Zebrafish rhabdomyosarcoma reflects the developmental stage of oncogene expression during myogenesis

Zebrafish-A Suitable Model for Rapid Translation of Effective Therapies for Pediatric Cancers

Pediatric cancers are the leading cause of disease-related deaths in children and adolescents. Most of these tumors are difficult to treat and have poor overall survival. Concerns have also been raised about drug toxicity and long-term detrimental side effects of therapies. In this review, we discuss the advantages and unique attributes of zebrafish as pediatric cancer models and their importance in targeted drug discovery and toxicity assays. We have also placed a special focus on zebrafish models of pediatric brain cancers-the most common and difficult solid tumor to treat.

The RRAS2 pathogenic variant (c.67G>T; p. Gly23Cys) produces Noonan syndrome with embryonal rhabdomyosarcoma

BACKGROUND

Noonan syndrome (NS) due to the RRAS2 gene, the pathogenic variant is an extremely rare RASopathies. Our objective was to identify the potential site of RRAS2, combined with the literature review, to find the correlation between clinical phenotype and genotype. De novo missense mutations affect different aspects of the RRAS2 function, leading to hyperactivation of the RAS-MAPK signaling cascade.

METHODS

Conventional G-banding was used to analyze the chromosome karyotype of the patient. Copy number variation sequencing (CNV-seq) was used to detect the chromosomal gene microstructure of the patient and her parents. The exomes of the patient and her parents were sequenced using trio-based whole exome sequencing (trio-WES) technology. The candidate variant was verified by Sanger sequencing. The pathogenicity of the variant was predicted with a variety of bioinformatics tools.

RESULTS

Chromosome analysis of the proband revealed 46, XX, and no abnormality was found by CNV-seq. After sequencing and bioinformatics filtering, the variant of RRAS2(c.67G>T; p. Gly23Cys) was found in the proband, while the mutation was absent in her parents. To the best of our knowledge, our patient was with the typical Noonan syndrome, such as short stature, facial dysmorphism, and developmental delay. Furthermore, our study is the first case of NS with embryonal rhabdomyosarcoma (ERMS) caused by the RRAS2 gene mutation reported in China.

CONCLUSIONS

Our investigations suggested that the heterozygous missense of RRAS2 may be a potential causal variant in a rare cause of Noonan syndrome, expanding our understanding of the causally relevant mutations for this disorder.

Rhabdomyosarcoma: Current Therapy, Challenges, and Future Approaches to Treatment Strategies

Rhabdomyosarcoma is a rare cancer arising in skeletal muscle that typically impacts children and young adults. It is a worldwide challenge in child health as treatment outcomes for metastatic and recurrent disease still pose a major concern for both basic and clinical scientists. The treatment strategies for rhabdomyosarcoma include multi-agent chemotherapies after surgical resection with or without ionization radiotherapy. In this comprehensive review, we first provide a detailed clinical understanding of rhabdomyosarcoma including its classification and subtypes, diagnosis, and treatment strategies. Later, we focus on chemotherapy strategies for this childhood sarcoma and discuss the impact of three mechanisms that are involved in the chemotherapy response including apoptosis, macro-autophagy, and the unfolded protein response. Finally, we discuss in vivo mouse and zebrafish models and in vitro three-dimensional bioengineering models of rhabdomyosarcoma to screen future therapeutic approaches and promote muscle regeneration.

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.

Myogenetic Oligodeoxynucleotides as Anti-Nucleolin Aptamers Inhibit the Growth of Embryonal Rhabdomyosarcoma Cells

Embryonal rhabdomyosarcoma (ERMS) is the muscle-derived tumor retaining myogenic ability. iSN04 and AS1411, which are myogenetic oligodeoxynucleotides (myoDNs) serving as anti-nucleolin aptamers, have been reported to inhibit the proliferation and induce the differentiation of myoblasts. The present study investigated the effects of iSN04 and AS1411 in vitro on the growth of multiple patient-derived ERMS cell lines, ERMS1, KYM1, and RD. RT-PCR and immunostaining revealed that nucleolin was abundantly expressed and localized in nucleoplasm and nucleoli in all ERMS cell lines, similar to myoblasts. Both iSN04 and AS1411 at final concentrations of 10-30 μM significantly decreased the number of all ERMS cells; however, their optimal conditions were different among the cell lines. In all ERMS cell lines, iSN04 at a final concentration of 10 μM markedly reduced the ratio of EdU+ cells, indicating the inhibition of cell proliferation. Quantitative RT-PCR or immunostaining of phosphorylated histone H3 and myosin heavy chain demonstrated that iSN04 suppressed the cell cycle and partially promoted myogenesis but did not induce apoptosis in ERMS cells. Finally, both iSN04 and AS1411 at final concentrations of 10-30 μM disrupted the formation and outgrowth of RD tumorspheres in three-dimensional culture mimicking in vivo tumorigenesis. In conclusion, ERMS cells expressed nucleolin, and their growth was inhibited by the anti-nucleolin aptamers, iSN04 and AS1411, which modulates several cell cycle-related and myogenic gene expression. The present study provides evidence that anti-nucleolin aptamers can be used as nucleic acid drugs for chemotherapy against ERMS.

Clinicopathologic and survival correlates of embryonal rhabdomyosarcoma driven by RAS/RAF mutations

Embryonal rhabdomyosarcoma (ERMS) is the most common subtype of rhabdomyosarcoma (RMS). Among RMS subtypes, ERMS is associated with a favorable outcome with an overall survival of 70% at 5 years for localized disease. The molecular profile of ERMS is heterogeneous, including mostly point mutations in various genes. Therapeutic strategies have remained relatively consistent irrespective of the molecular abnormalities. In this study, we focus on a homogeneous RAS/RAF mutated ERMS subset and correlate with clinicopathologic findings. Twenty-six cases (16 males and 10 females) were identified from screening 98 ERMS, either by targeted DNA sequencing (MSK-IMPACT) or by Sanger sequencing. Fourteen (54%) cases had NRAS mutations, 6 (23%) had KRAS mutations, 5 (19%) had HRAS mutations, and 1 case (4%) had BRAF mutation. Median age at diagnosis was 8 years (range 1-70) with two-thirds occurring in the children. Tumor sites varied with H&N and GU sites accounting for 62% of cases. RAS isoform hot spot mutations predominated: NRAS p.Q61K (57%), KRAS p.G12D (67%), and HRAS (codons 12, 14, and 61). Additional genetic abnormalities were identified in 85% of the RAS-mutated cases. At last follow-up, 29% of patients died of disease and 23% were alive with disease. The 3-year and 5-year survival rates were 75% and 61% respectively. In conclusion, RAS mutations occur in 27% of ERMS, with NRAS mutations encompassing half of the cases. Overall RAS-mutant RMS does not correlate with age or site, but most tumors show an undifferentiated and spindle cell morphology.

Preclinical In Vivo Modeling of Pediatric Sarcoma-Promises and Limitations

Pediatric sarcomas are an extremely heterogeneous group of genetically distinct diseases. Despite the increasing knowledge on their molecular makeup in recent years, true therapeutic advancements are largely lacking and prognosis often remains dim, particularly for relapsed and metastasized patients. Since this is largely due to the lack of suitable model systems as a prerequisite to develop and assess novel therapeutics, we here review the available approaches to model sarcoma in vivo. We focused on genetically engineered and patient-derived mouse models, compared strengths and weaknesses, and finally explored possibilities and limitations to utilize these models to advance both biological understanding as well as clinical diagnosis and therapy.

Reeling in the Zebrafish Cancer Models

Zebrafish are rapidly becoming a leading model organism for cancer research. The genetic pathways driving cancer are highly conserved between zebrafish and humans, and the ability to easily manipulate the zebrafish genome to rapidly generate transgenic animals makes zebrafish an excellent model organism. Transgenic zebrafish containing complex, patient-relevant genotypes have been used to model many cancer types. Here we present a comprehensive review of transgenic zebrafish cancer models as a resource to the field and highlight important areas of cancer biology that have yet to be studied in the fish. The ability to image cancer cells and niche biology in an endogenous tumor makes zebrafish an indispensable model organism in which we can further understand the mechanisms that drive tumorigenesis and screen for potential new cancer therapies.

Modeling the developmental origins of pediatric cancer to improve patient outcomes

In the treatment of children and adolescents with cancer, multimodal approaches combining surgery, chemotherapy and radiation can cure most patients, but may cause lifelong health problems in survivors. Current therapies only modestly reflect increased knowledge about the molecular mechanisms of these cancers. Advances in next-generation sequencing have provided unprecedented cataloging of genetic aberrations in tumors, but understanding how these genetic changes drive cellular transformation, and how they can be effectively targeted, will require multidisciplinary collaboration and preclinical models that are truly representative of the in vivo environment. Here, I discuss some of the key challenges in pediatric cancer from my perspective as a physician-scientist, and touch on some promising new approaches that have the potential to transform our understanding of these diseases.

Summary: This Perspective discusses the special features that make it challenging to develop new therapies for pediatric cancers, and the ways in which collaboration centered on improved models can meet these challenges.

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.

Inflammatory Responses during Tumour Initiation: From Zebrafish Transgenic Models of Cancer to Evidence from Mouse and Man

The zebrafish is now an important model organism for cancer biology studies and provides unique and complementary opportunities in comparison to the mammalian equivalent. The translucency of zebrafish has allowed in vivo live imaging studies of tumour initiation and progression at the cellular level, providing novel insights into our understanding of cancer. Here we summarise the available transgenic zebrafish tumour models and discuss what we have gleaned from them with respect to cancer inflammation. In particular, we focus on the host inflammatory response towards transformed cells during the pre-neoplastic stage of tumour development. We discuss features of tumour-associated macrophages and neutrophils in mammalian models and present evidence that supports the idea that these inflammatory cells promote early stage tumour development and progression. Direct live imaging of tumour initiation in zebrafish models has shown that the intrinsic inflammation induced by pre-neoplastic cells is tumour promoting. Signals mediating leukocyte recruitment to pre-neoplastic cells in zebrafish correspond to the signals that mediate leukocyte recruitment in mammalian tumours. The activation state of macrophages and neutrophils recruited to pre-neoplastic cells in zebrafish appears to be heterogenous, as seen in mammalian models, which provides an opportunity to study the plasticity of innate immune cells during tumour initiation. Although several potential mechanisms are described that might mediate the trophic function of innate immune cells during tumour initiation in zebrafish, there are several unknowns that are yet to be resolved. Rapid advancement of genetic tools and imaging technologies for zebrafish will facilitate research into the mechanisms that modulate leukocyte function during tumour initiation and identify targets for cancer prevention.

Pediatric Cancer Models in Zebrafish

Pediatric cancer is a leading cause of death in children and adolescents. Improvements in pediatric cancer treatment that include the alleviation of long-term adverse effects require a deeper understanding of the genetic, epigenetic, and developmental factors driving these cancers. Here, we review how the unique attributes of the zebrafish model system in embryology, imaging, and scalability have been used to identify new mechanisms of tumor initiation, progression, and relapse and for drug discovery. We focus on zebrafish models of leukemias, neural tumors and sarcomas - the most common and difficult childhood cancers to treat.

Serial Xenotransplantation in NSG Mice Promotes a Hybrid Epithelial/Mesenchymal Gene Expression Signature and Stemness in Rhabdomyosarcoma Cells

Serial xenotransplantation of sorted cancer cells in immunodeficient mice remains the most complex test of cancer stem cell (CSC) phenotype. However, we have demonstrated in various sarcomas that putative CSC surface markers fail to identify CSCs, thereby impeding the isolation of CSCs for subsequent analyses. Here, we utilized serial xenotransplantation of unsorted rhabdomyosarcoma cells in NOD/SCID gamma (NSG) mice as a proof-of-principle platform to investigate the molecular signature of CSCs. Indeed, serial xenotransplantation steadily enriched for rhabdomyosarcoma stem-like cells characterized by enhanced aldehyde dehydrogenase activity and increased colony and sphere formation capacity in vitro. Although the expression of core pluripotency factors (SOX2, OCT4, NANOG) and common CSC markers (CD133, ABCG2, nestin) was maintained over the passages in mice, gene expression profiling revealed gradual changes in several stemness regulators and genes linked with undifferentiated myogenic precursors, e.g., SOX4, PAX3, MIR145, and CDH15. Moreover, we identified the induction of a hybrid epithelial/mesenchymal gene expression signature that was associated with the increase in CSC number. In total, 60 genes related to epithelial or mesenchymal traits were significantly altered upon serial xenotransplantation. In silico survival analysis based on the identified potential stemness-associated genes demonstrated that serial xenotransplantation of unsorted rhabdomyosarcoma cells in NSG mice might be a useful tool for the unbiased enrichment of CSCs and the identification of novel CSC-specific targets. Using this approach, we provide evidence for a recently proposed link between the hybrid epithelial/mesenchymal phenotype and cancer stemness.

Insights into pediatric rhabdomyosarcoma research: Challenges and goals

Overall survival rates for pediatric patients with high-risk or relapsed rhabdomyosarcoma (RMS) have not improved significantly since the 1980s. Recent studies have identified a number of targetable vulnerabilities in RMS, but these discoveries have infrequently translated into clinical trials. We propose streamlining the process by which agents are selected for clinical evaluation in RMS. We believe that strong consideration should be given to the development of combination therapies that add biologically targeted agents to conventional cytotoxic drugs. One example of this type of combination is the addition of the WEE1 inhibitor AZD1775 to the conventional cytotoxic chemotherapeutics, vincristine and irinotecan.

The initiation of puberty in Atlantic salmon brings about large changes in testicular gene expression that are modulated by the energy status

Background

When puberty starts before males reach harvest size, animal welfare and sustainability issues occur in Atlantic salmon (Salmo salar) aquaculture. Hallmarks of male puberty are an increased proliferation activity in the testis and elevated androgen production. Examining transcriptional changes in salmon testis during the transition from immature to maturing testes may help understanding the regulation of puberty, potentially leading to procedures to modulate its start. Since differences in body weight influence, via unknown mechanisms, the chances for entering puberty, we used two feed rations to create body weight differences.

Results

Maturing testes were characterized by an elevated proliferation activity of Sertoli cells and of single undifferentiated spermatogonia. Pituitary gene expression data suggest increased Gnrh receptor and gonadotropin gene expression, potentially responsible for the elevated circulating androgen levels in maturing fish. Transcriptional changes in maturing testes included a broad variety of signaling systems (e.g. Tgfβ, Wnt, insulin/Igf, nuclear receptors), but also, activation of metabolic pathways such as anaerobic metabolism and protection against ROS. Feed restriction lowered the incidence of puberty. In males maturing despite feed restriction, plasma androgen levels were higher than in maturing fish receiving the full ration. A group of 449 genes that were up-regulated in maturing fully fed fish, was up-regulated more prominently in testis from fish maturing under caloric restriction. Moreover, 421 genes were specifically up-regulated in testes from fish maturing under caloric restriction, including carbon metabolism genes, a pathway relevant for nucleotide biosynthesis and for placing epigenetic marks.

Conclusions

Undifferentiated spermatogonia and Sertoli cell populations increased at the beginning of puberty, which was associated with the up-regulation of metabolic pathways (e.g. anaerobic and ROS pathways) known from other stem cell systems. The higher androgen levels in males maturing under caloric restriction may be responsible for the stronger up-regulation of a common set of (449) maturation-associated genes, and the specific up-regulation of another set of (421) genes. The latter opened regulatory and/or metabolic options for initiating puberty despite feed restriction. As a means to reduce the incidence of male puberty in salmon, however, caloric restriction seems unsuitable.

Electronic supplementary material

The online version of this article (10.1186/s12864-019-5869-9) contains supplementary material, which is available to authorized users.

Mutations in the RAS pathway as potential precision medicine targets in treatment of rhabdomyosarcoma

Precision medicine strategies for treating rhabdomyosarcoma (RMS), a childhood malignancy, have not been developed. We examined the effect of CH5126766, a potent selective dual RAF/MEK inhibitor, on RMS cell lines. Among the eleven cell lines studied, one NRAS and two HRAS mutated cell lines were detected. CH5126766 inhibited the proliferation and growth in all of the RAS-mutated RMS cell lines, while it induced G1 cell cycle arrest in two of them. G1 cell cycle arrest was accompanied by p21 up-regulation and RB dephosphorylation. CH5126766 also suppressed the in vivo growth of RAS-mutated RMS tumor, and the mice showed improved survival. Thus, our results demonstrate that CH5126766 is an effective RAF/MEK inhibitor in RAS-mutated RMS. This study not only shows that in RMS, mutations in the RAS pathway can be a target for precision medicine, but also demonstrates that the evaluation of the gene mutation status is important in childhood malignancies.

Generation and characterization of a zebrafish muscle specific inducible Cre line

Zebrafish transgenic lines provide valuable insights into gene functions, cell lineages and cell behaviors during development. Spatiotemporal control over transgene expression is a critical need in many experimental approaches, with applications in loss- and gain-of-function expression, ectopic expression and lineage tracing experiments. The Cre/loxP recombination system is a powerful tool to provide this control and the demand for validated Cre and loxP zebrafish transgenics is high. One of the major challenges to widespread application of Cre/loxP technology in zebrafish is comparatively small numbers of established tissue-specific Cre or CreERT2 lines. We used Tol2-mediated transgenesis to generate Tg(CrymCherry;-1.9mylz2:CreERT2) which provides an inducible CreERT2 source driven by muscle-specific mylz2 promoter. The transgenic specifically labels the trunk and tail skeletal muscles. We assessed the temporal responsiveness of the transgenic by screening with a validated loxP reporter transgenic ubi:Switch. Further, we evaluated the recombination efficiency in the transgenic with varying concentrations of 4-OHT, for different induction time periods and at different stages of embryogenesis and observed that higher recombination efficiency is achieved when embryos are induced with 10 μM 4-OHT from 10-somites or 24 hpf till 48 or 72 hpf. The transgenic is an addition to currently available zebrafish transgenesis toolbox and a significant tool to advance muscle biology studies in zebrafish.

Genetic Requirement of talin1 for Proliferation of Cranial Neural Crest Cells during Palate Development

Supplemental Digital Content is available in the text.

Background:

Craniofacial malformations are among the most common congenital anomalies. Cranial neural crest cells (CNCCs) form craniofacial structures involving multiple cellular processes, perturbations of which contribute to craniofacial malformations. Adhesion of cells to the extracellular matrix mediates bidirectional interactions of the cells with their extracellular environment that plays an important role in craniofacial morphogenesis. Talin (tln) is crucial in cell-matrix adhesion between cells, but its role in craniofacial morphogenesis is poorly understood.

Methods:

Talin gene expression was determined by whole mount in situ hybridization. Craniofacial cartilage and muscles were analyzed by Alcian blue in Tg(mylz2:mCherry) and by transmission electron microscopy. Pulse-chase photoconversion, 5-ethynyl-2’-deoxyuridine proliferation, migration, and apoptosis assays were performed for functional analysis.

Results:

Expression of tln1 was observed in the craniofacial cartilage structures, including the palate. The Meckel’s cartilage was hypoplastic, the palate was shortened, and the craniofacial muscles were malformed in tln1 mutants. Pulse-chase and EdU assays during palate morphogenesis revealed defects in CNCC proliferation in mutants. No defects were observed in CNCC migration and apoptosis.

Conclusions:

The work shows that tln1 is critical for craniofacial morphogenesis in zebrafish. Loss of tln1 leads to a shortened palate and Meckel’s cartilage along with disorganized skeletal muscles. Investigations into the cellular processes show that tln1 is required for CNCC proliferation during palate morphogenesis. The work will lead to a better understanding of the involvement of cytoskeletal proteins in craniofacial morphogenesis.

Zebrafish skeleton development: High resolution micro-CT and FIB-SEM block surface serial imaging for phenotype identification

Although bone is one of the most studied living materials, many questions about the manner in which bones form remain unresolved, including fine details of the skeletal structure during development. In this study, we monitored skeleton development of zebrafish larvae, using calcein fluorescence, high-resolution micro-CT 3D images and FIB-SEM in the block surface serial imaging mode. We compared calcein staining of the skeletons of the wild type and nacre mutants, which are transparent zebrafish, with micro-CT for the first 30 days post fertilization embryos, and identified significant differences. We quantified the bone volumes and mineral contents of bones, including otoliths, during development, and showed that such developmental differences, including otolith development, could be helpful in identifying phenotypes. In addition, high-resolution imaging revealed the presence of mineralized aggregates in the notochord, before the formation of the first bone in the axial skeleton. These structures might play a role in the storage of the mineral. Our results highlight the potential of these high-resolution 3D approaches to characterize the zebrafish skeleton, which in turn could prove invaluable information for better understanding the development and the characterization of skeletal phenotypes.

Innovative Disease Model: Zebrafish as an In Vivo Platform for Intestinal Disorder and Tumors

Colorectal cancer (CRC) is one of the world’s most common cancers and is the second leading cause of cancer deaths, causing more than 50,000 estimated deaths each year. Several risk factors are highly associated with CRC, including being overweight, eating a diet high in red meat and over-processed meat, having a history of inflammatory bowel disease, and smoking. Previous zebrafish studies have demonstrated that multiple oncogenes and tumor suppressor genes can be regulated through genetic or epigenetic alterations. Zebrafish research has also revealed that the activation of carcinogenesis-associated signal pathways plays an important role in CRC. The biology of cancer, intestinal disorders caused by carcinogens, and the morphological patterns of tumors have been found to be highly similar between zebrafish and humans. Therefore, the zebrafish has become an important animal model for translational medical research. Several zebrafish models have been developed to elucidate the characteristics of gastrointestinal diseases. This review article focuses on zebrafish models that have been used to study human intestinal disorders and tumors, including models involving mutant and transgenic fish. We also report on xenograft models and chemically-induced enterocolitis. This review demonstrates that excellent zebrafish models can provide novel insights into the pathogenesis of gastrointestinal diseases and help facilitate the evaluation of novel anti-tumor drugs.

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

Discovering novel oncogenic pathways and new therapies using zebrafish models of sarcoma

Sarcoma is a type of cancer affecting connective, supportive, or soft tissue of mesenchymal origin. Despite rare incidence in adults (<1%), over 15% of pediatric cancers are sarcoma. Sadly, both adults and children with relapsed or metastatic disease have devastatingly high rates of mortality. Current treatment options for sarcoma include surgery, radiation, and/or chemotherapy; however, significant limitations exist with respect to the efficacy of these strategies. Strong impetus has been placed on the development of novel therapies and preclinical models for uncovering mechanisms involved in the development, progression, and therapy resistance of sarcoma. Over the past 15 years, the zebrafish has emerged as a powerful genetic model of human cancer. High genetic conservation when combined with a unique susceptibility to develop sarcoma has made the zebrafish an effective tool for studying these diseases. Transgenic and gene-activation strategies have been employed to develop zebrafish models of rhabdomyosarcoma, malignant peripheral nerve sheath tumors, Ewing's sarcoma, chordoma, hemangiosarcoma, and liposarcoma. These models all display remarkable molecular and histopathological conservation with their human cancer counterparts and have offered excellent platforms for understanding disease progression in vivo. Short tumor latency and the amenability of zebrafish for ex vivo manipulation, live imaging studies, and tumor cell transplantation have allowed for efficient study of sarcoma initiation, growth, self-renewal, and maintenance. When coupled with facile chemical genetic approaches, zebrafish models of sarcoma have provided a strong translational tool to uncover novel drug pathways and new therapeutic strategies.

MicroRNA and gene co-expression networks characterize biological and clinical behavior of rhabdomyosarcomas

Rhabdomyosarcomas (RMS) in children and adolescents are heterogeneous sarcomas broadly defined by skeletal muscle features and the presence/absence of PAX3/7-FOXO1 fusion genes. MicroRNAs are small non-coding RNAs that regulate gene expression in a cell context specific manner. Sequencing analyses of microRNAs in 64 RMS revealed expression patterns separating skeletal muscle, fusion gene positive and negative RMS. Integration with parallel gene expression data assigned biological functions to 12 co-expression networks/modules that reassuringly included myogenic roles strongly correlated with microRNAs known in myogenesis and RMS development. Modules also correlated with clinical outcome and fusion status. Regulation of microRNAs by the fusion protein was demonstrated after PAX3-FOXO1 reduction, exemplified by miR-9-5p. MiR-9-5p levels correlated with poor outcome, even within fusion gene positive RMS, and were higher in metastatic versus non-metastatic disease. MiR-9-5p reduction inhibited RMS cell migration. Our findings reveal microRNAs in a regulatory framework of biological and clinical significance in RMS.

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RNAseq profiled miRNA expression in 64 rhabdomyosarcomas (RMS).

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MiRNA expression distinguished muscle and RMS on the basis of fusion gene status.

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Co-expression networks linked to function, clinical data and fusion gene status.

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Identified miRNAs, including miR-9-5p, altered by the PAX3-FOXO1 fusion protein.

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Demonstrated clinical and functional role for miR-9-5p in RMS.

Modeling Leukemogenesis in the Zebrafish Using Genetic and Xenograft Models

The zebrafish is a widely accepted model to study leukemia. The major advantage of studying leukemogenesis in zebrafish is attributed to its short life cycle and superior imaging capacity. This chapter highlights using transgenic- and xenograft-based models in zebrafish to study a specific leukemogenic mutation and analyze therapeutic responses in vivo.

Kras activation in p53-deficient myoblasts results in high-grade sarcoma formation with impaired myogenic differentiation

While genomic studies have improved our ability to classify sarcomas, the molecular mechanisms involved in the formation and progression of many sarcoma subtypes are unknown. To better understand developmental origins and genetic drivers involved in rhabdomyosarcomagenesis, we describe a novel sarcoma model system employing primary murine p53-deficient myoblasts that were isolated and lentivirally transduced with Kras^G12D. Myoblast cell lines were characterized and subjected to proliferation, anchorage-independent growth and differentiation assays to assess the effects of transgenic Kras^G12D expression. Kras^G12D overexpression transformed p53^−/− myoblasts as demonstrated by an increased anchorage-independent growth. Induction of differentiation in parental myoblasts resulted in activation of key myogenic regulators. In contrast, Kras-transduced myoblasts had impaired terminal differentiation. p53^−/− myoblasts transformed by Kras^G12D overexpression resulted in rapid, reproducible tumor formation following orthotopic injection into syngeneic host hindlimbs. Pathological analysis revealed high-grade sarcomas with myogenic differentiation based on the expression of muscle-specific markers, such as Myod1 and Myog. Gene expression patterns of murine sarcomas shared biological pathways with RMS gene sets as determined by gene set enrichment analysis (GSEA) and were 61% similar to human RMS as determined by metagene analysis. Thus, our novel model system is an effective means to model high-grade sarcomas along the RMS spectrum.

Actin capping protein CAPZB regulates cell morphology, differentiation, and neural crest migration in craniofacial morphogenesis†

CAPZB is an actin-capping protein that caps the growing end of F-actin and modulates the cytoskeleton and tethers actin filaments to the Z-line of the sarcomere in muscles. Whole-genome sequencing was performed on a subject with micrognathia, cleft palate and hypotonia that harbored a de novo, balanced chromosomal translocation that disrupts the CAPZB gene. The function of capzb was analyzed in the zebrafish model. capzb(-/-) mutants exhibit both craniofacial and muscle defects that recapitulate the phenotypes observed in the human subject. Loss of capzb affects cell morphology, differentiation and neural crest migration. Differentiation of both myogenic stem cells and neural crest cells requires capzb. During palate morphogenesis, defective cranial neural crest cell migration in capzb(-/-) mutants results in loss of the median cell population, creating a cleft phenotype. capzb is also required for trunk neural crest migration, as evident from melanophores disorganization in capzb(-/-) mutants. In addition, capzb over-expression results in embryonic lethality. Therefore, proper capzb dosage is important during embryogenesis, and regulates both cell behavior and tissue morphogenesis.

In Vivo Imaging of Cancer in Zebrafish

Zebrafish cancer models have greatly advanced our understanding of malignancy in humans. This is made possible due to the unique advantages of the zebrafish model including ex vivo development and large clutch sizes, which enable large-scale genetic and chemical screens. Transparency of the embryo and the creation of adult zebrafish devoid of pigmentation (casper) have permitted unprecedented ability to dynamically visualize cancer progression in live animals. When coupled with fluorescent reporters and transgenic approaches that drive oncogenesis, it is now possible to label entire or subpopulations of cancer cells and follow cancer growth in near real-time. Here, we will highlight aspects of in vivo imaging using the zebrafish and how it has enhanced our understanding of the fundamental aspects of tumor initiation, self-renewal, neovascularization, tumor cell heterogeneity, invasion and metastasis. Importantly, we will highlight the contribution of cancer imaging in zebrafish for drug discovery.

Rhabdomyosarcoma: Advances in Molecular and Cellular Biology

Rhabdomyosarcoma (RMS) is the most common soft tissue malignancy in childhood and adolescence. The two major histological subtypes of RMS are alveolar RMS, driven by the fusion protein PAX3-FKHR or PAX7-FKHR, and embryonic RMS, which is usually genetically heterogeneous. The prognosis of RMS has improved in the past several decades due to multidisciplinary care. However, in recent years, the treatment of patients with metastatic or refractory RMS has reached a plateau. Thus, to improve the survival rate of RMS patients and their overall well-being, further understanding of the molecular and cellular biology of RMS and identification of novel therapeutic targets are imperative. In this review, we describe the most recent discoveries in the molecular and cellular biology of RMS, including alterations in oncogenic pathways, miRNA (miR), in vivo models, stem cells, and important signal transduction cascades implicated in the development and progression of RMS. Furthermore, we discuss novel potential targeted therapies that may improve the current treatment of RMS.

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.

Probing for a deeper understanding of rhabdomyosarcoma: insights from complementary model systems

Rhabdomyosarcoma (RMS) is a mesenchymal malignancy composed of neoplastic primitive precursor cells that exhibit histological features of myogenic differentiation. Despite intensive conventional multimodal therapy, patients with high-risk RMS typically suffer from aggressive disease. The lack of directed therapies against RMS emphasizes the need to further uncover the molecular underpinnings of the disease. In this Review, we discuss the notable advances in the model systems now available to probe for new RMS-targetable pathogenetic mechanisms, and the possibilities for enhanced RMS therapeutics and improved clinical outcomes.

A CRISPR/Cas9 vector system for tissue-specific gene disruption in zebrafish

CRISPR/Cas9 technology of genome editing has greatly facilitated the targeted inactivation of genes in vitro and in vivo in a wide range of organisms. In zebrafish, it allows the rapid generation of knockout lines by simply injecting a guide RNA (gRNA) and Cas9 mRNA into one-cell stage embryos. Here, we report a simple and scalable CRISPR-based vector system for tissue-specific gene inactivation in zebrafish. As proof of principle, we used our vector with the gata1 promoter driving Cas9 expression to silence the urod gene, implicated in heme biosynthesis, specifically in the erythrocytic lineage. Urod targeting yielded red fluorescent erythrocytes in zebrafish embryos, recapitulating the phenotype observed in the yquem mutant. While F0 embryos displayed mosaic gene disruption, the phenotype appeared very penetrant in stable F1 fish. This vector system constitutes a unique tool to spatially control gene knockout and greatly broadens the scope of loss-of-function studies in zebrafish.

Pediatric Rhabdomyosarcoma

Rhabdomyosarcoma is the most common soft-tissue sarcoma of childhood, and despite clinical advances, subsets of these patients continue to suffer high levels of morbidity and mortality associated with their disease. Recent genetic and molecular characterization of these tumors using sophisticated genomics techniques, including next-generation sequencing experiments, has revealed multiple areas that can be exploited for new molecularly targeted therapies for this disease.

Zebrafish models of cancer: progress and future challenges

The need for scalable strategies to probe the biological consequences of candidate cancer genes has never been more pressing. The zebrafish, with its capacity for high-throughput transgenesis, in vivo imaging and chemical/genetic screening, has ideal features for undertaking this task. Unique biological insights from zebrafish have already led to the identification of novel oncogenic drivers and small molecules being used to treat the human cancer. This review summarizes the recent main findings and describes pertinent areas where the zebrafish can greatly contribute to our understanding of cancer biology and treatment.

Phosphocaveolin-1 enforces tumor growth and chemoresistance in rhabdomyosarcoma

Caveolin-1 (Cav-1) can ambiguously behave as either tumor suppressor or oncogene depending on its phosphorylation state and the type of cancer. In this study we show that Cav-1 was phosphorylated on tyrosine 14 (pCav-1) by Src-kinase family members in various human cell lines and primary mouse cultures of rhabdomyosarcoma (RMS), the most frequent soft-tissue sarcoma affecting childhood. Cav-1 overexpression in the human embryonal RD or alveolar RH30 cells yielded increased pCav-1 levels and reinforced the phosphorylation state of either ERK or AKT kinase, respectively, in turn enhancing in vitro cell proliferation, migration, invasiveness and chemoresistance. In contrast, reducing the pCav-1 levels by administration of a Src-kinase inhibitor or through targeted Cav-1 silencing counteracted the malignant in vitro phenotype of RMS cells. Consistent with these results, xenotransplantation of Cav-1 overexpressing RD cells into nude mice resulted in substantial tumor growth in comparison to control cells. Taken together, these data point to pCav-1 as an important and therapeutically valuable target for overcoming the progression and multidrug resistance of RMS.