The zebrafish: a new model organism for integrative physiology

Epigenetic and physiological alterations in zebrafish subjected to hypergravity

Gravity is one of the most constant environmental factors across Earth's evolution and all organisms are adapted to it. Consequently, spatial exploration has captured the interest in studying the biological changes that physiological alterations are caused by gravity. In the last two decades, epigenetics has explained how environmental cues can alter gene functions in organisms. Although many studies addressed gravity, the underlying biological and molecular mechanisms that occur in altered gravity for those epigenetics-related mechanisms, are mostly inexistent. The present study addressed the effects of hypergravity on development, behavior, gene expression, and most importantly, on the epigenetic changes in a worldwide animal model, the zebrafish (Danio rerio). To perform hypergravity experiments, a custom-centrifuge simulating the large diameter centrifuge (100 rpm ~ 3 g) was designed and zebrafish embryos were exposed during 5 days post fertilization (dpf). Results showed a significant decrease in survival at 2 dpf but no significance in the hatching rate. Physiological and morphological alterations including fish position, movement frequency, and swimming behavior showed significant changes due to hypergravity. Epigenetic studies showed significant hypermethylation of the genome of the zebrafish larvae subjected to 5 days of hypergravity. Downregulation of the gene expression of three epigenetic-related genes (dnmt1, dnmt3, and tet1), although not significant, was further observed. Taken altogether, gravity alterations affected biological responses including epigenetics in fish, providing a valuable roadmap of the putative hazards of living beyond Earth.

Acoustofluidic Actuation of Living Cells

Acoutofluidics is an increasingly developing and maturing technical discipline. With the advantages of being label-free, non-contact, bio-friendly, high-resolution, and remote-controllable, it is very suitable for the operation of living cells. After decades of fundamental laboratory research, its technical principles have become increasingly clear, and its manufacturing technology has gradually become popularized. Presently, various imaginative applications continue to emerge and are constantly being improved. Here, we introduce the development of acoustofluidic actuation technology from the perspective of related manipulation applications on living cells. Among them, we focus on the main development directions such as acoustofluidic sorting, acoustofluidic tissue engineering, acoustofluidic microscopy, and acoustofluidic biophysical therapy. This review aims to provide a concise summary of the current state of research and bridge past developments with future directions, offering researchers a comprehensive overview and sparking innovation in the field.

Zebrafish cardiac repolarization does not functionally depend on the expression of the hERG1b-like transcript

Zebrafish provide a translational model of human cardiac function. Their similar cardiac electrophysiology enables screening of human cardiac repolarization disorders, drug arrhythmogenicity, and novel antiarrhythmic therapeutics. However, while zebrafish cardiac repolarization is driven by delayed rectifier potassium channel current (IKr), the relative role of alternate channel transcripts is uncertain. While human ether-a-go-go-related-gene-1a (hERG1a) is the dominant transcript in humans, expression of the functionally distinct alternate transcript, hERG1b, modifies the electrophysiological and pharmacologic IKr phenotype. Studies of zebrafish IKr are frequently translated without consideration for the presence and impact of hERG1b in humans. Here, we performed phylogenetic analyses of all available KCNH genes from Actinopterygii (ray-finned fishes). Our findings confirmed zebrafish cardiac zkcnh6a as the paralog of human hERG1a (hKCNH2a), but also revealed evidence of a hERG1b (hKCNH2b)-like N-terminally truncated gene, zkcnh6b, in zebrafish. zkcnh6b is a teleost-specific variant that resulted from the 3R genome duplication. qRT-PCR showed dominant expression of zkcnh6a in zebrafish atrial and ventricular tissue, with low levels of zkcnh6b. Functional evaluation of zkcnh6b in a heterologous system showed no discernable function under the conditions tested, and no influence on zkcnh6a function during the zebrafish ventricular action potential. Our findings provide the first descriptions of the zkcnh6b gene, and show that, unlike in humans, zebrafish cardiac repolarization does not rely upon co-assembly of zERG1a/zERG1b. Given that hERG1b modifies IKr function and drug binding in humans, our findings highlight the need for consideration when translating hERG variant effects and toxicological screens in zebrafish, which lack a functional hERG1b-equivalent gene.

Life-cycle exposure to tris (2-chloroethyl) phosphate (TCEP) causes alterations in antioxidative status, ion regulation and histology of zebrafish gills

Tris (2-chloroethyl) phosphate (TCEP) has been receiving great concerns owing to its ubiquitous occurrence in various environmental compartments and potential risks to wildlife and humans. Gill is structural basis for ion regulation and homeostasis in fish and susceptible to xenobiotics. However, current knowledge on the impacts of long-term exposure to TCEP on the structure and physiological function of fish gills are insufficient. In this work, zebrafish were exposed to environmental realistic concentrations (0.8, 4, 20 and 100 μg/L) of TCEP from 3 h post ferterlization (hpf) till 120 days post ferterlization (dpf). Our results demonstrated that life-cycle exposure to TCEP significantly decreased the activity of glutathione S-transferase (GST), but elevated the activities of antioxidative enzymes including superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and increased malondialdehyde (MDA) content in zebrafish gills. Gene transcription analysis implied that the mRNA expressions of antioxidant-related genes (nrf2, cat and nqo1) were induced, while the transcription of gstα1, hmox1, keap1 were down-regulated, indicating that Nrf2-Keap1 pathway might be activated to defend the oxidative stress induced by TCEP. Additionally, the ion homeostasis was disrupted by TCEP exposure, evidenced by reduced activities of Na+/K+-ATPase (NKA), Ca2+-ATPase and Mg2+-ATPase and downregulated transcription levels of ncc, nkcc, cftr and clc-3. Besides, whole-life exposure to TCEP resulted in a series of structural damages to gills, including epithelial lifting, epithelial rupture, telangiectasis, vacuolation, edema and shortened gill lamellae. Overall, our results demonstrated that long-term TCEP exposure could induce oxidative stress, affect ion regulation and cause histological changes in zebrafish gills.

Single-cell analysis reveals distinct fibroblast plasticity during tenocyte regeneration in zebrafish

Despite their importance in tissue maintenance and repair, fibroblast diversity and plasticity remain poorly understood. Using single-cell RNA sequencing, we uncover distinct sclerotome-derived fibroblast populations in zebrafish, including progenitor-like perivascular/interstitial fibroblasts, and specialized fibroblasts such as tenocytes. To determine fibroblast plasticity in vivo, we develop a laser-induced tendon ablation and regeneration model. Lineage tracing reveals that laser-ablated tenocytes are quickly regenerated by preexisting fibroblasts. By combining single-cell clonal analysis and live imaging, we demonstrate that perivascular/interstitial fibroblasts actively migrate to the injury site, where they proliferate and give rise to new tenocytes. By contrast, perivascular fibroblast-derived pericytes or specialized fibroblasts, including tenocytes, exhibit no regenerative plasticity. Active Hedgehog (Hh) signaling is required for the proliferation of activated fibroblasts to ensure efficient tenocyte regeneration. Together, our work highlights the functional diversity of fibroblasts and establishes perivascular/interstitial fibroblasts as tenocyte progenitors that promote tendon regeneration in a Hh signaling-dependent manner.

Age- and dose-dependent susceptibility of axolotls (Ambystoma mexicanum) by bath exposure to Ambystoma tigrinum virus (ATV)

Ranaviruses are large, dsDNA viruses that have significant ecological and economic impact on cold-blooded vertebrates. However, our understanding of the viral proteins and subsequent host immune response(s) that impact susceptibility to infection and disease is not clear. The ranavirus Ambystoma tigrinum virus (ATV), originally isolated from the Sonoran tiger salamander (Ambystoma mavortium stebbinsi), is highly pathogenic at low doses of ATV at all tiger salamander life stages and this model has been used to explore the host-pathogen interactions of ATV infection. However, inconsistencies in the availability of laboratory reared larval tiger salamanders required us to look at the well characterized axolotl (A. mexicanum) as a model for ATV infection. Data obtained from five infection experiments over different developmental timepoints suggest that axolotls are susceptible to ATV in an age- and dose-dependent manner. These data support the use of the ATV-axolotl model to further explore the host-pathogen interactions of ranavirus infections.

Gonacin: A germ cell-derived hormone with glucogenic, orexigenic, and gonadal activities

Fish require abundant nutrients to generate a large number of eggs for spawning. Based on the evolutionary conservation of human FBN2 and its C-terminal placensin-like sequences in fish, we identified a peptide hormone gonacin (GONAdal Cell placensIN) and found its high expression in early-stage germ cells in the ovary and testis of zebrafish. We demonstrated that gonacin is essential for food intake, glucose release, and ovarian development in zebrafish. Similar expression patterns and functions of gonacin were also demonstrated in rainbow trout. Gonacin represents the first hormone secreted by germ cells with endocrine functions in vertebrates, bridging the energy homeostasis and reproduction.

Zebrafish as a model organism - can a fish mimic human?

From pre-historic era, all scientific discoveries have evolved around a concept - THINK BIG but for a change zebrafish as a model organism in research had managed to halt the entire medical community and made us realize that it's time to think small. From a barely imagined being in research few years ago to around 4,000 publications in just last year, zebrafish has definitely come a long way. Through these tiny fish, scientists have managed to find genes that caused human diseases and have also developed various specific models to know more about the pathology behind such diseases. This review will focus on zebrafish as a model organism from the time it was introduced to the most novel targets with particular emphasis on central nervous system (CNS) as it is rapidly evolving branch in zebrafish research these days. This review will try to shed light on the early stages of zebrafish as a model organism and will try to cover the journey of it developing as a successful model organism to map many diseases like diabetes, Alzheimer's and autism describing the rationale for using this specific model and briefly the techniques under each category and finally will summarize the pros and cons of the model with its expected future directions.

Physiological responses of mechanosensory systems in the head of larval zebrafish (Danio rerio)

The lateral line system of zebrafish consists of the anterior lateral line, with neuromasts distributed on the head, and the posterior lateral line, with neuromasts distributed on the trunk. The sensory afferent neurons are contained in the anterior and posterior lateral line ganglia, respectively. So far, the vast majority of physiological and developmental studies have focused on the posterior lateral line. However, studies that focus on the anterior lateral line, especially on its physiology, are very rare. The anterior lateral line involves different neuromast patterning processes, specific distribution of synapses, and a unique role in behavior. Here, we report our observations regarding the development of the lateral line and analyze the physiological responses of the anterior lateral line to mechanical and water jet stimuli. Sensing in the fish head may be crucial to avoid obstacles, catch prey, and orient in water current, especially in the absence of visual cues. Alongside the lateral line, the trigeminal system, with its fine nerve endings innervating the skin, could contribute to perceiving mechanosensory stimulation. Therefore, we compare the physiological responses of the lateral line afferent neurons to responses of trigeminal neurons and responsiveness of auditory neurons. We show that anterior lateral line neurons are tuned to the velocity of mechanosensory ramp stimulation, while trigeminal neurons either only respond to mechanical step stimuli or fast ramp and step stimuli. Auditory neurons did not respond to mechanical or water jet stimuli. These results may prove to be essential in designing underwater robots and artificial lateral lines, with respect to the spectra of stimuli that the different mechanosensory systems in the larval head are tuned to, and underline the importance and functionality of the anterior lateral line system in the larval fish head.

Acute toxicity of organoarsenic chemical warfare agents to Danio rerio embryos

During the 20th century, thousands of tons of munitions containing organoarsenic chemical warfare agents (CWAs) were dumped into oceans, seas and inland waters around the world. As a result, organoarsenic CWAs continue to leak from corroding munitions into sediments and their environmental concentrations are expected to peak over the next few decades. There remains, however, a lack of knowledge about their potential toxicity to aquatic vertebrates, such as fish. The aim of this study was to fill in this gap in research, by investigating the acute toxicity of organoarsenic CWAs on fish embryos, using the model species, Danio rerio. To estimate the acute toxicity thresholds of organoarsenic CWAs (Clark I, Adamsite, PDCA), a CWA-related compound (TPA), as well as four organoarsenic CWA degradation products (Clark I[ox], Adamsite[ox], PDCA[ox], TPA[ox]), standardized tests were performed following the OECD no. 236 Fish Embryo Acute Toxicity Test guidelines. Additionally, the detoxification response in D. rerio embryos was investigated by analysing the mRNA expression of five genes encoding antioxidant enzymes (CAT, SOD, GPx, GR and GST). During the 96 h of exposure, organoarsenic CWAs induced lethal effects in D. rerio embryos at very low concentrations (classified as 1st category pollutants according to GHS categorization), and were therefore deemed to be serious environmental hazards. Although TPA and the four CWA degradation products caused no acute toxicity even at their maximum solubility, the transcription of antioxidant-related genes was altered upon exposure to these compounds, indicating the need for further testing for chronic toxicity. Incorporating the results of this study into ecological risk assessments will provide a more accurate prediction of the environmental hazards posed by CWA-related organoarsenicals.

Enhancement of zebrafish sperm production via a large body-sized surrogate with germ cell transplantation

Zebrafish (Danio rerio) is a commonly-used vertebrate model species for many research areas. However, its low milt volume limits effective cryopreservation of sperm from a single individual and often precludes dividing a single semen sample to conduct multiple downstream procedures such as genomic DNA/RNA extraction and in-vitro fertilization. Here, we apply germ stem cell transplantation to increase zebrafish sperm production in a closely related larger species from the same subfamily, giant danio Devario aequipinnatus. The endogenous germ cell of the host is depleted by dead-end morpholino antisense oligonucleotide. Histology of the sterile gonad and quantitative PCR of gonadal tissue reveals all sterile giant danio develop the male phenotype. Spermatogonial cells of Tg(ddx4:egfp) transgenic zebrafish are transplanted into sterile giant danio larvae, and 22% of recipients (germline chimera) produce donor-derived sperm at sexual maturation. The germline chimera produce approximately three-fold the volume of sperm and 10-fold the spermatozoon concentration of the donor. The donor-derived sperm is functional and gives rise to viable progeny upon fertilization of donor oocytes. We show that the issue of low milt volume can be effectively addressed by employing a larger surrogate parent.

Impact of pharmaceutical products on zebrafish: An effective tool to assess aquatic pollution

Overuse of pharmaceuticals products (PPs) and sometimes ineffective wastewater purification systems have led to the accumulation of these residues in aquatic systems. Raising concerns about the likely harmful effects of these substances both to ecosystems and to human health. Animals as model organisms are nowadays increasingly used to track the health of environmental system around the world. They can be used to understand biological processes, to obtain information on the health status of the environment, and to better understand the effects of xenobiotics on organisms. Among model organisms, the zebrafish (Danio rerio) is one of the best models for studying evolution biology, cancer, toxicology, drug discovery, and genetics. This fish is a multipurpose model organism, due to its easy of maintenance and keeping and the transparency of the embryo during the early stages of development. In this paper, the toxicological effects of typical PPs, and their effects on zebrafish are reviewed. Many PPs have been found to be toxic or even fatal to zebrafish. Showing how these pharmaceuticals compound can affect zebrafish from the larval stage and even in the adult stage. Zebrafish is thus a model for how we can better understand how medications affect not only individual fish but the entire aquatic ecosystem, bringing about perturbations in their behaviour and putting their survival at risk.

Use of Zebrafish as a Model Organism to Study Oxidative Stress: A Review

Dioxygen is an integral part of every living organism, but its concentration varies from organ to organ. Production of metabolites from dioxygen may result in oxidative stress. Since oxidative stress has the potential to damage various biomolecules in the cell, therefore, it has presently become an active field of research. Oxidative stress has been studied in a wide range of model organisms from vertebrates to invertebrates, from rodents to piscine organisms, and from in vivo to in vitro models. But zebrafish (adults, larvae, or embryonic stage) emerged out to be the most promising vertebrate model organism to study oxidative stress because of its vast advantages (transparent embryo, cost-effectiveness, similarity to human genome, easy developmental processes, numerous offspring per spawning, and many more). This is evidenced by voluminous number of researches on oxidative stress in zebrafish exposed to chemicals, radiations, nanoparticles, pesticides, heavy metals, etc. On these backgrounds, this review attempts to highlight the potentiality of zebrafish as model of oxidative stress compared with other companion models. Several areas, from biomedical to environmental research, have been covered to explain it as a more convenient and reliable animal model for experimental research on oxidative mechanisms.

Environmental Impact of Pharmaceutical Pollutants: Synergistic Toxicity of Ivermectin and Cypermethrin

Veterinary antiparasitic pharmaceuticals as well as pesticides have been detected in surface waters, and they may cause several toxic effects in this environmental compartment. In the present study, we evaluated the toxicity after exposure of different concentration of ivermectin (IVM; 50, 100, and 200 μg L⁻¹) and cypermethrin (CYP; 5, 10, and 25 μg L⁻¹) and the combination of these two compounds at non-toxic concentration (IVM 100 + CYP 5 μg L⁻¹) in zebrafish embryos. Combination of IVM at 100 μg L⁻¹ with CYP at 5 μg L⁻¹ exposure induced hatching delay and malformations at 96 hpf in zebrafish larvae as well as significant induction of cell death in zebrafish larvae. At the same time, the two single concentrations of IVM and CYP did not show a toxic effect on zebrafish development. In conclusion, our study suggests that IVM and CYP show a synergistic effect at common, ineffective concentrations, promoting malformation and cell death in fish development.

Tollip-deficient zebrafish display no abnormalities in development, organ morphology or gene expression in response to lipopolysaccharide

Tollip is a multifunctional adaptor protein implicated in innate immunity, lysosomal trafficking/autophagy of protein aggregates and various signaling processes in mammalian models. To verify evolutionary conservation of these functions, we used CRISPR/Cas9 editing to construct a zebrafish line bearing a stable tollip knockout. In contrast to previously reported tollip morphants, Tollip‐deficient fish display normal development until adulthood, are fertile, and have no apparent physiological defects. When challenged with lipopolysaccharide (LPS), inflammatory gene expression is unaffected. Moreover, Tollip deficiency does not aggravate swimming deficiency resulting from lysosomal dysfunction and proteotoxicity in a fish model of Gaucher disease. Thus, individual functions of Tollip may be organism‐specific or manifest only upon certain conditions/challenges or disease backgrounds.

The amazing and anomalous axolotls as scientific models

Ambystoma mexicanum (axolotl) embryos and juveniles have been used as model organisms for developmental and regenerative research for many years. This neotenic aquatic species maintains the unique capability to regenerate most, if not all, of its tissues well into adulthood. With large externally developing embryos, axolotls were one of the original model species for developmental biology. However, increased access to, and use of, organisms with sequenced and annotated genomes, such as Xenopus laevis and tropicalis and Danio rerio, reduced the prevalence of axolotls as models in embryogenesis studies. Recent sequencing of the large axolotl genome opens up new possibilities for defining the recipes that drive the formation and regeneration of tissues like the limbs and spinal cord. However, to decode the large Ambystoma mexicanum genome will take a herculean effort, community resources, and the development of novel techniques. Here, we provide an updated axolotl-staging chart ranging from 1-cell stage to immature adult paired with a perspective on both historical and current axolotl research that spans from their use in early studies of development to the recent cutting-edge research, employment of transgenesis, high resolution imaging, and study of mechanisms deployed in regeneration. This article is protected by copyright. All rights reserved.

Zebrafish as a Model for Anticancer Nanomedicine Studies

Nanomedicine is a new approach to fight against cancer by the development of anticancer nanoparticles (NPs) that are of high sensitivity, specificity, and targeting ability to detect cancer cells, such as the ability of Silica NPs in targeting epithelial cancer cells. However, these anticancer NPs require preclinical testing, and zebrafish is a useful animal model for preclinical studies of anticancer NPs. This model affords a large sample size, optical imaging, and easy genetic manipulation that aid in nanomedicine studies. This review summarizes the numerous advantages of the zebrafish animal model for such investigation, various techniques for inducing cancer in zebrafish, and discusses the methods to assess cancer development in the model and to test for the toxicity of the anticancer drugs and NPs. In addition, it summarizes the recent studies that used zebrafish as a model to test the efficacy of several different anticancer NPs in treating cancer.

Optimization of Sperm Management and Fertilization in Zebrafish (Danio rerio (Hamilton))

Simple Summary

For scientific studies on the zebrafish model, simple and routine reproductive procedures should be used to ensure stable and repeatable results. When the milt is collected, spermatozoa are spontaneously activated by urine or excrement (low osmolarity) which routinely contaminates the samples, because of the minuscule size of the fish body. Therefore, whenever milt is collected from a zebrafish for short-term milt preservation and artificial fertilization, milt must be collected into an immobilizing solution, which because of its high osmolarity stops the movement of spermatozoa and keeps the sperm immobile until fertilization. Usually, the spermatozoa showed forward movement during the 35 s period following dilution in water. The sperm concentration ranged from 0.08 to 3.52 × 109/mL with a volume from 0.1 to 2.0 μL per male. The most suitable extender proved to be E400, which allowed storage of sperm for fertilization for 6 to 12 h at a temperature of 0–2 °C. To achieve a good level of fertilization and hatchability, a test tube with a precisely defined amount of sperm with extender, eggs and activating solution proved to be the most effective.

Abstract

The aim of the present study was to investigate the spontaneous motility of spermatozoa and to optimize sperm collection, short-term sperm storage, and fertilization in zebrafish Danio rerio. The movement of spermatozoon in water was propagated along the flagellum at 16 s after sperm activation then damped from the end of the flagellum for 35 s and fully disappeared at 61 s after activation. For artificial fertilization, milt must be added to an immobilizing solution, which stops the movement of sperm and keeps the sperm motionless until fertilization. E400 and Kurokura as isotonic solutions were shown to be suitable extenders to store sperm for fertilization for 6 h. E400 stored sperm for 12 h at 0–2 °C. Sperm motility decreased only to 36% at 12 h post stripping for the E400 extender and to 19% for the Kurokura extender. To achieve an optimal level of fertilization and swim-up larvae rates, a test tube with a well-defined amount of 6,000,000 spermatozoa in E400 extender per 100 eggs and 100 µL of activation solution has proven to be more successful than using a Petri dish. The highest fertilization and swim-up larvae rates reached 80% and 40–60%, respectively, with milt stored for 1.5 h in the E400 extender at 0–2 °C.

Color as an important biological variable in zebrafish models: Implications for translational neurobehavioral research

Color is an important environmental factor that in multiple ways affects human and animal behavior and physiology. Widely used in neuroscience research, various experimental (animal) models may help improve our understanding of how different colors impact brain and behavioral processes. Complementing laboratory rodents, the zebrafish (Danio rerio) is rapidly emerging as an important novel model species to explore complex neurobehavioral processes. The growing utility of zebrafish in biomedicine makes it timely to consider the role of colors in their behavioral and physiological responses. Here, we summarize mounting evidence implicating colors as a critical variable in zebrafish models and neurobehavioral traits, with a particular relevance to CNS disease modeling, genetic and pharmacological modulation, as well as environmental enrichment and animal welfare. We also discuss the growing value of zebrafish models to study color neurobiology and color-related neurobehavioral phenomics, and outline future directions of research in this field.

From sequence to information

Today massive amounts of sequenced metagenomic and metatranscriptomic data from different ecological niches and environmental locations are available. Scientific progress depends critically on methods that allow extracting useful information from the various types of sequence data. Here, we will first discuss types of information contained in the various flavours of biological sequence data, and how this information can be interpreted to increase our scientific knowledge and understanding. We argue that a mechanistic understanding of biological systems analysed from different perspectives is required to consistently interpret experimental observations, and that this understanding is greatly facilitated by the generation and analysis of dynamic mathematical models. We conclude that, in order to construct mathematical models and to test mechanistic hypotheses, time-series data are of critical importance. We review diverse techniques to analyse time-series data and discuss various approaches by which time-series of biological sequence data have been successfully used to derive and test mechanistic hypotheses. Analysing the bottlenecks of current strategies in the extraction of knowledge and understanding from data, we conclude that combined experimental and theoretical efforts should be implemented as early as possible during the planning phase of individual experiments and scientific research projects.

This article is part of the theme issue ‘Integrative research perspectives on marine conservation’.

Sub-second, super-resolved imaging of biological systems using parallel EO-STED

We present a parallel stimulated emission depletion (STED) nanoscope with no mechanical moving parts and sub-millisecond pixel dwell times, relying on electro-optical (EO) phase modulators. The nanoscope offers 1225-fold parallelization over single-doughnut-scanning STED and achieves a spatial resolution of 35 nm. We imaged immunostained nuclear pore complexes of zebrafish within their natural biological environment, demonstrating spatial and temporal resolutions of 56 nm and 0.2 s, respectively. Furthermore, we show parallel EO-STED sub-second imaging of microtubules inside living cells. Finally, we reveal the nanodomain organization of a eukaryotic initiation factor within the processing bodies of fixed cells. The potential of parallel EO-STED to offer microsecond pixel dwell times over large fields of view promises millisecond STED imaging.

Discovery and identification of antithrombotic chemical markers in Gardenia Fructus by herbal metabolomics and zebrafish model

ETHNOPHARMACOLOGICAL RELEVANCE

Gardenia Fructus (GF), a traditional Chinese medicine for clearing heat and purging fire, has been reported to use to treat thrombotic related diseases, but the antithrombotic components are not clear.

AIM OF THE STUDY

To develop efficient research methods for discovering some representative antithrombotic compounds of GF.

MATERIALS AND METHODS

AB line zebrafish induced by arachidonic acid (AA) was used as a fast and trace-sample-required valuation model for antithrombptic effect of GF samples. Among nine samples of GF from different production areas, two samples with the largest difference in bioactivity were selected for downstream analysis. High-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (HPLC-Q-TOF/MS) was applied to detect compounds in the GF samples. And herbal metabolomics and grey correlation analysis (GCA) were used to identify crucial compounds with potential antithrombotic activity. Then the bioactivity of those important compounds was verified on the zebrafish model. Network pharmacology was used to explore the protein targets and signaling pathways of these compounds.

RESULTS

Among the GF samples, S1 (Huoshan City, Anhui Province), and S6 (Jichun City, Hubei Province), significantly differed in thrombus inhibiting bioactivity. HPLC-Q-TOF/MS identified a total of 614 compounds in each GF sample. 19 compounds were selected as important potential variables from metabolomics data by orthogonal partial least squares discriminant analysis (OPLS-DA). And 10 compounds among them were further found to be positively correlated with the antithrombotic bioactivity of GF by GCA. Finally, 3 compounds in them, geniposide, citric acid, and quinic acid, were confirmed as representative antithrombotic chemical markers of GF. Using network pharmacology analysis, some key protein targets, such as proto-oncogene tyrosine-protein kinase Src (SRC) and cyclin-dependent kinase 2 (CDK2), and some signaling pathways were found to supply powerful evidence about antithrombotic mechanisms of three compounds and GF.

CONCLUSIONS

This research have succeeded to discover and identify three representative antithrombotic compounds of GF using an efficient integrated research strategy we established, an Omics Discriminant-Grey Correlation-Biological Activity strategy. The antithrombotic chemical makers we found could also contribute to provided more accurate index components for comprehensive quality control of GF.

Zebrafish as a preclinical in vivo screening model for nanomedicines

The interactions of nanomedicines with biological environments is heavily influenced by their physicochemical properties. Formulation design and optimization are therefore key steps towards successful nanomedicine development. Unfortunately, detailed assessment of nanomedicine formulations, at a macromolecular level, in rodents is severely limited by the restricted imaging possibilities within these animals. Moreover, rodent in vivo studies are time consuming and expensive, limiting the number of formulations that can be practically assessed in any one study. Consequently, screening and optimisation of nanomedicine formulations is most commonly performed in surrogate biological model systems, such as human-derived cell cultures. However, despite the time and cost advantages of classical in vitro models, these artificial systems fail to reflect and mimic the complex biological situation a nanomedicine will encounter in vivo. This has acutely hampered the selection of potentially successful nanomedicines for subsequent rodent in vivo studies. Recently, zebrafish have emerged as a promising in vivo model, within nanomedicine development pipelines, by offering opportunities to quickly screen nanomedicines under in vivo conditions and in a cost-effective manner so as to bridge the current gap between in vitro and rodent studies. In this review, we outline several advantageous features of the zebrafish model, such as biological conservation, imaging modalities, availability of genetic tools and disease models, as well as their various applications in nanomedicine development. Critical experimental parameters are discussed and the most beneficial applications of the zebrafish model, in the context of nanomedicine development, are highlighted.

Metabolite tracking to elucidate the effects of environmental pollutants

The purpose of this study was to determine whether behavioral tests and metabolic profiling of organisms can be promising alternatives for assessing the health of aquatic systems. Water samples from four potential pollution sources in South Korea were collected for toxicity evaluation. First, conventional acute toxicity test in Daphnia magna and behavioral test in zebrafish was conducted to assess water quality. Second, metabolomic analysis was performed on zebrafish exposed to water samples and on environmental fish collected from the same source. Acute toxicity test in D. magna showed that none of the water samples exerted significant adverse effects. However, activity of zebrafish larvae exposed to samples from the zinc smelter (ZS) and industrial complex (IND) sites decreased compared to those exposed to samples from the reference site (RS). Metabolomic analysis using the Manhattan plot and Partial Least Square (PLS)/Orthogonal PLS Discriminant Analysis (OPLS-DA) showed differences in metabolic profiles between RS and ZS, and between IND and abandoned mine site (M). Interestingly, applying the same metabolomic analysis to environmental fish revealed patterns similar to those for zebrafish, despite the uncontrollable variables involved in environmental sampling. This study shows that metabolomics is a promising tool in assessing the health of aquatic environments.

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.

A multi-institutional study benchmarking the zebrafish developmental assay for prediction of embryotoxic plasma concentrations from rat embryo-fetal development studies

Predicting embryotoxicity of pharmaceutical compounds or industrial chemicals is crucial for public safety. Conventional studies which monitor embryo-fetal development in rats and rabbits are costly and time consuming. Alternative assays which are simpler and less costly are being pursued. The purpose of this research was to assess the capacity for the zebrafish development assay to predict mammalian plasma levels that are embryotoxic. Previously published data on rat plasma levels associated with embryotoxicity were used to guide concentration ranges for each of 25 chemicals dissolved in the media bathing developing zebrafish embryos. Embryotoxic media concentrations were compared to embryotoxic rat plasma concentrations. Assays were conducted in parallel at multiple sites as a consortium effort through the Health and Environmental Sciences Institute (HESI). Considering results from all sites, the zebrafish embryo development assay predicted (within 1-log) the rat maternal exposure levels associated with embryotoxicity 75% of the time.

Behavior, Electrophysiology, and Robotics Experiments to Study Lateral Line Sensing in Fishes

The lateral line system is a sensory system unique to fishes and amphibians. It is composed of distributed mechanosensory hair cell organs on the head and body (neuromasts), which are sensitive to pressure gradients and water movements. Over the last decade, we have pursued an interdisciplinary approach by combining behavioral, electrophysiology, and robotics experiments to study this fascinating sensory system. In behavioral and electrophysiology experiments, we have studied the larval lateral line system in the model genetic organism, zebrafish (Danio rerio). We found that the lateral line system, even in 5-day-old larvae, is involved in an array of behaviors that are critical to survival, and the deflection of a single neuromast can elicit a swimming response. In robotics experiments, we used a range of physical models with distributed pressure sensors to better understand the hydrodynamic environments from the local perspective of a fish or robot. So far, our efforts have focused on extracting control-related information for a range of application scenarios including characterizing unsteady flows such as Kármán vortex streets for station holding. We also used robot models to test biological hypotheses on how morphology and movement of fishes affect lateral line sensing. Overall, with this review we aim to increase the visibility and accessibility of this multi-disciplinary research approach.

Gut Microbiota and Host Juvenile Growth

Good genes, good food, good friends. That is what parents hope will sustain and nurture the harmonious growth of their children. The impact of the genetic background and nutrition on postnatal growth has been in the spot light for long, but the good friends have come to the scene only recently. Among the good friends perhaps the most crucial ones are those that we are carrying within ourselves. They comprise the trillions of microbes that collectively constitute each individual's intestinal microbiota. Indeed, recent epidemiological and field studies in humans, supported by extensive experimental data on animal models, demonstrate a clear role of the intestinal microbiota on their host's juvenile growth, especially under suboptimal nutrient conditions. Genuinely integrative approaches applicable to invertebrate and vertebrate systems combine tools from genetics, developmental biology, microbiology, nutrition, and physiology to reveal how gut microbiota affects growth both positively and negatively, in healthy and pathological conditions. It appears that certain natural or engineered gut microbiota communities can positively impact insulin/IGF-1 and steroid hormone signaling, thus contributing to the host juvenile development and maturation.

Increased mechanical loading through controlled swimming exercise induces bone formation and mineralization in adult zebrafish

Exercise promotes gain in bone mass through adaptive responses of the vertebrate skeleton. This mechanism counteracts age- and disease-related skeletal degradation, but remains to be fully understood. In life sciences, zebrafish emerged as a vertebrate model that can provide new insights into the complex mechanisms governing bone quality. To test the hypothesis that musculoskeletal exercise induces bone adaptation in adult zebrafish and to characterize bone reorganization, animals were subjected to increased physical exercise for four weeks in a swim tunnel experiment. Cellular, structural and compositional changes of loaded vertebrae were quantified using integrated high-resolution analyses. Exercise triggered rapid bone adaptation with substantial increases in bone-forming osteoblasts, bone volume and mineralization. Clearly, modeling processes in zebrafish bone resemble processes in human bone. This study highlights how exercise experiments in adult zebrafish foster in-depth insight into aging-related bone diseases and can thus catalyze the search for appropriate prevention and new treatment options.

Comparative transcriptomics of cyprinid minnows and carp in a common wild setting: a resource for ecological genomics in freshwater communities

Comparative transcriptomics can now be conducted on organisms in natural settings, which has greatly enhanced understanding of genome–environment interactions. Here, we demonstrate the utility and potential pitfalls of comparative transcriptomics of wild organisms, with an example from three cyprinid fish species (Teleostei:Cypriniformes). We present extensively filtered and annotated transcriptome assemblies that provide a valuable resource for studies of genome evolution (e.g. polyploidy), ecological and morphological diversification, speciation, and shared and unique responses to environmental variation in cyprinid fishes. Our results and analyses address the following points: (i) ‘essential developmental genes’ are shown to be ubiquitously expressed in a diverse suite of tissues across later ontogenetic stages (i.e. juveniles and adults), making these genes are useful for assessing the quality of transcriptome assemblies, (ii) the influence of microbiomes and other exogenous DNA, (iii) potentially novel, species-specific genes, and (iv) genomic rearrangements (e.g. whole genome duplication). The data we present provide a resource for future comparative work in cypriniform fishes and other taxa across a variety of sub-disciplines, including stress response, morphological diversification, community ecology, ecotoxicology, and climate change.

Dietary Safety Assessment of Flk1-Transgenic Fish

Genetic engineering, also called genetic modification, is facing with growing demands of aquaculture and aquatic products. Although various genetically modified (GM) aquatics have been generated, it is important to evaluate biosafety of GM organisms on the human health before entering into our food chain. For this purpose, we establish a zebrafish wild adult feeding Flk1-transgenic larvae model to examine the predatory fish's histology in multiple tissues, and the global gene expression profile in the liver. 180 days of feeding trial show that there are no significantly morphological changes in intestine, liver, kidney, and sex gonads between fish fed with Flk1 transgenic fish diet (TFD) and fish fed with regular food meal (RFM). However, a characteristic skin spot and autofluorescence increase in the theca of follicle are observed in F1 generation of TFD fish. Liver RNA-sequencing analyses demonstrate that 53 out of 56712 genes or isoforms are differentially transcribed, and mostly involved in proteolysis in extracellular region. According to GO enrichment terms these deregulated genes function in catalytic activity, steroid storing, lipid metabolic process and N-Glycan biosynthesis. These results suggest that a long term of Flk1-transgenic fish diet could alter certain metabolic pathways and possibly cause related tissue deformation. Compared to the previous reports, our feasible transgenic dietary assess system could evaluate subchronic and potential health impact of transgenic fish diet by combining multi-tissue histology and liver transcriptome analyses.

Identification of a Quality Marker (Q-Marker) of Danhong Injection by the Zebrafish Thrombosis Model

Quality-marker (Q-marker) is an emerging concept to ensure the quality and batch-to-batch consistency of Chinese medicine (CM). However, significant difficulties remain in the identification of Q-markers due to the unclear relationship between complex chemical compositions and the pharmacological efficacy of CM. In the present study, we proposed a novel strategy to identify the potential Q-marker of danhong injection (DHI) by an in vivo zebrafish thrombosis model. The anti-thrombotic effects of DHI and its major constituents were evaluated by the zebrafish model of arachidonic acid (AA)-induced thrombosis. The results indicated that DHI can attenuate tail venous thrombus and recover the decrease of heart red blood cell (RBC) intensity in a dose-dependent manner. The result that DHI prevented the formulation of thrombosis in zebrafish was also validated in the zebrafish thrombosis model with green fluorescence protein (GFP)-labeled hemoglobin. The major components of DHI, namely danshen (DS) and honghua (HH), as well as the major chemical constituents of DHI, also exerted anti-thrombotic effects, among which rosmarinic acid (RA) and p-coumaric acid (pCA) showed moderate anti-thrombotic effects. This is the first time that pCA from HH has been found as an active compound exerting an anti-thrombotic effect in a dose-dependent manner, whose IC₅₀ value is approximately 147 μg/mL. By analyzing 10 batches of normal DHI samples and five abnormal samples by high-performance liquid chromatography (HPLC), we found the contents of pCA and RA can be positively correlated to the anti-thrombotic effect of DHI, suggesting that pCA and RA could be potential Q-markers of DHI to ensure batch-to-batch consistency. Our findings illustrated that discovering major active compounds from CM by in vivo pharmacological models can be a useful approach to identifying Q-markers of CM, and in vivo pharmacological models can be a potential tool to evaluate batch-to-batch consistency of CMs.

Zebrafish models for functional and toxicological screening of nanoscale drug delivery systems: promoting preclinical applications

Preclinical screening with animal models is an important initial step in clinical translation of new drug delivery systems. However, establishing efficacy, biodistribution, and biotoxicity of complex, multicomponent systems in small animal models can be expensive and time-consuming. Zebrafish models represent an alternative for preclinical studies for nanoscale drug delivery systems. These models allow easy optical imaging, large sample size, and organ-specific studies, and hence an increasing number of preclinical studies are employing zebrafish models. In this review, we introduce various models and discuss recent studies of nanoscale drug delivery systems in zebrafish models. Also in the end, we proposed a guideline for the preclinical trials to accelerate the progress in this field.

Identification and characterization of the zebrafish glutathione S-transferase Pi-1

Zebrafish has in recent years emerged as a popular vertebrate model for use in pharmacological and toxicological studies. While there have been sporadic studies on the zebrafish glutathione S-transferases (GSTs), the zebrafish GST gene superfamily still awaits to be fully elucidated. We report here the identification of 15 zebrafish cytosolic GST genes in NCBI GenBank database and the expression, purification, and enzymatic characterization of the zebrafish cytosolic GST Pi-1 (GSTP1). The cDNA encoding the zebrafish GSTP1 was cloned from a 3-month-old female zebrafish, expressed in Eschelichia coli host cells, and purified. Purified GSTP1 displayed glutathione-conjugating activity toward 1-chloro-2,4-dinitrobenzene as a representative substrate. The enzymatic characteristics of the zebrafish GSTP1, including pH-dependency, effects of metal cations, and kinetic parameters, were studied. Moreover, the expression of zebrafish GSTP1 at different developmental stages during embryogenesis, throughout larval development, onto maturity was examined.

Linking maternal and somatic 5S rRNA types with different sequence-specific non-LTR retrotransposons

5S rRNA is a ribosomal core component, transcribed from many gene copies organized in genomic repeats. Some eukaryotic species have two 5S rRNA types defined by their predominant expression in oogenesis or adult tissue. Our next-generation sequencing study on zebrafish egg, embryo, and adult tissue identified maternal-type 5S rRNA that is exclusively accumulated during oogenesis, replaced throughout the embryogenesis by a somatic-type, and thus virtually absent in adult somatic tissue. The maternal-type 5S rDNA contains several thousands of gene copies on chromosome 4 in tandem repeats with small intergenic regions, whereas the somatic-type is present in only 12 gene copies on chromosome 18 with large intergenic regions. The nine-nucleotide variation between the two 5S rRNA types likely affects TFIII binding and riboprotein L5 binding, probably leading to storage of maternal-type rRNA. Remarkably, these sequence differences are located exactly at the sequence-specific target site for genome integration by the 5S rRNA-specific Mutsu retrotransposon family. Thus, we could define maternal- and somatic-type MutsuDr subfamilies. Furthermore, we identified four additional maternal-type and two new somatic-type MutsuDr subfamilies, each with their own target sequence. This target-site specificity, frequently intact maternal-type retrotransposon elements, plus specific presence of Mutsu retrotransposon RNA and piRNA in egg and adult tissue, suggest an involvement of retrotransposons in achieving the differential copy number of the two types of 5S rDNA loci.

Disruption of pdgfra alters endocardial and myocardial fusion during zebrafish cardiac assembly

Cardiac development in vertebrates is a finely tuned process regulated by a set of conserved signaling pathways. Perturbations of these processes are often associated with congenital cardiac malformations. Platelet-derived growth factor receptor α (PDGFRα) is a highly conserved tyrosine kinase receptor, which is essential for development and organogenesis. Disruption of Pdgfrα function in murine models is embryonic lethal due to severe cardiovascular defects, suggesting a role in cardiac development, thus necessitating the use of alternative models to explore its precise function. In this study, we generated a zebrafish pdgfra mutant line by gene trapping, in which the Pdgfra protein is truncated and fused with mRFP (Pdgfra-mRFP). Our results demonstrate that pdgfra mutants have defects in cardiac morphology as a result of abnormal fusion of myocardial precursors. Expression analysis of the developing heart at later stages suggested that Pdgfra-mRFP is expressed in the endocardium. Further examination of the endocardium in pdgfra mutants revealed defective endocardial migration to the midline, where cardiac fusion eventually occurs. Together, our data suggests that pdgfra is required for proper medial migration of both endocardial and myocardial precursors, an essential step required for cardiac assembly and development.

Summary: The molecular mechanisms regulating cardiac fusion are not well understood. Here, we show that platelet-derived growth factor receptor alpha is essential for normal endocardial and myocardial fusion during zebrafish development.

Zebrafish (Danio rerio) behaviour is largely unaffected by elevated pCO2

Ocean acidification, the decrease in ocean pH caused by anthropogenic emission of carbon dioxide, can cause behavioural disturbances in marine teleost species. We investigated whether AB-strain zebrafish (Danio rerio) show similar behavioural disturbances in the presence of elevated CO₂, because this model species could open up a toolbox to investigate the physiological and neurological mechanisms of CO₂ exposure. We found no effect of elevated CO₂ (~1600 μatm) on the behaviour of zebrafish in the open field test, indicating that zebrafish are largely insensitive to this elevated CO₂ level. In the detour test of lateralization, however, zebrafish exposed to elevated CO₂ swam more often to the right, whereas individuals exposed to control CO₂ (~400 μatm) had no preference for left or right. This may indicate that some behaviours of some freshwater fishes can be altered by elevated CO₂ levels. Given that elevated CO₂ levels often occur in recirculating aquaculture and aquarium systems, we recommend that dissolved CO₂ levels are measured and, if necessary, the aquarium water should be aerated, in order to exclude CO₂ level as a confounding factor in experiments.

Modulation of antioxidant defense and immune response in zebra fish (Danio rerio) using dietary sodium propionate

The present study explores the effect of dietary sodium propionate on mucosal immune response and expression of antioxidant enzyme genes in zebra fish (Danio rerio). Six hundred healthy zebra fish (0.42 ± 0.06 g) supplied, randomly stocked in 12 aquariums and fed on basal diets supplemented with different levels of sodium propionate [0 (control), 5, 10 and 20 g kg^-1] for 8 weeks. At the end of the feeding trial, mucosal immune parameters (TNF-α, IL-1β, Lyz), antioxidant enzyme (SOD, CAT) as well as heat shock protein 70 (HSP70) gene expression were measured. The results revealed feeding on sodium propionate significantly up-regulated inflammatory response genes (TNF-α, IL-1β, Lyz) in a dose-dependent manner (P < 0.05). However, antioxidant enzyme genes significantly down-regulated in the treated group compared with control (P < 0.05). Also, HSP70 gene expression was higher in the liver of fish fed the basal diet and deceased with elevation of sodium propionate levels in the diet. These results showed beneficial effects of dietary sodium propionate on mucosal immune response as well as the antioxidant defense of zebra fish.

Zebrafish embryos as in vivo test tubes to unravel cell-specific mechanisms of neurogenesis during neurodevelopment and in diseases

Zebrafish has become a model of choice for developmental studies in particular for studying neural development and related mechanisms involved in diseases. Indeed, zebrafish provides a fast, handy and accurate model to perform functional genomics on a gene or network of genes of interest. Recently, we successfully purified neural stem cells (NSCs) by fluorescence-activated cell sorting (FACS) from whole embryos in order to analyze cell-specific transcriptomic effects by RNA sequencing. As a result, our work sheds light on signaling pathways that are more likely to be involved in our morpholino-induced neurogenesis phenotype. This cell purification strategy brings zebrafish to a higher level since it now allows one to investigate cell-specific effects of a genetic condition of interest (knockout, knock-down, gain-of-function etc.) at the genomic, transcriptomic and proteomic levels in a genuine in vivo context. With this new potential, there is no doubt that zebrafish will be of a major model with which to unravel complex underlying molecular mechanisms of neurological disorders such as epilepsy, autism spectrum disorders and schizophrenia.

Extract of Ganoderma formosanum Mycelium as a Highly Potent Tyrosinase Inhibitor

In this study, the inhibitory effect of Ganoderma formosanum mycelium extracts on tyrosinase, the central regulatory enzyme being responsible for cutaneous pigmentation, was investigated in both cell-free and cellular enzymatic systems, as well as in phenotype-based zebrafish model. Bioassay-guided purification indicated that the ethyl acetate fraction of G. fromosanum mycelium ethanolic extract (GFE-EA) demonstrated the highest inhibition toward cell-free tyrosinase (IC50 = 118.26 ± 13.34 ppm). The secreted and intracellular melanin of B16-F10 cells were reduced by GFE-EA through suppression of tyrosinase activity (IC50 = 102.27 ± 9.49 ppm) and its protein expression. Moreover, GFE-EA decreased surface pigmentation level of zebrafish via down-regulation of tyrosinase activity. Most of all, there is no significant difference in morphology and mortality between control and GFE-EA treated groups. Not only does GFE-EA exhibit similar depigmenting efficacy to kojic acid with lower dosage (approximately one-seventh of dose), but show less toxicity to zebrafish. It is worth noting that GFE-EA is extracted from mycelium, which subverts the general concept that mycelium lacks certain bioactivities possessed by fruit bodies. Altogether, it would appear that GFE-EA has great potential for application in the cosmetics industry.

Zebrafish heart as a model to study the integrative autonomic control of pacemaker function

The cardiac pacemaker sets the heart's primary rate, with pacemaker discharge controlled by the autonomic nervous system through intracardiac ganglia. A fundamental issue in understanding the relationship between neural activity and cardiac chronotropy is the identification of neuronal populations that control pacemaker cells. To date, most studies of neurocardiac control have been done in mammalian species, where neurons are embedded in and distributed throughout the heart, so they are largely inaccessible for whole-organ, integrative studies. Here, we establish the isolated, innervated zebrafish heart as a novel alternative model for studies of autonomic control of heart rate. Stimulation of individual cardiac vagosympathetic nerve trunks evoked bradycardia (parasympathetic activation) and tachycardia (sympathetic activation). Simultaneous stimulation of both vagosympathetic nerve trunks evoked a summative effect. Effects of nerve stimulation were mimicked by direct application of cholinergic and adrenergic agents. Optical mapping of electrical activity confirmed the sinoatrial region as the site of origin of normal pacemaker activity and identified a secondary pacemaker in the atrioventricular region. Strong vagosympathetic nerve stimulation resulted in a shift in the origin of initial excitation from the sinoatrial pacemaker to the atrioventricular pacemaker. Putative pacemaker cells in the sinoatrial and atrioventricular regions expressed adrenergic β2 and cholinergic muscarinic type 2 receptors. Collectively, we have demonstrated that the zebrafish heart contains the accepted hallmarks of vertebrate cardiac control, establishing this preparation as a viable model for studies of integrative physiological control of cardiac function by intracardiac neurons.

Estrogenic Effects of Several BPA Analogs in the Developing Zebrafish Brain

Important set of studies have demonstrated the endocrine disrupting activity of Bisphenol A (BPA). The present work aimed at defining estrogenic-like activity of several BPA structural analogs, including BPS, BPF, BPAF, and BPAP, on 4- or 7-day post-fertilization (dpf) zebrafish larva as an in vivo model. We measured the induction level of the estrogen-sensitive marker cyp19a1b gene (Aromatase B), expressed in the brain, using three different in situ/in vivo strategies: (1) Quantification of cyp19a1b transcripts using RT-qPCR in wild type 7-dpf larva brains exposed to bisphenols; (2) Detection and distribution of cyp19a1b transcripts using in situ hybridization on 7-dpf brain sections (hypothalamus); and (3) Quantification of the cyp19a1b promoter activity in live cyp19a1b-GFP transgenic zebrafish (EASZY assay) at 4-dpf larval stage. These three different experimental approaches demonstrated that BPS, BPF, or BPAF exposure, similarly to BPA, significantly activates the expression of the estrogenic marker in the brain of developing zebrafish. In vitro experiments using both reporter gene assay in a glial cell context and competitive ligand binding assays strongly suggested that up-regulation of cyp19a1b is largely mediated by the zebrafish estrogen nuclear receptor alpha (zfERα). Importantly, and in contrast to other tested bisphenol A analogs, the bisphenol AP (BPAP) did not show estrogenic activity in our model.

Distinct effects of ketamine and acetyl L-carnitine on the dopamine system in zebrafish

Ketamine, a noncompetitive N-methyl-D-aspartic acid (NMDA) receptor antagonist is commonly used as a pediatric anesthetic. We have previously shown that acetyl L-carnitine (ALCAR) prevents ketamine toxicity in zebrafish embryos. In mammals, ketamine is known to modulate the dopaminergic system. NMDA receptor antagonists are considered as promising anti-depressants, but the exact mechanism of their function is unclear. Here, we measured the levels of dopamine (DA) and its metabolites, 3, 4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in the zebrafish embryos exposed to ketamine in the presence and absence of 0.5 mM ALCAR. Ketamine, at lower doses (0.1-0.3 mM), did not produce significant changes in DA, DOPAC or HVA levels in 52 h post-fertilization embryos treated for 24 h. In these embryos, tyrosine hydroxylase (TH) mRNA expression remained unchanged. However, 2 mM ketamine (internal embryo exposure levels equivalent to human anesthetic plasma concentration) significantly reduced DA level and TH mRNA indicating that DA synthesis was adversely affected. In the presence or absence of 2 mM ketamine, ALCAR showed similar effects on DA level and TH mRNA, but increased DOPAC level compared to control. ALCAR reversed 2 mM ketamine-induced reduction in HVA levels. With ALCAR alone, the expression of genes encoding the DA metabolizing enzymes, MAO (monoamine oxidase) and catechol-O-methyltransferase (COMT), was not affected. However, ketamine altered MAO mRNA expression, except at the 0.1 mM dose. COMT transcripts were reduced in the 2 mM ketamine-treated group. These distinct effects of ketamine and ALCAR on the DA system may shed some light on the mechanism on how ketamine can work as an anti-depressant, especially at sub-anesthetic doses that do not affect DA metabolism and suppress MAO gene expression.

Nrf2 and Nrf2-related proteins in development and developmental toxicity: Insights from studies in zebrafish (Danio rerio)

Oxidative stress is an important mechanism of chemical toxicity, contributing to developmental toxicity and teratogenesis as well as to cardiovascular and neurodegenerative diseases and diabetic embryopathy. Developing animals are especially sensitive to effects of chemicals that disrupt the balance of processes generating reactive species and oxidative stress, and those anti-oxidant defenses that protect against oxidative stress. The expression and inducibility of anti-oxidant defenses through activation of NFE2-related factor 2 (Nrf2) and related proteins is an essential process affecting the susceptibility to oxidants, but the complex interactions of Nrf2 in determining embryonic response to oxidants and oxidative stress are only beginning to be understood. The zebrafish (Danio rerio) is an established model in developmental biology and now also in developmental toxicology and redox signaling. Here we review the regulation of genes involved in protection against oxidative stress in developing vertebrates, with a focus on Nrf2 and related cap'n'collar (CNC)-basic-leucine zipper (bZIP) transcription factors. Vertebrate animals including zebrafish share Nfe2, Nrf1, Nrf2, and Nrf3 as well as a core set of genes that respond to oxidative stress, contributing to the value of zebrafish as a model system with which to investigate the mechanisms involved in regulation of redox signaling and the response to oxidative stress during embryolarval development. Moreover, studies in zebrafish have revealed nrf and keap1 gene duplications that provide an opportunity to dissect multiple functions of vertebrate NRF genes, including multiple sensing mechanisms involved in chemical-specific effects.

Zebrafish as model organisms for studying drug-induced liver injury

Drug-induced liver injury (DILI) is a major challenge in clinical medicine and drug development. New models are needed for predicting which potential therapeutic compounds will cause DILI in humans, and new markers and mediators of DILI still need to be identified. This review highlights the strengths and weaknesses of using zebrafish as a high-throughput in vivo model for studying DILI. Although the zebrafish liver architecture is different from that of the mammalian liver, the main physiological processes remain similar. Zebrafish metabolize drugs using similar pathways to those in humans; they possess a wide range of cytochrome P450 enzymes that enable metabolic reactions including hydroxylation, conjugation, oxidation, demethylation and de-ethylation. Following exposure to a range of hepatotoxic drugs, the zebrafish liver develops histological patterns of injury comparable to those of mammalian liver, and biomarkers for liver injury can be quantified in the zebrafish circulation. The zebrafish immune system is similar to that of mammals, but the zebrafish inflammatory response to DILI is not yet defined. In order to quantify DILI in zebrafish, a wide variety of methods can be used, including visual assessment, quantification of serum enzymes and experimental serum biomarkers and scoring of histopathology. With further development, the zebrafish may be a model that complements rodents and may have value for the discovery of new disease pathways and translational biomarkers.