wnt10a is required for zebrafish median fin fold maintenance and adult unpaired fin metamorphosis

BACKGROUND

Mutations of human WNT10A are associated with odonto-ectodermal dysplasia syndromes. Here, we present analyses of wnt10a loss-of-function mutants in the zebrafish.

RESULTS

wnt10a mutant zebrafish embryos display impaired tooth development and a collapsing median fin fold (MFF). Rescue experiments show that wnt10a is essential for MFF maintenance both during embryogenesis and later metamorphosis. The MFF collapse could not be attributed to increased cell death or altered proliferation rates of MFF cell types. Rather, wnt10a mutants show reduced expression levels of dlx2a in distal-most MFF cells, followed by compromised expression of col1a1a and other extracellular matrix proteins encoding genes. Transmission electron microscopy analysis shows that although dermal MFF compartments of wnt10a mutants initially are of normal morphology, with regular collagenous actinotrichia, positioning of actinotrichia within the cleft of distal MFF cells becomes compromised, coinciding with actinotrichia shrinkage and MFF collapse.

CONCLUSIONS

MFF collapse of wnt10a mutant zebrafish is likely caused by the loss of distal properties in the developing MFF, strikingly similar to the proposed molecular pathomechanisms underlying the teeth defects caused by the loss of Wnt10 in fish and mammals. In addition, it points to thus fur unknown mechanisms controlling the linear growth and stability of actinotrichia and their collagen fibrils.

Zebrafish pigment cells develop directly from persistent highly multipotent progenitors

Neural crest cells are highly multipotent stem cells, but it remains unclear how their fate restriction to specific fates occurs. The direct fate restriction model hypothesises that migrating cells maintain full multipotency, whilst progressive fate restriction envisages fully multipotent cells transitioning to partially-restricted intermediates before committing to individual fates. Using zebrafish pigment cell development as a model, we show applying NanoString hybridization single cell transcriptional profiling and RNAscope in situ hybridization that neural crest cells retain broad multipotency throughout migration and even in post-migratory cells in vivo, with no evidence for partially-restricted intermediates. We find that leukocyte tyrosine kinase early expression marks a multipotent stage, with signalling driving iridophore differentiation through repression of fate-specific transcription factors for other fates. We reconcile the direct and progressive fate restriction models by proposing that pigment cell development occurs directly, but dynamically, from a highly multipotent state, consistent with our recently-proposed Cyclical Fate Restriction model.

Huriez syndrome: Additional pathogenic variants supporting allelism to SMARCAD syndrome

Huriez syndrome (HRZ, OMIM181600) is a rare genodermatosis characterized by scleroatrophic hands and feet, hypoplastic nails, palmoplantar keratoderma, and predisposition to cutaneous squamous cell carcinoma (cSCC). We report herein three HRZ families from Croatia, the Netherlands, and Germany. Deep sequencing followed by Sanger validation, confirmed the presence of germline causative SMARCAD1 heterozygous pathogenic variants. All seven HRZ patients displayed hypohidrosis, adermatoglyphia, and one patient developed cSCC at 32 years of age. Two novel monoallelic germline mutations were identified which are predicted to disrupt the first exon-intron boundary of the skin-specific SMARCAD1 isoform. On the basis of phenotypic and genotypic convergence with Adermatoglyphia (OMIM136000) and Basan syndrome (OMIM129200), our results lend credence to the notion that these three Mendelian disorders are allelic. We propose adding Huriez syndrome to the previously suggested SMARCAD syndrome designation, which was originally invoked to describe the spectrum of monogenic disorders between Adermatoglyphia and Basan syndrome.

The novel zebrafish model pretzel demonstrates a central role for SH3PXD2B in defective collagen remodelling and fibrosis in Frank-Ter Haar syndrome

Frank-Ter Haar syndrome (FTHS, MIM #249420) is a rare skeletal dysplasia within the defective collagen remodelling spectrum (DECORS), which is characterised by craniofacial abnormalities, skeletal malformations and fibrotic soft tissues changes including dermal fibrosis and joint contractures. FTHS is caused by homozygous or compound heterozygous loss-of-function mutation or deletion of SH3PXD2B (Src homology 3 and Phox homology domain-containing protein 2B; MIM #613293). SH3PXD2B encodes an adaptor protein with the same name, which is required for full functionality of podosomes, specialised membrane structures involved in extracellular matrix (ECM) remodelling. The pathogenesis of DECORS is still incompletely understood and, as a result, therapeutic options are limited. We previously generated an mmp14a/b knockout zebrafish and demonstrated that it primarily mimics the DECORS-related bone abnormalities. Here, we present a novel sh3pxd2b mutant zebrafish, pretzel, which primarily reflects the DECORS-related dermal fibrosis and contractures. In addition to relatively mild skeletal abnormalities, pretzel mutants develop dermal and musculoskeletal fibrosis, contraction of which seems to underlie grotesque deformations that include kyphoscoliosis, abdominal constriction and lateral folding. The discrepancy in phenotypes between mmp14a/b and sh3pxd2b mutants suggests that in fish, as opposed to humans, there are differences in spatiotemporal dependence of ECM remodelling on either sh3pxd2b or mmp14a/b The pretzel model presented here can be used to further delineate the underlying mechanism of the fibrosis observed in DECORS, as well as screening and subsequent development of novel drugs targeting DECORS-related fibrosis.This paper has an associated First Person interview with the first author of the article.

Dolastatin 15 from a Marine Cyanobacterium Suppresses HIF-1α Mediated Cancer Cell Viability and Vascularization

Chemical investigation of a benthic marine cyanobacterium yielded the anticancer agent dolastatin 15, originally isolated from a mollusk. Dolastatin 15 is a microtubule-destabilizing agent with analogues undergoing clinical evaluation. Profiling against a panel of isogenic HCT116 colorectal cancer cells showed remarkable differential cytotoxicity against the parental cells over isogenic cells lacking HIF or other key players in the pathway, including oncogenic KRAS and VEGF. Dolastatin 15 displayed an antivascularization effect in human endothelial cells and in zebrafish vhl mutants with activated Hif, thus signifying its clinical potential as a treatment for solid tumors with an angiogenic component. Global transcriptome analysis with RNA sequencing suggested that dolastatin 15 could affect other major cancer pathways that might not directly involve tubulin or HIF. The identification of the true producer of a clinically relevant agent is important for sustainable supply, as is understanding the biosynthesis, and future genetic manipulation of the biosynthetic gene cluster for analogue production.

Seaweed natural products modify the host inflammatory response via Nrf2 signaling and alter colon microbiota composition and gene expression

Seaweeds are an important component of human diets, especially in Asia and the Pacific islands, and have shown chemopreventive as well as anti-inflammatory properties. However, structural characterization and mechanistic insight of seaweed components responsible for their biological activities are lacking. We isolated cymopol and related natural products from the marine green alga Cymopolia barbata and demonstrated their function as activators of transcription factor Nrf2-mediated antioxidant response to increase the cellular antioxidant status. We probed the reactivity of the bioactivation product of cymopol, cymopol quinone, which was able to modify various cysteine residues of Nrf2's cytoplasmic repressor protein Keap1. The observed adducts are reflective of the polypharmacology at the level of natural product, due to multiple electrophilic centers, and at the amino acid level of the cysteine-rich target protein Keap1. The non-polar C. barbata extract and its major active component cymopol, reduced inflammatory gene transcription in vitro in macrophages and mouse embryonic fibroblasts in an Nrf2-dependent manner. Cymopol-containing extracts attenuated neutrophil migration in a zebrafish tail wound model. RNA-seq analysis of colonic tissues of mice exposed to non-polar extract or cymopol showed an antioxidant and anti-inflammatory response, with more pronounced effects exhibited by the extract. Cymopolia extract reduced DSS-induced colitis as measured by fecal lipocalin concentration. RNA-seq showed that mucosal-associated bacterial composition and transcriptional profile in large intestines were beneficially altered to varying degrees in mice treated with either the extract or cymopol. We conclude that seaweed-derived compounds, especially cymopol, alter Nrf2-mediated host and microbial gene expression, thereby providing polypharmacological effects.

Use of zebrafish to model chemotherapy and targeted therapy gastrointestinal toxicity

Gastrointestinal toxicity arising from cancer treatment remains a key reason for treatment discontinuation, significantly compromising remission. There are drawbacks to the currently used in vitro and rodent models, and a lack of translatability from in vitro to in vivo work. A screening-amenable alternative in vivo model such as zebrafish would, therefore, find immediate application. This study utilized a transgenic reporter line of zebrafish, Tg(cyp2k18:egfp), that shows eGFP induction as an indicator of drug-induced pathology. Here, we investigate its utility as an alternative vertebrate model to bridge the gap between simple in vitro cellular studies and complex in vivo models for understanding gastrointestinal toxicity induced by chemotherapy and targeted therapy. Transgenic zebrafish larvae were administered afatinib or SN38, and assessed for viability and eGFP induction. Adult zebrafish were administered afatinib via oral gavage, and SN38 via intraperitoneal injection. Fish were killed after 24 h, and had gastrointestinal tracts removed and assessed for histopathological damage, goblet cell changes, and apoptosis. While treatment with either compound did not induce eGFP in the gastrointestinal tract of larvae, SN38 caused histopathological damage to adult intestines. The lack of eGFP induction may be due to poor solubility of the drugs. Chemotherapy agents with high solubility and permeability would be more amenable to these models. Further progress in this area would be greatly facilitated by the generation of robust and reproducible genetic models of zebrafish intestinal toxicity that mimic the known pathobiological pathways in rodents and humans, and can be readily induced in a short time-frame.

Impact statement

Gastrointestinal toxicity secondary to cancer treatment remains a major reason for the termination of cancer drug candidates in the development pipeline as well as withdrawal or restrictions of marketed drugs. Current cancer treatment-induced gastrointestinal toxicity models available are limited to in vitro and rodent models that lack translatability and are prohibitively expensive and time consuming. An alternative model to study cancer treatment-induced gastrointestinal toxicity that allows rapid, miniaturized, multi-organ toxicity, screening-amenable testing is therefore warranted. The newly developed Tg( cyp2k18:egfp) zebrafish reporter line was found to induce eGFP in the gastrointestinal tract if toxicity was induced in this area. This paper explored utilizing this reporter line for cancer treatment-induced gastrointestinal toxicity, but found that it was not a useful reporter line in this setting. Further progress in this area would be greatly facilitated by the generation of robust and reproducible genetic models of zebrafish intestinal toxicity that mimic the known pathobiological pathways.

Functional analysis of a hypomorphic allele shows that MMP14 catalytic activity is the prime determinant of the Winchester syndrome phenotype

Winchester syndrome (WS, MIM #277950) is an extremely rare autosomal recessive skeletal dysplasia characterized by progressive joint destruction and osteolysis. To date, only one missense mutation in MMP14, encoding the membrane-bound matrix metalloprotease 14, has been reported in WS patients. Here, we report a novel hypomorphic MMP14 p.Arg111His (R111H) allele, associated with a mitigated form of WS. Functional analysis demonstrated that this mutation, in contrast to previously reported human and murine MMP14 mutations, does not affect MMP14’s transport to the cell membrane. Instead, it partially impairs MMP14’s proteolytic activity. This residual activity likely accounts for the mitigated phenotype observed in our patients. Based on our observations as well as previously published data, we hypothesize that MMP14’s catalytic activity is the prime determinant of disease severity. Given the limitations of our in vitro assays in addressing the consequences of MMP14 dysfunction, we generated a novel mmp14a/b knockout zebrafish model. The fish accurately reflected key aspects of the WS phenotype including craniofacial malformations, kyphosis, short-stature and reduced bone density owing to defective collagen remodeling. Notably, the zebrafish model will be a valuable tool for developing novel therapeutic approaches to a devastating bone disorder.

How a cofactor-free protein environment lowers the barrier to O2 reactivity

Molecular oxygen (O₂)-utilizing enzymes are among the most important in biology. The abundance of O₂, its thermodynamic power, and the benign nature of its end products have raised interest in oxidases and oxygenases for biotechnological applications. Although most O₂-dependent enzymes have an absolute requirement for an O₂-activating cofactor, several classes of oxidases and oxygenases accelerate direct reactions between substrate and O₂ using only the protein environment. Nogalamycin monooxygenase (NMO) from Streptomyces nogalater is a cofactor-independent enzyme that catalyzes rate-limiting electron transfer between its substrate and O₂ Here, using enzyme-kinetic, cyclic voltammetry, and mutagenesis methods, we demonstrate that NMO initially activates the substrate, lowering its pK_a by 1.0 unit (ΔG* = 1.4 kcal mol^-1). We found that the one-electron reduction potential, measured for the deprotonated substrate both inside and outside the protein environment, increases by 85 mV inside NMO, corresponding to a ΔΔG ⁰' of 2.0 kcal mol^-1 (0.087 eV) and that the activation barrier, ΔG ^‡, is lowered by 4.8 kcal mol^-1 (0.21 eV). Applying the Marcus model, we observed that this suggests a sizable decrease of 28 kcal mol^-1 (1.4 eV) in the reorganization energy (λ), which constitutes the major portion of the protein environment's effect in lowering the reaction barrier. A similar role for the protein has been proposed in several cofactor-dependent systems and may reflect a broader trend in O₂-utilizing proteins. In summary, NMO's protein environment facilitates direct electron transfer, and NMO accelerates rate-limiting electron transfer by strongly lowering the reorganization energy.

Multidimensional Screening Platform for Simultaneously Targeting Oncogenic KRAS and Hypoxia-Inducible Factors Pathways in Colorectal Cancer

Colorectal cancer (CRC) is a genetic disease, due to progressive accumulation of mutations in oncogenes and tumor suppressor genes. Large scale genomic sequencing projects revealed >100 mutations in any individual CRC. Many of these mutations are likely passenger mutations, and fewer are driver mutations. Of these, activating mutations in RAS proteins are essential for cancer initiation, progression, and/or resistance to therapy. There has been significant interest in developing drugs targeting mutated cancer gene products or downstream signaling pathways. Due to the number of mutations involved and inherent redundancy in intracellular signaling, drugs targeting one mutation or pathway have been either ineffective or led to rapid resistance. We have devised a strategy whereby multiple cancer pathways may be simultaneously targeted for drug discovery. For proof-of-concept, we targeted the oncogenic KRAS and HIF pathways, since oncogenic KRAS has been shown to be required for cancer initiation and progression, and HIF-1α and HIF-2α are induced by the majority of mutated oncogenes and tumor suppressor genes in CRC. We have generated isogenic cell lines defective in either oncogenic KRAS or both HIF-1α and HIF-2α and subjected them to multiplex genomic, siRNA, and high-throughput small molecule screening. We have identified potential drug targets and compounds for preclinical and clinical development. Screening of our marine natural product library led to the rediscovery of the microtubule agent dolastatin 10 and the class I histone deacetylase (HDAC) inhibitor largazole to inhibit oncogenic KRAS and HIF pathways. Largazole was further validated as an antiangiogenic agent in a HIF-dependent manner in human cells and in vivo in zebrafish using a genetic model with activated HIF. Our general strategy, coupling functional genomics with drug susceptibility or chemical-genetic interaction screens, enables the identification of potential drug targets and candidates with requisite selectivity. Molecules prioritized in this manner can easily be validated in suitable zebrafish models due to the genetic tractability of the system. Our multidimensional platform with cellular and organismal components can be extended to larger scale multiplex screens that include other mutations and pathways.

Electrode-electrolyte interface in Li-ion batteries: current understanding and new insights

Understanding reactions at the electrode/electrolyte interface (EEI) is essential to developing strategies to enhance cycle life and safety of lithium batteries. Despite research in the past four decades, there is still limited understanding by what means different components are formed at the EEI and how they influence EEI layer properties. We review findings used to establish the well-known mosaic structure model for the EEI (often referred to as solid electrolyte interphase or SEI) on negative electrodes including lithium, graphite, tin, and silicon. Much less understanding exists for EEI layers for positive electrodes. High-capacity Li-rich layered oxides yLi2-xMnO3·(1-y)Li1-xMO2, which can generate highly reactive species toward the electrolyte via oxygen anion redox, highlight the critical need to understand reactions with the electrolyte and EEI layers for advanced positive electrodes. Recent advances in in situ characterization of well-defined electrode surfaces can provide mechanistic insights and strategies to tailor EEI layer composition and properties.

M13 virus-directed synthesis of nanostructured metal oxides for lithium-oxygen batteries

Transition metal oxides are promising electrocatalysts for both water oxidations and metal-air batteries. Here, we report the virus-mediated synthesis of cobalt manganese oxide nanowires (NWs) to fabricate high capacity Li-O2 battery electrodes. Furthermore, we hybridized Ni nanoparticles (NPs) on bio Co3O4 NWs to improve the round trip efficiency as well as the cycle life of Li-O2 batteries. This biomolecular directed synthesis method is expected to provide a selection platform for future energy storage electrocatalysts.

p53 and TAp63 promote keratinocyte proliferation and differentiation in breeding tubercles of the zebrafish

p63 is a multi-isoform member of the p53 family of transcription factors. There is compelling genetic evidence that ΔNp63 isoforms are needed for keratinocyte proliferation and stemness in the developing vertebrate epidermis. However, the role of TAp63 isoforms is not fully understood, and TAp63 knockout mice display normal epidermal development. Here, we show that zebrafish mutants specifically lacking TAp63 isoforms, or p53, display compromised development of breeding tubercles, epidermal appendages which according to our analyses display more advanced stratification and keratinization than regular epidermis, including continuous desquamation and renewal of superficial cells by derivatives of basal keratinocytes. Defects are further enhanced in TAp63/p53 double mutants, pointing to partially redundant roles of the two related factors. Molecular analyses, treatments with chemical inhibitors and epistasis studies further reveal the existence of a linear TAp63/p53->Notch->caspase 3 pathway required both for enhanced proliferation of keratinocytes at the base of the tubercles and their subsequent differentiation in upper layers. Together, these studies identify the zebrafish breeding tubercles as specific epidermal structures sharing crucial features with the cornified mammalian epidermis. In addition, they unravel essential roles of TAp63 and p53 to promote both keratinocyte proliferation and their terminal differentiation by promoting Notch signalling and caspase 3 activity, ensuring formation and proper homeostasis of this self-renewing stratified epithelium.

The mammalian epidermis is a stratified self-renewing epithelium, in which cell loss at the surface is properly balanced by cell proliferation in basal layers to ensure tissue homeostasis. But how is this balance genetically controlled? Here, we address this question in zebrafish breeding tubercles, epidermal appendages in which keratinocytes undergo more advanced differentiation processes than in regular fish epidermis, sharing crucial features with the cornified mammalian skin. We identify a linear pathway consisting of the transcription factor p53 and its close relative TAp63, which activate Notch signalling and thereby caspase 3 to promote terminal differentiation and eventual shedding of keratinocytes in upper tubercle layers, while at the same time employing non-cell autonomous mechanisms to promote keratinocyte proliferation at the tubercle base, thereby ensuring proper development and homeostasis of this self-renewing tissue. Such a two-fold function of the pathway is consistent with the formerly reported dual role of a caspase during wing regeneration in the fruitfly. Our findings will help to better understand the seemingly contrary effects described for TAp63 in different mammalian systems, while demonstrating partial functional redundancy between p53 and TAp63 during epidermal development in fish.

Basal keratinocytes contribute to all strata of the adult zebrafish epidermis

The epidermis of terrestrial vertebrates is a stratified epithelium and forms an essential protective barrier. It is continually renewed, with dead corneocytes shed from the surface and replaced from a basal keratinocyte stem cell population. Whilst mouse is the prime model system used for epidermal studies, there is increasing employment of the zebrafish to analyse epidermis development and homeostasis, however the architecture and ontogeny of the epidermis in this system are incompletely described. In particular, it is unclear if adult zebrafish epidermis is derived entirely from the basal epidermal stem cell layer, as in the mouse, or if the most superficial keratinocyte layer is a remnant of the embryonic periderm. Furthermore, a relative paucity of cellular markers and genetic reagents to label and manipulate the basal epidermal stem cell compartment has hampered research. Here we show that the type I keratin, krtt1c19e, is a suitable marker of the basal epidermal layer and identify a krtt1c19e promoter fragment able to drive strong and specific expression in this cell type. Use of this promoter to express an inducible Cre recombinase allowed permanent labelling of basal cells during embryogenesis, and demonstrated that these cells do indeed generate keratinocytes of all strata in the adult epidermis. Further deployment of the Cre-Lox system highlighted the transient nature of the embryonic periderm. We thus show that the epidermis of adult zebrafish, as in the mouse, derives from basal stem cells, further expanding the similarities of epidermal ontogeny across vertebrates. Future use of this promoter will assist genetic analysis of basal keratinocyte biology in zebrafish.

An exclusively mesodermal origin of fin mesenchyme demonstrates that zebrafish trunk neural crest does not generate ectomesenchyme

The neural crest is a multipotent stem cell population that arises from the dorsal aspect of the neural tube and generates both non-ectomesenchymal (melanocytes, peripheral neurons and glia) and ectomesenchymal (skeletogenic, odontogenic, cartilaginous and connective tissue) derivatives. In amniotes, only cranial neural crest generates both classes, with trunk neural crest restricted to non-ectomesenchyme. By contrast, it has been suggested that anamniotes might generate derivatives of both classes at all axial levels, with trunk neural crest generating fin osteoblasts, scale mineral-forming cells and connective tissue cells; however, this has not been fully tested. The cause and evolutionary significance of this cranial/trunk dichotomy, and its absence in anamniotes, are debated. Recent experiments have disputed the contribution of fish trunk neural crest to fin osteoblasts and scale mineral-forming cells. This prompted us to test the contribution of anamniote trunk neural crest to fin connective tissue cells. Using genetics-based lineage tracing in zebrafish, we find that these fin mesenchyme cells derive entirely from the mesoderm and that neural crest makes no contribution. Furthermore, contrary to previous suggestions, larval fin mesenchyme cells do not generate the skeletogenic cells of the adult fin, but persist to form fibroblasts associated with adult fin rays. Our data demonstrate that zebrafish trunk neural crest does not generate ectomesenchymal derivatives and challenge long-held ideas about trunk neural crest fate. These findings have important implications for the ontogeny and evolution of the neural crest.

A transparent electrode based on a metal nanotrough network

Transparent conducting electrodes are essential components for numerous flexible optoelectronic devices, including touch screens and interactive electronics. Thin films of indium tin oxide-the prototypical transparent electrode material-demonstrate excellent electronic performances, but film brittleness, low infrared transmittance and low abundance limit suitability for certain industrial applications. Alternatives to indium tin oxide have recently been reported and include conducting polymers, carbon nanotubes and graphene. However, although flexibility is greatly improved, the optoelectronic performance of these carbon-based materials is limited by low conductivity. Other examples include metal nanowire-based electrodes, which can achieve sheet resistances of less than 10Ω □(-1) at 90% transmission because of the high conductivity of the metals. To achieve these performances, however, metal nanowires must be defect-free, have conductivities close to their values in bulk, be as long as possible to minimize the number of wire-to-wire junctions, and exhibit small junction resistance. Here, we present a facile fabrication process that allows us to satisfy all these requirements and fabricate a new kind of transparent conducting electrode that exhibits both superior optoelectronic performances (sheet resistance of ~2Ω □(-1) at 90% transmission) and remarkable mechanical flexibility under both stretching and bending stresses. The electrode is composed of a free-standing metallic nanotrough network and is produced with a process involving electrospinning and metal deposition. We demonstrate the practical suitability of our transparent conducting electrode by fabricating a flexible touch-screen device and a transparent conducting tape.

fras1 shapes endodermal pouch 1 and stabilizes zebrafish pharyngeal skeletal development

Lesions in the epithelially expressed human gene FRAS1 cause Fraser syndrome, a complex disease with variable symptoms, including facial deformities and conductive hearing loss. The developmental basis of facial defects in Fraser syndrome has not been elucidated. Here we show that zebrafish fras1 mutants exhibit defects in facial epithelia and facial skeleton. Specifically, fras1 mutants fail to generate a late-forming portion of pharyngeal pouch 1 (termed late-p1) and skeletal elements adjacent to late-p1 are disrupted. Transplantation studies indicate that fras1 acts in endoderm to ensure normal morphology of both skeleton and endoderm, consistent with well-established epithelial expression of fras1. Late-p1 formation is concurrent with facial skeletal morphogenesis, and some skeletal defects in fras1 mutants arise during late-p1 morphogenesis, indicating a temporal connection between late-p1 and skeletal morphogenesis. Furthermore, fras1 mutants often show prominent second arch skeletal fusions through space occupied by late-p1 in wild type. Whereas every fras1 mutant shows defects in late-p1 formation, skeletal defects are less penetrant and often vary in severity, even between the left and right sides of the same individual. We interpret the fluctuating asymmetry in fras1 mutant skeleton and the changes in fras1 mutant skeletal defects through time as indicators that skeletal formation is destabilized. We propose a model wherein fras1 prompts late-p1 formation and thereby stabilizes skeletal formation during zebrafish facial development. Similar mechanisms of stochastic developmental instability might also account for the high phenotypic variation observed in human FRAS1 patients.

Hemicentin 2 and Fibulin 1 are required for epidermal-dermal junction formation and fin mesenchymal cell migration during zebrafish development

Hemicentin 1 (Hmcn1) and Hemicentin 2 (Hmcn2) belong to the fibulin family of extracellular matrix (ECM) proteins that play pivotal roles during development and homeostasis of a variety of vertebrate tissues. Recently, we have shown that mutations in zebrafish Hmcn1, also called Fibulin 6, lead to massive fin blistering, similar to the defects caused by the Fraser syndrome gene Fras1. In contrast, the role of Hmcn2 during vertebrate development has thus far been uncharacterized. In zebrafish, hmcn2, like fibulin 1 (fbln1), another member of the fibulin family, is predominantly expressed in fin mesenchymal cells and developing somites, contrasting the strict epithelial expression of hmcn1. While antisense morpholino oligonucleotide (MO)-based knockdown of hmcn2 did not yield any discernable defects, hmcn2/fbln1 double knockdown fish displayed blistering in the trunk, pointing to an essential contribution of these proteins from mesodermal sources for proper epidermal-dermal junction formation. In contrast, and unlike hmcn1 mutants, epidermal-dermal junctions in the fin folds of hmcn2/fbln1 double knockdown fish were only moderately affected. Instead, they displayed impaired migration of fin mesenchymal cells into the fin folds, pointing to a crucial role of Hmcn2 and Fbln1 to remodel the ECM of the fin fold interepidermal space, which is a prerequisite for fibroblast ingrowth. TEM analyses suggest that this ECM remodeling occurs at the level of actinotrichia, the collageneous migration substrate of mesenchymal cells, and at the level of cross fibers, which resemble mammalian microfibers. This work provides first insights into the role of Hmcn2 during vertebrate development, identifying it as an evolutionary conserved protein that acts in functional redundancy with Fbln1C and/or Fbln1D isoforms to regulate tissue adhesion and cell migration, while extending the current knowledge of the functions of vertebrate Fbln1.

Passivation coating on electrospun copper nanofibers for stable transparent electrodes

Copper nanofiber networks, which possess the advantages of low cost, moderate flexibility, small sheet resistance, and high transmittance, are one of the most promising candidates to replace indium tin oxide films as the premier transparent electrode. However, the chemical activity of copper nanofibers causes a substantial increase in the sheet resistance after thermal oxidation or chemical corrosion of the nanofibers. In this work, we utilize atomic layer deposition to coat a passivation layer of aluminum-doped zinc oxide (AZO) and aluminum oxide onto electrospun copper nanofibers and remarkably enhance their durability. Our AZO-copper nanofibers show resistance increase of remarkably only 10% after thermal oxidation at 160 °C in dry air and 80 °C in humid air with 80% relative humidity, whereas bare copper nanofibers quickly become insulating. In addition, the coating and baking of the acidic PEDOT:PSS layer on our fibers increases the sheet resistance of bare copper nanofibers by 6 orders of magnitude, while the AZO-Cu nanofibers show an 18% increase.

Attenuated BMP1 function compromises osteogenesis, leading to bone fragility in humans and zebrafish

Bone morphogenetic protein 1 (BMP1) is an astacin metalloprotease with important cellular functions and diverse substrates, including extracellular-matrix proteins and antagonists of some TGFβ superfamily members. Combining whole-exome sequencing and filtering for homozygous stretches of identified variants, we found a homozygous causative BMP1 mutation, c.34G>C, in a consanguineous family affected by increased bone mineral density and multiple recurrent fractures. The mutation is located within the BMP1 signal peptide and leads to impaired secretion and an alteration in posttranslational modification. We also characterize a zebrafish bone mutant harboring lesions in bmp1a, demonstrating conservation of BMP1 function in osteogenesis across species. Genetic, biochemical, and histological analyses of this mutant and a comparison to a second, similar locus reveal that Bmp1a is critically required for mature-collagen generation, downstream of osteoblast maturation, in bone. We thus define the molecular and cellular bases of BMP1-dependent osteogenesis and show the importance of this protein for bone formation and stability.

Engineering empty space between Si nanoparticles for lithium-ion battery anodes

Silicon is a promising high-capacity anode material for lithium-ion batteries yet attaining long cycle life remains a significant challenge due to pulverization of the silicon and unstable solid-electrolyte interphase (SEI) formation during the electrochemical cycles. Despite significant advances in nanostructured Si electrodes, challenges including short cycle life and scalability hinder its widespread implementation. To address these challenges, we engineered an empty space between Si nanoparticles by encapsulating them in hollow carbon tubes. The synthesis process used low-cost Si nanoparticles and electrospinning methods, both of which can be easily scaled. The empty space around the Si nanoparticles allowed the electrode to successfully overcome these problems Our anode demonstrated a high gravimetric capacity (~1000 mAh/g based on the total mass) and long cycle life (200 cycles with 90% capacity retention).

Genetic analysis of fin development in zebrafish identifies furin and hemicentin1 as potential novel fraser syndrome disease genes

Using forward genetics, we have identified the genes mutated in two classes of zebrafish fin mutants. The mutants of the first class are characterized by defects in embryonic fin morphogenesis, which are due to mutations in a Laminin subunit or an Integrin alpha receptor, respectively. The mutants of the second class display characteristic blistering underneath the basement membrane of the fin epidermis. Three of them are due to mutations in zebrafish orthologues of FRAS1, FREM1, or FREM2, large basement membrane protein encoding genes that are mutated in mouse bleb mutants and in human patients suffering from Fraser Syndrome, a rare congenital condition characterized by syndactyly and cryptophthalmos. Fin blistering in a fourth group of zebrafish mutants is caused by mutations in Hemicentin1 (Hmcn1), another large extracellular matrix protein the function of which in vertebrates was hitherto unknown. Our mutant and dose-dependent interaction data suggest a potential involvement of Hmcn1 in Fraser complex-dependent basement membrane anchorage. Furthermore, we present biochemical and genetic data suggesting a role for the proprotein convertase FurinA in zebrafish fin development and cell surface shedding of Fras1 and Frem2, thereby allowing proper localization of the proteins within the basement membrane of forming fins. Finally, we identify the extracellular matrix protein Fibrillin2 as an indispensable interaction partner of Hmcn1. Thus we have defined a series of zebrafish mutants modelling Fraser Syndrome and have identified several implicated novel genes that might help to further elucidate the mechanisms of basement membrane anchorage and of the disease's aetiology. In addition, the novel genes might prove helpful to unravel the molecular nature of thus far unresolved cases of the human disease.

There are a large number of human genetic syndromes with limb and digit deformities. It has been shown that the genes underlying these syndromes are well conserved in evolution, and most perform the same role even in the fins of fish. One such human syndrome is Fraser Syndrome, characterized by a number of defects including fusion of the fingers (syndactyly). Data obtained with corresponding mouse mutants suggest that all of these defects are due to transient basement membrane disruptions and epithelial blistering during development. Whilst some of the Fraser Syndrome genes have been identified, others are unknown. We show that mutation of the known Fraser Syndrome genes in zebrafish generate comparable blistering defects in the fins. Importantly, we have also identified additional genes and mechanisms required for the same processes. Included in this are hemicentin1, a gene whose function had thus far only been studied in nematodes, and furinA, encoding a proprotein convertase, for which we reveal a novel role in ectodomain shedding of Fras/Frem proteins. This work thus expands our understanding, not only of Fraser Syndrome, but also of the common processes of basement membrane formation and function during fin and limb development.

The epithelial cell adhesion molecule EpCAM is required for epithelial morphogenesis and integrity during zebrafish epiboly and skin development

The aberrant expression of the transmembrane protein EpCAM is associated with tumor progression, affecting different cellular processes such as cell–cell adhesion, migration, proliferation, differentiation, signaling, and invasion. However, the in vivo function of EpCAM still remains elusive due to the lack of genetic loss-of-function studies. Here, we describe epcam (tacstd) null mutants in zebrafish. Maternal-zygotic mutants display compromised basal protrusive activity and epithelial morphogenesis in cells of the enveloping layer (EVL) during epiboly. In partial redundancy with E-cadherin (Ecad), EpCAM made by EVL cells is further required for cell–cell adhesion within the EVL and, possibly, for proper attachment of underlying deep cells to the inner surface of the EVL, thereby also affecting deep cell epiboly movements. During later development, EpCAM per se becomes indispensable for epithelial integrity within the periderm of the skin, secondarily leading to disrupted morphology of the underlying basal epidermis and moderate hyper-proliferation of skin cells. On the molecular level, EVL cells of epcam mutant embryos display reduced levels of membranous Ecad, accompanied by an enrichment of tight junction proteins and a basal extension of apical junction complexes (AJCs). Our data suggest that EpCAM acts as a partner of E-cadherin to control adhesiveness and integrity as well as plasticity and morphogenesis within simple epithelia. In addition, EpCAM is required for the interaction of the epithelia with underlying cell layers.

EpCAM is a well-established marker for carcinomas of epithelial origin and a potential target for immunotherapy. In vitro analyses have implicated EpCAM in a plethora of different cellular processes, such as adhesion, motility, proliferation, differentiation, and signaling. Strikingly, depending on the context, EpCAM displayed rather opposite effects, either promoting or attenuating cell–cell adhesion versus cell migration and tissue invasion, a phenomenon described as the “double-face” of EpCAM. However, the in vivo relevance of its different effects remained largely unclear. Here, we present the first genetic analysis of EpCAM function in vivo, based on loss-of-function mutants in the zebrafish. As it is in mammals, zebrafish EpCAM is expressed in simple epithelia. Mutant embryos display defects both in epithelial morphogenesis and in epithelial integrity. Reduced epithelial morphogenesis is accompanied, and possibly caused, by an extension of apical junctional complexes and compromised basal protrusive activity. Furthermore, mutant epithelia display alterations in the relative abundance of adherence junction versus tight junction components. In addition, EpCAM tightly cooperates with E-cadherin and has a previously unrecognized trans effect on the morphogenesis and integrity of underlying cell layers. Cell differentiation and proliferation in EpCAM mutants are not, or only secondarily, affected. During later development and adulthood, EpCAM is largely dispensable, reinforcing its suitability as a target for anti-carcinoma immunotherapy with minimal side effects.

An evolutionarily conserved intronic region controls the spatiotemporal expression of the transcription factor Sox10

Background

A major challenge lies in understanding the complexities of gene regulation. Mutation of the transcription factor SOX10 is associated with several human diseases. The disease phenotypes reflect the function of SOX10 in diverse tissues including the neural crest, central nervous system and otic vesicle. As expected, the SOX10 expression pattern is complex and highly dynamic, but little is known of the underlying mechanisms regulating its spatiotemporal pattern. SOX10 expression is highly conserved between all vertebrates characterised.

Results

We have combined in vivo testing of DNA fragments in zebrafish and computational comparative genomics to identify the first regulatory regions of the zebrafish sox10 gene. Both approaches converged on the 3' end of the conserved 1^st intron as being critical for spatial patterning of sox10 in the embryo. Importantly, we have defined a minimal region crucial for this function. We show that this region contains numerous binding sites for transcription factors known to be essential in early neural crest induction, including Tcf/Lef, Sox and FoxD3. We show that the identity and relative position of these binding sites are conserved between zebrafish and mammals. A further region, partially required for oligodendrocyte expression, lies in the 5' region of the same intron and contains a putative CSL binding site, consistent with a role for Notch signalling in sox10 regulation. Furthermore, we show that β-catenin, Notch signalling and Sox9 can induce ectopic sox10 expression in early embryos, consistent with regulatory roles predicted from our transgenic and computational results.

Conclusion

We have thus identified two major sites of sox10 regulation in vertebrates and provided evidence supporting a role for at least three factors in driving sox10 expression in neural crest, otic epithelium and oligodendrocyte domains.

Leukocyte tyrosine kinase functions in pigment cell development

A fundamental problem in developmental biology concerns how multipotent precursors choose specific fates. Neural crest cells (NCCs) are multipotent, yet the mechanisms driving specific fate choices remain incompletely understood. Sox10 is required for specification of neural cells and melanocytes from NCCs. Like sox10 mutants, zebrafish shady mutants lack iridophores; we have proposed that sox10 and shady are required for iridophore specification from NCCs. We show using diverse approaches that shady encodes zebrafish leukocyte tyrosine kinase (Ltk). Cell transplantation studies show that Ltk acts cell-autonomously within the iridophore lineage. Consistent with this, ltk is expressed in a subset of NCCs, before becoming restricted to the iridophore lineage. Marker analysis reveals a primary defect in iridophore specification in ltk mutants. We saw no evidence for a fate-shift of neural crest cells into other pigment cell fates and some NCCs were subsequently lost by apoptosis. These features are also characteristic of the neural crest cell phenotype in sox10 mutants, leading us to examine iridophores in sox10 mutants. As expected, sox10 mutants largely lacked iridophore markers at late stages. In addition, sox10 mutants unexpectedly showed more ltk-expressing cells than wild-type siblings. These cells remained in a premigratory position and expressed sox10 but not the earliest neural crest markers and may represent multipotent, but partially-restricted, progenitors. In summary, we have discovered a novel signalling pathway in NCC development and demonstrate fate specification of iridophores as the first identified role for Ltk.

Stem and other multipotent cells generate diverse cell-types, but our understanding of how they make these decisions, which is important for their therapeutic use, is incomplete. Neural crest cells are an important class of multipotent cells and generate multiple stem cell types. We have looked at how pigment cells are made from the neural crest in the zebrafish. The silver shine familiar in so many fish is due to specialised mirror-like pigment cells, called iridophores. We show that these cells are missing in zebrafish shady mutants. We identify the shady gene as encoding a cell signalling receptor, leukocyte tyrosine kinase (Ltk), that has recently been associated with human auto-immune disease. We show that in zebrafish this gene is most likely required to make iridophores from neural crest cells. Thus, we identify a novel pathway required for diversification of these multipotent cells. Our work defines the first role for Ltk in a vertebrate. It provides a mutant resource that will allow us to discover the full breadth of roles for this important gene. Furthermore, the loss of iridophores forms a simple visual screen for inhibition of LTK function and might well have implications in drug discovery.

Inactivation of serine protease Matriptase1a by its inhibitor Hai1 is required for epithelial integrity of the zebrafish epidermis

Epithelial integrity requires the adhesion of cells to each other as well as to an underlying basement membrane. The modulation of adherence properties is crucial to morphogenesis and wound healing, and deregulated adhesion has been implicated in skin diseases and cancer metastasis. Here, we describe zebrafish that are mutant in the serine protease inhibitor Hai1a (Spint1la), which display disrupted epidermal integrity. These defects are further enhanced upon combined loss of hai1a and its paralog hai1b. By applying in vivo imaging, we demonstrate that Hai1-deficient keratinocytes acquire mesenchymal-like characteristics, lose contact with each other, and become mobile and more susceptible to apoptosis. In addition, inflammation of the mutant skin is evident, although not causative of the epidermal defects. Only later, the epidermis exhibits enhanced cell proliferation. The defects of hai1 mutants can be phenocopied by overexpression and can be fully rescued by simultaneous inactivation of the serine protease Matriptase1a (St14a), indicating that Hai1 promotes epithelial integrity by inhibiting Matriptase1a. By contrast, Hepatocyte growth factor (Hgf), a well-known promoter of epithelial-mesenchymal transitions and a prime target of Matriptase1 activity, plays no major role. Our work provides direct genetic evidence for antagonistic in vivo roles of Hai1 and Matriptase1a to regulate skin homeostasis and remodeling.

Foxi3 transcription factors and Notch signaling control the formation of skin ionocytes from epidermal precursors of the zebrafish embryo

Ionocytes are specialized epithelial cell types involved in the maintenance of osmotic homeostasis. In amniotes, they are present in the renal system, while in water-living embryos of lower vertebrates additional ionocytes are found in the skin. Thus far, relatively little has been known about the mechanisms of ionocyte development. Here we demonstrate that skin ionocytes of zebrafish embryos derive from the same precursor cells as keratinocytes. Carrying out various combinations of gain- and loss-of-function studies, we show that the segregation of ionocytes from the epidermal epithelium is governed by an interplay between Notch signaling and two Forkhead-box transcription factors, Foxi3a and Foxi3b. The two foxi3 genes are expressed in ionocyte precursors and are required both for ionocyte-specific expression of the Notch ligand Jagged2a, and for ionocyte differentiation, characterized by the production of particular ATPases. Ionocytic Notch ligands, in turn, signal to neighboring cells, where activated Notch1 leads to a repression of foxi3 expression, allowing those cells to become keratinocytes. A model for ionocyte versus keratinocyte development will be presented, postulating additional thus far unidentified pro-ionocyte factors.

A direct role for Sox10 in specification of neural crest-derived sensory neurons

sox10 is necessary for development of neural and pigment cell derivatives of the neural crest (NC). However, whereas a direct role for Sox10 activity has been established in pigment and glial lineages, this is more controversial in NC-derived sensory neurons of the dorsal root ganglia (DRGs). We proposed that sox10 functioned in specification of sensory neurons, whereas others suggested that sensory neuronal defects were merely secondary to absence of glia. Here we provide evidence that in zebrafish,early DRG sensory neuron survival is independent of differentiated glia. Critically, we demonstrate that Sox10 is expressed transiently in the sensory neuron lineage, and specifies sensory neuron precursors by regulating the proneural gene neurogenin1. Consistent with this, we have isolated a novel sox10 mutant that lacks glia and yet displays a neurogenic DRG phenotype. In conjunction with previous findings, these data establish the generality of our model of Sox10 function in NC fate specification.

In vivo time-lapse imaging shows dynamic oligodendrocyte progenitor behavior during zebrafish development

Myelinating oligodendrocytes arise from migratory and proliferative oligodendrocyte progenitor cells (OPCs). Complete myelination requires that oligodendrocytes be uniformly distributed and form numerous, periodically spaced membrane sheaths along the entire length of target axons. Mechanisms that determine spacing of oligodendrocytes and their myelinating processes are not known. Using in vivo time-lapse confocal microscopy, we show that zebrafish OPCs continuously extend and retract numerous filopodium-like processes as they migrate and settle into their final positions. Process remodeling and migration paths are highly variable and seem to be influenced by contact with neighboring OPCs. After laser ablation of oligodendrocyte-lineage cells, nearby OPCs divide more frequently, orient processes toward the ablated cells and migrate to fill the unoccupied space. Thus, process activity before axon wrapping might serve as a surveillance mechanism by which OPCs determine the presence or absence of nearby oligodendrocyte-lineage cells, facilitating uniform spacing of oligodendrocytes and complete myelination.

Hedgehog signaling is required for cranial neural crest morphogenesis and chondrogenesis at the midline in the zebrafish skull

Neural crest cells that form the vertebrate head skeleton migrate and interact with surrounding tissues to shape the skull, and defects in these processes underlie many human craniofacial syndromes. Signals at the midline play a crucial role in the development of the anterior neurocranium, which forms the ventral braincase and palate, and here we explore the role of Hedgehog (Hh) signaling in this process. Using sox10:egfp transgenics to follow neural crest cell movements in the living embryo, and vital dye labeling to generate a fate map, we show that distinct populations of neural crest form the two main cartilage elements of the larval anterior neurocranium: the paired trabeculae and the midline ethmoid. By analyzing zebrafish mutants that disrupt sonic hedgehog (shh) expression, we demonstrate that shh is required to specify the movements of progenitors of these elements at the midline, and to induce them to form cartilage. Treatments with cyclopamine, to block Hh signaling at different stages, suggest that although requirements in morphogenesis occur during neural crest migration beneath the brain, requirements in chondrogenesis occur later, as cells form separate trabecular and ethmoid condensations. Cell transplantations indicate that these also reflect different sources of Shh, one from the ventral neural tube that controls trabecular morphogenesis and one from the oral ectoderm that promotes chondrogenesis. Our results suggest a novel role for Shh in the movements of neural crest cells at the midline, as well as in their differentiation into cartilage, and help to explain why both skeletal fusions and palatal clefting are associated with the loss of Hh signaling in holoprosencephalic humans.

Zebrafishcolourlessencodessox10and specifies non-ectomesenchymal neural crest fates

Waardenburg-Shah syndrome combines the reduced enteric nervous system characteristic of Hirschsprung’s disease with reduced pigment cell number, although the cell biological basis of the disease is unclear. We have analysed a zebrafish Waardenburg-Shah syndrome model. We show that the colourless gene encodes a sox10 homologue, identify sox10 lesions in mutant alleles and rescue the mutant phenotype by ectopic sox10 expression. Using iontophoretic labelling of neural crest cells, we demonstrate that colourless mutant neural crest cells form ectomesenchymal fates. By contrast, neural crest cells which in wild types form non-ectomesenchymal fates generally fail to migrate and do not overtly differentiate. These cells die by apoptosis between 35 and 45 hours post fertilisation. We provide evidence that melanophore defects in colourless mutants can be largely explained by disruption of nacre/mitf expression. We propose that all defects of affected crest derivatives are consistent with a primary role for colourless/sox10 in specification of non-ectomesenchymal crest derivatives. This suggests a novel mechanism for the aetiology of Waardenburg-Shah syndrome in which affected neural crest derivatives fail to be generated from the neural crest.