Transplantable tumor lines generated in clonal zebrafish

A syngeneic spontaneous zebrafish model of tp53-deficient, EGFRvIII, and PI3KCAH1047R-driven glioblastoma reveals inhibitory roles for inflammation during tumor initiation and relapse in vivo

High-throughput vertebrate animal model systems for the study of patient-specific biology and new therapeutic approaches for aggressive brain tumors are currently lacking, and new approaches are urgently needed. Therefore, to build a patient-relevant in vivo model of human glioblastoma, we expressed common oncogenic variants including activated human EGFRvIII and PI3KCAH1047R under the control of the radial glial-specific promoter her4.1 in syngeneic tp53 loss-of-function mutant zebrafish. Robust tumor formation was observed prior to 45 days of life, and tumors had a gene expression signature similar to human glioblastoma of the mesenchymal subtype, with a strong inflammatory component. Within early stage tumor lesions, and in an in vivo and endogenous tumor microenvironment, we visualized infiltration of phagocytic cells, as well as internalization of tumor cells by mpeg1.1:EGFP+ microglia/macrophages, suggesting negative regulatory pressure by pro-inflammatory cell types on tumor growth at early stages of glioblastoma initiation. Furthermore, CRISPR/Cas9-mediated gene targeting of master inflammatory transcription factors irf7 or irf8 led to increased tumor formation in the primary context, while suppression of phagocyte activity led to enhanced tumor cell engraftment following transplantation into otherwise immune-competent zebrafish hosts. Altogether, we developed a genetically relevant model of aggressive human glioblastoma and harnessed the unique advantages of zebrafish including live imaging, high-throughput genetic and chemical manipulations to highlight important tumor-suppressive roles for the innate immune system on glioblastoma initiation, with important future opportunities for therapeutic discovery and optimizations.

The posterity of Zebrafish in paradigm of in vivo molecular toxicological profiling

The aggrandised advancement in utility of advanced day-to-day materials and nanomaterials has raised serious concern on their biocompatibility with human and other biotic members. In last few decades, understanding of toxicity of these materials has been given the centre stage of research using many in vitro and in vivo models. Zebrafish (Danio rerio), a freshwater fish and a member of the minnow family has garnered much attention due to its distinct features, which make it an important and frequently used animal model in various fields of embryology and toxicological studies. Given that fertilization and development of zebrafish eggs take place externally, they serve as an excellent model organism for studying early developmental stages. Moreover, zebrafish possess a comparable genetic composition to humans and share almost 70% of their genes with mammals. This particular model organism has become increasingly popular, especially for developmental research. Moreover, it serves as a link between in vitro studies and in vivo analysis in mammals. It is an appealing choice for vertebrate research, when employing high-throughput methods, due to their small size, swift development, and relatively affordable laboratory setup. This small vertebrate has enhanced comprehension of pathobiology and drug toxicity. This review emphasizes on the recent developments in toxicity screening and assays, and the new insights gained about the toxicity of drugs through these assays. Specifically, the cardio, neural, and, hepatic toxicology studies inferred by applications of nanoparticles have been highlighted.

Zebrafish-based platform for emerging bio-contaminants and virus inactivation research

Emerging bio-contaminants such as viruses have affected health and environment settings of every country. Viruses are the minuscule entities resulting in severe contagious diseases like SARS, MERS, Ebola, and avian influenza. Recent epidemic like the SARS-CoV-2, the virus has undergone mutations strengthen them and allowing to escape from the remedies. Comprehensive knowledge of viruses is essential for the development of targeted therapeutic and vaccination treatments. Animal models mimicking human biology like non-human primates, rats, mice, and rabbits offer competitive advantage to assess risk of viral infections, chemical toxins, nanoparticles, and microbes. However, their economic maintenance has always been an issue. Furthermore, the redundancy of experimental results due to aforementioned aspects is also in examine. Hence, exploration for the alternative animal models is crucial for risk assessments. The current review examines zebrafish traits and explores the possibilities to monitor emerging bio-contaminants. Additionally, a comprehensive picture of the bio contaminant and virus particle invasion and abatement mechanisms in zebrafish and human cells is presented. Moreover, a zebrafish model to investigate the emerging viruses such as coronaviridae and poxviridae has been suggested.

Precision Medicine in Head and Neck Cancers: Genomic and Preclinical Approaches

Head and neck cancers (HNCs) represent the sixth most widespread malignancy worldwide. Surgery, radiotherapy, chemotherapeutic and immunotherapeutic drugs represent the main clinical approaches for HNC patients. Moreover, HNCs are characterised by an elevated mutational load; however, specific genetic mutations or biomarkers have not yet been found. In this scenario, personalised medicine is showing its efficacy. To study the reliability and the effects of personalised treatments, preclinical research can take advantage of next-generation sequencing and innovative technologies that have been developed to obtain genomic and multi-omic profiles to drive personalised treatments. The crosstalk between malignant and healthy components, as well as interactions with extracellular matrices, are important features which are responsible for treatment failure. Preclinical research has constantly implemented in vitro and in vivo models to mimic the natural tumour microenvironment. Among them, 3D systems have been developed to reproduce the tumour mass architecture, such as biomimetic scaffolds and organoids. In addition, in vivo models have been changed over the last decades to overcome problems such as animal management complexity and time-consuming experiments. In this review, we will explore the new approaches aimed to improve preclinical tools to study and apply precision medicine as a therapeutic option for patients affected by HNCs.

Carcinogenesis Models Using Small Fish

Experimental animals are indispensable in life science-related research, including cancer studies. After rats and mice, small fishes, such as zebrafish and medaka, are the second most frequently used model species. Fish models have some advantageous physical characteristics that make them suitable for research, including their small size, some transparency, genetic manipulability, ease of handling, and highly ortholog correspondence with humans. This review introduces technological advances in carcinogenesis model production using small fish. Carcinogenesis model production begins with chemical carcinogenesis, followed by mutagenesis. Gene transfer technology has made it possible to incorporate various mechanisms that act on cancer-related genes in individuals. For example, scientists may now spatiotemporally control gene expression in a single fish through methods including the localization of an expression site via a tissue-specific promoter and expression control using light, heat, or a chemical substance. In addition, genome editing technology is realizing more specific and more efficient gene disruption than conventional mutagenesis, in which the disruption of the gene of interest depends on chance. These technological advances have improved animal models and will soon create carcinogenesis models that better mimic human pathology. We conclude by discussing future expectations for cancer research using small fish.

Zebrafish as a Model for Anticancer Nanomedicine Studies

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

Protocol for rapid assessment of the efficacy of novel Wnt inhibitors using zebrafish models

Dysregulation of Wnt signaling is a hallmark of many cancers, and the development of effective, non-toxic small-molecule Wnt inhibitors is desirable. Off-target toxicities of new compounds are typically tested in mouse models, which is both costly and time consuming. Here, we present a rapid and inexpensive protocol to determine the in vivo toxicity and efficacy of novel Wnt inhibitors in zebrafish using a combination of a fluorescence reporter assay as well as eye rescue and fin regeneration assays. These experiments are completed within 1 week to rapidly narrow drug candidates before moving to more expensive pre-clinical testing. For complete details on the use and execution of this protocol, please refer to Zhang et al. (2020).

Benefits of Zebrafish Xenograft Models in Cancer Research

As a promising in vivo tool for cancer research, zebrafish have been widely applied in various tumor studies. The zebrafish xenograft model is a low-cost, high-throughput tool for cancer research that can be established quickly and requires only a small sample size, which makes it favorite among researchers. Zebrafish patient-derived xenograft (zPDX) models provide promising evidence for short-term clinical treatment. In this review, we discuss the characteristics and advantages of zebrafish, such as their transparent and translucent features, the use of vascular fluorescence imaging, the establishment of metastatic and intracranial orthotopic models, individual pharmacokinetics measurements, and tumor microenvironment. Furthermore, we introduce how these characteristics and advantages are applied other in tumor studies. Finally, we discuss the future direction of the use of zebrafish in tumor studies and provide new ideas for the application of it.

Generation of Functional Genetic Study Models in Zebrafish Using CRISPR-Cas9

CRISPR-Cas9 is a method for genome editing that can be used efficiently for in vivo applications; the basic implementation of this method is used to generate genome site-directed sequence eliminations. Here we describe a protocol for genome editing using CRISPR-Cas9 in zebrafish (Danio rerio) one-cell embryos.

Genetic Engineering of Zebrafish in Cancer Research

Zebrafish (Danio rerio) is an excellent model to study a wide diversity of human cancers. In this review, we provide an overview of the genetic and reverse genetic toolbox allowing the generation of zebrafish lines that develop tumors. The large spectrum of genetic tools enables the engineering of zebrafish lines harboring precise genetic alterations found in human patients, the generation of zebrafish carrying somatic or germline inheritable mutations or zebrafish showing conditional expression of the oncogenic mutations. Comparative transcriptomics demonstrate that many of the zebrafish tumors share molecular signatures similar to those found in human cancers. Thus, zebrafish cancer models provide a unique in vivo platform to investigate cancer initiation and progression at the molecular and cellular levels, to identify novel genes involved in tumorigenesis as well as to contemplate new therapeutic strategies.

Zebrafish In Vivo Models of Cancer and Metastasis

Metastasis, the dispersal of cancer cells from a primary tumor to secondary sites within the body, is the leading cause of cancer-related death. Animal models have been an indispensable tool to investigate the complex interactions between the cancer cells and the tumor microenvironment during the metastatic cascade. The zebrafish (Danio rerio) has emerged as a powerful vertebrate model for studying metastatic events in vivo. The zebrafish has many attributes including ex-utero development, which facilitates embryonic manipulation, as well as optically transparent tissues, which enables in vivo imaging of fluorescently labeled cells in real time. Here, we summarize the techniques which have been used to study cancer biology and metastasis in the zebrafish model organism, including genetic manipulation and transgenesis, cell transplantation, live imaging, and high-throughput compound screening. Finally, we discuss studies using the zebrafish, which have complemented and benefited metastasis research.

Zebrafish Models of Cancer-New Insights on Modeling Human Cancer in a Non-Mammalian Vertebrate

Zebrafish (Danio rerio) is a valuable non-mammalian vertebrate model widely used to study development and disease, including more recently cancer. The evolutionary conservation of cancer-related programs between human and zebrafish is striking and allows extrapolation of research outcomes obtained in fish back to humans. Zebrafish has gained attention as a robust model for cancer research mainly because of its high fecundity, cost-effective maintenance, dynamic visualization of tumor growth in vivo, and the possibility of chemical screening in large numbers of animals at reasonable costs. Novel approaches in modeling tumor growth, such as using transgene electroporation in adult zebrafish, could improve our knowledge about the spatial and temporal control of cancer formation and progression in vivo. Looking at genetic as well as epigenetic alterations could be important to explain the pathogenesis of a disease as complex as cancer. In this review, we highlight classic genetic and transplantation models of cancer in zebrafish as well as provide new insights on advances in cancer modeling. Recent progress in zebrafish xenotransplantation studies and drug screening has shown that zebrafish is a reliable model to study human cancer and could be suitable for evaluating patient-derived xenograft cell invasiveness. Rapid, large-scale evaluation of in vivo drug responses and kinetics in zebrafish could undoubtedly lead to new applications in personalized medicine and combination therapy. For all of the above-mentioned reasons, zebrafish is approaching a future of being a pre-clinical cancer model, alongside the mouse. However, the mouse will continue to be valuable in the last steps of pre-clinical drug screening, mostly because of the highly conserved mammalian genome and biological processes.

Tackling Acute Lymphoblastic Leukemia-One Fish at a Time

Despite advancements in the diagnosis and treatment of acute lymphoblastic leukemia (ALL), a need for improved strategies to decrease morbidity and improve cure rates in relapsed/refractory ALL still exists. Such approaches include the identification and implementation of novel targeted combination regimens, and more precise upfront patient risk stratification to guide therapy. New curative strategies rely on an understanding of the pathobiology that derives from systematically dissecting each cancer’s genetic and molecular landscape. Zebrafish models provide a powerful system to simulate human diseases, including leukemias and ALL specifically. They are also an invaluable tool for genetic manipulation, in vivo studies, and drug discovery. Here, we highlight and summarize contributions made by several zebrafish T-ALL models and newer zebrafish B-ALL models in translating the underlying genetic and molecular mechanisms operative in ALL, and also highlight their potential utility for drug discovery. These models have laid the groundwork for increasing our understanding of the molecular basis of ALL to further translational and clinical research endeavors that seek to improve outcomes in this important cancer.

Vangl2/RhoA Signaling Pathway Regulates Stem Cell Self-Renewal Programs and Growth in Rhabdomyosarcoma

Tumor growth and relapse are driven by tumor propagating cells (TPCs). However, mechanisms regulating TPC fate choices, maintenance, and self-renewal are not fully understood. Here, we show that Van Gogh-like 2 (Vangl2), a core regulator of the non-canonical Wnt/planar cell polarity (Wnt/PCP) pathway, affects TPC self-renewal in rhabdomyosarcoma (RMS)-a pediatric cancer of muscle. VANGL2 is expressed in a majority of human RMS and within early mononuclear progenitor cells. VANGL2 depletion inhibited cell proliferation, reduced TPC numbers, and induced differentiation of human RMS in vitro and in mouse xenografts. Using a zebrafish model of embryonal rhabdomyosarcoma (ERMS), we determined that Vangl2 expression enriches for TPCs and promotes their self-renewal. Expression of constitutively active and dominant-negative isoforms of RHOA revealed that it acts downstream of VANGL2 to regulate proliferation and maintenance of TPCs in human RMS. Our studies offer insights into pathways that control TPCs and identify new potential therapeutic targets.

The side population enriches for leukemia-propagating cell activity and Wnt pathway expression in zebrafish acute lymphoblastic leukemia

Cancer stem cells have been strongly linked to resistance and relapse in many malignancies. However, purifying them from within the bulk tumor has been challenging, so their precise genetic and functional characteristics are not well defined. The side population assay exploits the ability of some cells to efflux Hoechst dye via ATP-binding cassette transporters. Stem cells have increased expression of these transporters and this assay has been shown to enrich for stem cells in various tissues and cancers. This study identifies the side population within a zebrafish model of acute lymphoblastic leukemia and correlates the frequency of side population cells with the frequency of leukemia stem cells (more precisely referred to as leukemia-propagating cells within our transplantation model). In addition, the side population within the leukemia evolves with serial transplantation, increasing in tandem with leukemia-propagating cell frequency over subsequent generations. Sorted side population cells from these tumors are enriched for leukemia-propagating cells and have enhanced engraftment compared to sorted non-side population cells when transplanted into syngeneic recipients. RNA-sequencing analysis of sorted side population cells compared to non-side population cells identified a shared expression profile within the side population and pathway analysis yielded Wnt-signaling as the most overrepresented. Gene set enrichment analysis showed that stem cell differentiation and canonical Wnt-signaling were significantly upregulated in the side population. Overall, these results demonstrate that the side population in zebrafish acute lymphoblastic leukemia significantly enriches for leukemia-propagating cells and identifies the Wnt pathway as a likely genetic driver of leukemia stem cell fate.

Genetic Models of Leukemia in Zebrafish

The zebrafish animal model is gaining increasing popularity as a tool for studying human disease. Over the past 15 years, many models of leukemia and other hematological malignancies have been developed in the zebrafish. These confer some significant advantages over similar models in other animals and systems, representing a powerful resource for investigation of the molecular basis of human leukemia. This review discusses the various zebrafish models of lymphoid and myeloid leukemia available, the major discoveries that have been made possible by them, and opportunities for future exploration.

tp53 deficiency causes a wide tumor spectrum and increases embryonal rhabdomyosarcoma metastasis in zebrafish

The TP53 tumor-suppressor gene is mutated in >50% of human tumors and Li-Fraumeni patients with germ line inactivation are predisposed to developing cancer. Here, we generated tp53 deleted zebrafish that spontaneously develop malignant peripheral nerve-sheath tumors, angiosarcomas, germ cell tumors, and an aggressive Natural Killer cell-like leukemia for which no animal model has been developed. Because the tp53 deletion was generated in syngeneic zebrafish, engraftment of fluorescent-labeled tumors could be dynamically visualized over time. Importantly, engrafted tumors shared gene expression signatures with predicted cells of origin in human tissue. Finally, we showed that tp53^del/del enhanced invasion and metastasis in kRAS^G12D-induced embryonal rhabdomyosarcoma (ERMS), but did not alter the overall frequency of cancer stem cells, suggesting novel pro-metastatic roles for TP53 loss-of-function in human muscle tumors. In summary, we have developed a Li-Fraumeni zebrafish model that is amenable to large-scale transplantation and direct visualization of tumor growth in live animals.

Development of a novel zebrafish xenograft model in ache mutants using liver cancer cell lines

Acetylcholinesterase (AChE), an enzyme responsible for degradation of acetylcholine, has been identified as a prognostic marker in liver cancer. Although in vivo Ache tumorigenicity assays in mouse are present, no established liver cancer xenograft model in zebrafish using an ache mutant background exists. Herein, we developed an embryonic zebrafish xenograft model using epithelial (Hep3B) and mesenchymal (SKHep1) liver cancer cell lines in wild-type and ache sb55 sibling mutant larvae after characterization of cholinesterase expression and activity in cell lines and zebrafish larvae. The comparison of fluorescent signal reflecting tumor size at 3-days post-injection (dpi) revealed an enhanced tumorigenic potential and a reduced migration capacity in cancer cells injected into homozygous ache sb55 mutants when compared with the wild-type. Increased tumor load was confirmed using an ALU based tumor DNA quantification method modified for use in genotyped xenotransplanted zebrafish embryos. Confocal microscopy using the Huh7 cells stably expressing GFP helped identify the distribution of tumor cells in larvae. Our results imply that acetylcholine accumulation in the microenvironment directly or indirectly supports tumor growth in liver cancer. Use of this model system for drug screening studies holds potential in discovering new cholinergic targets for treatment of liver cancers.

Developmental Toxicity of Diethylnitrosamine in Zebrafish Embryos/Juveniles Related to Excessive Oxidative Stress

Diethylnitrosamine (DEN) is present in food, water, and daily supplies and is regarded as a toxicant of carcinogenicity. The developmental toxicity of DEN has been rarely reported as yet. In this study, zebrafish were exposed to different concentrations of DEN at 6 h post-fertilization (hpf) to access embryonic toxicity of the compound. The results show that DEN resulted in negative effects of hatching rate, heartbeat, body length, and spontaneous movement. Deformities, including notochord malformation, pericardium edema, embryonic membrane turbidity, tail hypoplasia, yolk sac deformity, and growth retardation, happened during exposure period. Moreover, production of reactive oxygen species (ROS) significantly increased after DEN treatment. Then, alterations of the expression level of oxidative stress-related genes were observed in our results. To our knowledge, this is the first study concerning the effect of DEN on zebrafish. And from the information of our research, we speculated that development toxicity of DEN should be related to the excessive oxidative stress.

Management and potentialities of primary cancer cultures in preclinical and translational studies

The use of patient-derived primary cell cultures in cancer preclinical assays has increased in recent years. The management of resected tumor tissue remains complex and a number of parameters must be respected to obtain complete sample digestion and optimal vitality yield. We provide an overview of the benefits of correct primary cell culture management using different preclinical methodologies, and describe the pros and cons of this model with respect to other kinds of samples. One important advantage is that the heterogeneity of the cell populations composing a primary culture partially reproduces the tumor microenvironment and crosstalk between malignant and healthy cells, neither of which is possible with cell lines. Moreover, the use of patient-derived specimens in innovative preclinical technologies, such as 3D systems or bioreactors, represents an important opportunity to improve the translational value of the results obtained. In vivo models could further our understanding of the crosstalk between tumor and other tissues as they enable us to observe the systemic and biological interactions of a complete organism. Although engineered mice are the most common model used in this setting, the zebrafish (Danio rerio) species has recently been recognized as an innovative experimental system. In fact, the transparent body and incomplete immune system of zebrafish embryos are especially useful for evaluating patient-derived tumor tissue interactions in healthy hosts. In conclusion, ex vivo systems represent an important tool for cancer research, but samples require correct manipulation to maximize their translational value.

Transplantation of Zebrafish Pediatric Brain Tumors into Immune-competent Hosts for Long-term Study of Tumor Cell Behavior and Drug Response

Tumor cell transplantation is an important technique to define the mechanisms controlling cancer cell growth, migration, and host response, as well as to assess potential patient response to therapy. Current methods largely depend on using syngeneic or immune-compromised animals to avoid rejection of the tumor graft. Such methods require the use of specific genetic strains that often prevent the analysis of immune-tumor cell interactions and/or are limited to specific genetic backgrounds. An alternative method in zebrafish takes advantage of an incompletely developed immune system in the embryonic brain before 3 days, where tumor cells are transplanted for use in short-term assays (i.e., 3 to 10 days). However, these methods cause host lethality, which prevents the long-term study of tumor cell behavior and drug response. This protocol describes a simple and efficient method for the long-term orthotopic transplantation of zebrafish brain tumor tissue into the fourth ventricle of a 2-day-old immune-competent zebrafish. This method allows: 1) long-term study of tumor cell behaviors, such as invasion and dissemination; 2) durable tumor response to drugs; and 3) re-transplantation of tumors for the study of tumor evolution and/or the impact of different host genetic backgrounds. In summary, this technique allows cancer researchers to assess engraftment, invasion, and growth at distant sites, as well as to perform chemical screens and cell competition assays over many months. This protocol can be extended to studies of other tumor types and can be used to elucidate mechanisms of chemoresistance and metastasis.

Isolation of the Side Population in Myc-induced T-cell Acute Lymphoblastic Leukemia in Zebrafish

Heterogeneous cell populations, from either healthy or malignant tissues, may contain a population of cells characterized by a differential ability to efflux the DNA-binding dye Hoechst 33342. This "side population" of cells can be identified using flow cytometric methods after the Hoechst 33342 dye is excited by an ultraviolet (UV) laser. The side population of many cell types contains stem- or progenitor-like cells. However, not all cell types have an identifiable side population. Danio rerio, zebrafish, have a robust in vivo model of T-cell acute lymphoblastic leukemia (T-ALL), but whether these zebrafish T-ALLs have a side population is unknown. The method described here outlines how to isolate the side population cells in zebrafish T-ALL. To begin, the T-ALL in zebrafish is generated via the microinjection of tol2 plasmids into one-cell stage embryos. Once the tumors have grown to a stage at which they expand into more than half of the animal's body, the T-ALL cells can be harvested. The cells are then stained with Hoechst 33342 and examined by flow cytometry for side population cells. This method has broad applications in zebrafish T-ALL research. While there are no known cell surface markers in zebrafish that confirm whether these side population cells are cancer stem cell-like, in vivo functional transplantation assays are possible. Furthermore, single-cell transcriptomics could be applied to identify the genetic features of these side population cells.

Invasive Behavior of Human Breast Cancer Cells in Embryonic Zebrafish

In many cases, cancer patients do not die of a primary tumor, but rather because of metastasis. Although numerous rodent models are available for studying cancer metastasis in vivo, other efficient, reliable, low-cost models are needed to quickly access the potential effects of (epi)genetic changes or pharmacological compounds. As such, we illustrate and explain the feasibility of xenograft models using human breast cancer cells injected into zebrafish embryos to support this goal. Under the microscope, fluorescent proteins or chemically labeled human breast cancer cells are transplanted into transgenic zebrafish embryos, Tg (fli:EGFP), at the perivitelline space or duct of Cuvier (Doc) 48 h after fertilization. Shortly afterwards, the temporal-spatial process of cancer cell invasion, dissemination, and metastasis in the living fish body is visualized under a fluorescent microscope. The models using different injection sites, i.e., perivitelline space or Doc are complementary to one another, reflecting the early stage (intravasation step) and late stage (extravasation step) of the multistep metastatic cascade of events. Moreover, peritumoral and intratumoral angiogenesis can be observed with the injection into the perivitelline space. The entire experimental period is no more than 8 days. These two models combine cell labeling, micro-transplantation, and fluorescence imaging techniques, enabling the rapid evaluation of cancer metastasis in response to genetic and pharmacological manipulations.

Tumor immunology viewed from alternative animal models-the Xenopus story

A PURPOSE OF REVIEW

Nonmammalian comparative animal models are important not only to gain fundamental evolutionary understanding of the complex interactions of tumors with the immune system, but also to better predict the applicability of novel immunotherapeutic approaches to humans. After reviewing recent advances in developing alternative models, we focus on the amphibian Xenopus laevis and its usefulness in deciphering the perplexing roles of MHC class I-like molecules and innate (i)T cells in tumor immunity.

B RECENT FINDINGS

Experiments using MHC-defined inbred and cloned animals, tumor cell lines, effective reagents, sequenced genomes, and adapted gene editing techniques in Xenopus, have revealed that the critical involvement of class I-like molecules and iT cells in tumor immunity has been conserved during evolution.

C SUMMARY

Comparative studies with the X. laevis tumor immunity model can contribute to the development of better and more efficient cancer immunotherapies.

Myogenic regulatory transcription factors regulate growth in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) is a pediatric malignacy of muscle with myogenic regulatory transcription factors MYOD and MYF5 being expressed in this disease. Consensus in the field has been that expression of these factors likely reflects the target cell of transformation rather than being required for continued tumor growth. Here, we used a transgenic zebrafish model to show that Myf5 is sufficient to confer tumor-propagating potential to RMS cells and caused tumors to initiate earlier and have higher penetrance. Analysis of human RMS revealed that MYF5 and MYOD are mutually-exclusively expressed and each is required for sustained tumor growth. ChIP-seq and mechanistic studies in human RMS uncovered that MYF5 and MYOD bind common DNA regulatory elements to alter transcription of genes that regulate muscle development and cell cycle progression. Our data support unappreciated and dominant oncogenic roles for MYF5 and MYOD convergence on common transcriptional targets to regulate human RMS growth.

DOI:http://dx.doi.org/10.7554/eLife.19214.001

Single-cell imaging of normal and malignant cell engraftment into optically clear prkdc-null SCID zebrafish

Cell transplantation into immunodeficient mice has revolutionized our understanding of regeneration, stem cell self-renewal, and cancer; yet models for direct imaging of engrafted cells has been limited. Here, we characterize zebrafish with mutations in recombination activating gene 2 (rag2), DNA-dependent protein kinase (prkdc), and janus kinase 3 (jak3). Histology, RNA sequencing, and single-cell transcriptional profiling of blood showed that rag2 hypomorphic mutant zebrafish lack T cells, whereas prkdc deficiency results in loss of mature T and B cells and jak3 in T and putative Natural Killer cells. Although all mutant lines engraft fluorescently labeled normal and malignant cells, only the prkdc mutant fish reproduced as homozygotes and also survived injury after cell transplantation. Engraftment into optically clear casper, prkdc-mutant zebrafish facilitated dynamic live cell imaging of muscle regeneration, repopulation of muscle stem cells within their endogenous niche, and muscle fiber fusion at single-cell resolution. Serial imaging approaches also uncovered stochasticity in fluorescently labeled leukemia regrowth after competitive cell transplantation into prkdc mutant fish, providing refined models to assess clonal dominance and progression in the zebrafish. Our experiments provide an optimized and facile transplantation model, the casper, prkdc mutant zebrafish, for efficient engraftment and direct visualization of fluorescently labeled normal and malignant cells at single-cell resolution.

Imaging Cancer Angiogenesis and Metastasis in a Zebrafish Embryo Model

Tumor angiogenesis and metastasis are key steps of cancer progression. In vitro and animal model studies have contributed to partially elucidating the mechanisms involved in these processes and in developing therapies. Besides the improvements in fundamental research and the optimization of therapeutic regimes, cancer still remains a major health threatening condition and therefore the development of new models is needed. The zebrafish is a powerful tool to study tumor angiogenesis and metastasis, because it allows the visualization of fluorescently labelled tumor cells inducing vessel remodeling, disseminating and invading surrounding tissues in a whole transparent embryo. The embryo model has also been used to address the contribution of the tumor stroma in sustaining tumor angiogenesis and spreading. Simultaneously, new anti-angiogenic drugs and compounds affecting malignant cell survival and migration can be tested by simply adding the compound into the water of living embryos. Therefore the zebrafish model offers the opportunity to gain more knowledge on cancer angiogenesis and metastasis in vivo with the final aim of providing new translational insights into therapeutic approaches to help patients.

The Zebrafish Xenograft Platform: Evolution of a Novel Cancer Model and Preclinical Screening Tool

Animal xenografts of human cancers represent a key preclinical tool in the field of cancer research. While mouse xenografts have long been the gold standard, investigators have begun to use zebrafish (Danio rerio) xenotransplantation as a relatively rapid, robust and cost-effective in vivo model of human cancers. There are several important methodological considerations in the design of an informative and efficient zebrafish xenotransplantation experiment. Various transgenic fish strains have been created that facilitate microscopic observation, ranging from the completely transparent casper fish to the Tg(fli1:eGFP) fish that expresses fluorescent GFP protein in its vascular tissue. While human cancer cell lines have been used extensively in zebrafish xenotransplantation studies, several reports have also used primary patient samples as the donor material. The zebrafish is ideally suited for transplanting primary patient material by virtue of the relatively low number of cells required for each embryo (between 50 and 300 cells), the absence of an adaptive immune system in the early zebrafish embryo, and the short experimental timeframe (5-7 days). Following xenotransplantation into the fish, cells can be tracked using in vivo or ex vivo measures of cell proliferation and migration, facilitated by fluorescence or human-specific protein expression. Importantly, assays have been developed that allow for the reliable detection of in vivo human cancer cell growth or inhibition following administration of drugs of interest. The zebrafish xenotransplantation model is a unique and effective tool for the study of cancer cell biology.

Zebrafish xenotransplantation as a tool for in vivo cancer study

Zebrafish represents a powerful model for cancer research. Particularly, the xenotransplantation of human cancer cells into zebrafish has enormous potential for further evaluation of cancer progression and drug discovery. Various cancer models have been established in adults, juveniles and embryos of zebrafish. This xenotransplantation zebrafish model provides a unique opportunity to monitor cancer proliferation, tumor angiogenesis, metastasis, self-renewal of cancer stem cells, and drug response in real time in vivo. This review summarizes the use of zebrafish as a model for cancer xenotransplantation, and highlights its advantages and disadvantages.

Expansion of the Known Host Range of the Microsporidium, Pseudoloma neurophilia

The microsporidium, Pseudoloma neurophilia, is the most common infectious organism found in laboratory zebrafish colonies. Many currently used zebrafish lines originally came from pet store fish, and the initial description of P. neurophilia came from zebrafish obtained from a retail pet store. However, as P. neurophilia has not been described from wild-caught zebrafish, whether P. neurophilia is a natural pathogen of zebrafish is an open question. The pooling of fish of different species in the aquarium fish trade is common and a generalist parasite could be transmitted to novel hosts in this scenario. We determined that P. neurophilia can infect seven species of fishes from five families by cohabitation with infected zebrafish: Betta splendens, Xiphophorus maculatus, Devario aequipinnatus, Pimephales promelas, Oryzias latipes, Carassius auratus and Paracheirodon innesi. Infections in these fishes were histologically similar to those of zebrafish. We include a case report of a laboratory population of fathead minnows with naturally acquired P. neurophilia infections. With such a broad host range, including several fish families, other laboratory fishes should be screened routinely for this and other microsporidian parasites.

Allograft Cancer Cell Transplantation in Zebrafish

Allogeneic cell transplantation is the transfer of cells from one individual into another of the same species and has become an indispensable technique for studying development, immunology, regeneration and cancer biology. In experimental settings, tumor cell engraftment into immunologically competent recipients has greatly increased our understanding of the mechanisms that drive self-renewal, progression and metastasis in vivo. Zebrafish have quickly emerged as a powerful genetic model of cancer that has benefited greatly from allogeneic transplantation. Efficient engraftment can be achieved by transplanting cells into either early larval stage zebrafish that have not yet developed a functional acquired immune system or adult zebrafish following radiation or chemical ablation of the immune system. Alternatively, transplantation can be completed in adult fish using either clonal syngeneic strains or newly-generated immune compromised zebrafish models that have mutations in genes required for proper immune cell function. Here, we discuss the current state of cell transplantation as it pertains to zebrafish cancer and the available models used for dissecting important processes underlying cancer. We will also use the zebrafish model to highlight the power of cell transplantation, including its capacity to dynamically assess functional heterogeneity within individual cancer cells, visualize cancer progression and evolution, assess tumor-propagating potential and self-renewal, image cancer cell invasion and dissemination and identify novel therapies for treating cancer.

Histone Deacetylase Inhibitors Antagonize Distinct Pathways to Suppress Tumorigenesis of Embryonal Rhabdomyosarcoma

Embryonal rhabdomyosarcoma (ERMS) is the most common soft tissue cancer in children. The prognosis of patients with relapsed or metastatic disease remains poor. ERMS genomes show few recurrent mutations, suggesting that other molecular mechanisms such as epigenetic regulation might play a major role in driving ERMS tumor biology. In this study, we have demonstrated the diverse roles of histone deacetylases (HDACs) in the pathogenesis of ERMS by characterizing effects of HDAC inhibitors, trichostatin A (TSA) and suberoylanilide hydroxamic acid (SAHA; also known as vorinostat) in vitro and in vivo. TSA and SAHA suppress ERMS tumor growth and progression by inducing myogenic differentiation as well as reducing the self-renewal and migratory capacity of ERMS cells. Differential expression profiling and pathway analysis revealed downregulation of key oncogenic pathways upon HDAC inhibitor treatment. By gain-of-function, loss-of-function, and chromatin immunoprecipitation (ChIP) studies, we show that Notch1- and EphrinB1-mediated pathways are regulated by HDACs to inhibit differentiation and enhance migratory capacity of ERMS cells, respectively. Our study demonstrates that aberrant HDAC activity plays a major role in ERMS pathogenesis. Druggable targets in the molecular pathways affected by HDAC inhibitors represent novel therapeutic options for ERMS patients.

A fresh look at zebrafish from the perspective of cancer research

Zebrafish represent a vertebrate model organism that has been widely, and increasingly, employed over the last decade in the study of developmental processes, wound healing, microbe-host interactions, and drug screening. With the increase in the laboratory use of zebrafish, several advantages, such as a high genetic homology to humans and transparent embryos, which allow clear disease evaluation, have greatly widened its use as a model for studying tumor development in vivo. The use of zebrafish has been applied in several areas of cancer research, mainly in the following domains: (1) establishing cancer models by carcinogenic chemical, genetic technology, and xenotransplantation; (2) evaluating tumor angiogenesis; (3) studying tumor metastasis; and (4) anti-tumor drug screening and drug toxicity evaluation. In this study, we provide a comprehensive overview of the role of zebrafish in order to underline the advantages of using them as a model organism in cancer research. Several related successful events are also reviewed.

The promise of zebrafish as a chemical screening tool in cancer therapy

Cancer progression in zebrafish recapitulates many aspects of human cancer and as a result, zebrafish have been gaining popularity for their potential use in basic and translational cancer research. Human cancer can be modeled in zebrafish by induction using chemical mutagens, xenotransplantation or by genetic manipulation. Chemical screens based on zebrafish cancer models offer a rapid, powerful and inexpensive means of evaluating the potential of suppression or prevention on cancer. The identification of small molecules through such screens will serve as ideal entry points for novel chemical therapies for cancer treatment. This article outlines advances that have been made within the growing field of zebrafish cancer models and presents their advantages for chemical drug screening.

Normal and malignant muscle cell transplantation into immune compromised adult zebrafish

Zebrafish have become a powerful tool for assessing development, regeneration, and cancer. More recently, allograft cell transplantation protocols have been developed that permit engraftment of normal and malignant cells into irradiated, syngeneic, and immune compromised adult zebrafish. These models when coupled with optimized cell transplantation protocols allow for the rapid assessment of stem cell function, regeneration following injury, and cancer. Here, we present a method for cell transplantation of zebrafish adult skeletal muscle and embryonal rhabdomyosarcoma (ERMS), a pediatric sarcoma that shares features with embryonic muscle, into immune compromised adult rag2(E450fs) homozygous mutant zebrafish. Importantly, these animals lack T cells and have reduced B cell function, facilitating engraftment of a wide range of tissues from unrelated donor animals. Our optimized protocols show that fluorescently labeled muscle cell preparations from α-actin-RFP transgenic zebrafish engraft robustly when implanted into the dorsal musculature of rag2 homozygous mutant fish. We also demonstrate engraftment of fluorescent-transgenic ERMS where fluorescence is confined to cells based on differentiation status. Specifically, ERMS were created in AB-strain myf5-GFP; mylpfa-mCherry double transgenic animals and tumors injected into the peritoneum of adult immune compromised fish. The utility of these protocols extends to engraftment of a wide range of normal and malignant donor cells that can be implanted into dorsal musculature or peritoneum of adult zebrafish.

Histopathological lesions, P-glycoprotein and PCNA expression in zebrafish (Danio rerio) liver after a single exposure to diethylnitrosamine

The presence of carcinogenic compounds in the aquatic environment is a recognized problem. ABC transporters are well known players in the multidrug-resistance (MDR) phenomenon in mammals associated with resistance to chemotherapy, however little is known in fish species. Thus, the aim of this study was to induce hepatic tumours and evaluate long-term effects on P-glycoprotein (P-gp) and proliferating cell nuclear antigen (PCNA) proteins in Danio rerio liver, after exposure to diethylnitrosamine (DEN). Several hepatic histopathological alterations were observed in zebrafish after exposure to DEN including pre-neoplastic lesions 6 and 9 months post-exposure. After 3, 6 and 9 months of exposure to DEN, P-gp and PCNA proteins expression were up-regulated. In conclusion, this study has shown that zebrafish ABC transporters can play a similar role as in human disease, hence zebrafish can be used also as a biological model to investigate in more deep mechanisms involved in disease processes.

Plasmonic nanobubbles as tunable cellular probes for cancer theranostics

This review is focused on a novel cellular probe, the plasmonic nanobubble (PNB), which has the dynamically tunable and multiple functions of imaging, diagnosis, delivery, therapy and, ultimately, theranostics. The concept of theranostics was recently introduced in order to unite the clinically important stages of treatment, namely diagnosis, therapy and therapy guidance, into one single, rapid and highly accurate procedure. Cell level theranostics will have far-reaching implications for the treatment of cancer and other diseases at their earliest stages. PNBs were developed to support cell level theranostics as a new generation of on-demand tunable cellular probes. A PNB is a transient vapor nanobubble that is generated within nanoseconds around an overheated plasmonic nanoparticle with a short laser pulse. In the short term, we expect that PNB technology will be rapidly adaptable to clinical medicine, where the single cell resolution it provides will be critical for diagnosing incipient or residual disease and eliminating cancer cells, while leaving healthy cells intact. This review discusses mechanisms of plasmonic nanobubbles and their biomedical applications with the focus on cancer cell theranostics.

Zebrafish cancer: the state of the art and the path forward

The zebrafish is a recent addition to animal models of human cancer, and studies using this model are rapidly contributing major insights. Zebrafish develop cancer spontaneously, after mutagen exposure and through transgenesis. The tumours resemble human cancers at the histological, gene expression and genomic levels. The ability to carry out in vivo imaging, chemical and genetic screens, and high-throughput transgenesis offers a unique opportunity to functionally characterize the cancer genome. Moreover, increasingly sophisticated modelling of combinations of genetic and epigenetic alterations will allow the zebrafish to complement what can be achieved in other models, such as mouse and human cell culture systems.

Molecular characterization of prosomeric and intraprosomeric subdivisions of the embryonic zebrafish diencephalon

During development of the early neural tube, positional information provided by signaling gradients is translated into a grid of transverse and longitudinal transcription factor expression domains. Transcription factor specification codes defining distinct histogenetic domains within this grid are evolutionarily conserved across vertebrates and may reflect an underlying common vertebrate bauplan. When compared to the rich body of comparative gene expression studies of tetrapods, there is considerably less comparative data available for teleost fish. We used sensitive multicolor fluorescent in situ hybridization to generate a detailed map of regulatory gene expression domains in the embryonic zebrafish diencephalon. The high resolution of this technique allowed us to resolve abutting and overlapping gene expression of different transcripts. We found that the relative topography of gene expression patterns in zebrafish was highly similar to those of orthologous genes in tetrapods and consistent with a three-prosomere organization of the alar and basal diencephalon. Our analysis further demonstrated a conservation of intraprosomeric subdivisions within prosomeres 1, 2, and 3 (p1, p2, and p3). A tripartition of zebrafish p1 was identified reminiscent of precommissural (PcP), juxtacommissural (JcP), and commissural (CoP) pretectal domains of tetrapods. The constructed detailed diencephalic transcription factor gene expression map further identified molecularly distinct thalamic and prethalamic rostral and caudal domains and a prethalamic eminence histogenetic domain in zebrafish. Our comparative gene expression analysis conformed with the idea of a common bauplan for the diencephalon of anamniote and amniote vertebrates from fish to mammals.

Factors affecting people's acceptance of the use of zebrafish and mice in research

The species of laboratory animal used is known to influence people's willingness to support animal-based research. An online experiment was used to test people's willingness to accept the use of zebrafish or mice, two of the most commonly used species, in research involving either induced mutation (specifically, ethyl-N-nitrosourea [ENU] mutagenesis) or genetic modification, with and without regulatory oversight. Participants who were willing to support research on zebrafish (31.9%) were also willing to support the same research on mice. The participants expressed low levels of support for research involving ENU mutagenesis of zebrafish in both unregulated (30.7%) and regulated (38.5%) research programmes. A reason for the rejection of ENU mutagenesis was the perception that the procedure is painful. Some participants expressed a preference for the use of genetically-modified (GM) animal models over ENU mutagenesis, based on the belief that the former involves less pain and improves both the accuracy and efficiency of the animal models. Better informing the public about scientific practice, and scientists about public attitudes, may help reduce the disconnect between scientific practice and societal values.

Emergence of zebrafish models in oncology for validating novel anticancer drug targets and nanomaterials

The in vivo zebrafish models have recently attracted great attention in molecular oncology to investigate multiple genetic alterations associated with the development of human cancers and validate novel anticancer drug targets. Particularly, the transparent zebrafish models can be used as a xenotransplantation system to rapidly assess the tumorigenicity and metastatic behavior of cancer stem and/or progenitor cells and their progenies. Moreover, the zebrafish models have emerged as powerful tools for an in vivo testing of novel anticancer agents and nanomaterials for counteracting tumor formation and metastases and improving the efficacy of current radiation and chemotherapeutic treatments against aggressive, metastatic and lethal cancers.

A proteoliposome containing apolipoprotein A-I mutant (V156K) enhances rapid tumor regression activity of human origin oncolytic adenovirus in tumor-bearing zebrafish and mice

We recently reported that the efficiency of adenoviral gene delivery and virus stability are significantly enhanced when a proteoliposome (PL) containing apolipoprotein (apo) A-I is used in an animal model. In the current study, we tested tumor removal activity of oncolytic adenovirus (Ad) using PL-containing wildtype (WT) or V156K. Oncolytic Ad with or without PL was injected into tumors of zebrafish and nude mice as a Hep3B tumor xenograft model. The V156K-PL-Ad-injected zebrafish, group showed the lowest tumor tissue volume and nucleic acids in the tumor area, whereas injection of Ad alone did not result in adequate removal of tumor activity. Reactive oxygen species (ROS) contents increased two-fold in tumor-bearing zebrafish; however, the V156K-PL-Ad injected group showed a 40% decrease in ROS levels compared to that in normal zebrafish. After reducing the tumor volume with the V156K-PL-Ad injection, the swimming pattern of the zebrafish changed to be more active and energetic. The oncolytic effect of PL-Ad containing either V156K or WT was about two-fold more enhanced in mice than that of Ad alone 34 days after the injection. Immunohistochemical analysis revealed that the PL-Ad-injected groups showed enhanced efficiency of viral delivery with elevated Ad-E1A staining and a diminished number of proliferating tumor cells. Thus, the antitumor effect of oncolytic Ad was strongly enhanced by a PL-containing apoA-I and its mutant (V156K) without causing side effects in mice and zebrafish models.

Through the looking glass: visualizing leukemia growth, migration, and engraftment using fluorescent transgenic zebrafish

Zebrafish have emerged as a powerful model of development and cancer. Human, mouse, and zebrafish malignancies exhibit striking histopathologic and molecular similarities, underscoring the remarkable conservation of genetic pathways required to induce cancer. Zebrafish are uniquely suited for large-scale studies in which hundreds of animals can be used to investigate cancer processes. Moreover, zebrafish are small in size, optically clear during development, and amenable to genetic manipulation. Facile transgenic approaches and new technologies in gene inactivation have provided much needed genomic resources to interrogate the function of specific oncogenic and tumor suppressor pathways in cancer. This manuscript focuses on the unique attribute of labeling leukemia cells with fluorescent proteins and directly visualizing cancer processes in vivo including tumor growth, dissemination, and intravasation into the vasculature. We will also discuss the use of fluorescent transgenic approaches and cell transplantation to assess leukemia-propagating cell frequency and response to chemotherapy.

Histocompatibility and hematopoietic transplantation in the zebrafish

The zebrafish has proven to be an excellent model for human disease, particularly hematopoietic diseases, since these fish make similar types of blood cells as humans and other mammals. The genetic program that regulates the development and differentiation of hematopoietic cells is highly conserved. Hematopoietic stem cells (HSCs) are the source of all the blood cells needed by an organism during its lifetime. Identifying an HSC requires a functional assay, namely, a transplantation assay consisting of multilineage engraftment of a recipient and subsequent serial transplant recipients. In the past decade, several types of hematopoietic transplant assays have been developed in the zebrafish. An understanding of the major histocompatibility complex (MHC) genes in the zebrafish has lagged behind transplantation experiments, limiting the ability to perform unbiased competitive transplantation assays. This paper summarizes the different hematopoietic transplantation experiments performed in the zebrafish, both with and without immunologic matching, and discusses future directions for this powerful experimental model of human blood diseases.

Transplantation in zebrafish

Tissue or cell transplantation has been an extremely valuable technique for studying developmental potential of certain cell population, dissecting cell-environment interaction relationship, identifying stem cells, and many other applications. One key technical requirement for performing transplantation assay is the capability of distinguishing the transplanted donor cells from the endogenous host cells, and tracing the donor cells over time. Zebrafish has emerged as an excellent model organism for performing transplantation assay, thanks to the transparency of embryos during development and even certain adults. Using transgenic techniques and fast-evolving imaging technology, fluorescence-labeled donor cells can be easily identified and studied in vivo. In this chapter, we will first discuss the rationale of different types of zebrafish transplantation in both embryos and adults, and then focus on detailed methods of three types of transplantation: blastula/gastrula transplantation for mosaic analysis, stem cell transplantation, and tumor transplantation.

Zebrafish as a model for the study of human cancer

Zebrafish provide an exciting animal model system for the study of human cancers. During the last few years many zebrafish models of cancer have been generated that recapitulate human hematologic malignancies and solid tumors. Concurrent technological advances have significantly improved the genetic tractability and unique advantage of in vivo imaging in zebrafish, providing a means to dissect the molecular pathways underlying tumor initiation, progression and metastasis. Comparisons of cancer-associated gene expression profiles have demonstrated a high degree of similarity in the gene signatures of specific types of tumor cells in fish and humans, indicating that the contributing genetic pathways leading to cancer are evolutionarily conserved. Furthermore, the high fecundity, optical clarity and small embryo size of zebrafish continue to make it particularly amenable to performing whole-organism small molecule screens to identify targets for therapeutic development. This chapter reviews a wide array of these zebrafish cancer models and illustrates the advantages of the zebrafish system for exploring the molecular mechanisms governing cancer-related cellular processes.