GATA-1 expression pattern can be recapitulated in living transgenic zebrafish using GFP reporter gene

Single-cell RNA sequencing reveals tissue-specific transcriptomic changes induced by perfluorooctanesulfonic acid (PFOS) in larval zebrafish (Danio rerio)

Perfluorooctanesulfonic acid (PFOS) elicits adverse effects on numerous organs and developmental processes but the mechanisms underlying these effects are not well understood. Here, we use single-cell RNA-sequencing to assess tissue-specific transcriptomic changes in zebrafish (Danio rerio) larvae exposed to 16 µM PFOS or dimethylsulfoxide (0.01 %) from 3-72 h post fertilization (hpf). Data analysis was multi-pronged and included pseudo-bulk, untargeted clustering, informed pathway queries, and a cluster curated for hepatocyte biomarkers (fabp10a, and apoa2). Overall, 8.63 % (2390/27698) genes were significantly differentially expressed. Results from untargeted analysis revealed 22 distinct clusters that were manually annotated to specific tissues using a weight-of-evidence approach. The clusters with the highest number of significant differentially expressed genes (DEGs) were digestive organs, muscle, and otolith. Additionally, we assessed the distribution of pathway-specific genes known to be involved in PFOS toxicity: the PPAR pathway, β-oxidation of fatty acids, the Nfe2l2 pathway, and epigenetic modifications by DNA methylation, across clusters and identified the blood-related tissue to be the most sensitive. The curated hepatocyte cluster showed 220 significant DEGs and was enriched for the Notch signaling pathway. These findings provide insights into both established and novel sensitive target tissues and molecular mechanisms of developmental toxicity of PFOS.

Establishment of a novel clonal GFP-expressing transgenic ginbuna crucian carp

The clonal triploid ginbuna crucian carp Carassius auratus langsdorfii, a naturally occurring gynogenetic fish, is suitable for cell transplantation studies to reveal the roles of stem cells and immune cells. To ensure long-term traceability of donor cells within recipient fish, we have established a transgenic ginbuna line that expresses green fluorescent protein (GFP). The Xenopus laevis ef1a promoter was introduced for regulating GFP expression. Tol2 transposon-based transgenesis to ginbuna embryos resulted in producing a putative founder fish (F0) in a mosaic fluorescent fashion; the frequency of germline transmission was 14.9%. All embryos of GFP-positive offspring (F1)-derived F2 generation expressed GFP widely across the body. The result of Southern blot analysis showed that the transgene was present on a single DNA fragment of equivalent size among F1 and F2 individuals tested, indicating that the transgene was stably transmitted without translocation. Analysis of the fluorescence intensity of organs obtained from F1 and F2 juveniles using fluorescence microscope showed that eyes, brain, skeletal muscle, heart and gonad exhibited a strong GFP fluorescence while gill, spleen and intestine gave a weak signal; no fluorescence was observed in erythrocytes. Flow cytometric analyses of peripheral leukocytes from F1 and F2 adult fish revealed all cell populations expressed GFP. Scale grafts from the transgenic fish to the wild-type fish exhibited persistent engraftment. Together, our transgenic line can be a powerful tool for studying cellular dynamics by cell transplantation and provide a solid basis for further immunological research advances in teleost.

Primed conversion: The emerging player of precise and nontoxic photoconversion

In 2015, we reported primed conversion, a novel way to convert green-to-red photoconvertible fluorescent proteins, which emerges as a powerful tool for precision optical imaging. Primed conversion uses the intercept of blue and red-to-far-red light instead of traditional violet or near-UV light illumination which offers a series of advantages. Here, we review the fundamental principles and applications of primed conversion with a focus on its use in single-cell labelling and lineage tracing. We provide a historical perspective of lineage tracing techniques, thereby covering basic principles of fluorescence, photoconvertible fluorescent proteins, and eventually primed conversion. We then present the molecular requirements for primed conversion to take place and showcase how it can be used for dual-colour high-fidelity lineage tracing. Further, we discuss potential future developments of the primed conversion imaging toolkit that can benefit the study of both development and disease progression.

The Role of the Neurotrophin Network in Skin Squamous Cell Cancer and the Novel Use of the Zebrafish System

Cutaneous squamous cell carcinoma (cSCC) is the second most prevalent form of skin cancer. An increasing number of cSCCs are associated with dysregulation of key molecules that control skin homeostasis. These observations have increased interest in the role of neurotrophins and their receptors in the pathogenesis of cSCC. They have been demonstrated to have a considerable impact on the aggressiveness potential of skin cancer by both in vitro and in vivo models. In this context, mouse models are classically used to dissect proliferation versus differentiation balance, but they have some limitations in terms of time, space, and costs. Recently, zebrafish models have been implemented as a new tool to obtain information regarding the invasive capacity and metastasis of neoplastic cells. By xenotransplantation technique, cSCC cells from a patient's biopsy or cell line can be successfully characterized, with or without the presence of genetic manipulation or treatments. In addition, the evaluation of the immune microenvironment contributes to potentially identifying connections and homologies with humans. In this review, we retrace the role of the neurotrophin network in healthy and pathological skin, particularly in cSCC. We review how zebrafish models can be important tools for studying cSCC development, growth, and potential treatments.

Rbm8a deficiency causes hematopoietic defects by modulating Wnt/PCP signaling

Defects in blood development frequently occur among syndromic congenital anomalies. Thrombocytopenia-Absent Radius (TAR) syndrome is a rare congenital condition with reduced platelets (hypomegakaryocytic thrombocytopenia) and forelimb anomalies, concurrent with more variable heart and kidney defects. TAR syndrome associates with hypomorphic gene function for RBM8A/Y14 that encodes a component of the exon junction complex involved in mRNA splicing, transport, and nonsense-mediated decay. How perturbing a general mRNA-processing factor causes the selective TAR Syndrome phenotypes remains unknown. Here, we connect zebrafish rbm8a perturbation to early hematopoietic defects via attenuated non-canonical Wnt/Planar Cell Polarity (PCP) signaling that controls developmental cell re-arrangements. In hypomorphic rbm8a zebrafish, we observe a significant reduction of cd41-positive thrombocytes. rbm8a-mutant zebrafish embryos accumulate mRNAs with individual retained introns, a hallmark of defective nonsense-mediated decay; affected mRNAs include transcripts for non-canonical Wnt/PCP pathway components. We establish that rbm8a-mutant embryos show convergent extension defects and that reduced rbm8a function interacts with perturbations in non-canonical Wnt/PCP pathway genes wnt5b, wnt11f2, fzd7a, and vangl2. Using live-imaging, we found reduced rbm8a function impairs the architecture of the lateral plate mesoderm (LPM) that forms hematopoietic, cardiovascular, kidney, and forelimb skeleton progenitors as affected in TAR Syndrome. Both mutants for rbm8a and for the PCP gene vangl2 feature impaired expression of early hematopoietic/endothelial genes including runx1 and the megakaryocyte regulator gfi1aa. Together, our data propose aberrant LPM patterning and hematopoietic defects as consequence of attenuated non-canonical Wnt/PCP signaling upon reduced rbm8a function. These results also link TAR Syndrome to a potential LPM origin and a developmental mechanism.

Thyroid-stimulating hormone-thyroid hormone signaling contributes to circadian regulation through repressing clock2/npas2 in zebrafish

Thyroid-stimulating hormone (TSH) is important for the thyroid gland, development, growth, and metabolism. Defects in TSH production or the thyrotrope cells within the pituitary gland cause congenital hypothyroidism (CH), resulting in growth retardation and neurocognitive impairment. While human TSH is known to display rhythmicity, the molecular mechanisms underlying the circadian regulation of TSH and the effects of TSH-thyroid hormone (TH) signaling on the circadian clock remain elusive. Here we show that TSH, thyroxine (T4), triiodothyronine (T3), and tshba display rhythmicity in both larval and adult zebrafish and tshba is regulated directly by the circadian clock via both E'-box and D-box. Zebrafish tshba-/- mutants manifest congenital hypothyroidism, with the characteristics of low levels of T4 and T3 and growth retardation. Loss or overexpression of tshba alters the rhythmicity of locomotor activities and expression of core circadian clock genes and hypothalamic-pituitary-thyroid (HPT) axis-related genes. Furthermore, TSH-TH signaling regulates clock2/npas2 via the thyroid response element (TRE) in its promoter, and transcriptome analysis reveals extensive functions of Tshba in zebrafish. Together, our results demonstrate that zebrafish tshba is a direct target of the circadian clock and in turn plays critical roles in circadian regulation along with other functions.

Cancer Modeling by Transgene Electroporation in Adult Zebrafish (TEAZ)

Transgenic expression of genes is a mainstay of cancer modeling in zebrafish. Traditional transgenic techniques rely upon injection into one-cell embryos, but ideally these transgenes would be expressed only in adult somatic tissues. We provide a method to model cancer in adult zebrafish in which transgenes can be expressed via electroporation. Using melanoma as an example, we demonstrate the feasibility of expressing oncogenes such as BRAFV600E as well as CRISPR/Cas9 inactivation of tumor suppressors such as PTEN. These approaches can be performed in any genetic background such as existing fluorophore reporter lines or the casper line. These methods can readily be extended to other cell types allowing for rapid adult modeling of cancer in zebrafish.

Next-generation plasmids for transgenesis in zebrafish and beyond

Transgenesis is an essential technique for any genetic model. Tol2-based transgenesis paired with Gateway-compatible vector collections has transformed zebrafish transgenesis with an accessible modular system. Here, we establish several next-generation transgenesis tools for zebrafish and other species to expand and enhance transgenic applications. To facilitate gene regulatory element testing, we generated Gateway middle entry vectors harboring the small mouse beta-globin minimal promoter coupled to several fluorophores, CreERT2 and Gal4. To extend the color spectrum for transgenic applications, we established middle entry vectors encoding the bright, blue-fluorescent protein mCerulean and mApple as an alternative red fluorophore. We present a series of p2A peptide-based 3' vectors with different fluorophores and subcellular localizations to co-label cells expressing proteins of interest. Finally, we established Tol2 destination vectors carrying the zebrafish exorh promoter driving different fluorophores as a pineal gland-specific transgenesis marker that is active before hatching and through adulthood. exorh-based reporters and transgenesis markers also drive specific pineal gland expression in the eye-less cavefish (Astyanax). Together, our vectors provide versatile reagents for transgenesis applications in zebrafish, cavefish and other models.

Leukemia-associated truncation of granulocyte colony-stimulating factor receptor impacts granulopoiesis throughout the life-course

Introduction

The granulocyte colony-stimulating factor receptor (G-CSFR), encoded by the CSF3R gene, is involved in the production and function of neutrophilic granulocytes. Somatic mutations in CSF3R leading to truncated G-CSFR forms are observed in acute myeloid leukemia (AML), particularly those subsequent to severe chronic neutropenia (SCN), as well as in a subset of patients with other leukemias.

Methods

This investigation introduced equivalent mutations into the zebrafish csf3r gene via genome editing and used a range of molecular and cellular techniques to understand the impact of these mutations on immune cells across the lifespan.

Results

Zebrafish harboring truncated G-CSFRs showed significantly enhanced neutrophil production throughout successive waves of embryonic hematopoiesis and a neutrophil maturation defect in adults, with the mutations acting in a partially dominant manner.

Discussion

This study has elucidated new insights into the impact of G-CSFR truncations throughout the life-course and created a bone fide zebrafish model for further investigation.

Fishing for answers to hemostatic and thrombotic disease: Genome editing in zebrafish

Over the past two decades, the teleost vertebrate Danio rerio (zebrafish) has emerged as a model for hemostasis and thrombosis. At genomic and functional levels, there is a high degree of conservation of the hemostatic system with that of mammals. Numerous features of the fish model offer unique advantages for investigating hemostasis and thrombosis. These include high fecundity, rapid and external development, optical transparency, and extensive functional homology with mammalian hemostasis and thrombosis. Zebrafish are particularly suited to genome-wide mutagenesis experiments for the study of modifier genes. They are also amenable to whole-organism small-molecule screens, a feature that is exceptionally relevant to hemostasis and thrombosis. Zebrafish coagulation factor knockouts that are in utero or neonatal lethal in mammals survive into adulthood before succumbing to hemorrhage or thrombosis, enabling studies not possible in mammals. In this illustrated review, we outline how zebrafish have been employed for the study of hemostasis and thrombosis using modern genome editing techniques, coagulation assays in larvae, and in vivo evaluation of patient-specific variants to infer causality and demonstrate pathogenicity. Zebrafish hemostasis and thrombosis models will continue to serve as a clinically directed basic research tool and powerful alternative to mammals for the development of new diagnostic markers and novel therapeutics for coagulation disorders through high-throughput genetic and small-molecule studies.

Zebrafish: an underutilized tool for discovery in host-microbe interactions

Zebrafish are relatively new to the field of host-pathogen interactions, although they have been a valuable vertebrate model for decades in developmental biology and neuroscience. Transparent zebrafish larvae have most components of the human innate immune system, and adult zebrafish also produce cells of the adaptive immune system. Recent discoveries using zebrafish infection models include mechanisms of pathogen survival and host cell sensing of microbes. These discoveries were enabled by zebrafish technology, which is constantly evolving and providing new opportunities for immunobiology research. Recent tools include CRISPR/Cas9 mutagenesis, in vivo biotinylation, and genetically encoded biosensors. We argue that the zebrafish model - which remains underutilized in immunology - provides fertile ground for a new understanding of host-microbe interactions in a transparent host.

Zebrafish models of acute leukemias: Current models and future directions

Acute myeloid leukemias (AML) and acute lymphoid leukemias (ALL) are heterogenous diseases encompassing a wide array of genetic mutations with both loss and gain of function phenotypes. Ultimately, these both result in the clonal overgrowth of blast cells in the bone marrow, peripheral blood, and other tissues. As a consequence of this, normal hematopoietic stem cell function is severely hampered. Technologies allowing for the early detection of genetic alterations and understanding of these varied molecular pathologies have helped to advance our treatment regimens toward personalized targeted therapies. In spite of this, both AML and ALL continue to be a major cause of morbidity and mortality worldwide, in part because molecular therapies for the plethora of genetic abnormalities have not been developed. This underscores the current need for better model systems for therapy development. This article reviews the current zebrafish models of AML and ALL and discusses how novel gene editing tools can be implemented to generate better models of acute leukemias. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cells and Disease Technologies > Perturbing Genes and Generating Modified Animals.

Definitive hematopoietic stem cells minimally contribute to embryonic hematopoiesis

Hematopoietic stem cells (HSCs) are rare cells that arise in the embryo and sustain adult hematopoiesis. Although the functional potential of nascent HSCs is detectable by transplantation, their native contribution during development is unknown, in part due to the overlapping genesis and marker gene expression with other embryonic blood progenitors. Using single-cell transcriptomics, we define gene signatures that distinguish nascent HSCs from embryonic blood progenitors. Applying a lineage-tracing approach to selectively track HSC output in situ, we find significantly delayed lymphomyeloid contribution. An inducible HSC injury model demonstrates a negligible impact on larval lymphomyelopoiesis following HSC depletion. HSCs are not merely dormant at this developmental stage, as they showed robust regeneration after injury. Combined, our findings illuminate that nascent HSCs self-renew but display differentiation latency, while HSC-independent embryonic progenitors sustain developmental hematopoiesis. Understanding these differences could improve de novo generation and expansion of functional HSCs.

Transgenic fluorescent zebrafish lines that have revolutionized biomedical research

Since its debut in the biomedical research fields in 1981, zebrafish have been used as a vertebrate model organism in more than 40,000 biomedical research studies. Especially useful are zebrafish lines expressing fluorescent proteins in a molecule, intracellular organelle, cell or tissue specific manner because they allow the visualization and tracking of molecules, intracellular organelles, cells or tissues of interest in real time and in vivo. In this review, we summarize representative transgenic fluorescent zebrafish lines that have revolutionized biomedical research on signal transduction, the craniofacial skeletal system, the hematopoietic system, the nervous system, the urogenital system, the digestive system and intracellular organelles.

Zebrafish as a Model for In-Depth Mechanistic Study for Stroke

Stroke is one of the world's leading causes of death and disability, posing enormous burden to the society. However, the pathogenesis and mechanisms that underlie brain injury and brain repair remain largely unknown. There's an unmet need of in-depth mechanistic research in this field. Zebrafish (Danio rerio) is a powerful tool in brain science research mainly due to its small size and transparent body, high genome synteny with human, and similar nervous system structures. It can be used to establish both hemorrhagic and ischemic stroke models easily and effectively through different ways. After the establishment of stroke model, research methods including behavioral test, in vivo imaging, and drug screening are available to explore mechanisms that underlie the brain injury and brain repair after stroke. This review focuses on the advantages and the feasibility of zebrafish stroke model, and will also introduce the key methods available for stroke studies in zebrafish, which may drive future mechanistic studies in the pursuit of discovering novel therapeutic targets for stroke patients.

Fish-Ing for Enhancers in the Heart

Precise control of gene expression is crucial to ensure proper development and biological functioning of an organism. Enhancers are non-coding DNA elements which play an essential role in regulating gene expression. They contain specific sequence motifs serving as binding sites for transcription factors which interact with the basal transcription machinery at their target genes. Heart development is regulated by intricate gene regulatory network ensuring precise spatiotemporal gene expression program. Mutations affecting enhancers have been shown to result in devastating forms of congenital heart defect. Therefore, identifying enhancers implicated in heart biology and understanding their mechanism is key to improve diagnosis and therapeutic options. Despite their crucial role, enhancers are poorly studied, mainly due to a lack of reliable way to identify them and determine their function. Nevertheless, recent technological advances have allowed rapid progress in enhancer discovery. Model organisms such as the zebrafish have contributed significant insights into the genetics of heart development through enabling functional analyses of genes and their regulatory elements in vivo. Here, we summarize the current state of knowledge on heart enhancers gained through studies in model organisms, discuss various approaches to discover and study their function, and finally suggest methods that could further advance research in this field.

Does hypoxia-inducible factor 1α play a role in regulating cutaneous oxygen flux in larval zebrafish (Danio rerio)?

Previous studies have demonstrated that hypoxia tolerance is improved in zebrafish (Danio rerio) larvae after prior exposure to lowered ambient O₂ levels. Such improved hypoxia performance was attributed in part, to increased levels of hypoxia-inducible factor 1α (Hif-1α) exerting downstream effects on various physiological processes including promotion of trunk skin angiogenesis. Since O₂ uptake ([Formula: see text]) in larvae is facilitated largely by O₂ diffusion across the skin, enhanced cutaneous vascularization is expected to enhance [Formula: see text] during hypoxia and thus contribute to improved hypoxia tolerance. In this study, we used the scanning micro-optrode technique together with quantification of cutaneous vascularity in wild types (WT) and Hif-1α knockouts (hif1aa^-/-ab^-/-) to test the hypothesis that improved hypoxia tolerance after hypoxia acclimation in larvae at 4 or 7 days post-fertilization (dpf) was associated with Hif-1α-dependent increases in skin vascularity and regional cutaneous O₂ fluxes (JO₂). Hypoxia tolerance, as determined by measurements of critical PO₂ (P_crit), was unaltered by hypoxia pre-exposure in larvae at 4 dpf and there were no significant differences in P_crit between WT and hif1aa^-/-ab^-/- larvae at this developmental stage. However, at 7 dpf there was a significant effect of genotype with WT larvae showing a lower P_crit than hif1aa^-/-ab^-/- larvae, an effect that was being driven by a reduced P_crit in the WT larvae after hypoxia pre-exposure (19.2 ± 1.9 mmHg) compared to hif1aa^-/-ab^-/- fish (35.5 ± 3.5 mmHg). Regardless of genotype, pre-exposure status or developmental age, JO₂ decreased along the body in the anterior-to-posterior direction. Neither hypoxia pre-exposure nor genotype affected JO₂ at any region along the body. The lack of any effect of hypoxia pre-exposure or genotype on JO₂ was consistent with the lack of any effect on skin vascularity as measured in Tg(fli1:EGFP)^yl transgenic larvae. Thus, the decreased hypoxia performance (increased P_crit) at 7 dpf in the hif1aa^-/-ab^-/- larvae did not appear to be reliant on changes in trunk vascularity or cutaneous O₂ diffusion.

Zebrafish Hif3α modulates erythropoiesis via regulation of gata1 to facilitate hypoxia tolerance

The hypoxia-inducible factors 1α and 2α (HIF1α and HIF2α) are master regulators of the cellular response to O_2. In addition to HIF1α and HIF2α, HIF3α is another identified member of the HIFα family. Even though the question of whether some HIF3α isoforms have transcriptional activity or repressive activity is still under debate, it is evident that the full length of HIF3α acts as a transcription factor. However, its function in hypoxia signaling is largely unknown. Here, we show that loss of hif3 a in zebrafish reduced hypoxia tolerance. Further assays indicated that erythrocyte number was decreased because red blood cell maturation was impeded by hif3 a disruption. We found that gata1 expression was downregulated in hif3 a null zebrafish, as were several hematopoietic marker genes, including alas2, band3, hbae1, hbae3 and hbbe1 Hif3α recognized the hypoxia response element located in the promoter of gata1 and directly bound to the promoter to transactivate gata1 expression. Our results suggested that hif3 a facilities hypoxia tolerance by modulating erythropoiesis via gata1 regulation.

Zebrafish for thrombocytopoiesis- and hemostasis-related researches and disorders

Platelets play vital roles in hemostasis, inflammation, and vascular biology. Platelets are also active participants in the immune responses. As vertebrates, zebrafish have a highly conserved hematopoietic system in the developmental, cellular, functional, biochemical, and genetic levels with mammals. Thrombocytes in zebrafish are functional homologs of mammalian platelets. Here, we summarized thrombocyte development, function, and related research techniques in zebrafish, and reviewed available zebrafish models of platelet-associated disorders, including congenital amegakaryocytic thrombocytopenia, inherited thrombocytopenia, essential thrombocythemia, and blood coagulation disorders such as gray platelet syndrome. These elegant zebrafish models and methods are crucial for understanding the molecular and genetic mechanisms of thrombocyte development and function, and provide deep insights into related human disease pathophysiology and drug development.

The NOTCH1-dependent HIF1α/VGLL4/IRF2BP2 oxygen sensing pathway triggers erythropoiesis terminal differentiation

Hypoxia is widely considered as a limiting factor in vertebrate embryonic development, which requires adequate oxygen delivery for efficient energy metabolism, while nowadays some researches have revealed that hypoxia can induce stem cells so as to improve embryonic development. Erythroid differentiation is the oxygen delivery method employed by vertebrates at the very early step of embryo development, however, the mechanism how erythroid progenitor cell was triggered into mature erythrocyte is still not clear. In this study, after detecting the upregulation of vgll4b in response to oxygen levels, we generated vgll4b mutant zebrafish using CRISPR/Cas9, and verified the resulting impaired heme and dysfunctional erythroid terminal differentiation phenotype. Neither the vgll4b-deficient nor the γ-secretase inhibitor IX (DAPT)-adapted zebrafish were able to mediate HIF1α-induced heme generation. In addition, we showed that vgll4b mutant zebrafish were associated with an impaired erythroid phenotype, induced by the downregulation of alas2, which could be rescued by irf2bp2 depletion. Further mechanistic studies revealed that zebrafish VGLL4 sequesters IRF2BP2, thereby inhibiting its repression of alas2 expression and heme biosynthesis. These processes occur primarily via the VGLL4 TDU1 and IRF2BP2 ring finger domains. Our study also indicates that VGLL4 is a key player in the mediation of NOTCH1-dependent HIF1α-regulated erythropoiesis and can be sensitively regulated by oxygen concentrations. On the other hand, VGLL4 is a pivotal regulator of heme biosynthesis and erythroid terminal differentiation, which collectively improve oxygen metabolism.

Zebrafish as a model system to delineate the role of heme and iron metabolism during erythropoiesis

Coordination of iron acquisition and heme synthesis is required for effective erythropoiesis. The small teleost zebrafish (Danio rerio) is an ideal vertebrate animal model to replicate various aspects of human physiology and provides an efficient and cost-effective way to model human pathophysiology. Importantly, zebrafish erythropoiesis largely resembles mammalian erythropoiesis. Gene discovery by large-scale forward mutagenesis screening has identified key components in heme and iron metabolism. Reverse genetic screens, using morpholino-knockdown and CRISPR/Cas9, coupled with the genetic tractability of the developing embryo have further accelerated functional studies. Ultimately, the ex utero development of zebrafish embryos combined with their transparency and developmental plasticity could provide a deeper understanding of the role of iron and heme metabolism during early vertebrate embryonic development.

The splicing factor Sf3b1 regulates erythroid maturation and proliferation via TGFβ signaling in zebrafish

The spliceosomal component Splicing Factor 3B, subunit 1 (SF3B1) is one of the most prevalently mutated factors in the bone marrow failure disorder myelodysplastic syndrome. There is a strong clinical correlation between SF3B1 mutations and erythroid defects, such as refractory anemia with ringed sideroblasts, but the role of SF3B1 in normal erythroid development is largely unknown. Loss-of-function zebrafish mutants for sf3b1 develop a macrocytic anemia. Here, we explore the underlying mechanism for anemia associated with sf3b1 deficiency in vivo. We found that sf3b1 mutant erythroid progenitors display a G0/G1 cell-cycle arrest with mutant erythrocytes showing signs of immaturity. RNA-sequencing analysis of sf3b1 mutant erythroid progenitors revealed normal expression of red blood cell regulators such as gata1, globin genes, and heme biosynthetic factors, but upregulation of genes in the transforming growth factor β (TGFβ) pathway. As TGFβ signaling is a known inducer of quiescence, the data suggest that activation of the pathway could trigger sf3b1 deficiency-induced anemia via cell-cycle arrest. Indeed, we found that inhibition of TGFβ signaling released the G0/G1 block in erythroid progenitors. Surprisingly, removal of this checkpoint enhanced rather than suppressed the anemia, indicating that the TGFβ-mediated cell-cycle arrest is protective for sf3b1-mutant erythrocytes. Together, these data suggest that macrocytic anemia arising from Sf3b1 deficiency is likely due to pleiotropic and distinct effects on cell-cycle progression and maturation.

Ezh2 promotes clock function and hematopoiesis independent of histone methyltransferase activity in zebrafish

EZH2 is a subunit of polycomb repressive complex 2 (PRC2) that silences gene transcription via H3K27me3 and was shown to be essential for mammalian liver circadian regulation and hematopoiesis through gene silencing. Much less, however, is known about how Ezh2 acts in live zebrafish. Here, we show that zebrafish ezh2 is regulated directly by the circadian clock via both E-box and RORE motif, while core circadian clock genes per1a, per1b, cry1aa and cry1ab are down-regulated in ezh2 null mutant and ezh2 morphant zebrafish, and either knockdown or overexpression of ezh2 alters locomotor rhythms, indicating that Ezh2 is required for zebrafish circadian regulation. In contrast to its canonical silencing function, zebrafish Ezh2 up-regulates these key circadian clock genes independent of histone methyltransferase activity by directly binding to key circadian clock proteins. Similarly, Ezh2 contributes to hematopoiesis by enhancing expression of hematopoietic genes such as cmyb and lck. Together, our findings demonstrate for the first time that Ezh2 acts in both circadian regulation and hematopoiesis independent of silencing PRC2.

Loss of atrx cooperates with p53-deficiency to promote the development of sarcomas and other malignancies

The SWI/SNF-family chromatin remodeling protein ATRX is a tumor suppressor in sarcomas, gliomas and other malignancies. Its loss of function facilitates the alternative lengthening of telomeres (ALT) pathway in tumor cells, while it also affects Polycomb repressive complex 2 (PRC2) silencing of its target genes. To further define the role of inactivating ATRX mutations in carcinogenesis, we knocked out atrx in our previously reported p53/nf1-deficient zebrafish line that develops malignant peripheral nerve sheath tumors and gliomas. Complete inactivation of atrx using CRISPR/Cas9 was lethal in developing fish and resulted in an alpha-thalassemia-like phenotype including reduced alpha-globin expression. In p53/nf1-deficient zebrafish neither peripheral nerve sheath tumors nor gliomas showed accelerated onset in atrx+/- fish, but these fish developed various tumors that were not observed in their atrx+/+ siblings, including epithelioid sarcoma, angiosarcoma, undifferentiated pleomorphic sarcoma and rare types of carcinoma. These cancer types are included in the AACR Genie database of human tumors associated with mutant ATRX, indicating that our zebrafish model reliably mimics a role for ATRX-loss in the early pathogenesis of these human cancer types. RNA-seq of p53/nf1- and p53/nf1/atrx-deficient tumors revealed that down-regulation of telomerase accompanied ALT-mediated lengthening of the telomeres in atrx-mutant samples. Moreover, inactivating mutations in atrx disturbed PRC2-target gene silencing, indicating a connection between ATRX loss and PRC2 dysfunction in cancer development.

Somatic mutations in genes coding for epigenetic regulators such as ATRX are found across a diverse group of cancer types, suggesting their broad relevance in tumor induction and progression. However, tumors that have been linked to these chromatin remodelers can arise in many different molecular and cellular contexts, requiring studies with new experimental models to understand the extent and mechanisms of tumor development mediated by these regulatory proteins. Thus, we analyzed the tumor suppressive role of atrx in zebrafish that already harbored inactivating mutations of p53 and nf1. Homozygous deletion of atrx was lethal in developing fish, whereas the partial loss of this gene (atrx+/-) within the p53/nf1-deficient background led to a diverse spectrum of tumors not observed in animals that were wildtype for atrx, including epithelioid sarcoma, angiosarcoma, and rare carcinomas. Most of the cancer types we identified correspond to human tumors in the ATRX-mutant tumor sample cohort within the AACR Genie database, attesting to the relevance of our findings to human cancer. Further analysis revealed downregulation of telomerase during the lengthening of the telomeres through the ALT pathway, and disturbed function of the polycomb repressive complex 2 as key mechanistic components underlying atrx-linked tumorigenesis. These results demonstrate how a p53/nf1 compromised genetic background combined with ATRX haploinsufficiency leads to a broad spectrum of sarcomas and carcinomas associated with loss of this chromatin modulator.

bif1, a new BMP signaling inhibitor, regulates embryonic hematopoiesis in the zebrafish

Hematopoiesis maintains the entire blood system, and dysregulation of this process can lead to malignancies (leukemia), immunodeficiencies or red blood cell diseases (anemia, polycythemia vera). We took advantage of the zebrafish model that shares most of the genetic program involved in hematopoiesis with mammals to characterize a new gene of unknown function, si:ch73-299h12.2, which is expressed in the erythroid lineage during primitive, definitive and adult hematopoiesis. This gene, required during primitive and definitive erythropoiesis, encodes a C2H2 zinc-finger protein that inhibits BMP signaling. We therefore named this gene blood-inducing factor 1 and BMP inhibitory factor 1 (bif1). We identified a bif1 ortholog in Sinocyclocheilus rhinocerous, another fish, and in the mouse genome. Both genes also inhibit BMP signaling when overexpressed in zebrafish. In conclusion, we have deorphanized a new zebrafish gene of unknown function: bif1 codes for a zinc-finger protein that inhibits BMP signaling and also regulates primitive erythropoiesis and definitive hematopoiesis.

Integrated zebrafish-based tests as an investigation strategy for water quality assessment

Water pollution risks to human health and the environment are emerging as serious concerns in the European Union and worldwide. With the aim to achieve good ecological and chemical status of all European water bodies, the "European Water Framework Directive" (WFD) was enacted. With the framework, bioanalytical techniques have been recognized as an important aspect. However, there are limitations to the application of bioassays directly for water quality assessment. Such approaches often fail to identify pollutants of concern, since the defined priority and monitored pollutants often fail to explain the observed toxicity. In this study, we integrated an effect-based risk assessment with a zebrafish-based investigation strategy to evaluate water sample extracts and fractions collected from the Danube. Four tiered bioassays were implemented, namely RNA-level gene expression assay, protein-level ethoxyresorufin-O-deethylase (EROD) assay, cell-level micronucleus assay and organism-level fish embryo test (FET). The results show that teratogenicity and lethality during embryonic development might be induced by molecular or cellular damages mediated by the aryl hydrocarbon receptor (AhR) -mediated activity, estrogenic activity and genotoxic activity. With the combination of high-throughput fractionation, this effect-based strategy elucidated the major responsible mixtures of each specific toxic response. In particularly, the most toxic mixture in faction F4, covering a log Kow range from 2.83 to 3.42, was composed by 12 chemicals, which were then evaluated as a designed mixture. Our study applied tiered bioassays with zebrafish to avoid interspecies differences and highlights effect-based approaches to address toxic mixtures in water samples. This strategy can be applied for large throughput screenings to support the main toxic compounds identification in water quality assessment.

Rescue of hematopoietic stem/progenitor cells formation in plcg1 zebrafish mutant

Hematopoietic stem/progenitor cells (HSPC) in zebrafish emerge from the aortic hemogenic endothelium (HE) and migrate towards the caudal hematopoietic tissue (CHT), where they expand and differentiate during definitive hematopoiesis. Phospholipase C gamma 1 (Plcγ1) has been implicated for hematopoiesis in vivo and in vitro and is also required to drive arterial and HSPC formation. Genetic mutation in plcg1-/- (y10 allele) completely disrupts the aortic blood flow, specification of arterial fate, and HSPC formation in zebrafish embryos. We previously demonstrated that ginger treatment promoted definitive hematopoiesis via Bmp signaling. In this paper, we focus on HSPC development in plcg1-/- mutants and show that ginger/10-gingerol (10-G) can rescue the expression of arterial and HSPC markers in the HE and CHT in plcg1-/- mutant embryos. We demonstrate that ginger can induce scl/runx1 expression, and that rescued HE fate is dependent on Bmp and Notch. Bmp and Notch are known to regulate nitric oxide (NO) production and NO can induce hematopoietic stem cell fate. We show that ginger produces a robust up-regulation of NO. Taken together, we suggest in this paper that Bmp, Notch and NO are potential players that mediate the effect of ginger/10-G for rescuing the genetic defects in blood vessel specification and HSPC formation in plcg1-/- mutants. Understanding the molecular mechanisms of HSPC development in vivo is critical for understanding HSPC expansion, which will have a positive impact in regenerative medicine.

The zebrafish: A fintastic model for hematopoietic development and disease

Hematopoiesis is a complex process with a variety of different signaling pathways influencing every step of blood cell formation from the earliest precursors to final differentiated blood cell types. Formation of blood cells is crucial for survival. Blood cells carry oxygen, promote organ development and protect organs in different pathological conditions. Hematopoietic stem and progenitor cells (HSPCs) are responsible for generating all adult differentiated blood cells. Defects in HSPCs or their downstream lineages can lead to anemia and other hematological disorders including leukemia. The zebrafish has recently emerged as a powerful vertebrate model system to study hematopoiesis. The developmental processes and molecular mechanisms involved in zebrafish hematopoiesis are conserved with higher vertebrates, and the genetic and experimental accessibility of the fish and the optical transparency of its embryos and larvae make it ideal for in vivo analysis of hematopoietic development. Defects in zebrafish hematopoiesis reliably phenocopy human blood disorders, making it a highly attractive model system to screen small molecules to design therapeutic strategies. In this review, we summarize the key developmental processes and molecular mechanisms of zebrafish hematopoiesis. We also discuss recent findings highlighting the strengths of zebrafish as a model system for drug discovery against hematopoietic disorders. This article is categorized under: Adult Stem Cells, Tissue Renewal, and Regeneration > Stem Cell Differentiation and Reversion Vertebrate Organogenesis > Musculoskeletal and Vascular Nervous System Development > Vertebrates: Regional Development Comparative Development and Evolution > Organ System Comparisons Between Species.

How the expression of green fluorescent protein and human cardiac actin in the heart influences cardiac function and aerobic performance in zebrafish Danio rerio

The present study examined how the expression of enhanced green fluorescent protein (eGFP) and human cardiac actin (ACTC) in zebrafish Danio rerio influences embryonic heart rate (R_H ) and the swim performance and metabolic rate of adult fish. Experiments with the adults involved determining the critical swimming speed (U_crit , the highest speed sustainable and measure of aerobic capacity) while measuring oxygen consumption. Two different transgenic D. rerio lines were examined: one expressed eGFP in the heart (tg(cmlc:egfp)), while the second expressed ACTC in the heart and eGFP throughout the body (tg(cmlc:actc,ba:egfp)). It was found that R_H was significantly lower in the tg(cmlc:actc,ba:egfp) embryos 4 days post-fertilization compared to wild-type (WT) and tg(cmlc:egfp). The swim experiments demonstrated that there was no significant difference in U_crit between the transgenic lines and the wild-type fish, but metabolic rate and cost of transport (oxygen used to travel a set distance) was nearly two-fold higher in the tg(cmlc:actc,ba:egfp) fish compared to WT at their respective U_crit . These results suggest that the expression of ACTC in the D. rerio heart and the expression of eGFP throughout the animal, alters cardiac function in the embryo and reduces the aerobic efficiency of the animal at high levels of activity.

Single-cell RNA-sequencing uncovers transcriptional states and fate decisions in haematopoiesis

The success of marker-based approaches for dissecting haematopoiesis in mouse and human is reliant on the presence of well-defined cell surface markers specific for diverse progenitor populations. An inherent problem with this approach is that the presence of specific cell surface markers does not directly reflect the transcriptional state of a cell. Here, we used a marker-free approach to computationally reconstruct the blood lineage tree in zebrafish and order cells along their differentiation trajectory, based on their global transcriptional differences. Within the population of transcriptionally similar stem and progenitor cells, our analysis reveals considerable cell-to-cell differences in their probability to transition to another committed state. Once fate decision is executed, the suppression of transcription of ribosomal genes and upregulation of lineage-specific factors coordinately controls lineage differentiation. Evolutionary analysis further demonstrates that this haematopoietic programme is highly conserved between zebrafish and higher vertebrates.

Modeling human diseases: an education in interactions and interdisciplinary approaches

Traditionally, most investigators in the biomedical arena exploit one model system in the course of their careers. Occasionally, an investigator will switch models. The selection of a suitable model system is a crucial step in research design. Factors to consider include the accuracy of the model as a reflection of the human disease under investigation, the numbers of animals needed and ease of husbandry, its physiology and developmental biology, and the ability to apply genetics and harness the model for drug discovery. In my lab, we have primarily used the zebrafish but combined it with other animal models and provided a framework for others to consider the application of developmental biology for therapeutic discovery. Our interdisciplinary approach has led to many insights into human diseases and to the advancement of candidate drugs to clinical trials. Here, I draw on my experiences to highlight the importance of combining multiple models, establishing infrastructure and genetic tools, forming collaborations, and interfacing with the medical community for successful translation of basic findings to the clinic.

Zebrafish B Cell Development without a Pre-B Cell Stage, Revealed by CD79 Fluorescence Reporter Transgenes

CD79a and CD79b proteins associate with Ig receptors as integral signaling components of the B cell Ag receptor complex. To study B cell development in zebrafish, we isolated orthologs of these genes and performed in situ hybridization, finding that their expression colocalized with IgH-μ in the kidney, which is the site of B cell development. CD79 transgenic lines were made by linking the promoter and upstream regulatory segments of CD79a and CD79b to enhanced GFP to identify B cells, as demonstrated by PCR analysis of IgH-μ expression in sorted cells. We crossed these CD79-GFP lines to a recombination activating gene (Rag)2:mCherry transgenic line to identify B cell development stages in kidney marrow. Initiation of CD79:GFP expression in Rag2:mCherry⁺ cells and the timing of Ig H and L chain expression revealed simultaneous expression of both IgH-μ- and IgL-κ-chains, without progressing through the stage of IgH-μ-chain alone. Rag2:mCherry⁺ cells without CD79:GFP showed the highest Rag1 and Rag2 mRNAs compared with CD79a and CD79b:GFP⁺ B cells, which showed strongly reduced Rag mRNAs. Thus, B cell development in zebrafish does not go through a Rag^hi CD79⁺IgH-μ⁺ pre-B cell stage, different from mammals. After the generation of CD79:GFP⁺ B cells, decreased CD79 expression occurred upon differentiation to Ig secretion, as detected by alteration from membrane to secreted IgH-μ exon usage, similar to in mammals. This confirmed a conserved role for CD79 in B cell development and differentiation, without the requirement of a pre-B cell stage in zebrafish.

Loss of the homologous recombination gene rad51 leads to Fanconi anemia-like symptoms in zebrafish

RAD51 is an indispensable homologous recombination protein, necessary for strand invasion and crossing over. It has recently been designated as a Fanconi anemia (FA) gene, following the discovery of two patients carrying dominant-negative mutations. FA is a hereditary DNA-repair disorder characterized by various congenital abnormalities, progressive bone marrow failure, and cancer predisposition. In this report, we describe a viable vertebrate model of RAD51 loss. Zebrafish rad51 loss-of-function mutants developed key features of FA, including hypocellular kidney marrow, sensitivity to cross-linking agents, and decreased size. We show that some of these symptoms stem from both decreased proliferation and increased apoptosis of embryonic hematopoietic stem and progenitor cells. Comutation of p53 was able to rescue the hematopoietic defects seen in the single mutants, but led to tumor development. We further demonstrate that prolonged inflammatory stress can exacerbate the hematological impairment, leading to an additional decrease in kidney marrow cell numbers. These findings strengthen the assignment of RAD51 as a Fanconi gene and provide more evidence for the notion that aberrant p53 signaling during embryogenesis leads to the hematological defects seen later in life in FA. Further research on this zebrafish FA model will lead to a deeper understanding of the molecular basis of bone marrow failure in FA and the cellular role of RAD51.

γ2 and γ1AP-1 complexes: Different essential functions and regulatory mechanisms in clathrin-dependent protein sorting

γ2 adaptin is homologous to γ1, but is only expressed in vertebrates while γ1 is found in all eukaryotes. We know little about γ2 functions and their relation to γ1. γ1 is an adaptin of the heterotetrameric AP-1 complexes, which sort proteins in and do form clathrin-coated transport vesicles and they also regulate maturation of early endosomes. γ1 knockout mice develop only to blastocysts and thus γ2 does not compensate γ1-deficiency in development. γ2 has not been classified as a clathrin-coated vesicle adaptor protein in proteome analyses and functions for monomeric γ2 in endosomal protein sorting have been proposed, but adaptin interaction studies suggested formation of heterotetrameric AP-1/γ2 complexes. We detected γ2 at the trans-Golgi network, on peripheral vesicles and identified γ2 clathrin-coated vesicles in mice. Ubiquitous σ1A and tissue-specific σ1B adaptins bind γ2 and γ1. σ1B knockout in mice does not effect γ1/σ1A AP-1 levels, but γ2/σ1A AP-1 levels are increased in brain and adipocytes. Also γ2 is essential in development. In zebrafish AP-1/γ2 and AP-1/γ1 fulfill different, essential functions in brain and the vascular system.

Caspase-mediated apoptosis induction in zebrafish cerebellar Purkinje neurons

The zebrafish is a well-established model organism in which to study in vivo mechanisms of cell communication, differentiation and function. Existing cell ablation methods are either invasive or they rely on the cellular expression of prokaryotic enzymes and the use of antibiotic drugs as cell death-inducing compounds. We have recently established a novel inducible genetic cell ablation system based on tamoxifen-inducible Caspase 8 activity, thereby exploiting mechanisms of cell death intrinsic to most cell types. Here, we prove its suitability in vivo by monitoring the ablation of cerebellar Purkinje cells (PCs) in transgenic zebrafish that co-express the inducible caspase and a fluorescent reporter. Incubation of larvae in tamoxifen for 8 h activated endogenous Caspase 3 and cell death, whereas incubation for 16 h led to the near-complete loss of PCs by apoptosis. We observed synchronous cell death autonomous to the PC population and phagocytosing microglia in the cerebellum, reminiscent of developmental apoptosis in the forebrain. Thus, induction of apoptosis through targeted activation of caspase by tamoxifen (ATTAC^TM) further expands the repertoire of genetic tools for conditional interrogation of cellular functions.

Differentiation of Induced Pluripotent Stem Cells to Lentoid Bodies Expressing a Lens Cell-Specific Fluorescent Reporter

Curative approaches for eye cataracts and other eye abnormalities, such as myopia and hyperopia currently suffer from a lack of appropriate models. Here, we present a new approach for in vitro growth of lentoid bodies from induced pluripotent stem (iPS) cells as a tool for ophthalmological research. We generated a transgenic mouse line with lens-specific expression of a fluorescent reporter driven by the alphaA crystallin promoter. Fetal fibroblasts were isolated from transgenic fetuses, reprogrammed to iPS cells, and differentiated to lentoid bodies exploiting the specific fluorescence of the lens cell-specific reporter. The employment of cell type-specific reporters for establishing and optimizing differentiation in vitro seems to be an efficient and generally applicable approach for developing differentiation protocols for desired cell populations.

Spliceosomal component Sf3b1 is essential for hematopoietic differentiation in zebrafish

SF3B1 (Splicing factor 3b, subunit 1) is one of the most commonly mutated factors in myelodysplastic syndrome (MDS). Although the genetic correlation between SF3B1 mutations and MDS etiology are quite strong, no in vivo model currently exists to explore how SF3B1 loss alters blood cell development. Using zebrafish mutants, we show here that proper function of Sf3b1 is required for all hematopoietic lineages. As in MDS patients, zebrafish sf3b1 mutants develop a macrocytic-anemia-like phenotype due to a block in maturation at a late progenitor stage. The mutant embryos also develop neutropenia, because their primitive myeloid cells fail to mature and turn on differentiation markers such as l-plastin and myeloperoxidase. In contrast, production of definitive hematopoietic stem and progenitor cells (HSPCs) from hemogenic endothelial cells within the dorsal aorta is greatly diminished, whereas arterial endothelial cells are correctly fated. Notch signaling, imperative for the endothelial-to-hematopoietic transition, is also normal, indicating that HSPC induction is blocked in sf3b1 mutants downstream or independent of Notch signaling. The data demonstrate that Sf3b1 function is necessary during key differentiation fate decisions in multiple blood cell types. Zebrafish sf3b1 mutants offer a novel animal model with which to explore the role of splicing in hematopoietic development and provide an excellent in vivo system with which to delve into the question of why and how Sf3b1 dysfunction is detrimental to hematopoietic differentiation, which could improve MDS diagnosis and treatment.

Cyp2aa9 regulates haematopoietic stem cell development in zebrafish

Definitive haematopoiesis occurs during the lifetime of an individual, which continuously replenishes all blood and immune cells. During embryonic development, haematopoietic stem cell (HSC) formation is tightly controlled by growth factors, signalling molecules and transcription factors. But little is known about roles of the cytochrome P450 (CYP) 2 family member in the haematopoiesis. Here we report characterization and functional studies of Cyp2aa9, a novel zebrafish Cyp2 family member. And demonstrate that the cyp2aa9 is required for the HSC formation and homeostasis. Knockdown of cyp2aa9 by antisense morpholino oligos resulted the definitive HSC development is defective and the Wnt/β-catenin activity becomes reduced. The impaired HSC formation caused by cyp2aa9 morpholino can be rescued by administration of PGE2 through the cAMP/PKA pathway. Furthermore, the in vivo PGE2 level decreases in the cyp2aa9 morphants, and none of the PGE2 precursors is able to rescue phenotypes in the Cyp2aa9-deficient embryos. Taken together, these data indicate that Cyp2aa9 is functional in the step of PGE2 synthesis from PGH2, thus promoting Wnt activation and definitive HSC development.

Cellular dissection of zebrafish hematopoiesis

Zebrafish as a model system have been instrumental in understanding early vertebrate development, especially of the hematopoietic system. The external development of zebrafish and their genetic amenability have allowed in-depth studies of multiple blood cell types and their respective genetic regulation. This chapter highlights some new data in zebrafish hematopoiesis regarding primitive and definitive hematopoiesis in the embryonic and adult fish, allowing the isolation of prospective progenitor subsets. It also highlights assays developed to examine the function of these progenitors in vivo and in vitro, allowing an evolutionary understanding of the hematopoietic system and how zebrafish can be better utilized as a model system for a multitude of hematopoietic disorders.

Advances in the Study of Heart Development and Disease Using Zebrafish

Animal models of cardiovascular disease are key players in the translational medicine pipeline used to define the conserved genetic and molecular basis of disease. Congenital heart diseases (CHDs) are the most common type of human birth defect and feature structural abnormalities that arise during cardiac development and maturation. The zebrafish, Danio rerio, is a valuable vertebrate model organism, offering advantages over traditional mammalian models. These advantages include the rapid, stereotyped and external development of transparent embryos produced in large numbers from inexpensively housed adults, vast capacity for genetic manipulation, and amenability to high-throughput screening. With the help of modern genetics and a sequenced genome, zebrafish have led to insights in cardiovascular diseases ranging from CHDs to arrhythmia and cardiomyopathy. Here, we discuss the utility of zebrafish as a model system and summarize zebrafish cardiac morphogenesis with emphasis on parallels to human heart diseases. Additionally, we discuss the specific tools and experimental platforms utilized in the zebrafish model including forward screens, functional characterization of candidate genes, and high throughput applications.

Zebrafish as an Emerging Model Organism to Study Angiogenesis in Development and Regeneration

Angiogenesis is the process through which new blood vessels are formed from preexisting ones and plays a critical role in several conditions including embryonic development, tissue repair and disease. Moreover, enhanced therapeutic angiogenesis is a major goal in the field of regenerative medicine and efficient vascularization of artificial tissues and organs is one of the main hindrances in the implementation of tissue engineering approaches, while, on the other hand, inhibition of angiogenesis is a key therapeutic target to inhibit for instance tumor growth. During the last decades, the understanding of cellular and molecular mechanisms involved in this process has been matter of intense research. In this regard, several in vitro and in vivo models have been established to visualize and study migration of endothelial progenitor cells, formation of endothelial tubules and the generation of new vascular networks, while assessing the conditions and treatments that either promote or inhibit such processes. In this review, we address and compare the most commonly used experimental models to study angiogenesis in vitro and in vivo. In particular, we focus on the implementation of the zebrafish (Danio rerio) as a model to study angiogenesis and discuss the advantages and not yet explored possibilities of its use as model organism.

Zebrafish and Medaka: new model organisms for modern biomedical research

Although they are primitive vertebrates, zebrafish (Danio rerio) and medaka (Oryzias latipes) have surpassed other animals as the most used model organisms based on their many advantages. Studies on gene expression patterns, regulatory cis-elements identification, and gene functions can be facilitated by using zebrafish embryos via a number of techniques, including transgenesis, in vivo transient assay, overexpression by injection of mRNAs, knockdown by injection of morpholino oligonucleotides, knockout and gene editing by CRISPR/Cas9 system and mutagenesis. In addition, transgenic lines of model fish harboring a tissue-specific reporter have become a powerful tool for the study of biological sciences, since it is possible to visualize the dynamic expression of a specific gene in the transparent embryos. In particular, some transgenic fish lines and mutants display defective phenotypes similar to those of human diseases. Therefore, a wide variety of fish model not only sheds light on the molecular mechanisms underlying disease pathogenesis in vivo but also provides a living platform for high-throughput screening of drug candidates. Interestingly, transgenic model fish lines can also be applied as biosensors to detect environmental pollutants, and even as pet fish to display beautiful fluorescent colors. Therefore, transgenic model fish possess a broad spectrum of applications in modern biomedical research, as exampled in the following review.

Diverse of Erythropoiesis Responding to Hypoxia and Low Environmental Temperature in Vertebrates

Erythrocytes are responsible for transporting oxygen to tissue and are essential for the survival of almost all vertebrate animals. Circulating erythrocyte counts are tightly regulated and respond to erythrocyte mass and oxygen tension. Since the discovery of erythropoietin, the erythropoietic responses to environment and tissue oxygen tension have been investigated in mice and human. Moreover, it has recently become increasingly clear that various environmental stresses could induce the erythropoiesis via various modulating systems, while all vertebrates live in various environments and habitually adapt to environmental stress. Therefore, it is considered that investigations of erythropoiesis in vertebrates provide a lead to the various erythropoietic responses to environmental stress. This paper comparatively introduces the present understanding of erythropoiesis in vertebrates. Indeed, there is a wide range of variations in vertebrates' erythropoiesis. This paper also focused on erythropoietic responses to environmental stress, hypoxia, and lowered temperature in vertebrates.

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 models of cardiovascular diseases and their applications in herbal medicine research

The zebrafish (Danio rerio) has recently become a powerful animal model for cardiovascular research and drug discovery due to its ease of maintenance, genetic manipulability and ability for high-throughput screening. Recent advances in imaging techniques and generation of transgenic zebrafish have greatly facilitated in vivo analysis of cellular events of cardiovascular development and pathogenesis. More importantly, recent studies have demonstrated the functional similarity of drug metabolism systems between zebrafish and humans, highlighting the clinical relevance of employing zebrafish in identifying lead compounds in Chinese herbal medicine with potential beneficial cardiovascular effects. This paper seeks to summarise the scope of zebrafish models employed in cardiovascular studies and the application of these research models in Chinese herbal medicine to date.