveal phenotypes consistent with defects in WNT1 and WNT3A signaling, data from complementary gain-of-function experiments have not yet been reported. Here, we report the phenotypic consequences of WLS overexpression in cultured cells and in the developing chick spinal cord.

RESULTS

Overexpression of small amounts of WLS along with either WNT1 or WNT3A promotes the Wnt/β-catenin pathway in HEK293T cells, while overexpression of higher levels of WLS inhibits the Wnt/β-catenin pathway in these cells. Similarly, overexpressed WLS inhibits the Wnt/β-catenin pathway in the developing spinal cord, as assessed by cell proliferation and specification. These effects appear to be Wnt-specific as overexpression of WLS inhibits the expression of FZD10, a target of β-catenin-dependent transcription.

CONCLUSIONS

Our results show that overexpression of WLS inhibits Wnt/β-catenin signaling in the spinal cord. As the activation of the Wnt/β-catenin pathway in the spinal cord requires WNT1 or WNT3A, our results are consistent with a model in which the relative concentration of WLS to Wnt regulates WNT1/3A signaling in the developing spinal cord.