Activation of Sonic hedgehog signaling in neural progenitor cells promotes glioma development in the zebrafish optic pathway

Sonic hedgehog signalling pathway in CNS tumours: its role and therapeutic implications

CNS tumours encompass a diverse group of neoplasms with significant morbidity and mortality. The SHH signalling pathway plays a critical role in the pathogenesis of several CNS tumours, including gliomas, medulloblastomas and others. By influencing cellular proliferation, differentiation and migration in CNS tumours, the SHH pathway has emerged as a promising target for therapeutic intervention. Current strategies such as vismodegib and sonidegib have shown efficacy in targeting SHH pathway activation. However, challenges such as resistance mechanisms and paradoxical effects observed in clinical settings underscore the complexity of effectively targeting this pathway. Advances in gene editing technologies, particularly CRISPR/Cas9, have provided valuable tools for studying SHH pathway biology, validating therapeutic targets and exploring novel treatment modalities. These innovations have paved the way for a better understanding of pathway dynamics and the development of more precise therapeutic interventions. In addition, the identification and validation of biomarkers of SHH pathway activation are critical to guide clinical decision making and improve patient outcomes. Molecular profiling and biomarker discovery efforts are critical steps towards personalised medicine approaches in the treatment of SHH pathway-associated CNS tumours. While significant progress has been made in understanding the role of the SHH pathway in CNS tumorigenesis, ongoing research is essential to overcome current therapeutic challenges and refine treatment strategies. The integration of molecular insights with advanced technologies and clinical expertise holds great promise for developing more effective and personalised therapies for patients with SHH pathway-driven CNS tumours.

Differential regulation of Shh-Gli1 cell signalling pathway on homeodomain transcription factors Nkx2.2 and Pax6 during the medulloblastoma genesis

BACKGROUND

Medulloblastoma is a pediatric malignant brain tumor associated with an aberrantly activated Shh pathway. The Shh pathway acts via downstream effector molecules, including Pax6 and Nkx2.2. Transcription factor Nkx2.2 plays crucial roles during early embryonic patterning and development. In this study, we aimed to determine the role of transcription factor Nkx2.2 in medulloblastoma development.

METHODS AND RESULTS

Here, whole transcriptome levels and suppressive effect of transcription factor Nkx2.2 on Pax6 were assessed using one normal human brain and three surgically removed medulloblastoma samples. Additionally, protein levels of Shh, Gli1, Pax6, and Nkx2.2 and co-expression patterns of Pax6 and Nkx2.2 were assessed in 14 medulloblastoma samples. Quantitative reverse transcription-polymerase chain reaction revealed the suppressive effect of Nkx2.2 on Pax6. D283 cells were treated with the Shh pathway activator, SAG, and Gli1 inhibitor, GANT61, which revealed Pax6-Nkx2.2 regulation. Increased cell proliferation was observed in D283 cells transfected with Nkx2.2 small interfering RNA. Moreover, mRNA expression levels of Shh, Pax6, Nkx2.2, and Gli1 were assessed in Daoy cells transfected with Gli1 and Nkx2.2 small interfering RNAs using quantitative reverse transcription-polymerase chain reaction. Pax6 levels were increased in Nkx2.2 siRNA-transfected cells.

CONCLUSIONS

Aberrantly activated Shh pathway leads to the ectopic expression of Pax6 in granular cells, inducing medulloblastoma development. Moreover, Nkx2.2 transcription factor acts as a suppressor of Pax6 during medulloblastoma development and maintenance. Overall, this study provides novel insights for the development of effective therapeutic strategies and suggests potential targets for medulloblastoma.

Mutations in cdon and boc affect trunk neural crest cell migration and slow-twitch muscle development in zebrafish

The transmembrane proteins cdon and boc are implicated in regulating hedgehog signaling during vertebrate development. Recent work showing roles for these genes in axon guidance and neural crest cell migration suggest that cdon and boc may play additional functions in regulating directed cell movements. We use newly generated and existing mutants to investigate a role for cdon and boc in zebrafish neural crest cell migration. We find that single mutant embryos exhibit normal neural crest phenotypes, but that neural crest migration is strikingly disrupted in double cdon;boc mutant embryos. We further show that this migration phenotype is associated with defects in the differentiation of slow-twitch muscle cells, and the loss of a Col1a1a-containing extracellular matrix, suggesting that neural crest defects may be a secondary consequence to defects in mesoderm development. Combined, our data add to a growing literature showing that cdon and boc act synergistically to promote hedgehog signaling during vertebrate development, and suggest that the zebrafish can be used to study the function of hedgehog receptor paralogs.

Differential role of Pax6 and its interaction with Shh-Gli1-IDH2 axis in regulation of glioma growth and chemoresistance

Glioma is a major brain tumor, and the associated mortality rate is very high. Contemporary therapies provide a chance of survival for 9-12 months. Therefore, a novel approach is essential to improve the survival rate. Sonic hedgehog (Shh) cell signaling is critical for early development in various tumors. This investigation attempted to explore the potential interaction and regulation of Shh-Gli1 cell signaling in association with paired box 6 (Pax6) and isocitrate dehydrogenase 2 (IDH2). The expression pattern of Shh, Gli1, Pax6, and IDH2 was examined by transcriptome analysis, immunohistochemistry, and confocal images. The results suggest the interaction of Shh-Gli1 cell signaling pathway with Pax6 and IDH2 and potential regulation. Thereafter, we performed protein-protein docking and molecular dynamic simulations (MDS) of Gli1 with Pax6 and IDH2. The results suggest differential dynamic interactions of Gli1-IDH2 and Gli1-Pax6. Gli1 knockdown downregulated the expression of Pax6 and upregulated the expression of IDH2. Moreover, Gli1 knockdown decreased the expression of the drug resistance gene MRP1. The knockdown of Pax6 gene in glioma cells downregulated the expression of Gli1 and IDH2 and promoted cell proliferation. Moreover, the efficacy of the treatment of glioma cells with temozolomide (TMZ) and Gli1 inhibitor GANT61 was higher than that of TMZ alone. MDS results revealed that the interactions of Gli1 with IDH2 were stronger and more stable than those with Pax6. Intriguingly, inhibition of Pax6 promoted glioma growth even in the presence of TMZ. However, the tumor-suppressive nature of Pax6 was altered when Gli1 was inhibited by GANT61, and it showed potential oncogenic character, as observed in other cancers. Therefore, we conclude that Pax6 interacted with IDH2 and Gli1 in glioma. Moreover, the Shh-Gli1-IDH2/Pax6 cell signaling axis provides a new therapeutic approach for inhibiting the progression of the disease and mitigating drug resistance in glioma.

Zebrafish Models of Paediatric Brain Tumours

Paediatric brain cancer is the second most common childhood cancer and is the leading cause of cancer-related deaths in children. Despite significant advancements in the treatment modalities and improvements in the 5-year survival rate, it leaves long-term therapy-associated side effects in paediatric patients. Addressing these impairments demands further understanding of the molecularity and heterogeneity of these brain tumours, which can be demonstrated using different animal models of paediatric brain cancer. Here we review the use of zebrafish as potential in vivo models for paediatric brain tumour modelling, as well as catalogue the currently available zebrafish models used to study paediatric brain cancer pathophysiology, and discuss key findings, the unique attributes that these models add, current challenges and therapeutic significance.

Garcinone C Suppresses Tumorsphere Formation and Invasiveness by Hedgehog/Gli1 Signaling in Colorectal Cancer Stem-like Cells

Hyperactivation of hedgehog signaling occurs in colorectal cancer stem-like cells (CSCs), a rare subpopulation, potentially involved in metastasis, chemotherapy resistance, and cancer relapse. Garcinone C, a xanthone isolated from mangosteen (Garcinia mangostana), suppresses colorectal cancer in vivo and in vitro by inhibiting Gli1-dependent noncanonical hedgehog signaling. Herein, we investigated the effect of garcinone C on cancer stemness and invasiveness in colorectal cancer; Gli1 was noted as pivotal in maintaining stemness and invasiveness in HCT116 and HT29 CSCs. Garcinone C inhibited the proliferation and self-renewal of HCT116 and HT29 CSCs. Colon cancer stemness markers such as CD44, CD133, ALDH1, and Nanog were significantly decreased by garcinone C. Computational studies showed that garcinone C showed a high affinity with the Gli1 protein ZF domain by forming hydrogen bonds with amino acid residues of ASP244, ARG223, and ASP216. Besides, MG132 blocked the effects of garcinone C on Gli1. Thus, garcinone C suppressed colorectal CSCs by binding to Gli1 and enhancing its degradation. MMP2 and MMP9 levels, invasive-related markers, were increased in HCT116 CSCs but decreased by garcinone C. E-cadherin level was reduced in HCT116 CSCs, while the presence of garcinone C was restored. Garcinone C inhibited the proliferation and invasiveness of colorectal CSCs by targeting Gli1-dependent Hh signaling. Garcinone C may be a potent natural agent against colorectal cancer relapse.

Modeling Brain Tumors: A Perspective Overview of in vivo and Organoid Models

Brain tumors are a large and heterogeneous group of neoplasms that affect the central nervous system and include some of the deadliest cancers. Almost all the conventional and new treatments fail to hinder tumoral growth of the most malignant brain tumors. This is due to multiple factors, such as intra-tumor heterogeneity, the microenvironmental properties of the human brain, and the lack of reliable models to test new therapies. Therefore, creating faithful models for each tumor and discovering tailored treatments pose great challenges in the fight against brain cancer. Over the years, different types of models have been generated, and, in this review, we investigated the advantages and disadvantages of the models currently used.

Impact of airborne total suspended particles (TSP) and fine particulate matter (PM2.5 )-induced developmental toxicity in zebrafish (Danio rerio) embryos

Airborne total suspended particles (TSP) and particulate matter (PM_2.5 ) threaten global health and their potential impact on cardiovascular and respiratory diseases are extensively studied. Recent studies attest premature deaths, low birth weight, and congenital anomalies in the fetus of pregnant women exposed to air pollution. In this regard, only few studies have explored the effects of TSP and PM_2.5 on cardiovascular and cerebrovascular development. As both TSP and PM_2.5 differ in size and composition, this study is attempted to assess the variability in toxicity effects between TSP and PM_2.5 on the development of cardiovascular and cerebrovascular systems and the underlying mechanisms in a zebrafish model. To explore the potential toxic effects of TSP and PM_2.5 , zebrafish embryos/larvae were exposed to 25, 50, 100, 200, and 400 μg/ml of TSP and PM_2.5 from 24 to 120 hpf (hours post-fertilization). Both TSP and PM_2.5 exposure increased the rate of mortality, malformations, and oxidative stress, whereas locomotor behavior, heart rate, blood flow velocity, development of cardiovasculature and neurovasculature, and dopaminergic neurons were reduced. The expression of genes involved in endoplasmic reticulum stress (ERS), Wnt signaling, and central nervous system (CNS) development were altered in a dose- and time-dependent manner. This study provides evidence for acute exposure to TSP and PM_2.5 -induced cardiovascular and neurodevelopmental toxicity, attributed to enhanced oxidative stress and aberrant gene expression. Comparatively, the effects of PM_2.5 were more pronounced than TSP.

Modeling human brain tumors in flies, worms, and zebrafish: From proof of principle to novel therapeutic targets

For decades, cell biologists and cancer researchers have taken advantage of non-murine species to increase our understanding of the molecular processes that drive normal cell and tissue development, and when perturbed, cause cancer. The advent of whole-genome sequencing has revealed the high genetic homology of these organisms to humans. Seminal studies in non-murine organisms such as Drosophila melanogaster, Caenorhabditis elegans, and Danio rerio identified many of the signaling pathways involved in cancer. Studies in these organisms offer distinct advantages over mammalian cell or murine systems. Compared to murine models, these three species have shorter lifespans, are less resource intense, and are amenable to high-throughput drug and RNA interference screening to test a myriad of promising drugs against novel targets. In this review, we introduce species-specific breeding strategies, highlight the advantages of modeling brain tumors in each non-mammalian species, and underscore the successes attributed to scientific investigation using these models. We conclude with an optimistic proposal that discoveries in the fields of cancer research, and in particular neuro-oncology, may be expedited using these powerful screening tools and strategies.

Cellular and Molecular Mechanisms Underlying Glioblastoma and Zebrafish Models for the Discovery of New Treatments

Glioblastoma (GBM) is the most common of all brain malignant tumors; it displays a median survival of 14.6 months with current complete standard treatment. High heterogeneity, aggressive and invasive behavior, the impossibility of completing tumor resection, limitations for drug administration and therapeutic resistance to current treatments are the main problems presented by this pathology. In recent years, our knowledge of GBM physiopathology has advanced significantly, generating relevant information on the cellular heterogeneity of GBM tumors, including cancer and immune cells such as macrophages/microglia, genetic, epigenetic and metabolic alterations, comprising changes in miRNA expression. In this scenario, the zebrafish has arisen as a promising animal model to progress further due to its unique characteristics, such as transparency, ease of genetic manipulation, ethical and economic advantages and also conservation of the major brain regions and blood-brain-barrier (BBB) which are similar to a human structure. A few papers described in this review, using genetic and xenotransplantation zebrafish models have been used to study GBM as well as to test the anti-tumoral efficacy of new drugs, their ability to interact with target cells, modulate the tumor microenvironment, cross the BBB and/or their toxicity. Prospective studies following these lines of research may lead to a better diagnosis, prognosis and treatment of patients with GBM.

Loss-of-function mutation of c-Ret causes cerebellar hypoplasia in mice with Hirschsprung disease and Down's syndrome

The c-RET proto-oncogene encodes a receptor-tyrosine kinase. Loss-of-function mutations of RET have been shown to be associated with Hirschsprung disease and Down's syndrome (HSCR-DS) in humans. DS is known to involve cerebellar hypoplasia, which is characterized by reduced cerebellar size. Despite the fact that c-Ret has been shown to be associated with HSCR-DS in humans and to be expressed in Purkinje cells (PCs) in experimental animals, there is limited information about the role of activity of c-Ret/c-RET kinase in cerebellar hypoplasia. We found that a loss-of-function mutation of c-Ret Y1062 in PCs causes cerebellar hypoplasia in c-Ret mutant mice. Wild-type mice had increased phosphorylation of c-Ret in PCs during postnatal development, while c-Ret mutant mice had postnatal hypoplasia of the cerebellum with immature neurite outgrowth in PCs and granule cells (GCs). c-Ret mutant mice also showed decreased numbers of glial fibers and mitogenic sonic hedgehog (Shh)-positive vesicles in the external germinal layer of PCs. c-Ret-mediated cerebellar hypoplasia was rescued by subcutaneous injection of a smoothened agonist (SAG) as well as by reduced expression of Patched1, a negative regulator for Shh. Our results suggest that the loss-of-function mutation of c-Ret Y1062 results in the development of cerebellar hypoplasia via impairment of the Shh-mediated development of GCs and glial fibers in mice with HSCR-DS.

The Role of Feed in Aquatic Laboratory Animal Nutrition and the Potential Impact on Animal Models and Study Reproducibility

Feed plays a central role in the physiological development of terrestrial and aquatic animals. Historically, the feeding practice of aquatic research species derived from aquaculture, farmed, or ornamental trades. These diets are highly variable, with limited quality control, and have been typically selected to provide the fastest growth or highest fecundity. These variations of quality and composition of diets may affect animal/colony health and can introduce confounding experimental variables into animal-based studies that impact research reproducibility.

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.

Tumor initiating cells induce Cxcr4-mediated infiltration of pro-tumoral macrophages into the brain

It is now clear that microglia and macrophages are present in brain tumors, but whether or how they affect initiation and development of tumors is not known. Exploiting the advantages of the zebrafish (Danio rerio) model, we showed that macrophages and microglia respond immediately upon oncogene activation in the brain. Overexpression of human AKT1 within neural cells of larval zebrafish led to a significant increase in the macrophage and microglia populations. By using a combination of transgenic and mutant zebrafish lines, we showed that this increase was caused by the infiltration of peripheral macrophages into the brain mediated via Sdf1b-Cxcr4b signaling. Intriguingly, confocal live imaging reveals highly dynamic interactions between macrophages/microglia and pre-neoplastic cells, which do not result in phagocytosis of pre-neoplastic cells. Finally, depletion of macrophages and microglia resulted in a significant reduction of oncogenic cell proliferation. Thus, macrophages and microglia show tumor promoting functions already during the earliest stages of the developing tumor microenvironment.

Visual Experience Facilitates BDNF-Dependent Adaptive Recruitment of New Neurons in the Postembryonic Optic Tectum

Postembryonic brain development is sensitive to environmental input and sensory experience, but the mechanisms underlying healthy adaptive brain growth are poorly understood. Here, we tested the importance of visual experience on larval zebrafish (Danio rerio) postembryonic development of the optic tectum (OT), a midbrain structure involved in visually guided behavior. We first characterized postembryonic neurogenic growth in OT, in which new neurons are generated along the caudal tectal surface and contribute appositionally to anatomical growth. Restricting visual experience during development by rearing larvae in dim light impaired OT anatomical and neurogenic growth, specifically by reducing the survival of new neurons in the medial periventricular gray zone. Neuronal survival in the OT was reduced only when visual experience was restricted for the first 5 d following new neuron generation, suggesting that tectal neurons exhibit an early sensitive period in which visual experience protects these cells from subsequent neuronal loss. The effect of dim rearing on neuronal survival was mimicked by treatment with an NMDA receptor antagonist early, but not later, in a new neuron's life. Both dim rearing and antagonist treatment reduced BDNF production in the OT, and supplementing larvae with exogenous BDNF during dim rearing prevented neuronal loss, suggesting that visual experience protects new tectal neurons through neural activity-dependent BDNF expression. Collectively, we present evidence for a sensitive period of neurogenic adaptive growth in the larval zebrafish OT that relies on visual experience-dependent mechanisms.SIGNIFICANCE STATEMENT Early brain development is shaped by environmental factors via sensory input; however, this form of experience-dependent neuroplasticity is traditionally studied as structural and functional changes within preexisting neurons. Here, we found that restricting visual experience affects development of the larval zebrafish optic tectum, a midbrain structure involved in visually guided behavior, by limiting the survival of newly generated neurons. We found that new tectal neurons exhibit a sensitive period soon after cell birth in which adequate visual experience, likely mediated by neuronal activity driving BDNF production within the tectum, would protect them from subsequent neuronal loss over the following week. Collectively, we present evidence for neurogenic adaptive tectal growth under different environmental lighting conditions.

Zebrafish in Translational Cancer Research: Insight into Leukemia, Melanoma, Glioma and Endocrine Tumor Biology

Over the past 15 years, zebrafish have emerged as a powerful tool for studying human cancers. Transgenic techniques have been employed to model different types of tumors, including leukemia, melanoma, glioblastoma and endocrine tumors. These models present histopathological and molecular conservation with their human cancer counterparts and have been fundamental for understanding mechanisms of tumor initiation and progression. Moreover, xenotransplantation of human cancer cells in embryos or adult zebrafish offers the advantage of studying the behavior of human cancer cells in a live organism. Chemical-genetic screens using zebrafish embryos have uncovered novel druggable pathways and new therapeutic strategies, some of which are now tested in clinical trials. In this review, we will report on recent advances in using zebrafish as a model in cancer studies—with specific focus on four cancer types—where zebrafish has contributed to novel discoveries or approaches to novel therapies.

Quo natas, Danio?-Recent Progress in Modeling Cancer in Zebrafish

Over the last decade, zebrafish has proven to be a powerful model in cancer research. Zebrafish form tumors that histologically and genetically resemble human cancers. The live imaging and cost-effective compound screening possible with zebrafish especially complement classic mouse cancer models. Here, we report recent progress in the field, including genetically engineered zebrafish cancer models, xenotransplantation of human cancer cells into zebrafish, promising approaches toward live investigation of the tumor microenvironment, and identification of therapeutic strategies by performing compound screens on zebrafish cancer models. Given the recent advances in genome editing, personalized zebrafish cancer models are now a realistic possibility. In addition, ongoing automation will soon allow high-throughput compound screening using zebrafish cancer models to be part of preclinical precision medicine approaches.

Penfluridol suppresses glioblastoma tumor growth by Akt-mediated inhibition of GLI1

Glioblastoma (GBM) is the most common brain tumor with poor survival rate. Our results show that penfluridol, an antipsychotic drug significantly reduced the survival of ten adult and pediatric glioblastoma cell lines with IC50 ranging 2-5 μM after 72 hours of treatment and induced apoptosis. Penfluridol treatment suppressed the phosphorylation of Akt at Ser473 and reduced the expression of GLI1, OCT4, Nanog and Sox2 in several glioblastoma cell lines in a concentration-dependent manner. Inhibiting Akt with LY294002 and siRNA, or inhibiting GLI1 using GANT61, cyclopamine, siRNA and CRISPR/Cas9 resulted in enhanced cell growth suppressive effects of penfluridol. On the other hand, overexpression of GLI1 significantly attenuated the effects of penfluridol. Our results further demonstrated that penfluridol treatment inhibited the growth of U87MG tumors by 65% and 72% in subcutaneous and intracranial in vivo glioblastoma tumor models respectively. Immunohistochemical and western blot analysis of tumors revealed reduced pAkt (Ser 473), GLI1, OCT4 and increase in caspase-3 cleavage and TUNEL staining, confirming in vitro findings. Taken together, our results indicate that overall glioblastoma tumor growth suppression by penfluridol was associated with Akt-mediated inhibition of GLI1.

Intracranial undifferentiated malign neuroglial tumor in Smith-Lemli-Opitz syndrome: A theory of a possible predisposing factor for primary brain tumors via a case report

BACKGROUND

Smith-Lemli-Opitz Syndrome (SLOS) is a rare hereditary autosomal recessive disorder with broken cholesterol synthesis causing by 7-dehydrocholesterol reductase deficiency. Although the clinical features and pathogenesis is well-defined, it is unknown whether there is a relationship between SLOS and neoplastic processes, especially brain neoplasms.

PURPOSE

We aimed to attract the attentions to any possibility of relation between SLOS and intracranial tumor development via a pediatric case with both intracranial high-grade neuroglial tumor and SLOS, and thus to contribute an additional data to the literature on togetherness of these two clinical conditions.

METHOD

In our clinic, we experienced an interesting case of a 10-year-old child with both SLOS and huge brain tumor as rarely seen. Here, we reviewed the features and pathophysiology of SLOS and brain tumors via this case.

RESULTS

The patient was operated in our clinic, after, his brain tumor had been diagnosed, and his histopathology was resulted in undifferentiated malignant neuroglial WHO grade 4 tumor.

CONCLUSION

According to current literature, our case is the first report on coexisting of SLOS and intracranial undifferentiated malignant neuroglial tumor. Common pathways like impaired sonic hedgehog (Shh) signaling pathway may be considered for pathogenesis of a probable link between SLOS and brain tumors in further studies.

A novel brain tumour model in zebrafish reveals the role of YAP activation in MAPK- and PI3K-induced malignant growth

Somatic mutations activating MAPK and PI3K signalling play a pivotal role in both tumours and brain developmental disorders. We developed a zebrafish model of brain tumours based on somatic expression of oncogenes that activate MAPK and PI3K signalling in neural progenitor cells and found that HRASV12 was the most effective in inducing both heterotopia and invasive tumours. Tumours, but not heterotopias, require persistent activation of phospho (p)-ERK and express a gene signature similar to the mesenchymal glioblastoma subtype, with a strong YAP component. Application of an eight-gene signature to human brain tumours establishes that YAP activation distinguishes between mesenchymal glioblastoma and low grade glioma in a wide The Cancer Genome Atlas (TCGA) sample set including gliomas and glioblastomas (GBMs). This suggests that the activation of YAP might be an important event in brain tumour development, promoting malignant versus benign brain lesions. Indeed, co-expression of dominant-active YAP (YAPS5A) and HRASV12 abolishes the development of heterotopias and leads to the sole development of aggressive tumours. Thus, we have developed a model proving that neurodevelopmental disorders and brain tumours might originate from the same activation of oncogenes through somatic mutations, and established that YAP activation is a hallmark of malignant brain tumours.

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.

Uncharted Waters: Zebrafish Cancer Models Navigate a Course for Oncogene Discovery

Over a decade has elapsed since the first genetically-engineered zebrafish cancer model was described. During this time remarkable progress has been made. Sophisticated genetic tools have been built to generate oncogene expressing cancers and characterize multiple models of solid and blood tumors. These models have led to unique insights into mechanisms of tumor initiation and progression. New drug targets have been identified, particularly through the functional analysis of cancer genomes. Now in the second decade, zebrafish cancer models are poised for even faster growth as they are used in high-throughput genetic analyses to elucidate key mechanisms underlying critical cancer phenotypes.

Characterization of Proliferating Neural Progenitors after Spinal Cord Injury in Adult Zebrafish

Zebrafish can repair their injured brain and spinal cord after injury unlike adult mammalian central nervous system. Any injury to zebrafish spinal cord would lead to increased proliferation and neurogenesis. There are presences of proliferating progenitors from which both neuronal and glial loss can be reversed by appropriately generating new neurons and glia. We have demonstrated the presence of multiple progenitors, which are different types of proliferating populations like Sox2⁺ neural progenitor, A2B5⁺ astrocyte/ glial progenitor, NG2⁺ oligodendrocyte progenitor, radial glia and Schwann cell like progenitor. We analyzed the expression levels of two common markers of dedifferentiation like msx-b and vimentin during regeneration along with some of the pluripotency associated factors to explore the possible role of these two processes. Among the several key factors related to pluripotency, pou5f1 and sox2 are upregulated during regeneration and associated with activation of neural progenitor cells. Uncovering the molecular mechanism for endogenous regeneration of adult zebrafish spinal cord would give us more clues on important targets for future therapeutic approach in mammalian spinal cord repair and regeneration.

Transcriptional profiles of pilocytic astrocytoma are related to their three different locations, but not to radiological tumor features

Background

Pilocytic astrocytoma is the most common type of brain tumor in the pediatric population, with a generally favorable prognosis, although recurrences or leptomeningeal dissemination are sometimes also observed. For tumors originating in the supra-or infratentorial location, a different molecular background was suggested, but plausible correlations between the transcriptional profile and radiological features and/or clinical course are still undefined. The purpose of this study was to identify gene expression profiles related to the most frequent locations of this tumor, subtypes based on various radiological features, and the clinical pattern of the disease.

Methods

Eighty six children (55 males and 31 females) with histologically verified pilocytic astrocytoma were included in this study. Their age at the time of diagnosis ranged from fourteen months to seventeen years, with a mean age of seven years. There were 40 cerebellar, 23 optic tract/hypothalamic, 21 cerebral hemispheric, and two brainstem tumors. According to the radiological features presented on MRI, all cases were divided into four subtypes: cystic tumor with a non-enhancing cyst wall; cystic tumor with an enhancing cyst wall; solid tumor with central necrosis; and solid or mainly solid tumor. In 81 cases primary surgical resection was the only and curative treatment, and in five cases progression of the disease was observed. In 47 cases the analysis was done by using high density oligonucleotide microarrays (Affymetrix HG-U133 Plus 2.0) with subsequent bioinformatic analyses and confirmation of the results by independent RT-qPCR (on 39 samples).

Results

Bioinformatic analyses showed that the gene expression profile of pilocytic astrocytoma is highly dependent on the tumor location. The most prominent differences were noted for IRX2, PAX3, CXCL14, LHX2, SIX6, CNTN1 and SIX1 genes expression even within different compartments of the supratentorial region. Analysis of the genes potentially associated with radiological features showed much weaker transcriptome differences. Single genes showed association with the tendency to progression.

Conclusions

Here we have shown that pilocytic astrocytomas of three different locations can be precisely differentiated on the basis of their gene expression level, but their transcriptional profiles does not strongly reflect the radiological appearance of the tumor or the course of the disease.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1810-z) contains supplementary material, which is available to authorized users.

Rapid tumor induction in zebrafish by TALEN-mediated somatic inactivation of the retinoblastoma1 tumor suppressor rb1

Investigating the in vivo role of tumor suppressor genes in cancer is technically challenging due to their essential requirement during early animal development. To address this bottleneck, we generated genetic mosaic adult zebrafish using TALEN genome editing and demonstrate somatic inactivation of the tumor suppressor retinoblastoma1 (rb1) induces tumorigenesis at high frequency. 11–33% of 1-cell stage embryos injected with TALEN mRNAs targeting rb1 exon 2 or 3 develop tumors beginning as early as 3.5 months of age. Lesions predominantly arise in the brain and show features of neuroectodermal-like and glial-like tumors. Mutant allele analysis is consistent with tumor initiation due to somatic inactivation of rb1, revealing a conserved role for rb1 in tumor suppression across vertebrates. In contrast to genetic mosaics, heterozygous rb1−/+ adults show no evidence of neoplasia, while homozygous mutant rb1−/− are larval lethal. This is the first demonstration that somatic inactivation of a tumor suppressor causes cancer in zebrafish, and highlights the utility of site-specific nucleases to create genetic mosaic zebrafish for tumor suppressor gene discovery. Somatic inactivation with site-directed nucleases in zebrafish presents a rapid and scalable strategy to study tumor suppressor gene function in cancer.

Activation of sonic hedgehog signaling enhances cell migration and invasion by induction of matrix metalloproteinase-2 and -9 via the phosphoinositide-3 kinase/AKT signaling pathway in glioblastoma

Aberrant hedgehog signaling contributes to the development of various malignancies, including glioblastoma (GBM). However, the potential mechanism of hedgehog signaling in GBM migration and invasion has remained to be elucidated. The present study showed that enhanced hedgehog signaling by recombinant human sonic hedgehog N-terminal peptide (rhSHH) promoted the adhesion, invasion and migration of GBM cells, accompanied by increases in mRNA and protein levels of matrix metalloproteinase-2 (MMP-2) and MMP-9. However, inhibition of hedgehog signaling with cyclopamine suppressed the adhesion, invasion and migration of GBM cells, accompanied by decreases in mRNA and protein levels of MMP-2 and -9. Furthermore, it was found that MMP-2- and MMP-9-neutralizing antibodies or GAM6001 reversed the inductive effects of rhSHH on cell migration and invasion. In addition, enhanced hedgehog signaling by rhSHH increased AKT phosphorylation, whereas blockade of hedgehog signaling decreased AKT phosphorylations. Further experiments showed that LY294002, an inhibitor of phosphoinositide-3 kinase (PI3K), decreased rhSHH-induced upregulation of MMP-2 and -9. Finally, the protein expression of glioblastoma-associated oncogene 1 was positively correlated with levels of phosphorylated AKT as well as protein expressions of MMP-2 and -9 in GBM tissue samples. In conclusion, the present study indicated that the hedgehog pathway regulates GBM-cell migration and invasion by increasing MMP-2 and MMP-9 production via the PI3K/AKT pathway.

A vascular perspective on neuronal migration

During CNS development and adult neurogenesis, immature neurons travel from the germinal zones towards their final destination using cellular substrates for their migration. Classically, radial glia and neuronal axons have been shown to act as physical scaffolds to support neuroblast locomotion in processes known as gliophilic and neurophilic migration, respectively (Hatten, 1999; Marin and Rubenstein, 2003; Rakic, 2003). In adulthood, long distance neuronal migration occurs in a glial-independent manner since radial glia cells differentiate into astrocytes after birth. A series of studies highlight a novel mode of neuronal migration that uses blood vessels as scaffolds, the so-called vasophilic migration. This migration mode allows neuroblast navigation in physiological and also pathological conditions, such as neuronal precursor migration after ischemic stroke or cerebral invasion of glioma tumor cells. Here we review the current knowledge about how vessels pave the path for migrating neurons and how trophic factors derived by glio-vascular structures guide neuronal migration both during physiological as well as pathological processes.

Sex-determining region of Y chromosome-related high-mobility-group box 2 in malignant tumors: current opinions and anticancer therapy

OBJECTIVE

To gain insight into the mechanism by which sex-determining region of Y chromosome (SRY)-related high-mobility-group box 2 (SOX2) involved in carcinogenesis and cancer stem cells (CSCs).

DATA SOURCES

The data used in this review were mainly published in English from 2000 to present obtained from PubMed. The search terms were "SOX2," "cancer," "tumor" or "CSCs."

STUDY SELECTION

Articles studying the mitochondria-related pathologic mechanism and treatment of glaucoma were selected and reviewed.

RESULTS

SOX2, a transcription factor that is the key in maintaining pluripotent properties of stem cells, is a member of SRY-related high-mobility group domain proteins. SOX2 participates in many biological processes, such as modulation of cell proliferation, regulation of cell death signaling, cell apoptosis, and most importantly, tumor formation and development. Although SOX2 has been implicated in the biology of various tumors and CSCs, the findings are highly controversial, and information regarding the underlying mechanism remains limited. Moreover, the mechanism by which SOX2 involved in carcinogenesis and tumor progression is rather unclear yet.

CONCLUSIONS

Here, we review the important biological functions of SOX2 in different tumors and CSCs, and the function of SOX2 signaling in the pathobiology of neoplasia, such as Wnt/β-catenin signaling pathway, Hippo signaling pathway, Survivin signaling pathway, PI3K/Akt signaling pathway, and so on. Targeting towards SOX2 may be an effective therapeutic strategy for cancer therapy.

Oncogenic KRAS promotes malignant brain tumors in zebrafish

Background

Zebrafish have been used as a vertebrate model to study human cancers such as melanoma, rhabdomyosarcoma, liver cancer, and leukemia as well as for high-throughput screening of small molecules of therapeutic value. However, they are just emerging as a model for human brain tumors, which are among the most devastating and difficult to treat. In this study, we evaluated zebrafish as a brain tumor model by overexpressing a human version of oncogenic KRAS (KRAS^G12V).

Methods

Using zebrafish cytokeratin 5 (krt5) and glial fibrillary acidic protein (gfap) gene promoters, we activated Ras signaling in the zebrafish central nervous system (CNS) through transient and stable transgenic overexpression. Immunohistochemical analyses were performed to identify activated pathways in the resulting brain tumors. The effects of the MEK inhibitor U0126 on oncogenic KRAS were evaluated.

Results

We demonstrated that transient transgenic expression of KRAS^G12V in putative neural stem and/or progenitor cells induced brain tumorigenesis. When expressed under the control of the krt5 gene promoter, KRAS^G12V induced brain tumors in ventricular zones (VZ) at low frequency. The majority of other tumors were composed mostly of spindle and epithelioid cells, reminiscent of malignant peripheral nerve sheath tumors (MPNSTs). In contrast, when expressed under the control of the gfap gene promoter, KRAS^G12V induced brain tumors in both VZs and brain parenchyma at higher frequency. Immunohistochemical analyses indicated prominent activation of the canonical RAS-RAF-ERK pathway, variable activation of the mTOR pathway, but no activation of the PI3K-AKT pathway. In a krt5-derived stable and inducible transgenic line, expression of oncogenic KRAS resulted in skin hyperplasia, and the MEK inhibitor U0126 effectively suppressed this pro-proliferative effects. In a gfap-derived stable and inducible line, expression of oncogenic KRAS led to significantly increased mitotic index in the spinal cord.

Conclusions

Our studies demonstrate that zebrafish could be explored to study cellular origins and molecular mechanisms of brain tumorigenesis and could also be used as a platform for studying human oncogene function and for discovering oncogenic RAS inhibitors.

Electronic supplementary material

The online version of this article (doi:10.1186/s12943-015-0288-2) contains supplementary material, which is available to authorized users.

Molecular and cellular characterization of a zebrafish optic pathway tumor line implicates glia-derived progenitors in tumorigenesis

In this study we describe the molecular and cellular characterization of a zebrafish mutant that develops tumors in the optic pathway. Heterozygous Tg(flk1:RFP)is18 transgenic adults develop tumors of the retina, optic nerve and optic tract. Molecular and genetic mapping demonstrate the tumor phenotype is linked to a high copy number transgene array integrated in the lincRNA gene lincRNAis18/Zv9_00007276 on chromosome 3. TALENs were used to isolate a 147kb deletion allele that removes exons 2–5 of the lincRNAis18 gene. Deletion allele homozygotes are viable and do not develop tumors, indicating loss of function of the lincRNAis18 locus is not the trigger for tumor onset. Optic pathway tumors in the Tg(flk1:RFP)is18 mutant occur with a penetrance of 80–100% by 1 year of age. The retinal tumors are highly vascularized and composed of rosettes of various sizes embedded in a fibrous matrix. Immunohistochemical analysis showed increased expression of the glial markers GFAP and BLBP throughout retinal tumors and in dysplastic optic nerve. We performed transcriptome analysis of pre-tumorous retina and retinal tumor tissue and found changes in gene expression signatures of radial glia and astrocytes (slc1a3), activated glia (atf3, blbp, apoeb), proliferating neural progenitors (foxd3, nestin, cdh2, her9/hes1), and glioma markers (S100β, vim). The transcriptome also revealed activation of cAMP, Stat3 and Wnt signal transduction pathways. qRT-PCR confirmed >10-fold overexpression of the Wnt pathway components hbegfa, ascl1a, and insm1a. Together the data indicate Müller glia and/or astrocyte-derived progenitors could contribute to the zebrafish Tg(flk1:RFP)is18 optic pathway tumors.