Zebrafish: an emerging model of vascular development and remodelling

Do zebrafish become blind or is it too much red dye in water? Distinguishing the embryo-larval development and physiology effects of DR 60, 73, and 78

Some dyes currently used by the textile, pharmaceutical, food, cosmetic, and photographic industries have been shown to be toxic and/or mutagenic to aquatic life. Most of these dyes resist degradation processes available for treating wastewater, and these processes might generate even more toxic by-products. Despite the large number of available dyes and the large quantity of dyes released into the environment, studies on their toxicity are still scarce. We evaluated and compared the effects in the animal model Danio rerio (zebrafish) of environmentally relevant concentrations of Disperse Red 60 (DR 60), 73 (DR 73), and 78 (DR 78) using the fish embryo acute toxicity (FET) test, morphometric analysis, immunofluorescence imaging, and behavioral parameters. DR 60 caused ocular modifications, while the DR 73 caused non-inflation of the swim bladder (NISB), pericardial edema (PE), scoliosis (S) and abnormal yolk sac (AYS) from at 0.125 mg/L. In behavioral tests, all the dyes induced changes in velocity and time spent swimming of exposed larvae. However, these alterations in behavior seem to be caused by different factors dependent on the dye and its concentration. Nevertheless, behavior seems to add valuable information concerning the hazards analysis of dyes, since it reveals to be the most sensitive group of parameters tested in the current study. In conclusion, of the behavioral and developmental alterations caused by these dyes should be interpreted as an alert for greater attention when registering new dyes and releasing them into the environment. In the particular case of DR 60 the possibility that directly affects the eye of larvae is of great environmental concern, but also from the human health perspective.

Analysis of Vascular Morphogenesis in Zebrafish

Analysis of cardiovascular development in zebrafish embryos has become a major driver of vascular research in recent years. Imaging-based analyses have allowed the discovery or verification of morphologically distinct processes and mechanisms of, e.g., endothelial cell migration, angiogenic sprouting, tip or stalk cell behavior, and vessel anastomosis. In this chapter, we describe the techniques and tools used for confocal imaging of zebrafish endothelial development in combination with general experimental approaches for molecular dissection of involved signaling pathways.

MicroRNA-29c affects zebrafish cardiac development via targeting Wnt4

As a single cardiac malformation, ventricular septal defect (VSD) is the most common form of congenital heart disease. However, the precise molecular mechanisms underlying VSD are not completely understood. Numerous microRNAs (miRs/miRNAs) are associated with ventricular septal defects. miR-29c inhibits the proliferation and promotes the apoptosis and differentiation of P19 embryonal carcinoma cells, possibly via suppressing Wnt4 signaling. However, to the best of our knowledge, no in vivo studies have been published to determine whether overexpression of miR-29c leads to developmental abnormalities. The present study was designed to observe the effect of miRNA-29c on cardiac development and its possible mechanism in vivo. Zebrafish embryos were microinjected with different doses (1, 1.6 and 2 µmol) miR-29c mimics or negative controls, and hatchability, mortality and cardiac malformation were subsequently observed. The results showed that in zebrafish embryos, miR-29c overexpression attenuated heart development in a dose-dependent manner, manifested by heart rate slowdown, pericardial edema and heart looping disorder. Further experiments showed that overexpression of miR-29c was associated with the Wnt4/β-catenin signaling pathway to regulate zebrafish embryonic heart development. In conclusion, the present results demonstrated that miR-29c regulated the lateral development and cardiac circulation of zebrafish embryo by targeting Wnt4.

Hydrogen peroxide in neutrophil inflammation: Lesson from the zebrafish

The zebrafish has become an excellent model for the study of inflammation and immunity. Its unique advantages for in vivo imaging and gene and drug screening have allowed the visualization of dual oxidase 1 (Duox1)-derived hydrogen peroxide (H₂O₂) tissue gradients and its crosstalk with neutrophil infiltration to inflamed tissue. Thus, it has been shown that H₂O₂ directly recruits neutrophils via the Src-family tyrosine kinase Lyn and indirectly by the activation of several signaling pathways involved in inflammation, such as nuclear factor κB (NF-κB), mitogen activated kinases and the transcription factor AP1. In addition, this model has also unmasked the unexpected ability of H₂O₂ to induce the expression of the gene encoding the key neutrophil chemoattractant CXC chemokine ligand 8 by facilitating the accessibility of transcription factors to its promoter through histone covalent modifications. Finally, zebrafish models of psoriasis have shown that a H₂O₂/NF-κB/Duox1 positive feedback inflammatory loop operates in this chronic inflammatory disorder and that pharmacological inhibition of Duox1, but not of downstream mediators, inhibits inflammation and restores epithelial homeostasis. Therefore, these results have pointed out DUOX1 and H₂O₂ as therapeutic targets for the treatment of skin inflammatory disorders, such as psoriasis.

The effect of hyperglycemia on neurovascular coupling and cerebrovascular patterning in zebrafish

Neurovascular coupling (through which local cerebral blood flow changes in response to neural activation are mediated) is impaired in many diseases including diabetes. Current preclinical rodent models of neurovascular coupling rely on invasive surgery and instrumentation, but transgenic zebrafish coupled with advances in imaging techniques allow non-invasive quantification of cerebrovascular anatomy, neural activation, and cerebral vessel haemodynamics. We therefore established a novel non-invasive, non-anaesthetised zebrafish larval model of neurovascular coupling, in which visual stimulus evokes neuronal activation in the optic tectum that is associated with a specific increase in red blood cell speed in tectal blood vessels. We applied this model to the examination of the effect of glucose exposure on cerebrovascular patterning and neurovascular coupling. We found that chronic exposure of zebrafish to glucose impaired tectal blood vessel patterning and neurovascular coupling. The nitric oxide donor sodium nitroprusside rescued all these adverse effects of glucose exposure on cerebrovascular patterning and function. Our results establish the first non-mammalian model of neurovascular coupling, offering the potential to perform more rapid genetic modifications and high-throughput screening than is currently possible using rodents. Furthermore, using this zebrafish model, we reveal a potential strategy to ameliorate the effects of hyperglycemia on cerebrovascular function.

Profiles analysis reveals circular RNAs involving zebrafish physiological development

Recent studies have found that known functions of circular RNAs (circRNAs) include sequestration of microRNAs (miRNAs) or proteins, modulation of transcription and interference with splicing, and even translation to produce polypeptides. The zebrafish model is also demonstrably similar to humans in many studies. To explore the changes in circRNAs during embryonic development and to further research the mechanism of action of circRNAs in development-related diseases, Zebrafish embryos at the blastula period, gastrula period, segmentation period, throat stage, and incubation period were collected. Illumina deep-sequencing technology and CircRNA Identifier (CIRI) algorithm were used to detect circRNAs. In total, we identified 1,028 circRNAs (junction reads ≥5 and p < 0.05). Considering that the function of circRNAs is related to host genes, a bioinformatics analysis revealed these differentially expressed host genes are involved in NOTCH signaling pathways, cardiovascular system development, retinal ganglion cell axon guidance, and so on. Moreover, circRNAs can participate in biological regulation through the function of miRNA sponges. TargetScan and miRanda were used to predict 73 miRNAs binding to circRNAs such as miR-19b, miR-124, and so on. Some miRNAs play important roles in embryogenesis. The peak expression of circRNAs is distributed at different time points, suggesting that it may be involved in embryogenesis at different stages. Our study provides a foundation for understanding the dynamic regulation of circRNA transcriptomes during embryogenesis and identifies novel key circRNAs that might control embryonic development in a zebrafish model.

The zebrafish: A research model to understand the evolution of vertebrate immunity

The zebrafish has unique advantages for understanding the evolution of vertebrate immunity and to model human diseases. In this review, we will firstly give an overview of the current knowledge on vertebrate innate immune receptors with special emphasis on the inflammasome and then summarize the main contribution of the zebrafish model to this field, including to the identification of novel inflammasome components and to the mechanisms involved in its activation, assembly and clearance of intracellular bacteria.

Endoglin is a conserved regulator of vasculogenesis in zebrafish - implications for hereditary haemorrhagic telangiectasia

Hereditary haemorrhagic telangiectasia (HHT) is a progressive vascular disease with high mortality and prevalence. There is no effective treatment of HHT due to the lack of comprehensive knowledge of its underlying pathological mechanisms. The majority of HHT1 patients carry endoglin (ENG) mutations. Here, we used Danio rerio (zebrafish) as an in vivo model to investigate the effects of endoglin knockdown on vascular development. According to phylogenetic analyses and amino acid sequence similarity analyses, we confirmed that endoglin is conserved in vertebrates and descended from a single common ancestor. Endoglin is highly expressed in the vasculature beginning at the segmentation period in zebrafish. Upon endoglin knockdown by morpholinos, we observed disruption in the intersegmental vessels (ISVs) and decreased expression of several vascular markers. RNA sequencing (RNA-Seq) results implied that the BMP-binding endothelial regulator (bmper) is a gene affected by endoglin knockdown. Rescue experiments demonstrated that overexpression of bmper significantly increased the number of endothelial cells (ECs) and reduced the defects at ISVs in zebrafish. Moreover, there was enhanced tube formation in ENG mutant ECs derived from a HHT patient after human recombinant BMPER (hrBMPER) stimulation. Taken together, our results suggest that bmper, a potential downstream gene of ENG, could be targeted to improve vascular integrity in HHT.

Sequence Variations in pxr (nr1i2) From Zebrafish (Danio rerio) Strains Affect Nuclear Receptor Function

Regulators of biotransformation are of particular interest in pharmacology and toxicology, determining in part the metabolism, disposition, and toxicity of chemicals. The nuclear receptor NR1I2 (pregnane X receptor, PXR) is a prominent xenosensor that regulates the expression of biotransformation enzymes governing elimination of many exogenous as well as endogenous compounds. Zebrafish (Danio rerio) has only one gene locus for pxr, but different genetic variants have been identified in zebrafish. However, the prevalence and significance of these variants are unknown. We hypothesize that sequence variation occurring in the Pxr gene of zebrafish may affect the action and fate of many chemicals in this species, a key model organism in various fields of research, including environmental toxicology. Here, we examine variation in Pxr sequences from four different strains of zebrafish and assess the responses of each Pxr to clotrimazole and butyl-4-aminobenzoate. The Pxr variants differed in both their ability to bind these structurally different ligands and to regulate reporter gene expression in vitro. We infer that the observed sequence variations in zebrafish Pxrs likely affect the response to putative Pxr agonists in vivo and potentially cause strain-specific biotransformation of xenobiotics in zebrafish. Thus, the choice of zebrafish strain could affect the outcome of downstream toxicological studies.

Vascular toxicity of silver nanoparticles to developing zebrafish (Danio rerio)

Nanoparticles (NPs, 1-100 nm) can enter the environment and result in exposure to humans and other organisms leading to potential adverse health effects. The aim of the present study is to evaluate the effects of early life exposure to polyvinylpyrrolidone-coated silver nanoparticles (PVP-AgNPs, 50 nm), particularly with respect to vascular toxicity on zebrafish embryos and larvae (Danio rerio). Previously published data has suggested that PVP-AgNP exposure can inhibit the expression of genes within the vascular endothelial growth factor (VEGF) signaling pathway, leading to delayed and abnormal vascular development. Here, we show that early acute exposure (0-12 h post-fertilization, hpf) of embryos to PVP-AgNPs at 1 mg/L or higher results in a transient, dose-dependent induction in VEGF-related gene expression that returns to baseline levels at hatching (72 hpf). Hatching results in normoxia, negating the effects of AgNPs on vascular development. Interestingly, increased gene transcription was not followed by the production of associated proteins within the VEGF pathway, which we attribute to NP-induced stress in the endoplasmic reticulum (ER). The impaired translation may be responsible for the observed delays in vascular development at later stages, and for smaller larvae size at hatching. Silver ion (Ag(+)) concentrations were < 0.001 mg/L at all times, with no significant effects on the VEGF pathway. We propose that PVP-AgNPs temporarily delay embryonic vascular development by interfering with oxygen diffusion into the egg, leading to hypoxic conditions and ER stress.

K. Rothman A, Elworthy S, van Eeden FJM, Chico TJA. klf2ash317 Mutant Zebrafish Do Not Recapitulate Morpholino-Induced Vascular and Haematopoietic Phenotypes

Introduction and Objectives

The zinc-finger transcription factor Krϋppel-like factor 2 (KLF2) transduces blood flow into molecular signals responsible for a wide range of responses within the vasculature. KLF2 maintains a healthy, quiescent endothelial phenotype. Previous studies report a range of phenotypes following morpholino antisense oligonucleotide-induced klf2a knockdown in zebrafish. Targeted genome editing is an increasingly applied method for functional assessment of candidate genes. We therefore generated a stable klf2a mutant zebrafish and characterised its cardiovascular and haematopoietic development.

Methods and Results

Using Transcription Activator-Like Effector Nucleases (TALEN) we generated a klf2a mutant (klf2a^sh317) with a 14bp deletion leading to a premature stop codon in exon 2. Western blotting confirmed loss of wild type Klf2a protein and the presence of a truncated protein in klf2a^sh317 mutants. Homozygous klf2a^sh317 mutants exhibit no defects in vascular patterning, survive to adulthood and are fertile, without displaying previously described morphant phenotypes such as high-output cardiac failure, reduced haematopoetic stem cell (HSC) development or impaired formation of the 5^th accessory aortic arch. Homozygous klf2a^sh317 mutation did not reduce angiogenesis in zebrafish with homozygous mutations in von Hippel Lindau (vhl), a form of angiogenesis that is dependent on blood flow. We examined expression of three klf family members in wildtype and klf2a^sh317 zebrafish. We detected vascular expression of klf2b (but not klf4a or biklf/klf4b/klf17) in wildtypes but found no differences in expression that might account for the lack of phenotype in klf2a^sh317 mutants. klf2b morpholino knockdown did not affect heart rate or impair formation of the 5^th accessory aortic arch in either wildtypes or klf2a^sh317 mutants.

Conclusions

The klf2a^sh317 mutation produces a truncated Klf2a protein but, unlike morpholino induced klf2a knockdown, does not affect cardiovascular development.

Zebrafish embryo intersegmental vessels: a tool for investigating sprouting angiogenesis

Angiogenesis leads to the formation of the intersegmental vessels (ISVs) of the trunk in teleost zebrafish (Danio rerio) embryo. Here we describe experimental procedures, including in vivo observation of transgenic zebrafish embryo and whole mount in situ hybridization, to investigate ISV development in zebrafish embryos and assess the effect of antiangiogenic compounds on these vessels.

Toxic effects of polychlorinated biphenyls on cardiac development in zebrafish

Polychlorinated biphenyls (PCBs) are ubiquitous environmental pollutants that may pose significant health-risks to various organisms including humans. Although the mixed PCB Aroclor 1254 is widespread in the environment, its potential toxic effect on heart development and the mechanism underlying its developmental toxicity have not been previously studied. Here, we used the zebrafish as a toxicogenomic model to examine the effects of Aroclor 1254 on heart development. We found that PCB exposure during zebrafish development induced heart abnormalities including pericardial edema and cardiac looping defects. Further malformations of the zebrafish embryo were observed and death of the larvae occurred in a time- and dose-dependent manner. Our mechanistic studies revealed that abnormalities in the arylhydrocarbon receptor, Wnt and retinoic acid signaling pathways may underlie the effects of PCBs on zebrafish heart development. Interestingly, co-administration of Aroclor 1254 and diethylaminobenzaldehyde, an inhibitor of retinaldehyde dehydrogenase, partially rescued the toxic effects of PCBs on zebrafish heart development. In conclusion, PCBs can induce developmental defects in the zebrafish heart, which may be mediated by abnormal RA signaling.

Embryonic exposure to sodium arsenite perturbs vascular development in zebrafish

Exposure to arsenic in its inorganic form, arsenite, causes adverse effects to many different organs and tissues. Here, we have investigated arsenite-induced adverse effects on vascular tissues in the model organism zebrafish, Danio rerio. Zebrafish embryos were exposed to arsenite at different exposure windows and the susceptibility to vascular tissue damage was recorded at 72hours post fertilization (hpf). Intersegmental vessel sprouting and growth was most perturbed by exposure to arsenite during the 24-48hpf window, while disruption in the condensation of the caudal vein plexus was more often observed at the 48-72hpf exposure window, reflecting when these structures develop during normal embryogenesis. The vascular growth rate was decreased by arsenite exposure, and deviated from that of control embryos at around 24-26.5hpf. We further mapped changes in expression of key regulators of angiogenesis and vasculogenesis. Downregulation of vascular endothelial growth factor receptor 1/fms-related tyrosine kinase 1 (vegfr1/flt1) expression was evident already at 24hpf, coinciding with the decreased vascular growth rate. At later time points, matrix metalloproteinase 9 (mmp9) expression was upregulated, suggesting that arsenite affects the composition of the extracellular matrix. In total, the expression of eight key factors involved in different aspects of vascularization was significantly altered by arsenic exposure. In conclusion, our results show that arsenite is a potent vascular disruptor in the developing zebrafish embryo, a finding that calls for an evaluation of arsenite as a developmental vascular toxicant in mammalian model systems.

Zebrafish cardiac muscle thick filaments: isolation technique and three-dimensional structure

To understand how mutations in thick filament proteins such as cardiac myosin binding protein-C or titin, cause familial hypertrophic cardiomyopathies, it is important to determine the structure of the cardiac thick filament. Techniques for the genetic manipulation of the zebrafish are well established and it has become a major model for the study of the cardiovascular system. Our goal is to develop zebrafish as an alternative system to the mammalian heart model for the study of the structure of the cardiac thick filaments and the proteins that form it. We have successfully isolated thick filaments from zebrafish cardiac muscle, using a procedure similar to those for mammalian heart, and analyzed their structure by negative-staining and electron microscopy. The isolated filaments appear well ordered with the characteristic 42.9 nm quasi-helical repeat of the myosin heads expected from x-ray diffraction. We have performed single particle image analysis on the collected electron microscopy images for the C-zone region of these filaments and obtained a three-dimensional reconstruction at 3.5 nm resolution. This reconstruction reveals structure similar to the mammalian thick filament, and demonstrates that zebrafish may provide a useful model for the study of the changes in the cardiac thick filament associated with disease processes.

Zebrafish as an innovative model for neuroendocrine tumors

Tumor models have a relevant role in furthering our understanding of the biology of malignant disease and in preclinical cancer research. Only few models are available for neuroendocrine tumors (NETs), probably due to the rarity and heterogeneity of this group of neoplasms. This review provides insights into the current state-of-the-art of zebrafish as a model in cancer research, focusing on potential applications in NETs. Zebrafish has a complex circulatory system similar to that of mammals. A novel angiogenesis assay based on the injection of human NET cell lines (TT and DMS79 cells) into the subperidermal space of the zebrafish embryos has been developed. Proangiogenic factors locally released by the tumor graft affect the normal developmental pattern of the subintestinal vessels by stimulating the migration and growth of sprouting vessels toward the implant. In addition, a description of the striking homology between zebrafish and humans of molecular targets involved in tumor angiogenesis (somatostatin receptors, dopamine receptors, mammalian target of rapamycin), and currently used as targeted therapy of NETs, is reported.

3D quantitative analyses of angiogenic sprout growth dynamics

BACKGROUND

Zebrafish intersegmental vessel (ISV) growth is widely used to study angiogenesis and to screen drugs and toxins that perturb angiogenesis. Most current ISV growth assays observe the presence or absence of ISVs or perturbation of ISV morphology but do not measure growth dynamics. We have developed a four-dimensional (4D, space plus time) quantitative analysis of angiogenic sprout growth dynamics for characterization of both normal and perturbed growth.

RESULTS

We tracked the positions of the ISV base and tip for each ISV sprout in 4D. Despite immobilization, zebrafish embryos translocated globally and non-uniformly during development. We used displacement of the ISV base and the angle between the ISV and the dorsal aorta to correct for displacement and rotation during development. From corrected tip cell coordinates, we computed average ISV trajectories. We fitted a quadratic curve to the average ISV trajectories to produce a canonical ISV trajectory for each experimental group, arsenic treated and untreated. From the canonical ISV trajectories, we computed curvature, average directed migration speed and directionality. Canonical trajectories from treated (arsenic exposed) and untreated groups differed in curvature, average directed migration speed and angle between the ISV and dorsal aorta.

CONCLUSIONS

4D analysis of angiogenic sprout growth dynamics: (1) Allows quantitative assessment of ISV growth dynamics and perturbation, and (2) provides critical inputs for computational models of angiogenesis.