Zebrafish as a model to study cardiac development and human cardiac disease

Role of the ADCY9 gene in cardiac abnormalities of the Rubinstein-Taybi syndrome

BACKGROUND

Rubinstein-Taybi syndrome (RTS) is a rare, congenital, plurimalformative, and neurodevelopmental disorder. Previous studies have reported that large deletions contribute to more severe RTS phenotypes than those caused by CREBBP point mutations, suggesting a concurrent pathogenetic role of flanking genes, typical of contiguous gene syndromes, but the detailed genetics are unclear.

RESULTS

This study presented a rare case of Rubinstein-Taybi (RT) syndrome with serious cardiac abnormalities. Based on the clinical and genetic analysis of the patient, the ADCY9 gene deletion was highlighted as a plausible explanation of cardiac abnormalities. In adcy9 morphant zebrafish, cardiac malformation was observed. Immunofluorescence study disclosed increased macrophage migration and cardiac apoptosis. RNA sequencing in zebrafish model highlighted the changes of a number of genes, including increased expression of the mmp9 gene which encodes a matrix metalloproteinase with the main function to degrade and remodel extracellular matrix.

CONCLUSIONS

In this study, we identified a plausible new candidate gene ADCY9 of CHD through the clinical and genetic analysis of a rare case of Rubinstein-Taybi (RT) syndrome with serious cardiac abnormalities. By functional study of zebrafish, we demonstrated that deletion of adcy9 is the causation for the cardiac abnormalities. Cardiac apoptosis and increased expression of the MMP9 gene are involved in the pathogenesis.

Zebrafish ambra1a and ambra1b Silencing Affect Heart Development

In zebrafish, two paralogous genes, activating molecule in beclin-1 (BECN1)-regulated autophagy ambra1a and ambra1b, both required for the autophagic process and during development, encode the protein AMBRA1, a positive regulator of early steps of autophagosome formation. As transcripts for both genes are expressed during embryogenesis in the heart region, in this work, we investigated the effects of ambra1a and ambra1b knockdown on heart development by means of morpholino oligonucleotides (MOs). Silencing of the two proteins by MOs directed against the ATG translation initiation codon affects cardiac morphogenesis, resulting in a small, string-like heart with pericardial edema, whereas treatment with splice-blocking MOs does not lead to overt cardiac phenotypes, thus revealing the relevance of maternally supplied ambra1 transcripts for heart development. Co-injection of both ATG-MOs determines a more severe cardiac phenotype, with prominent pericardial edema. Whole-mount in situ hybridization (WMISH) for myosin light chain 7 (myl7), as well as ambra1 ATG-MO microinjection in zebrafish transgenic line expressing green fluorescent protein in the heart, revealed defects with the heart jogging process followed by imperfect cardiac looping. Moreover, WMISH of homeodomain transcription factor 2 isoform c (pitx2c) transcripts showed both bilateral and reversed pitx2c expression in morphants. The morphants' cardiac phenotypes were effectively rescued by co-injection of MOs with human AMBRA1 (hAMBRA1) messenger RNA (mRNA), pointing at the conservation of Ambra1 functions during evolution. Co-injections of ambra1 ATG-MOs with a hAMBRA1 mRNA mutated in the protein phosphatase 2a (PP2A) binding sites (hAMBRA1PXP) were not able to rescue the cardiac phenotypes, at the difference from wild-type hAMBRA1 mRNA, and treatment of zebrafish embryos with the specific PP2A inhibitor cantharidin resulted in similar developmental cardiac defects. These results suggest a critical role for AMBRA1 in vertebrate heart development, likely involving the binding site for the PP2A phosphatase.

Retinoic Acid Signaling and Heart Development

As the first organ to form and function in all vertebrates, the heart is crucial to development. Tightly-regulated levels of retinoic acid (RA) are critical for the establishment of the regulatory networks that drive normal cardiac development. Thus, the heart is an ideal organ to investigate RA signaling, with much work remaining to be done in this area. Herein, we highlight the role of RA signaling in vertebrate heart development and provide an overview of the field's inception, its current state, and in what directions it might progress so that it may yield fruitful insight for therapeutic applications within the domain of regenerative medicine.

Isoniazid causes heart looping disorder in zebrafish embryos by the induction of oxidative stress

BACKGROUND

The cardiotoxicity of isoniazid on zebrafish embryos and its underlying mechanism is unclear.

METHODS

Here, we exposed zebrafish embryos at 4 h post-fertilization to different levels of isoniazid and recorded the morphology and number of malformed and dead embryos under the microscope.

RESULTS

The high concentration of isoniazid group showed more malformed and dead embryos than the low concentration of isoniazid group and control group. The morphology of the heart and its alteration were visualized using transgenic zebrafish (cmlc2: GFP) and confirmed by in situ hybridization. The negative effects of isoniazid on the developing heart were characterized by lower heart rate and more heart looping disorders. Mechanistically, PCR showed decreased expression of heart-specific transcription factors when exposed to isoniazid. Oxidative stress was induced by isoniazid in cardiomyocytes, mediated by decreased activities of catalase and superoxide dismutase, which were rescued by scavengers of reactive oxygen species.

CONCLUSION

In conclusion, this study demonstrated that isoniazid led to heart looping disturbance by the downregulation of cardiac-specific transcription factors and induction of cardiomyocyte apoptosis.

Effect of Plant Growth Regulators on Coloured Callus Formation and Accumulation of Azadirachtin, an Essential Biopesticide in Azadirachta indica

For centuries, Azadirachta indica or neem has been utilized as a primary source of medicine due to its antimicrobial, larvacidal, antimalarial and antifungal properties. Recently, its potential as an effective biopesticide has garnered attention, especially towards efficient and continuous production of its bioactive compounds. The present study investigated the effect of the plant growth regulators (PGRs) thiadiazuron (TDZ) and 2,4-dichlorophenoxyacetic acid (2,4-D) on the induction of colored callus formation and subsequent accumulation of azadirachtin (AZA) in A. indica. An efficient protocol was established for micropropagation and colored callus production of this species, followed by quantification of AZA (a mixture of azadirachtin A and B) and its safety assessment. For induction of the callus, leaf and petiole explants obtained from a young growing neem plant were excised and cultured on Murashige and Skoog (MS) medium supplemented with TDZ (0.2-0.6 mg L-1) and 2,4-D (0.2-0.6 mg L-1), either applied singly or in combination. Callus was successfully induced from both explant types at different rates, where media with 0.6 mg L-1 of TDZ resulted in the highest fresh weight (3.38 ± 0.08 g). In general, media with a single hormone (particularly TDZ) was more effective in producing a high mass of callus compared to combined PGRs. A culture duration of six weeks resulted in the production of green, brown and cream colored callus. The highest callus weight and accumulation of AZA was recorded in green callus (214.53 ± 33.63 mg g-1 dry weight (DW)) induced using TDZ. On the other hand, small amounts of AZA were detected in both brown and cream callus. Further experimentation indicated that the green callus with the highest AZA was found to be non-toxic (LC50 at 4606 µg mL-1) to the zebrafish animal model. These results suggested that the addition of different PGRs during in vitro culture could prominently affect callus and secondary metabolite production and can further be manipulated as a sustainable method for the production of a natural and environmentally friendly pesticide.

Systematic evaluation of mechanistic data in assessing in utero exposures to trichloroethylene and development of congenital heart defects

The hypothesis that in utero exposures to low levels of trichloroethylene (TCE) may increase the risk of congenital heart defects (CHDs) in offspring remains a subject of substantial controversy within the scientific community due primarily to the reliance on an inconsistent and unreproducible experimental study in rats. To build on previous assessments that have primarily focused on epidemiological and experimental animal studies in developing conclusions, the objective of the current study is to conduct a systematic evaluation of mechanistic data related to in utero exposures to TCE and the development of CHDs. The evidence base was heterogeneous; 79 mechanistic datasets were identified, characterizing endpoints which ranged from molecular to organismal responses in seven species, involving both in vivo and in vitro study designs in mammalian and non-mammalian models. Of these, 24 datasets were considered reliable following critical appraisal using a study quality tool that employs metrics specific to the study type. Subsequent synthesis and integration demonstrated that the available mechanistic data: 1) did not support the potential for CHD hazard in humans, 2) did not support the biological plausibility of a response in humans based on organization via a putative adverse outcome pathway for valvulo-septal cardiac defects, and 3) were not suitable for serving as candidate studies in risk assessment. Findings supportive of an association were generally limited to in ovo chicken studies, in which TCE was administered in high concentration solutions via direct injection. Results of these in ovo studies were difficult to interpret for human health risk assessment given the lack of generalizability of the study models (including dose relevance, species-specific biological differences, variations in the construct of the study design, etc.). When the mechanistic data are integrated with findings from previous evaluations of human and animal evidence streams, the totality of evidence does not support CHDs as a critical effect in TCE human health risk assessment.

Evaluation of the Developmental Toxicity Induced by E804 in Zebrafish Embryos

E804, a derivative of indirubin, have multi-biological activities such as anticancer and anti-inflammatory activities, but little is known about its developmental toxicity. In this study, we investigated the toxicity of E804 on the developments of zebrafish embryos. Our results showed that E804 treatment caused a significant increase of the malformation rate compared with the control groups. Pericardial edema and curved body shape were the most morphological abnormalities observed in E804-treated group. The hatching rates and body length of the zebrafish larvae was significantly decreased in E804-treated groups. E804 also affect the development of heart, liver, phagocytes and vascular formation. Further studies showed that the level of reactive oxygen species was significantly increased. The activity of total superoxide dismutase decreased and the concentration of malondialdehyde were increased. Much more apoptotic cells were detected in E804-treated group, compared with the control. In addition, gene-expression results showed that the pathways of oxidative stress and apoptosis were provoked in E804 treated groups. Taken together, our findings will be helpful to understanding E804-induced developmental toxicity and the underlying mechanism.

α-asarone induces cardiac defects and QT prolongation through mitochondrial apoptosis pathway in zebrafish

α-asarone is a natural phenylpropene found in several plants, which are widely used for flavoring foods and treating diseases. Previous studies have demonstrated that α-asarone has many pharmacological functions, while some reports indicated its toxicity. However, little is known about its cardiovascular effects. This study investigated developmental toxicity of α-asarone in zebrafish, especially the cardiotoxicity. Zebrafish embryos were exposed to different concentrations of α-asarone (1, 3, 5, 10, and 30 μM). Developmental toxicity assessments revealed that α-asarone did not markedly affect mortality and hatching rate. In contrast, there was a concentration-dependent increase in malformation rate of zebrafish treated with α-asarone. The most representative cardiac defects were increased heart malformation rate, pericardial edema areas, sinus venosus-bulbus arteriosus distance, and decreased heart rate. Notably, we found that α-asarone impaired the cardiac function of zebrafish by prolonging the mean QTc duration and causing T-wave abnormalities. The expressions of cardiac development-related key transcriptional regulators tbx5, nkx2.5, hand2, and gata5 were all changed under α-asarone exposure. Further investigation addressing the mechanism indicated that α-asarone triggered apoptosis mainly in the heart region of zebrafish. Moreover, the elevated expression of puma, cyto C, afap1, caspase 3, and caspase 9 in treated zebrafish suggested that mitochondrial apoptosis is likely to be the main reason for α-asarone induced cardiotoxicity. These findings revealed the cardiac developmental toxicity of α-asarone, expanding our knowledge about the toxic effect of α-asarone on living organisms.

Calcium Imaging in the Zebrafish

The zebrafish (Danio rerio) has emerged as a widely used model system during the last four decades. The fact that the zebrafish larva is transparent enables sophisticated in vivo imaging, including calcium imaging of intracellular transients in many different tissues. While being a vertebrate, the reduced complexity of its nervous system and small size make it possible to follow large-scale activity in the whole brain. Its genome is sequenced and many genetic and molecular tools have been developed that simplify the study of gene function in health and disease. Since the mid 90's, the development and neuronal function of the embryonic, larval, and later, adult zebrafish have been studied using calcium imaging methods. This updated chapter is reviewing the advances in methods and research findings of zebrafish calcium imaging during the last decade. The choice of calcium indicator depends on the desired number of cells to study and cell accessibility. Synthetic calcium indicators, conjugated to dextrans and acetoxymethyl (AM) esters, are still used to label specific neuronal cell types in the hindbrain and the olfactory system. However, genetically encoded calcium indicators, such as aequorin and the GCaMP family of indicators, expressed in various tissues by the use of cell-specific promoters, are now the choice for most applications, including brain-wide imaging. Calcium imaging in the zebrafish has contributed greatly to our understanding of basic biological principles during development and adulthood, and the function of disease-related genes in a vertebrate system.

Microfluidic Transportation Control of Larval Zebrafish through Optomotor Regulations under a Pressure-Driven Flow

To perform zebrafish larvae-related experiments within a microfluidic environment, the larvae need to be anesthetized and subsequently transported into respective test sections through mechanical or manual means. However, anesthetization tends to affect larval sensory perceptions, hindering their natural behaviors. Taking into account that juvenile larvae move naturally within their environment by accessing visual as well as hydromechanical cues, this work proposes an experimental framework to transport nonanesthetized larvae within a microfluidic environment by harmonically tuning both of the aforementioned cues. To provide visual cues, computer-animated moving gratings were provided through an in-house-developed control interface that drove the larval optomotor response. In the meantime, to provide hydromechanical cues, the flow rate was tuned using a syringe pump that affected the zebrafish larvae’s lateral line movement. The results obtained (corresponding to different test conditions) suggest that the magnitude of both modalities plays a crucial role in larval transportation and orientation control. For instance, with a flow rate tuning of 0.1 mL/min along with grating parameters of 1 Hz temporal frequency, the average transportation time for larvae that were 5 days postfertilization was recorded at 1.29 ± 0.49 s, which was approximately three times faster than the transportation time required only in the presence of hydromechanical cues.

Preliminary safety assessment of oridonin in zebrafish

Context: Oridonin, isolated from the leaves of Isodon rubescens (Hemsl.) H.Hara (Lamiaceae), has good antitumor activity. However, its safety in vivo is still unclear. Objective: To investigate the preliminary safety of oridonin in zebrafish. Materials and methods: Embryo, larvae and adult zebrafish (n = 40) were used. Low, medium and high oridonin concentrations (100, 200 and 400 mg/L for embryo; 150, 300 and 600 mg/L for larvae; 200, 400 and 800 mg/L for adult zebrafish) and blank samples were administered. At specific stages of zebrafish development, spontaneous movement, heartbeat, hatching rate, etc., were recorded to assess the developmental effects of oridonin. VEGFA, VEGFR2 and VEGFR3 gene expression were also examined. Results: Low-dose oridonin increased spontaneous movement and hatching rate with median effective doses (ED₅₀) of 115.17 mg/L at 24 h post-fertilization (hpf) and 188.59 mg/L at 54 hpf, but these values decreased at high doses with half maximal inhibitory concentrations (IC₅₀) of 209.11 and 607.84 mg/L. Oridonin decreased heartbeat with IC₅₀ of 285.76 mg/L at 48 hpf, and induced malformation at 120 hpf with half maximal effective concentration (EC₅₀) of 411.94 mg/L. Oridonin also decreased body length with IC₅₀ of 324.78 mg/L at 144 hpf, and increased swimming speed with ED₅₀ of 190.98 mg/L at 120 hpf. The effects of oridonin on zebrafish embryo development may be attributed to the downregulation of VEGFR3 gene expression. Discussions and conclusions: Oridonin showed adverse effects at early stages of zebrafish development. We will perform additional studies on mechanism of oridonin based on VEGFR3.

Lipid Alterations during Zebrafish Embryogenesis Revealed by Dynamic Mass Spectrometry Profiling with C=C Specificity

Lipids exert substantial influences on vertebrate embryogenesis, but their metabolic dynamics at detailed structural levels remains elusive, primarily owing to the lack of a tool capable of resolving their huge structural diversity. Herein, we present the first large-scale and spatiotemporal monitoring of unsaturated lipids with C=C specificity in single developing zebrafish embryos enabled by photochemical derivatization and tandem mass spectrometry (MS). The lipid isomer composition was found extremely stable in yolk throughout embryogenesis, while notable differences in ratios of C=C location (e.g., PC 16:0_16:1 (7) vs. 16:0_16:1 (9)) and fatty acyl composition isomers (e.g., PC 16:1_18:1 vs. 16:0_18:2) were unveiled between blastomeres and yolk from zygote to 4 h post fertilization (hpf). From 24 hpf onwards, lipid isomer compositions in embryo head and tail evolved distinctively with development, suggesting a meticulously regulated lipid remodeling essential for cell division and differentiation. This work has laid the foundation for functional studies of structurally defined lipids in vertebrate embryology.

Morphogenetic control of zebrafish cardiac looping by Bmp signaling

Cardiac looping is an essential and highly conserved morphogenetic process that places the different regions of the developing vertebrate heart tube into proximity of their final topographical positions. High-resolution 4D live imaging of mosaically labelled cardiomyocytes reveals distinct cardiomyocyte behaviors that contribute to the deformation of the entire heart tube. Cardiomyocytes acquire a conical cell shape, which is most pronounced at the superior wall of the atrioventricular canal and contributes to S-shaped bending. Torsional deformation close to the outflow tract contributes to a torque-like winding of the entire heart tube between its two poles. Anisotropic growth of cardiomyocytes based on their positions reinforces S-shaping of the heart. During cardiac looping, bone morphogenetic protein pathway signaling is strongest at the future superior wall of the atrioventricular canal. Upon pharmacological or genetic inhibition of bone morphogenetic protein signaling, myocardial cells at the superior wall of the atrioventricular canal maintain cuboidal cell shapes and S-shaped bending is impaired. This description of cellular rearrangements and cardiac looping regulation may also be relevant for understanding the etiology of human congenital heart defects.

The Impact of Brain Lateralization and Anxiety-Like Behaviour in an Extensive Operant Conditioning Task in Zebrafish (Danio rerio)

Several studies in mammals, birds, and fish have documented better cognitive abilities associated with an asymmetrical distribution of cognitive functions in the two halves of the brain, also known as ‘functional brain lateralization’. However, the role of brain lateralization in learning abilities is still unclear. In addition, although recent studies suggest a link between some personality traits and accuracy in cognitive tasks, the relation between anxiety and learning skills in Skinner boxes needs to be clarified. In the present study, we tested the impact of brain lateralization and anxiety-like behaviour in the performance of an extensive operant conditioning task. Zebrafish tested in a Skinner box underwent 500 trials in a colour discrimination task (red vs. yellow and green vs. blue). To assess the degree of lateralization, fish were observed in a detour test in the presence of a dummy predator, and anxiety-like behaviour was studied by observing scototaxis response in an experimental tank divided into light and dark compartments. Although the low performance in the colour discrimination task did not permit the drawing of firm conclusions, no correlation was found between the accuracy in the colour discrimination task and the behaviour in the detour and scototaxis tests. This suggests that neither different degrees of asymmetries in brain lateralization nor anxiety may significantly impact the learning skills of zebrafish.

Early sarcomere and metabolic defects in a zebrafish pitx2c cardiac arrhythmia model

Atrial fibrillation (AF) is the most common type of cardiac arrhythmia. The major AF susceptibility locus 4q25 establishes long-range interactions with the promoter of PITX2, a transcription factor gene with critical functions during cardiac development. While many AF-linked loci have been identified in genome-wide association studies, mechanistic understanding into how genetic variants, including those at the 4q25 locus, increase vulnerability to AF is mostly lacking. Here, we show that loss of pitx2c in zebrafish leads to adult cardiac phenotypes with substantial similarities to pathologies observed in AF patients, including arrhythmia, atrial conduction defects, sarcomere disassembly, and altered cardiac metabolism. These phenotypes are also observed in a subset of pitx2c ^+/- fish, mimicking the situation in humans. Most notably, the onset of these phenotypes occurs at an early developmental stage. Detailed analyses of pitx2c loss- and gain-of-function embryonic hearts reveal changes in sarcomeric and metabolic gene expression and function that precede the onset of cardiac arrhythmia first observed at larval stages. We further find that antioxidant treatment of pitx2c ^-/- larvae significantly reduces the incidence and severity of cardiac arrhythmia, suggesting that metabolic dysfunction is an important driver of conduction defects. We propose that these early sarcomere and metabolic defects alter cardiac function and contribute to the electrical instability and structural remodeling observed in adult fish. Overall, these data provide insight into the mechanisms underlying the development and pathophysiology of some cardiac arrhythmias and importantly, increase our understanding of how developmental perturbations can predispose to functional defects in the adult heart.

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.

The cardiovascular toxicity induced by high doses of gatifloxacin and ciprofloxacin in zebrafish

As a new type of pollutant, fluoroquinolones (FQs) antibiotics are ubiquitous in environment and have some threat to human health and ecological environment. Their ecological toxicity to the environment urgently need to be assessed. Therefore, we firstly explored the toxic effects and possible mechanism of cardiovascular toxicity induced by gatifloxacin (GTFX) and ciprofloxacin (CPFX) using zebrafish model. After 24 h exposure, the zebrafish treated with GTFX showed pericardial edema which was further investigated by histopathological examination, while CPFX exposure did not induce morphological abnormalities. However, both of them induced cardiac dysfunction, such as decreased heart rate and cardiac output which was showed a positive correlation with the concentration. To better understand the possible molecular mechanisms underlying cardiovascular toxicity in zebrafish, we investigated the transcriptional level of genes related to calcium signaling pathway and cardiac muscle contraction. The results indicated that the expression of ATPase (atp2a1l) and cardiac troponin C (tnnc1a) genes were significantly inhibited, the expression of calcium channel (cacna1ab) gene showed slight promoted trend after CPFX exposure. For zebrafish treated with GTFX, the expression of atp2a1l genes was also significantly inhibited, while the expression of tnnc1a genes was slightly inhibited and cacna1ab genes expression had no obvious effect. The present study firstly revealed that GTFX exposure can induce morphological and functional abnormalities on the cardiovascular system of zebrafish. Though CPFX exposure did not induce morphological abnormalities, the function of cardiovascular system was still damaged. Mechanistically, this toxicity might result from the pressure of down-regulation of genes associated with calcium signaling pathway and cardiac muscle contraction. The results of this study can provide a valuable theoretical basis for the establishment of FQs environmental quality standards in water environment, environmental drug regulation and risk management.

Exposure to low-level metalaxyl impacts the cardiac development and function of zebrafish embryos

Metalaxyl is an anilide pesticide that is widely used to control plant diseases caused by Peronosporales species. In order to study the toxic effects, zebrafish embryos were exposed to metalaxyl at nominal concentrations of 5, 50 and 500 ng/L for 72 hr, and the cardiac development and functioning of larvae were observed. The results showed that metalaxyl exposure resulted in increased rates of pericardial edema, heart hemorrhage and cardiac malformation. The distance between the sinus venosus and bulbus arteriosus, stroke volume, cardiac output and heart rate were significantly increased in larvae exposed to 50 and 500 ng/L metalaxyl compared to solvent control larvae. Significant upregulation in the transcription of tbx5, gata4 and myh6 was observed in the 50 and 500 ng/L treatments, and that of nkx2.5 and myl7 was observed in the 5, 50 and 500 ng/L groups. These disturbances may be related to cardiac developmental and functional defects in the larvae. The activity of Na⁺/K⁺-ATPase and Ca²⁺-ATPase was significantly increased in zebrafish embryos exposed to 500 ng/L metalaxyl, and the mRNA levels of genes related to ATPase (atp2a11, atp1b2b, and atp1a3b) (in the 50 and 500 ng/L groups) and calcium channels (cacna1ab) (in the 500 ng/L group) were significantly downregulated; these changes might be associated with heart arrhythmia and functional failure.

Deep learning enables automated volumetric assessments of cardiac function in zebrafish

Although the zebrafish embryo is a powerful animal model of human heart failure, the methods routinely employed to monitor cardiac function produce rough approximations that are susceptible to bias and inaccuracies. We developed and validated a deep learning-based image-analysis platform for automated extraction of volumetric parameters of cardiac function from dynamic light-sheet fluorescence microscopy (LSFM) images of embryonic zebrafish hearts. This platform, the Cardiac Functional Imaging Network (CFIN), automatically delivers rapid and accurate assessments of cardiac performance with greater sensitivity than current approaches.

This article has an associated First Person interview with the first author of the paper.

Summary: The authors present CFIN, a deep learning-based image-analysis platform to automatically analyze dynamic light-sheet fluorescence microscopy images and determine volumetric indices of cardiac function in embryonic zebrafish.

Myomesin is part of an integrity pathway that responds to sarcomere damage and disease

The structure and function of the sarcomere of striated muscle is well studied but the steps of sarcomere assembly and maintenance remain under-characterized. With the aid of chaperones and factors of the protein quality control system, muscle proteins can be folded and assembled into the contractile apparatus of the sarcomere. When sarcomere assembly is incomplete or the sarcomere becomes damaged, suites of chaperones and maintenance factors respond to repair the sarcomere. Here we show evidence of the importance of the M-line proteins, specifically myomesin, in the monitoring of sarcomere assembly and integrity in previously characterized zebrafish muscle mutants. We show that myomesin is one of the last proteins to be incorporated into the assembling sarcomere, and that in skeletal muscle, its incorporation requires connections with both titin and myosin. In diseased zebrafish sarcomeres, myomesin1a shows an early increase of gene expression, hours before chaperones respond to damaged muscle. We found that myomesin expression is also more specific to sarcomere damage than muscle creatine kinase, and our results and others support the use of myomesin assays as an early, specific, method of detecting muscle damage.

Developmental toxicity and alteration of gene expression in zebrafish embryo exposed to 6-benzylaminopurine

6-benzylaminopurine (6-BA) is widely used in agriculture and horticulture as plant growth regulator. Its excessive use may pose a potential risk to both environment and human health, which is causing great concern. This study was undertaken to assess the acute developmental toxicity of 6-BA to zebrafish embryos based on OECD protocols and mortality, hatching rate and malformation were investigated. Results showed that the 96 h-LC₅₀ and 96 h- EC₅₀ values were 63.29 mg/L and 41.86 mg/L, respectively. No mortality or teratogenic effects were found at concentrations lower than 10 mg/L 6-BA at concentrations higher than 50 mg/L significantly inhibited hatchability and embryo development, induced serious toxicity characterized by morphologic abnormalities (elongated pericardium, heart and yolk sac edema, spine curvature) and functional failure (slow spontaneous movement and heart rate, growth retardation, yolk sac absorption retention). Moreover, 6-BA-induced apoptosis was observed in embryos by the acridine orange staining and confirmed by the apoptotic-related genes, all of which p53 was significantly up-regulated at concentrations higher than 10 mg/L, bax at concentrations higher than 12.5 mg/L, while bcl2 was down-regulated at concentrations higher than 25 mg/L. As for genes of cardiac development, qPCR results demonstrated that nkx2.5, gata5, and amhc were significantly down-regulated at concentrations higher than 25 mg/L, vmhc and atp2a2a at concentration of 50 mg/L, in contrast, hand2 was up-regulated at concentration of 50 mg/L. Our data indicate that 6-BA induces a dose-dependent toxicity resulting in apoptosis through the involvement of p53-dependent pathways and hindering normal heart development in zebrafish embryos.

Streamlining drug discovery assays for cardiovascular disease using zebrafish

Introduction: In the last decade, our armamentarium of cardiovascular drug therapy has expanded significantly. Using innovative functional genomics strategies such as genome editing by CRISPR/Cas9 as well as high-throughput assays to identify bioactive small chemical compounds has significantly facilitated elaboration of the underlying pathomechanism in various cardiovascular diseases. However, despite scientific progress approvals for cardiovascular drugs has stagnated significantly compared to other fields of drug discovery and therapy during the past years.Areas covered: In this review, the authors discuss the aspects and pitfalls during the early phase of cardiovascular drug discovery and describe the advantages of zebrafish as an in vivo organism to model human cardiovascular diseases (CVD) as well as an in vivo platform for high-throughput chemical compound screening. They also highlight the emerging, promising techniques of automated read-out systems during high-throughput screening (HTS) for the evaluation of important cardiac functional parameters in zebrafish with the potential to streamline CVD drug discovery.Expert opinion: The successful identification of novel drugs to treat CVD is a major challenge in modern biomedical and clinical research. In this context, the definition of the etiologic fundamentals of human cardiovascular diseases is the prerequisite for an efficient and straightforward drug discovery.

Biotoxicity of diclofenac on two larval amphibians: Assessment of development, growth, cardiac function and rhythm, behavior and antioxidant system

The non-steroidal anti-inflammatory drug diclofenac (DCF) threatens the health of aquatic animals and ecosystems. In the present study, different biological endpoints (mortality, development and growth, abnormalities, cardiotoxicity, neurotoxicity and antioxidant system) were used to characterize the acute and chronic effects of DCF (at concentrations ranging between 125 and 4000 μg L^-1) on two amphibian species from Argentina (Trachycephalus typhonius and Physalaemus albonotatus). Results showed that the larval developmental, growth rates, and body condition of DCF-exposed individuals of both species were significantly reduced. DCF-exposed individuals also showed several morphological abnormalities, including significantly altered body axis, chondrocranium and hyobranchial skeleton, and organ and visceral abnormalities including cardiac hypoplasia, malrotated guts, asymmetrically inverted guts, and cholecystitis. DCF also had a significant effect on the swimming performance of both species: at low concentrations (125 and 250 μg L^-1), swimming distance, velocity and global activity decreased, whereas, at high concentrations (1000 and 2000 μg L^-1), these behavioral responses increased. Regarding cardiac function and rhythm, at DCF concentrations higher than 1000 μg L^-1, the heart frequency and ventricular systole interval of both species were significantly reduced. Regarding the antioxidant system, the activity of acetylcholinesterase indicated that DCF is neurotoxic and thus related to the changes in behavioral performance. The DCF concentrations studied produced a biochemical imbalance between radical oxygen species production and antioxidant systems. The sensitivities to sublethal and chronic DCF exposure in both anuran species were similar, thus indicating the inherent complexity involved in understanding the biotoxic effects of DCF.

Chlorpyrifos exposure induces lipid metabolism disorder at the physiological and transcriptomic levels in larval zebrafish

Chlorpyrifos (CPF) is a widely used insecticide in pest control, and it can affect aquatic animals by contaminating the water. In this study, larval zebrafish were exposed to CPF at concentrations of 30, 100 and 300 μg/l for 7 days. In the CPF-treated group, lipid droplet accumulation was reduced in larval zebrafish. The levels of triglyceride (TG), total cholesterol (TC), and pyruvate were also decreased after CPF exposure. Cellular apoptosis were significantly increased in the heart tissue after CPF exposure compared with the control. Transcription changes in cardiovascular genes were also observed. Through transcriptome analysis, we found that the transcription of 465 genes changed significantly, with 398 upregulated and 67 downregulated in the CPF-treated group, indicating that CPF exposure altered the transcription of genes. Among these altered genes, a number of genes were closely related to the glucose and lipid metabolism pathways. Furthermore, we also confirmed that the transcription of genes related to fatty acid synthesis, TC synthesis, and lipogenesis were significantly decreased in larval zebrafish after exposure to CPF. These results indicated that CPF exposure induced lipid metabolism disorders associated with cardiovascular toxicity in larval zebrafish.

Clinical value of non-coding RNAs in cardiovascular, pulmonary, and muscle diseases

Although a majority of the mammalian genome is transcribed to RNA, mounting evidence indicates that only a minor proportion of these transcriptional products are actually translated into proteins. Since the discovery of the first non-coding RNA (ncRNA) in the 1980s, the field has gone on to recognize ncRNAs as important molecular regulators of RNA activity and protein function, knowledge of which has stimulated the expansion of a scientific field that quests to understand the role of ncRNAs in cellular physiology, tissue homeostasis, and human disease. Although our knowledge of these molecules has significantly improved over the years, we have limited understanding of their precise functions, protein interacting partners, and tissue-specific activities. Adding to this complexity, it remains unknown exactly how many ncRNAs there are in existence. The increased use of high-throughput transcriptomics techniques has rapidly expanded the list of ncRNAs, which now includes classical ncRNAs (e.g., ribosomal RNAs and transfer RNAs), microRNAs, and long ncRNAs. In addition, splicing by-products of protein-coding genes and ncRNAs, so-called circular RNAs, are now being investigated. Because there is substantial heterogeneity in the functions of ncRNAs, we have summarized the present state of knowledge regarding the functions of ncRNAs in heart, lungs, and skeletal muscle. This review highlights the pathophysiologic relevance of these ncRNAs in the context of human cardiovascular, pulmonary, and muscle diseases.

Hepatotoxicity evaluation of Euphorbia kansui on zebrafish larvae in vivo

BACKGROUND

Euphorbia kansui is effective in treating various diseases, such as ascites and edema, but its liver toxicity is a major obstacle in its wide use in the clinic. However, further investigations have suggested that Euphorbia kansui can cause liver injury.

HYPOTHESIS

The study aims to investigate the effect of Euphorbia kansui exposure on zebrafish, and explain the underlying toxicity mechanisms from a comprehensive perspective.

STUDY DESIGN

The 4dpf zebrafish larvae were exposed to Euphorbia kansui at a sub-lethal concentration.

METHODS

We evaluated the effect of Euphorbia kansui on the ultrastructure and function of the liver, apoptosis of liver cells by PCR and western blot, and metabolic profile by GC-MS based on sub-lethal concentrations.

RESULTS

Our results suggested Euphorbia kansui could lead to liver injury and significant alteration of the metabolomics of the zebrafish larvae in sub-lethal concentration conditions. It could also induce alterations in liver microstructure, hepatic function, gene expression and protein associated with the apoptosis process, as well as endogenous metabolism. KEGG pathway analysis identified some biological processes on the basis of different metabolisms and their associated processes especially for amino acid metabolism.

CONCLUSION

The results bring us closer to an in-depth understanding of the toxic effects of Euphorbia kansui on zebrafish liver, which will be significantly helpful in effectively guiding safer clinical application of this herb in the clinic. Furthermore, our results also showed the zebrafish model is reliable for evaluation of Euphorbia kansui extract hepatotoxicity and as a methodological reference for the evaluation of Traditional Chinese Medicine with underlying liver toxicity.

Mechanosensitive Pathways Involved in Cardiovascular Development and Homeostasis in Zebrafish

Cardiovascular diseases such as coronary heart disease, myocardial infarction, and cardiac arrhythmia are the leading causes of morbidity and mortality in developed countries and are steadily increasing in developing countries. Fundamental mechanistic studies at the molecular, cellular, and animal model levels are critical for the diagnosis and treatment of these diseases. Despite being phylogenetically distant from humans, zebrafish share remarkable similarity in the genetics and electrophysiology of the cardiovascular system. In the last 2 decades, the development and deployment of innovative genetic manipulation techniques greatly facilitated the application of zebrafish as an animal model for studying basic biology and diseases. Hemodynamic shear stress is intimately involved in vascular development and homeostasis. The critical mechanosensitive signaling pathways in cardiovascular development and pathophysiology previously studied in mammals have been recapitulated in zebrafish. In this short article, we reviewed recent knowledge about the role of mechanosensitive pathways such as Notch, PKCε/PFKFB3, and Wnt/Ang2 in cardiovas-cular development and homeostasis from studies in the -zebrafish model.

Cardiac Fibroblasts and the Extracellular Matrix in Regenerative and Nonregenerative Hearts

During the postnatal period in mammals, the heart undergoes significant remodeling and cardiac cells progressively lose their embryonic characteristics. At the same time, notable changes in the extracellular matrix (ECM) composition occur with a reduction in the components considered facilitators of cellular proliferation, including fibronectin and periostin, and an increase in collagen fiber organization. Not much is known about the postnatal cardiac fibroblast which is responsible for producing the majority of the ECM, but during the days after birth, mammalian hearts can regenerate after injury with only a transient scar formation. This phenomenon has also been described in adult urodeles and teleosts, but relatively little is known about their cardiac fibroblasts or ECM composition. Here, we review the pre-existing knowledge about cardiac fibroblasts and the ECM during the postnatal period in mammals as well as in regenerative environments.

Exogenous WNT5A and WNT11 proteins rescue CITED2 dysfunction in mouse embryonic stem cells and zebrafish morphants

Mutations and inadequate methylation profiles of CITED2 are associated with human congenital heart disease (CHD). In mouse, Cited2 is necessary for embryogenesis, particularly for heart development, and its depletion in embryonic stem cells (ESC) impairs cardiac differentiation. We have now determined that Cited2 depletion in ESC affects the expression of transcription factors and cardiopoietic genes involved in early mesoderm and cardiac specification. Interestingly, the supplementation of the secretome prepared from ESC overexpressing CITED2, during the onset of differentiation, rescued the cardiogenic defects of Cited2-depleted ESC. In addition, we demonstrate that the proteins WNT5A and WNT11 held the potential for rescue. We also validated the zebrafish as a model to investigate cited2 function during development. Indeed, the microinjection of morpholinos targeting cited2 transcripts caused developmental defects recapitulating those of mice knockout models, including the increased propensity for cardiac defects and severe death rate. Importantly, the co-injection of anti-cited2 morpholinos with either CITED2 or WNT5A and WNT11 recombinant proteins corrected the developmental defects of Cited2-morphants. This study argues that defects caused by the dysfunction of Cited2 at early stages of development, including heart anomalies, may be remediable by supplementation of exogenous molecules, offering the opportunity to develop novel therapeutic strategies aiming to prevent CHD.

mRNA-Sequencing Identifies Liver as a Potential Target Organ for Triphenyl Phosphate in Embryonic Zebrafish

Triphenyl phosphate (TPHP) is a commonly used organophosphate flame retardant and plasticizer in the United States. Using zebrafish as a model, the overall objective of this study was to identify potential organs that might be targeted by TPHP during embryonic development. Based on mRNA-sequencing, TPHP exposure from 24 to 30 h post fertilization (hpf) and 24 to 48 hpf significantly affected the abundance of 305 and 274 transcripts, respectively, relative to vehicle (0.1% DMSO) controls. In addition to minor effects on cardiotoxicity- and nephrotoxicity-related pathways, Ingenuity Pathway Analysis (IPA) of significantly affected transcripts within 30- and 48-hpf embryos revealed that hepatotoxicity-related pathways were strongly affected following exposure to TPHP alone. Moreover, while pre-treatment with fenretinide (a retinoic acid receptor agonist) mitigated TPHP-induced pericardial edema and liver enlargement at 72 hpf and 128 hpf, respectively, IPA revealed that fenretinide was unable to block TPHP-induced effects on cardiotoxicity-, nephrotoxicity-, and hepatotoxicity-related pathways at 48 hpf, suggesting that TPHP-induced effects on the transcriptome were not associated with toxicity later in development. In addition, based on Oil Red O staining, we found that exposure to TPHP nearly abolished neutral lipids from the embryonic head and trunk and, based on metabolomics, significantly decreased the total abundance of metabolites - including betaine, a known osmoprotectant - at 48 and 72 hpf. Overall, our data suggest that, in addition to the heart, TPHP exposure during early development results in adverse effects on the liver, lipid utilization, and osmoregulation within embryonic zebrafish.

Bitter gourd (Momordica charantia) possess developmental toxicity as revealed by screening the seeds and fruit extracts in zebrafish embryos

Background

Bitter gourd (Momordica charantia) has attracted the focus of researchers owing to its excellent anti-diabetic action. The beneficial effect of Momordica charantia on heart has been reported by in vitro and in vivo studies. However the developmental toxicity or potential risk of M. charantia on fetus heart development is largely unknown. Hence this study was designed to find out the developmental toxicity of M. charantia using zebrafish (Danio rerio) embryos.

Methods

The crude extracts were prepared from fruit and seeds of M. charantia. The Zebrafish embryos were exposed to serial dilution of each of the crude extract. The biologically active fractions were fractionated by C18 column using high pressure liquid chromatography. Fourier-transform infrared spectroscopy and gas chromatography coupled with mass spectrophotometry was done to identify chemical constituents in fruit and seed extract of M. charantia.

Results

The seed extract of M. charantia was lethal with LD₅₀ values of 50 μg/ml to zebrafish embryos and multiple anomalies were observed in zebrafish embryos at sub-lethal concentration. However, the fruit extract was much safe and exposing the zebrafish embryos even to 200 μg/ml did not result any lethality. The fruit extract induced severe cardiac hypertrophy in treated embryos. The time window treatment showed that M. charantia perturbed the cardiac myoblast specification process in treated zebrafish embryos. The Fourier-transform infrared spectroscopy analyses revealed diverse chemical group in the active fruit fraction and five new type of compounds were identified in the crude seeds extract of M. charantia by gas chromatography and mass spectrophotometry.

Conclusion

The teratogenicity of seeds extract and cardiac toxicity by the fruit extract of M. charantia warned that the supplementation made from the fruit and seeds of M. charantia should be used with much care in pregnant diabetic patients to avoid possible damage to developing fetus.

Electronic supplementary material

The online version of this article (10.1186/s12906-019-2599-0) contains supplementary material, which is available to authorized users.

Mapping glutathione utilization in the developing zebrafish (Danio rerio) embryo

Glutathione (GSH), the most abundant vertebrate endogenous redox buffer, plays key roles in organogenesis and embryonic development, however, organ-specific GSH utilization during development remains understudied. Monochlorobimane (MCB), a dye conjugated with GSH by glutathione-s-transferase (GST) to form a fluorescent adduct, was used to visualize organ-specific GSH utilization in live developing zebrafish (Danio rerio) embryos. Embryos were incubated in 20 μM MCB for 1 h and imaged on an epifluorescence microscope. GSH conjugation with MCB was high during early organogenesis, decreasing as embryos aged. The heart had fluorescence 21-fold above autofluorescence at 24 hpf, dropping to 8.5-fold by 48 hpf; this increased again by 72 hpf to 23.5-fold, and stayed high till 96 hpf (18-fold). The brain had lower fluorescence (10-fold) at 24 and 48 hpf, steadily increasing to 30-fold by 96 hpf. The sensitivity and specificity of MCB staining was then tested with known GSH modulators. A 10-min treatment at 48 hpf with 750 μM tert-butylhydroperoxide, caused organ-specific reductions in staining, with the heart losing 30% fluorescence, and, the brain ventricle losing 47% fluorescence. A 24 h treatment from 24-48 hpf with 100 μM of N-Acetylcysteine (NAC) resulted in significantly increased fluorescence, with the brain ventricle and heart showing 312% and 240% increases respectively, these were abolished upon co-treatment with 5 μM BSO, an inhibitor of the enzyme that utilizes NAC to synthesize GSH. A 60 min 100 μM treatment with ethacrynic acid, a specific GST inhibitor, caused 30% reduction in fluorescence across all measured structures. MCB staining was then applied to test for GSH disruptions caused by the toxicants perfluorooctanesulfonic acid and mono-(2-ethyl-hexyl)phthalate; MCB fluorescence responded in a dose, structure and age-dependent manner. MCB staining is a robust, sensitive method to detect spatiotemporal changes in GSH utilization, and, can be applied to identify sensitive target tissues of toxicants.

Reiterative Mechanisms of Retinoic Acid Signaling during Vertebrate Heart Development

Tightly-regulated levels of retinoic acid (RA) are critical for promoting normal vertebrate development. The extensive history of research on RA has shown that its proper regulation is essential for cardiac progenitor specification and organogenesis. Here, we discuss the roles of RA signaling and its establishment of networks that drive both early and later steps of normal vertebrate heart development. We focus on studies that highlight the drastic effects alternative levels of RA have on early cardiomyocyte (CM) specification and cardiac chamber morphogenesis, consequences of improper RA synthesis and degradation, and known effectors downstream of RA. We conclude with the implications of these findings to our understanding of cardiac regeneration and the etiologies of congenital heart defects.

Advantages and Challenges of Cardiovascular and Lymphatic Studies in Zebrafish Research

Since its introduction, the zebrafish has provided an important reference system to model and study cardiovascular development as well as lymphangiogenesis in vertebrates. A scientific workshop, held at the 2018 European Zebrafish Principal Investigators Meeting in Trento (Italy) and chaired by Massimo Santoro, focused on the most recent methods and studies on cardiac, vascular and lymphatic development. Daniela Panáková and Natascia Tiso described new molecular mechanisms and signaling pathways involved in cardiac differentiation and disease. Arndt Siekmann and Wiebke Herzog discussed novel roles for Wnt and VEGF signaling in brain angiogenesis. In addition, Brant Weinstein's lab presented data concerning the discovery of endothelium-derived macrophage-like perivascular cells in the zebrafish brain, while Monica Beltrame's studies refined the role of Sox transcription factors in vascular and lymphatic development. In this article, we will summarize the details of these recent discoveries in support of the overall value of the zebrafish model system not only to study normal development, but also associated disease states.

Ventricular remodeling of single-chambered myh6-/- adult zebrafish hearts occurs via a hyperplastic response and is accompanied by elastin deposition in the atrium

Zebrafish (Danio rerio) is widely used as an animal model to understand the pathophysiology of cardiovascular diseases. Here, we present the adult cardiac phenotype of weak atrium, myh6^-/-, which carry mutations in the zebrafish atrial myosin heavy chain. Homozygous mutants survive to adulthood and are fertile despite their initial weak atrial beat. In adult mutants, the atrium remains hypoplastic and shows elastin deposition while mutant ventricles exhibit increased size. In mammals, hypertrophy is the most common mechanism resulting in cardiomegaly. Using immunohistochemistry and confocal microscopy to measure cardiomyocyte cell size, density and proliferation, we show that the enlargement of the myh6^-/- ventricle is predominantly due to hyperplasia. However, we identified similar transcriptional profiles to the mammalian hypertrophy response via RT-PCR of the hyperplastic ventricles. Furthermore, we show activation of the ER-stress pathway by western blot analysis. In conclusion, we can assume, based on our model, that molecular signaling pathways associated with hypertrophy in mammals, in combination with ER-stress activation, result in hyperplasia in zebrafish. In addition, to our knowledge, this is the first time to report elastin deposition in the atrium.

Adaptation of a Mice Doppler Echocardiography Platform to Measure Cardiac Flow Velocities for Embryonic Chicken and Adult Zebrafish

Ultrasonography is the most widely used imaging technique in cardiovascular medicine. In this technique, a piezoelectric crystal produces, sends, and receives high frequency ultrasound waves to the body to create an image of internal organs. It enables practical real time visualization in a non-invasive manner, making the modality especially useful to image dynamic cardiac structures. In the last few decades, echocardiography has been applied to in vivo cardiac disease models, mainly to rodents. While clinical echocardiography platforms can be used for relatively large animals such as pigs and rats, specialized systems are needed for smaller species. Theoretically, as the size of the imaged sample decreases, the frequency of the ultrasound transducer needed to image the sample increases. There are multiple modes of echocardiography imaging. In Doppler mode, erythrocytes blood flow velocities are measured from the frequency shift of the sent ultrasound waves compared to received echoes. Recorded data are then used to calculate cardiac function parameters such as cardiac output, as well as the hemodynamic shear stress levels in the heart and blood vessels. The multi-mode (i.e., b-mode, m-mode, Pulsed Doppler, Tissue Doppler, etc.) small animal ultrasound systems in the market can be used for most in vivo cardiac disease models including mice, embryonic chick and zebrafish. These systems are also associated with significant costs. Alternatively, there are more economical single-mode echocardiography platforms. However, these are originally built for mice studies and they need to be tested and evaluated for smaller experimental models. We recently adapted a mice Doppler echocardiography system to measure cardiac flow velocities for adult zebrafish and embryonic chicken. We successfully assessed cardiac function and hemodynamic shear stress for normal as well as for diseased embryonic chicken and zebrafish. In this paper, we will present our detailed protocols for Doppler flow measurements and further cardiac function analysis on these models using the setup. The protocols will involve detailed steps for animal stabilization, probe orientation for specific measurements, data acquisition, and data analysis. We believe this information will help cardiac researchers to establish similar echocardiography platforms in their labs in a practical and economical manner.

Identification of a 42-bp heart-specific enhancer of the notch1b gene in zebrafish embryos

BACKGROUND

NOTCH1 plays a key role in the differentiation of ventricles, and mutations are strongly associated with both sporadic and familial bicuspid aortic valves. However, few heart-specific enhancers have been identified to date.

RESULTS

In this study, we investigated evolutionary conserved regions (ECRs) that might act as potential enhancers within the region approximately 150-kb upstream and downstream of the NOTCH1 gene. Functional validation revealed that one 127-bp ECR located ~85-kb downstream of the NOTCH1 gene drives green fluorescent protein expression in the zebrafish embryo heart. Transcription factor (TF) prediction and core TF distribution analyses were performed to identify the core region. Dissection of ECR3 was performed to identify the 42-bp sequence, which is sufficient for heart-specific expression. In situ hybridization experiments showed that notch1b is expressed in the heart. Overexpression experiments in cells indicated that NKX2-5 is critical for enhancer activity. Mutation of the NKX-5 binding site significantly decreased reporter gene expression. Next, compared with the commonly used myocardium-labeled zebrafish transgenic strain Tg(cmlc2: mCherry), this 42-bp enhancer-labeled stable line mediated a similar expression pattern but with a smaller core region.

CONCLUSION

This study identified a 42-bp heart-specific enhancer near the NOTCH1 gene and further verified its functional targeting by NKX2-5.

Inhibition of let-7c Regulates Cardiac Regeneration after Cryoinjury in Adult Zebrafish

The let-7c family of micro-RNAs (miRNAs) is expressed during embryonic development and plays an important role in cell differentiation. We have investigated the role of let-7c in heart regeneration after injury in adult zebrafish. let-7c antagomir or scramble injections were given at one day after cryoinjury (1 dpi). Tissue samples were collected at 7 dpi, 14 dpi and 28 dpi and cardiac function was assessed before cryoinjury, 1 dpi, 7 dpi, 14 dpi and 28 dpi. Inhibition of let-7c increased the rate of fibrinolysis, increased the number of proliferating cell nuclear antigen (PCNA) positive cardiomyocytes at 7 dpi and increased the expression of the epicardial marker raldh2 at 7 dpi. Additionally, cardiac function measured with echocardiography recovered slightly more rapidly after inhibition of let-7c. These results reveal a beneficial role of let-7c inhibition in adult zebrafish heart regeneration.

Developmental neurotoxicity and immunotoxicity induced by graphene oxide in zebrafish embryos

Graphene oxide (GO) has emerged as the worldwide promising candidate for biomedical application, such as for drug delivery, bio-sensing and anti-cancer therapy. This study was focused on the zebrafish and RAW264.7 cell line as in vivo and in vitro models to assess the potential developmental neurotoxicity and immunotoxicity of GO. No obvious acute developmental toxicity was observed upon treatments with 0.01, 0.1, and 1 μg/mL GO for five consecutive days. However, decreased hatching rate, increased malformation rate, heart beat rate and hypoactivity of locomotor behavior were detected when exposed to 10 μg/mL GO. Also, RT-PCR analysis revealed that expressions of genes related to the nervous system were up-regulated. The potential risk of GO for developmental neurotoxicity may be ascribed to the high level of oxidative stress induced by high concentration of GO. Most importantly, the mRNA levels of immune response associated genes, such as interleukin-6 (IL-6), interleukin-8 (IL-8), tumor necrosis factor-α (TNFα), interferon-γ (IFN-γ) were significantly increased under environmental concentration exposure. The activation of pro-inflammatory immune response was also observed in macrophage cell line. Taken together, our results demonstrated that immunotoxicity is a sensitive indicator for assessment of bio-compatibility of GO.

Purification of high-quality RNA from a small number of fluorescence activated cell sorted zebrafish cells for RNA sequencing purposes

Background

Transgenic zebrafish lines with the expression of a fluorescent reporter under the control of a cell-type specific promoter, enable transcriptome analysis of FACS sorted cell populations. RNA quality and yield are key determinant factors for accurate expression profiling. Limited cell number and FACS induced cellular stress make RNA isolation of sorted zebrafish cells a delicate process. We aimed to optimize a workflow to extract sufficient amounts of high-quality RNA from a limited number of FACS sorted cells from Tg(fli1a:GFP) zebrafish embryos, which can be used for accurate gene expression analysis.

Results

We evaluated two suitable RNA isolation kits (the RNAqueous micro and the RNeasy plus micro kit) and determined that sorting cells directly into lysis buffer is a critical step for success. For low cell numbers, this ensures direct cell lysis, protects RNA from degradation and results in a higher RNA quality and yield. We showed that this works well up to 0.5× dilution of the lysis buffer with sorted cells. In our sort settings, this corresponded to 30,000 and 75,000 cells for the RNAqueous micro kit and RNeasy plus micro kit respectively. Sorting more cells dilutes the lysis buffer too much and requires the use of a collection buffer. We also demonstrated that an additional genomic DNA removal step after RNA isolation is required to completely clear the RNA from any contaminating genomic DNA. For cDNA synthesis and library preparation, we combined SmartSeq v4 full length cDNA library amplification, Nextera XT tagmentation and sample barcoding. Using this workflow, we were able to generate highly reproducible RNA sequencing results.

Conclusions

The presented optimized workflow enables to generate high quality RNA and allows accurate transcriptome profiling of small populations of sorted zebrafish cells.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5608-2) contains supplementary material, which is available to authorized users.

Loss of the Polycomb group protein Rnf2 results in derepression of tbx-transcription factors and defects in embryonic and cardiac development

The Polycomb group (PcG) protein family is a well-known group of epigenetic modifiers. We used zebrafish to investigate the role of Rnf2, the enzymatic subunit of PRC1. We found a positive correlation between loss of Rnf2 and upregulation of genes, especially of those whose promoter is normally bound by Rnf2. The heart of rnf2 mutants shows a tubular shaped morphology and to further understand the underlying mechanism, we studied gene expression of single wildtype and rnf2 mutant hearts. We detected the most pronounced differences at 3 dpf, including upregulation of heart transcription factors, such as tbx2a, tbx2b, and tbx3a. These tbx genes were decorated by broad PcG domains in wildtype whole embryo lysates. Chamber specific genes such as vmhc, myh6, and nppa showed downregulation in rnf2 mutant hearts. The marker of the working myocard, nppa, is negatively regulated by Tbx2 and Tbx3. Based on our findings and literature we postulate that loss of Rnf2-mediated repression results in upregulation and ectopic expression of tbx2/3, whose expression is normally restricted to the cardiac conductive system. This could lead to repression of chamber specific gene expression, a misbalance in cardiac cell types, and thereby to cardiac defects observed in rnf2 mutants.

Screening drugs for myocardial disease in vivo with zebrafish: an expert update

INTRODUCTION

Our understanding of the complexity of cardiovascular disease pathophysiology remains very incomplete and has hampered cardiovascular drug development over recent decades. The prevalence of cardiovascular diseases and their increasing global burden call for novel strategies to address disease biology and drug discovery. Areas covered: This review describes the recent history of cardiovascular drug discovery using in vivo phenotype-based screening in zebrafish. The rationale for the use of this model is highlighted and the initial efforts in the fields of disease modeling and high-throughput screening are illustrated. Finally, the advantages and limitations of in vivo zebrafish screening are discussed, highlighting newer approaches, such as genome editing technologies, to accelerate our understanding of disease biology and the development of precise disease models. Expert opinion: Full understanding and faithful modeling of specific cardiovascular disease is a rate-limiting step for cardiovascular drug discovery. The resurgence of in vivo phenotype screening together with the advancement of systems biology approaches allows for the identification of lead compounds which show efficacy on integrative disease biology in the absence of validated targets. This strategy bypasses current gaps in knowledge of disease biology and paves the way for successful drug discovery and downstream molecular target identification.

Ioxynil and diethylstilbestrol disrupt vascular and heart development in zebrafish

BACKGROUND

Endocrine disruption is one of the consequences of industrialization and chemicals released into the environment have a profound impact on organisms. Waterborne micromolar concentrations of ioxynil (IOX) and diethylstilbestrol (DES) in fish affect the development of the heart, vasculature and thyroid gland.

OBJECTIVES

The present study aimed to determine how IOX and DES disrupt the crosstalk between the developing thyroid gland and cardio-vascular system in zebrafish.

METHODS

Twelve hours post fertilization (hpf) wild type, Tg(fli1:GFP) or Tg(cmalc2:GFPCaaX) zebrafish embryos were exposed to 0.1 μM IOX or DES for 36 h (up until 48 hpf) or 60 h (up until 72 hpf). Embryos were used for vascular endothelial cell sorting, whole-mount immunohistochemistry, tissue selective transcriptomics, selected gene expression analysis by quantitative real-time polymerase chain reaction analysis and determination of heart rate by live imaging.

RESULTS

Exposure of zebrafish embryos to IOX and DES (0.1 μM) increased heart beat frequency and reduced ventricle volume and aorta diameter. The transcriptome of endothelial cells from blood vessels of hypertrophic, dilated and arrhythmogenic right ventricular cardiomyopathy was significantly changed and compound-specific toxic effects were found in IOX and DES exposed embryos. Both DES and IOX directly affected vascular and heart development and this indirectly impaired thyroid gland development in zebrafish. Even though the toxicity end-point of the two chemicals was similar, their action seemed to be via different gene regulatory pathways and physiological mechanisms.

CONCLUSION

IOX and DES directly disrupt cardiovascular development and there is an associated disruption of thyroid tissue that most likely has long term consequences for this endocrine axis.

Possible involvement of Fas/FasL-dependent apoptotic pathway in α-bisabolol induced cardiotoxicity in zebrafish embryos

α-Bisabolol, an unsaturated monocyclic sesquiterpene alcohol, is a common ingredient in many pharmaceuticals and personal care products (PPCPs). Despite being widely used, little is known about its toxic effects on organisms and aquatic environment. In this study, we investigated the developmental toxicity of α-Bisabolol, especially its effects on the cardiac development using zebrafish embryos as a model. Embryos at 4 h post-fertilization (hpf) were exposed to 10, 30, 50, 70, 90, and 100 μM α-Bisabolol until 144 hpf. α-Bisabolol caused phenotypic defects and the most striking one is the heart malformation. Treatment of α-Bisabolol significantly increased the cardiac malformation rate, the SV-BA distance, as well as the pericardial edema area, and reduced heart rate in a concentration-dependent manner. Notably, considerable numbers of apoptotic cells were mainly observed in the heart region of zebrafish treated with α-Bisabolol. Further study on α-Bisabolol induced apoptosis in the zebrafsh heart suggested that an activation of Fas/FasL-dependent apoptotic pathway. Taken together, our study investigated the cardiotoxicity of α-Bisabolol on zebrafish embryonic development and its underlying molecular mechanism, shedding light on the full understanding of α-Bisabolol toxicity on living organisms and its environmental impact.

Exposure to DBP induces the toxicity in early development and adverse effects on cardiac development in zebrafish (Danio rerio)

Dibutyl phthalate (DBP) is one of the most ubiquitous plasticizers used worldwide and has been frequently detected in soil, water, atmosphere, and other environmental media. DBP has become a ubiquitous environment contaminant and causes serious pollution. However, much attention has been paid to the toxicity of DBP, with only limited attention paid to its detrimental effects on the heart. In the present study, we investigated the toxicity of DBP in zebrafish embryo development, especially adverse effects on cardiac development. Embryos at 4-h post-fertilization (hpf) were exposed to different concentrations of DBP (0, 0.36, 1.8 and 3.6 μM) until 72 hpf. Exposure to DBP resulted in morphological abnormalities in zebrafish embryos. Exposure to 1.8 μM DBP significantly affected the growth, malformation rate, cardiac malformation rate and cardiac looping. Exposure to 3.6 μM DBP significantly affected all endpoints. To preliminarily understand the underlying mechanisms of toxic effects of DBP on the embryo heart, we examined the expression of master cardiac transcription factors such as NKX2.5 and TBX5. The expression of this two transcription factors was significantly reduced with DBP treatment in a dose-dependent manner. Our results demonstrate that exposure to DBP resulted in zebrafish developmental toxicity, pericardial edema, cardiac structure deformities and function alteration, and changed the expression of master cardiac transcription factors such as NKX2.5 and TBX5.

Cardiovascular toxicity and anxiety-like behavior induced by deltamethrin in zebrafish (Danio rerio) larvae

Deltamethrin is widely used because of its low toxicity and high efficiency. Although its potential toxicity has been reported, its effects on cardiovascular system and motor behavior and its underlying mechanisms have remained unclear. In this study, the effects of deltamethrin on the development, cardiovascular system and motor behavior of zebrafish larvae and their possible mechanisms were evaluated using the transgenic zebrafish Tg (kdrl:mCherry) and Tg(myl7:GFP). At 72 hpf, the body length of larvae shortened, the head and eye area decreased, and the hatching rate increased. Acridine orange staining showed that treated zebrafish larvae produced different degrees of apoptosis in the head, body, heart and tail regions. Quantitative fluorescence intensity showed a dose-dependent increase in apoptosis signal, indicating that deltamethrin could induce apoptosis. Confocal images and fluorescence intensity quantification of red fluorescent protein-labeled vascular endothelial cell and green fluorescent protein-labeled transgenic zebrafish more clearly reflected the dose-dependent cardiac and vascular morphology and the damage caused by deltamethrin. Deltamethrin significantly induced vascular endothelial growth factor flk1 and fli-1, cardiac development-related gene myl7 decreased in a dose-dependent manner. In addition, deltamethrin increased the thigmotaxis of zebrafish larvae, causing anxiety-like behavior. Our study showed that deltamethrin could cause developmental toxicity, apoptosis, cardiovascular system damage and anxiety-like behavior, which provided a reference for the use of deltamethrin in agricultural production.

Cardiogenesis impairment promoted by bisphenol A exposure is successfully counteracted by epigallocatechin gallate

Exposure to the emerging contaminant bisphenol A (BPA) is ubiquitous and associated with cardiovascular disorders. BPA effect as endocrine disruptor is widely known but other mechanisms underlying heart disease, such as epigenetic modifications, remain still unclear. A compound of green tea, epigallocatechin gallate (EGCG), may act both as anti-estrogen and as inhibitor of some epigenetic enzymes. The aims of this study were to analyze the molecular processes related to BPA impairment of heart development and to prove the potential ability of EGCG to neutralize the toxic effects caused by BPA on cardiac health. Zebrafish embryos were exposed to 2000 and 4000 μg/L BPA and treated with 50 and 100 μM EGCG. Heart malformations were assessed at histological level and by confocal imaging. Expression of genes involved in cardiac development, estrogen receptors and epigenetic enzymes was analyzed by qPCR whereas epigenetic modifications were evaluated by whole mount immunostaining. BPA embryonic exposure led to changes in cardiac phenotype, induced an overexpression of hand2, a crucial factor for cardiomyocyte differentiation, increased the expression of estrogen receptor (esr2b), promoted an overexpression of a histone acetyltransferase (kat6a) and also caused an increase in histone acetylation, both mechanisms being able to act in sinergy. EGCG treatment neutralized all the molecular alterations caused by BPA, allowing the embryos to go on with a proper heart development. Both molecular mechanisms of BPA action (estrogenic and epigenetic) likely lying behind cardiogenesis impairment were successfully counteracted by EGCG treatment.

On Zebrafish Disease Models and Matters of the Heart

Coronary artery disease (CAD) is the leading form of cardiovascular disease (CVD), which is the primary cause of mortality worldwide. It is a complex disease with genetic and environmental risk factor contributions. Reports in human and mammalian models elucidate age-associated changes in cardiac function. The diverse mechanisms involved in cardiac diseases remain at the center of the research interest to identify novel strategies for prevention and therapy. Zebrafish (Danio rerio) have emerged as a valuable vertebrate model to study cardiovascular development over the last few decades. The facile genetic manipulation via forward and reverse genetic approaches combined with noninvasive, high-resolution imaging and phenotype-based screening has provided new insights to molecular pathways that orchestrate cardiac development. Zebrafish can recapitulate human cardiac pathophysiology due to gene and regulatory pathways conservation, similar heart rate and cardiac morphology and function. Thus, generations of zebrafish models utilize the functional analysis of genes involved in CAD, which are derived from large-scale human population analysis. Here, we highlight recent studies conducted on cardiovascular research focusing on the benefits of the combination of genome-wide association studies (GWAS) with functional genomic analysis in zebrafish. We further summarize the knowledge obtained from zebrafish studies that have demonstrated the architecture of the fundamental mechanisms underlying heart development, homeostasis and regeneration at the cellular and molecular levels.

Aconitum alkaloids induce cardiotoxicity and apoptosis in embryonic zebrafish by influencing the expression of cardiovascular relative genes

Aconitine (AC) and mesaconitine (MA) are major bioactive diterpenoid alkaloids derived from herbal aconitum plants. Emerging evidence indicates that AC plays a pivotal role in the cardiotoxicity for aconite poisoning. However, the cardiotoxicity data of MA, especially those on the difference between AC and MA are quite limited. Zebrafish embryos were used in this study for toxicological screening, and the cardiac morphology and function were observed. Embryos were analyzed by means of high-performance liquid chromatography (HPLC) after exposure and pharmacokinetic behaviors were also investigated. Results showed that 1.5% of the aconitum alkaloids penetrated into the zebrafish embryos. 2.5 μg/L AC and 20 μg/L MA caused a deficient cardiovascular system with yolk sac hemorrhage and early cardiac dysfunctions were observed in 96 h post-fertilization. AC showed greater cardiotoxicity than MA by comparing the EC₅₀ of pericardium edema. Aconitum alkaloids exposure also resulted in a significant decrease in the expression of cardiac genes (Tbx5, Gata4, and Nkx2.5) from an early stage (12-24 hpf), which may partly explained that the death caused by aconitum is most likely to occur within the first 24 h. In addition, a high percentage of apoptotic cells was observed in the brain region, which identified another potential target of the DDA action in zebrafish embryos.