Transparent adult zebrafish as a tool for in vivo transplantation analysis

TEMPO enables sequential genetic labeling and manipulation of vertebrate cell lineages

During development, regulatory factors appear in a precise order to determine cell fates over time. Consequently, to investigate complex tissue development, it is necessary to visualize and manipulate cell lineages with temporal control. Current strategies for tracing vertebrate cell lineages lack genetic access to sequentially produced cells. Here, we present TEMPO (Temporal Encoding and Manipulation in a Predefined Order), an imaging-readable genetic tool allowing differential labeling and manipulation of consecutive cell generations in vertebrates. TEMPO is based on CRISPR and powered by a cascade of gRNAs that drive orderly activation and inactivation of reporters and/or effectors. Using TEMPO to visualize zebrafish and mouse neurogenesis, we recapitulated birth-order-dependent neuronal fates. Temporally manipulating cell-cycle regulators in mouse cortex progenitors altered the proportion and distribution of neurons and glia, revealing the effects of temporal gene perturbation on serial cell fates. Thus, TEMPO enables sequential manipulation of molecular factors, crucial to study cell-type specification.

Genetically engineered zebrafish as models of skeletal development and regeneration

Zebrafish (Danio rerio) are aquatic vertebrates with significant homology to their terrestrial counterparts. While zebrafish have a centuries-long track record in developmental and regenerative biology, their utility has grown exponentially with the onset of modern genetics. This is exemplified in studies focused on skeletal development and repair. Herein, the numerous contributions of zebrafish to our understanding of the basic science of cartilage, bone, tendon/ligament, and other skeletal tissues are described, with a particular focus on applications to development and regeneration. We summarize the genetic strengths that have made the zebrafish a powerful model to understand skeletal biology. We also highlight the large body of existing tools and techniques available to understand skeletal development and repair in the zebrafish and introduce emerging methods that will aid in novel discoveries in skeletal biology. Finally, we review the unique contributions of zebrafish to our understanding of regeneration and highlight diverse routes of repair in different contexts of injury. We conclude that zebrafish will continue to fill a niche of increasing breadth and depth in the study of basic cellular mechanisms of skeletal biology.

Three-dimensional cerebral vasculature topological parameter extraction of transgenic zebrafish embryos with a filling-enhancement deep learning network

Quantitative analysis of zebrafish cerebral vasculature is essential for the study of vascular development and disease. We developed a method to accurately extract the cerebral vasculature topological parameters of transgenic zebrafish embryos. The intermittent and hollow vascular structures of transgenic zebrafish embryos, obtained from 3D light-sheet imaging, were transformed into continuous solid structures with a filling-enhancement deep learning network. The enhancement enables the extraction of 8 vascular topological parameters accurately. Quantitation of the zebrafish cerebral vasculature vessels with the topological parameters show a developmental pattern transition from 2.5 to 5.5 dpf.

Oxoeicosanoid signaling mediates early antimicrobial defense in zebrafish

5-oxoETE is a bioactive lipid derived from arachidonic acid generated when phospholipase A₂ activation coincides with oxidative stress. Through its G protein-coupled receptor OXER1, pure 5-oxoETE is a potent leukocyte chemoattractant. Yet, its physiological function has remained elusive owing to the unusual OXER1 conservation pattern. OXER1 is conserved from fish to primates but not in rodents, precluding genetic loss-of-function studies in mouse. To determine its physiological role, we combine transcriptomic, lipidomic, and intravital imaging assays with genetic perturbations of the OXER1 ortholog hcar1-4 in zebrafish. Pseudomonas aeruginosa infection induces the synthesis of 5-oxoETE and its receptor, along with other inflammatory pathways. Hcar1-4 deletion attenuates neutrophil recruitment and decreases post-infection survival, which could be rescued by ectopic expression of hcar1-4 or human OXER1. By revealing 5-oxoETE as dominant lipid regulator of the early antimicrobial response in a non-rodent vertebrate, our work expands the current, rodent-centric view of early inflammation.

Insights into the control and consequences of breathing adjustments in fishes-from larvae to adults

Adjustments of ventilation in fishes to regulate the volume of water flowing over the gills are critically important responses to match branchial gas transfer with metabolic needs and to defend homeostasis during environmental fluctuations in O₂ and/or CO₂ levels. In this focused review, we discuss the control and consequences of ventilatory adjustments in fish, briefly summarizing ventilatory responses to hypoxia and hypercapnia before describing the current state of knowledge of the chemoreceptor cells and molecular mechanisms involved in sensing O₂ and CO₂. We emphasize, where possible, insights gained from studies on early developmental stages. In particular, zebrafish (Danio rerio) larvae have emerged as an important model for investigating the molecular mechanisms of O₂ and CO₂ chemosensing as well as the central integration of chemosensory information. Their value stems, in part, from their amenability to genetic manipulation, which enables the creation of loss-of-function mutants, optogenetic manipulation, and the production of transgenic fish with specific genes linked to fluorescent reporters or biosensors.

Label-free imaging of red blood cells and oxygenation with color third-order sum-frequency generation microscopy

Mapping red blood cells (RBCs) flow and oxygenation is of key importance for analyzing brain and tissue physiology. Current microscopy methods are limited either in sensitivity or in spatio-temporal resolution. In this work, we introduce a novel approach based on label-free third-order sum-frequency generation (TSFG) and third-harmonic generation (THG) contrasts. First, we propose a novel experimental scheme for color TSFG microscopy, which provides simultaneous measurements at several wavelengths encompassing the Soret absorption band of hemoglobin. We show that there is a strong three-photon (3P) resonance related to the Soret band of hemoglobin in THG and TSFG signals from zebrafish and human RBCs, and that this resonance is sensitive to RBC oxygenation state. We demonstrate that our color TSFG implementation enables specific detection of flowing RBCs in zebrafish embryos and is sensitive to RBC oxygenation dynamics with single-cell resolution and microsecond pixel times. Moreover, it can be implemented on a 3P microscope and provides label-free RBC-specific contrast at depths exceeding 600 µm in live adult zebrafish brain. Our results establish a new multiphoton contrast extending the palette of deep-tissue microscopy.

Dysregulation of Mycobacterium marinum ESX-5 Secretion by Novel 1,2,4-oxadiazoles

The ESX-5 secretion system is essential for the viability and virulence of slow-growing pathogenic mycobacterial species. In this study, we identified a 1,2,4-oxadiazole derivative as a putative effector of the ESX-5 secretion system. We confirmed that this 1,2,4-oxadiazole and several newly synthesized derivatives inhibited the ESX-5-dependent secretion of active lipase LipY by Mycobacterium marinum (M. marinum). Despite reduced lipase activity, we did not observe a defect in LipY secretion itself. Moreover, we found that several other ESX-5 substrates, especially the high molecular-weight PE_PGRS MMAR_5294, were even more abundantly secreted by M. marinum treated with several 1,2,4-oxadiazoles. Analysis of M. marinum grown in the presence of different oxadiazole derivatives revealed that the secretion of LipY and the induction of PE_PGRS secretion were, in fact, two independent phenotypes, as we were able to identify structural features in the compounds that specifically induced only one of these phenotypes. Whereas the three most potent 1,2,4-oxadiazoles displayed only a mild effect on the growth of M. marinum or M. tuberculosis in culture, these compounds significantly reduced bacterial burden in M. marinum-infected zebrafish models. In conclusion, we report a 1,2,4-oxadiazole scaffold that dysregulates ESX-5 protein secretion.

A tessellated lymphoid network provides whole-body T cell surveillance in zebrafish

Homeostatic trafficking to lymph nodes allows T cells to efficiently survey the host for cognate antigen. Non-mammalian jawed vertebrates lack lymph nodes but maintain similarly diverse T cell pools. Here, we exploit in vivo imaging of transparent zebrafish to investigate how T cells organize and survey for antigen in an animal devoid of lymph nodes. We find that naïve-like T cells in zebrafish organize into a previously undescribed whole-body lymphoid network that supports streaming migration and coordinated trafficking through the host. This network has the cellular hallmarks of a mammalian lymph node, including naïve T cells and CCR7-ligand expressing non-hematopoietic cells, and facilitates rapid collective migration. During infection, T cells transition to a random walk that supports antigen presenting cell interactions and subsequent activation. Our results reveal that T cells can toggle between collective migration and individual random walks to prioritize either large-scale trafficking or antigen search in situ . This novel lymphoid network thus facilitates whole-body T cell trafficking and antigen surveillance in the absence of a lymph node system.

Significance Statement

In mammals, lymph nodes play a critical role in the initiation of adaptive immune responses by providing a dedicated place for T cells to scan antigen-presenting cells. Birds, reptiles, amphibians, and fish all maintain diverse repertoires of T cells but lack lymph nodes, raising questions about how adaptive immunity functions in lower jawed vertebrates. Here, we describe a novel network of lymphocytes in zebrafish that supports whole-body T cell trafficking and provides a site for antigen search, mirroring the function of mammalian lymph nodes. Within this network, T cells can prioritize large-scale trafficking or antigen scanning by toggling between two distinct modes of migration. This network provides valuable insights into the evolution of adaptive immunity.

Identifying the Transcriptional Drivers of Metastasis Embedded within Localized Melanoma

In melanoma, predicting which tumors will ultimately metastasize guides treatment decisions. Transcriptional signatures of primary tumors have been utilized to predict metastasis, but which among these are driver or passenger events remains unclear. We used data from the adjuvant AVAST-M trial to identify a predictive gene signature in localized tumors that ultimately metastasized. Using a zebrafish model of primary melanoma, we interrogated the top genes from the AVAST-M signature in vivo. This identified GRAMD1B, a cholesterol transfer protein, as a bona fide metastasis suppressor, with a majority of knockout animals rapidly developing metastasis. Mechanistically, excess free cholesterol or its metabolite 27-hydroxycholesterol promotes invasiveness via activation of an AP-1 program, which is associated with increased metastasis in humans. Our data demonstrate that the transcriptional seeds of metastasis are embedded within localized tumors, suggesting that early targeting of these programs can be used to prevent metastatic relapse.

SIGNIFICANCE

We analyzed human melanoma transcriptomics data to identify a gene signature predictive of metastasis. To rapidly test clinical signatures, we built a genetic metastasis platform in adult zebrafish and identified GRAMD1B as a suppressor of melanoma metastasis. GRAMD1B-associated cholesterol overload activates an AP-1 program to promote melanoma invasion. This article is highlighted in the In This Issue feature, p. 1.

Advances in the Application of Preclinical Models in Photodynamic Therapy for Tumor: A Narrative Review

Photodynamic therapy (PDT) is a non-invasive laser light local treatment that has been utilized in the management of a wide variety of solid tumors. Moreover, the evaluation of efficacy, adverse reactions, the development of new photosensitizers and the latest therapeutic regimens are inseparable from the preliminary exploration in preclinical studies. Therefore, our aim was to better comprehend the characteristics and limitations of these models and to provide a reference for related research.

METHODS

We searched the databases, including PubMed, Web of Science and Scopus for the past 25 years of original research articles on the feasibility of PDT in tumor treatment based on preclinical experiments and animal models. We provided insights into inclusion and exclusion criteria and ultimately selected 40 articles for data synthesis.

RESULTS

After summarizing and comparing the methods and results of these studies, the experimental model selection map was drawn. There are 7 main preclinical models, which are used for different research objectives according to their characteristics.

CONCLUSIONS

Based on this narrative review, preclinical experimental models are crucial to the development and promotion of PDT for tumors. The traditional animal models have some limitations, and the emergence of organoids may be a promising new insight.

Hematopoietic Stem and Progenitor Cell Identification and Transplantation in Zebrafish

The zebrafish as a model organism is well known for its versatile genetics, rapid development, and straightforward live imaging. It is an excellent model to study hematopoiesis because of its highly conserved ontogeny and gene regulatory networks. Recently developed highly specific transgenic reporter lines have allowed direct imaging and tracking of hematopoietic stem and progenitor cells (HSPCs) in live zebrafish. These reporter lines can also be used for fluorescence-activated cell sorting (FACS) of HSPCs. Similar to mammalian models, HSPCs can be transplanted to reconstitute the entire hematopoietic system of zebrafish recipients. However, the zebrafish provides unique advantages to study HSPC biology, such as transplants into embryos and high-throughput chemical screening. This chapter will outline the methods needed to identify, isolate, and transplant HSPCs in zebrafish.

Silica crystals activate toll-like receptors and inflammasomes to promote local and systemic immune responses in zebrafish

Silica crystals are potent activators of the inflammasome that cause a fibrotic lung disease, called silicosis, with no effective treatment available. We report here that injection of silica crystals into the hindbrain ventricle of zebrafish embryos led to the initiation of local and systemic immune responses driven through both Toll-like receptors (TLR)- and inflammasome-dependent signaling pathways, followed by induction of pro-fibrotic markers. Genetic and pharmacological analysis revealed that the Nlrp3 inflammasome regulated silica crystal-induced inflammation and pyroptotic cell death, but not emergency myelopoiesis. In addition, Cxcl8a/Cxcr2-dependent recruitment of myeloid cells to silica crystals was required to promote emergency myelopoiesis and systemic inflammation. The zebrafish model of silicosis developed here shed light onto the molecular mechanisms involved in the activation of the immune system by silica crystals.

A Drosophila model of the neurological symptoms in Mpv17-related diseases

Mutations in the Mpv17 gene are responsible for MPV17-related hepatocerebral mitochondrial DNA depletion syndrome and Charcot-Marie-Tooth (CMT) disease. Although several models including mouse, zebrafish, and cultured human cells, have been developed, the models do not show any neurological defects, which are often observed in patients. Therefore, we knocked down CG11077 (Drosophila Mpv17; dMpv17), an ortholog of human MPV17, in the nervous system in Drosophila melanogaster and investigated the behavioral and cellular phenotypes. The resulting dMpv17 knockdown larvae showed impaired locomotor activity and learning ability consistent with mitochondrial defects suggested by the reductions in mitochondrial DNA and ATP production and the increases in the levels of lactate and reactive oxygen species. Furthermore, an abnormal morphology of the neuromuscular junction, at the presynaptic terminal, was observed in dMpv17 knockdown larvae. These results reproduce well the symptoms of human diseases and partially reproduce the phenotypes of Mpv17-deficient model organisms. Therefore, we suggest that neuron-specific dMpv17 knockdown in Drosophila is a useful model for investigation of MPV17-related hepatocerebral mitochondrial DNA depletion syndrome and CMT caused by Mpv17 dysfunction.

In Vivo Fast Nonlinear Microscopy Reveals Impairment of Fast Axonal Transport Induced by Molecular Motor Imbalances in the Brain of Zebrafish Larvae

Cargo transport by molecular motors along microtubules is essential for the function of eukaryotic cells, in particular neurons in which axonal transport defects constitute the early pathological features of neurodegenerative diseases. Mainly studied in motor and sensory neurons, axonal transport is still difficult to characterize in neurons of the brain in absence of appropriate in vivo tools. Here, we measured fast axonal transport by tracing the second harmonic generation (SHG) signal of potassium titanyl phosphate (KTP) nanocrystals (nanoKTP) endocytosed by brain neurons of zebrafish (Zf) larvae. Thanks to the optical translucency of Zf larvae and to the perfect photostability of nanoKTP SHG, we achieved a high scanning speed of 20 frames (of ≈90 μm × 60 μm size) per second in Zf brain. We focused our study on endolysosomal vesicle transport in axons of known polarization, separately analyzing kinesin and dynein motor-driven displacements. To validate our assay, we used either loss-of-function mutations of dynein or kinesin 1 or the dynein inhibitor dynapyrazole and quantified several transport parameters. We successfully demonstrated that dynapyrazole reduces the nanoKTP mobile fraction and retrograde run length consistently, while the retrograde run length increased in kinesin 1 mutants. Taking advantage of nanoKTP SHG directional emission, we also quantified fluctuations of vesicle orientation. Thus, by combining endocytosis of nanocrystals having a nonlinear response, fast two-photon microscopy, and high-throughput analysis, we are able to finely monitor fast axonal transport in vivo in the brain of a vertebrate and reveal subtle axonal transport alterations. The high spatiotemporal resolution achieved in our model may be relevant to precisely investigate axonal transport impairment associated with disease models.

Glassfrogs conceal blood in their liver to maintain transparency

Transparency in animals is a complex form of camouflage involving mechanisms that reduce light scattering and absorption throughout the organism. In vertebrates, attaining transparency is difficult because their circulatory system is full of red blood cells (RBCs) that strongly attenuate light. Here, we document how glassfrogs overcome this challenge by concealing these cells from view. Using photoacoustic imaging to track RBCs in vivo, we show that resting glassfrogs increase transparency two- to threefold by removing ~89% of their RBCs from circulation and packing them within their liver. Vertebrate transparency thus requires both see-through tissues and active mechanisms that "clear" respiratory pigments from these tissues. Furthermore, glassfrogs' ability to regulate the location, density, and packing of RBCs without clotting offers insight in metabolic, hemodynamic, and blood-clot research.

Lessons on transparency from the glassfrog

Transparency in glassfrogs has potential implications for human blood clotting.

A brainstem integrator for self-location memory and positional homeostasis in zebrafish

To track and control self-location, animals integrate their movements through space. Representations of self-location are observed in the mammalian hippocampal formation, but it is unknown if positional representations exist in more ancient brain regions, how they arise from integrated self-motion, and by what pathways they control locomotion. Here, in a head-fixed, fictive-swimming, virtual-reality preparation, we exposed larval zebrafish to a variety of involuntary displacements. They tracked these displacements and, many seconds later, moved toward their earlier location through corrective swimming ("positional homeostasis"). Whole-brain functional imaging revealed a network in the medulla that stores a memory of location and induces an error signal in the inferior olive to drive future corrective swimming. Optogenetically manipulating medullary integrator cells evoked displacement-memory behavior. Ablating them, or downstream olivary neurons, abolished displacement corrections. These results reveal a multiregional hindbrain circuit in vertebrates that integrates self-motion and stores self-location to control locomotor behavior.

Longitudinal in vivo imaging of adult Danionella cerebrum using standard confocal microscopy

Danionella cerebrum is a new vertebrate model that offers an exciting opportunity to visualize dynamic biological processes in intact adult animals. Key advantages of this model include its small size, life-long optical transparency, genetic amenability and short generation time. Establishing a reliable method for longitudinal in vivo imaging of adult D. cerebrum while maintaining viability will allow in-depth image-based studies of various processes involved in development, disease onset and progression, wound healing, and aging in an intact live animal. Here, a method for both prolonged and longitudinal confocal live imaging of adult D. cerebrum using custom-designed and 3D-printed imaging chambers is described. Two transgenic D. cerebrum lines were created to test the imaging system, i.e. Tg(mpeg1:dendra2) and Tg(kdrl:mCherry-caax). The first line was used to visualize macrophages and microglia, and the second for spatial registration. By using this approach, differences in immune cell morphology and behavior during homeostasis as well as in response to a stab wound or two-photon-induced brain injury were observed in intact adult fish over the course of several days.

Human JAK1 gain of function causes dysregulated myelopoeisis and severe allergic inflammation

Primary atopic disorders are a group of inborn errors of immunity that skew the immune system toward severe allergic disease. Defining the biology underlying these extreme monogenic phenotypes reveals shared mechanisms underlying common polygenic allergic disease and identifies potential drug targets. Germline gain-of-function (GOF) variants in JAK1 are a cause of severe atopy and eosinophilia. Modeling the JAK1GOF (p.A634D) variant in both zebrafish and human induced pluripotent stem cells (iPSCs) revealed enhanced myelopoiesis. RNA-Seq of JAK1GOF human whole blood, iPSCs, and transgenic zebrafish revealed a shared core set of dysregulated genes involved in IL-4, IL-13, and IFN signaling. Immunophenotypic and transcriptomic analysis of patients carrying a JAK1GOF variant revealed marked Th cell skewing. Moreover, long-term ruxolitinib treatment of 2 children carrying the JAK1GOF (p.A634D) variant remarkably improved their growth, eosinophilia, and clinical features of allergic inflammation. This work highlights the role of JAK1 signaling in atopic immune dysregulation and the clinical impact of JAK1/2 inhibition in treating eosinophilic and allergic disease.

Pneumolysin promotes host cell necroptosis and bacterial competence during pneumococcal meningitis as shown by whole-animal dual RNA-seq

Pneumolysin is a major virulence factor of Streptococcus pneumoniae that plays a key role in interaction with the host during invasive disease. How pneumolysin influences these dynamics between host and pathogen interaction during early phase of central nervous system infection in pneumococcal meningitis remains unclear. Using a whole-animal in vivo dual RNA sequencing (RNA-seq) approach, we identify pneumolysin-specific transcriptional responses in both S. pneumoniae and zebrafish (Danio rerio) during early pneumococcal meningitis. By functional enrichment analysis, we identify host pathways known to be activated by pneumolysin and discover the importance of necroptosis for host survival. Inhibition of this pathway using the drug GSK'872 increases host mortality during pneumococcal meningitis. On the pathogen's side, we show that pneumolysin-dependent competence activation is crucial for intra-host replication and virulence. Altogether, this study provides new insights into pneumolysin-specific transcriptional responses and identifies key pathways involved in pneumococcal meningitis.

Optical Coherence Tomography Is a Promising Tool for Zebrafish-Based Research-A Review

The zebrafish is an established vertebrae model in the field of biomedical research. With its small size, rapid maturation time and semi-transparency at early development stages, it has proven to be an important animal model, especially for high-throughput studies. Three-dimensional, high-resolution, non-destructive and label-free imaging techniques are perfectly suited to investigate these animals over various development stages. Optical coherence tomography (OCT) is an interferometric-based optical imaging technique that has revolutionized the diagnostic possibilities in the field of ophthalmology and has proven to be a powerful tool for many microscopic applications. Recently, OCT found its way into state-of-the-art zebrafish-based research. This review article gives an overview and a discussion of the relevant literature and an outlook for this emerging field.

The impact of deleting the mitfa gene in zebrafish on the intestinal microbiota community

To explore the relationship between the mitfa gene and intestinal microbiota, the 16S rRNA gene amplicon sequencing was performed to compare the intestinal microbiota composition of the mitfa knockout zebrafish line (CKO group) and the wild-type zebrafish (WT group) in this study. The results showed that the Fusobacteria and Firmicutes were significantly decreased and the Dependentiae and Patescibacteria were significantly increased in the CKO group at the phylum level. Furthermore, the relative abundance of Citrobacter, Gordonia, Mesorhizobium, Legionella, and Bradyrhizobium were extremely higher in the CKO group, whereas the other four genera Nocardia, Pannonibacter, Shinella, and Cetobacterium were significantly declined in the CKO group at the genus level. Due to these changed intestinal microbiota appear to be related to lipid metabolism and immunity, eight lipid metabolism-related genes and nine inflammation-related genes were detected in the intestinal. The results showed that the expression levels of these genes were significant differences between the CKO and WT group. These results indicated that the deletion of mitfa can affect the expression levels of immune and metabolism-related genes, and causing changes in the composition of the intestinal microbiota.

Modeling leukemia with zebrafish (Danio rerio): Towards precision medicine

Leukemia is a type of blood cancer characterized by high genetic heterogeneity and fatality. While chemotherapy remains the primary form of treatment for leukemia, its effectiveness was profoundly diminished by the genetic heterogeneity and cytogenetic abnormalities of leukemic cells. Therefore, there is an unmet need to develop precision medicine for leukemia with distinct genetic backgrounds. Zebrafish (Danio rerio), a freshwater fish with exceptional feasibility in genome editing, is a powerful tool for rapid human cancer modeling. In the past decades, zebrafish have been adopted in modeling human leukemia, exploring the molecular mechanisms of underlying genetic abnormalities, and discovering novel therapeutic agents. Although many recurrent mutations of leukemia have been modeled in zebrafish for pathological study and drug discovery, its great potential in leukemia modeling was not yet fully exploited, particularly in precision medicine. In this review, we evaluated the current zebrafish models of leukemia/pre-leukemia and genetic techniques and discussed the potential of zebrafish models with novel techniques, which may contribute to the development of zebrafish as a disease model for precision medicine in treating leukemia.

A new software tool for computer assisted in vivo high-content analysis of transplanted fluorescent cells in intact zebrafish larvae

Acute myeloid leukemia and myelodysplastic syndromes are cancers of the bone marrow with poor prognosis in frail and older patients. To investigate cancer pathophysiology and therapies, confocal imaging of fluorescent cancer cells and their response to treatments in zebrafish larvae yields valuable information. While zebrafish larvae are well suited for confocal imaging, the lack of efficient processing of large datasets remains a severe bottleneck. To alleviate this problem, we present a software tool that segments cells from confocal images and track characteristics such as volume, location in the larva and fluorescent intensity on a single-cell basis. Using this software tool, we were able to characterise the responses of the cancer cell lines Molm-13 and MDS-L to established treatments. By utilizing the computer-assisted processing of confocal images as presented here, more information can be obtained while being less time-consuming and reducing the demand of manual data handling, when compared to a manual approach, thereby accelerating the pursuit of novel anti-cancer treatments. The presented software tool is available as an ImageJ java-plugin at https://zenodo.org/10.5281/zenodo.7383160 and the source code at https://github.com/Jfo004/ConfocalCellSegmentation.

Evaluation of Cardiovascular Toxicity of Folic Acid and 6S-5-Methyltetrahydrofolate-Calcium in Early Embryonic Development

Folic acid (FA) is a synthetic and highly stable version of folate, while 6S-5-methyltetrahydrofolate is the predominant form of dietary folate in circulation and is used as a crystalline form of calcium salt (MTHF-Ca). The current study aims to evaluate the toxicity and safety of FA and MTHF-Ca on embryonic development, with a focus on cardiovascular defects. We began to analyze the toxicity of FA and MTHF-Ca in zebrafish from four to seventy-two hours postfertilization and assessed the efficacy of FA and MTHF-Ca in a zebrafish angiogenesis model. We then analyzed the differently expressed genes in in vitro fertilized murine blastocysts cultured with FA and MTHF-Ca. By using gene-expression profiling, we identified a novel gene in mice that encodes an essential eukaryotic translation initiation factor (Eif1ad7). We further applied the morpholino-mediated gene-knockdown approach to explore whether the FA inhibition of this gene (eif1axb in zebrafish) caused cardiac development disorders, which we confirmed with qRT-PCR. We found that FA, but not MTHF-Ca, could inhibit angiogenesis in zebrafish and result in abnormal cardiovascular development, leading to embryonic death owing to the downregulation of eif1axb. MTHF-Ca, however, had no such cardiotoxicity, unlike FA. The current study thereby provides experimental evidence that FA, rather than MTHF-Ca, has cardiovascular toxicity in early embryonic development and suggests that excessive supplementation of FA in perinatal women may be related to the potential risk of cardiovascular disorders, such as congenital heart disease.

Optical transparency and label-free vessel imaging of zebrafish larvae in shortwave infrared range as a tool for prolonged studying of cardiovascular system development

Optical techniques are utilized for the non-invasive analysis of the zebrafish cardiovascular system at early developmental stages. Being based mainly on conventional optical microscopy components and image sensors, the wavelength range of the collected and analyzed light is not out of the scope of 400-900 nm. In this paper, we compared the non-invasive optical approaches utilizing visible and near infrared range (VISNIR) 400-1000 and the shortwave infrared range (SWIR) 900-1700 nm. The transmittance spectra of zebrafish tissues were measured in these wavelength ranges, then vessel maps, heart rates, and blood flow velocities were calculated from data in VISNIR and SWIR. An increased pigment pattern transparency was registered in SWIR, while the heart and vessel detection quality in this range is not inferior to VISNIR. Obtained results indicate an increased efficiency of SWIR imaging for monitoring heart function and hemodynamic analysis of zebrafish embryos and larvae and suggest a prolonged registration period in this range compared to other optical techniques that are limited by pigment pattern development.

Macrophage Reprogramming with Anti-miR223-Loaded Artificial Protocells Enhances In Vivo Cancer Therapeutic Potential

Several immune cell-expressed miRNAs (miRs) are associated with altered prognostic outcome in cancer patients, suggesting that they may be potential targets for development of cancer therapies. Here, translucent zebrafish (Danio rerio) is utilized to demonstrate that genetic knockout or knockdown of one such miR, microRNA-223 (miR223), globally or specifically in leukocytes, does indeed lead to reduced cancer progression. As a first step toward potential translation to a clinical therapy, a novel strategy is described for reprogramming neutrophils and macrophages utilizing miniature artificial protocells (PCs) to deliver anti-miRs against the anti-inflammatory miR223. Using genetic and live imaging approaches, it is shown that phagocytic uptake of anti-miR223-loaded PCs by leukocytes in zebrafish (and by human macrophages in vitro) effectively prolongs their pro-inflammatory state by blocking the suppression of pro-inflammatory cytokines, which, in turn, drives altered immune cell-cancer cell interactions and ultimately leads to a reduced cancer burden by driving reduced proliferation and increased cell death of tumor cells. This PC cargo delivery strategy for reprogramming leukocytes toward beneficial phenotypes has implications also for treating other systemic or local immune-mediated pathologies.

Commentary: Zebrafish as a Model for Osteoporosis-An Approach to Accelerating Progress in Drug and Exercise-Based Treatment

Osteoporosis (OP) is a degenerative disease characterized by reduced bone strength and increased fracture risk. As the global population continues to age, the prevalence and economic burden of osteoporosis can be expected to rise substantially, but there remain various gaps in the field of OP care. For instance, there is a lack of anti-fracture drugs with proven long-term efficacy. Likewise, though exercise remains widely recommended in OP prevention and management, data regarding the safety and efficacy for patients after vertebral fracture remain limited. This lack of evidence may be due to the cost and inherent difficulties associated with exercise-based OP research. Thus, the current research landscape highlights the need for novel research strategies that accelerate OP drug discovery and allow for the low-cost study of exercise interventions. Here, we outline an example of one strategy, the use of zebrafish, which has emerged as a potential model for the discovery of anti-osteoporosis therapeutics and study of exercise interventions. The strengths, limitations, and potential applications of zebrafish in OP research will be outlined.

Quantification of functional recovery in a larval zebrafish model of spinal cord injury

Human spinal cord injury (SCI) is characterized by permanent loss of damaged axons, resulting in chronic disability. In contrast, zebrafish can regenerate axonal projections following central nervous system injury and re-establish synaptic contacts with distant targets; elucidation of the underlying molecular events is an important goal with translational potential for improving outcomes in SCI patients. We generated transgenic zebrafish with GFP-labeled axons and transected their spinal cords at 10 days post-fertilization. Intravital confocal microscopy revealed robust axonal regeneration following the procedure, with abundant axons bridging the transection site by 48 h post-injury. In order to analyze neurological function in this model, we developed and validated new open-source software to measure zebrafish lateral trunk curvature during propulsive and turning movements at high temporal resolution. Immediately following spinal cord transection, axial movements were dramatically decreased caudal to the lesion site, but preserved rostral to the injury, suggesting the induction of motor paralysis below the transection level. Over the subsequent 96 h, the magnitude of movements caudal to the lesion recovered to baseline, but the rate of change of truncal curvature did not fully recover, suggesting incomplete restoration of caudal strength over this time course. Quantification of both morphological and functional recovery following SCI will be important for the analysis of axonal regeneration and downstream events necessary for restoration of motor function. An extensive array of genetic and pharmacological interventions can be deployed in the larval zebrafish model to investigate the underlying molecular mechanisms.

Pilot study of jadomycin B pharmacokinetics and anti-tumoral effects in zebrafish larvae and mouse breast cancer xenograft models

Despite numerous therapeutic options, multidrug resistance (MDR) remains an obstacle to successful breast cancer therapy. Jadomycin B, a natural product derived from Streptomyces venezuelae ISP5230, maintains cytotoxicity in MDR human breast cancer cells. Our objectives were to evaluate the pharmacokinetics, toxicity, anti-tumoral, and anti-metastatic effects of jadomycin B in zebrafish larvae and mice. In a zebrafish larval xenograft model, jadomycin B significantly reduced the proliferation of human MDA-MB-231 cells at or below its maximum tolerated dose (40 µm). In female Balb/C mice, a single intraperitoneal dose (6 mg/kg) was rapidly absorbed with a maximum serum concentration of 3.4 ± 0.27 µm. Jadomycin B concentrations declined biphasically with an elimination half-life of 1.7 ± 0.058 h. In the 4T1 mouse mammary carcinoma model, jadomycin B (12 mg/kg every 12 h from day 6 to 15 after tumor cell injection) decreased primary tumor volume compared to vehicle control. Jadomycin B-treated mice did not exhibit weight loss, nor significant increases in biomarkers of impaired hepatic (alanine aminotransferase) and renal (creatinine) function. In conclusion, jadomycin B demonstrated a good safety profile and provided partial anti-tumoral effects, warranting further dose-escalation safety and efficacy studies in MDR breast cancer models.

A review on the impacts of nanomaterials on neuromodulation and neurological dysfunction using a zebrafish animal model

Nanomaterials have been widely employed from industrial to medical fields due to their small sizes and versatile characteristics. However, nanomaterials can also induce unexpected adverse effects on health. In particular, exposure of the nervous system to nanomaterials can cause serious neurological dysfunctions and neurodegenerative diseases. A number of studies have adopted various animal models to evaluate the neurotoxic effects of nanomaterials. Among them, zebrafish has become an attractive animal model for neurotoxicological studies due to several advantages, including the well-characterized nervous system, efficient genome editing, convenient generation of transgenic lines, high-resolution in vivo imaging, and an array of behavioral assays. In this review, we summarize recent studies on the neurotoxicological effects of nanomaterials, particularly engineered nanomaterials and nanoplastics, using zebrafish and discuss key findings with advantages and limitations of the zebrafish model in neurotoxicological studies.

Increasing the field-of-view in oblique plane microscopy via optical tiling

Fast volumetric imaging of large fluorescent samples with high-resolution is required for many biological applications. Oblique plane microscopy (OPM) provides high spatiotemporal resolution, but the field of view is typically limited by its optical train and the pixel number of the camera. Mechanically scanning the sample or decreasing the overall magnification of the imaging system can partially address this challenge, albeit by reducing the volumetric imaging speed or spatial resolution, respectively. Here, we introduce a novel dual-axis scan unit for OPM that facilitates rapid and high-resolution volumetric imaging throughout a volume of 800 × 500 × 200 microns. This enables us to perform volumetric imaging of cell monolayers, spheroids and zebrafish embryos with subcellular resolution. Furthermore, we combined this microscope with a multi-perspective projection imaging technique that increases the volumetric interrogation rate to more than 10 Hz. This allows us to rapidly probe a large field of view in a dimensionality reduced format, identify features of interest, and volumetrically image these regions with high spatiotemporal resolution.

Zebrafish Avatars of rectal cancer patients validate the radiosensitive effect of metformin

Neoadjuvant chemoradiation (nCRT) followed by surgery represents the standard of care in patients with locally advanced rectal cancer. Increasing radiotherapy (RT) doses and chemotherapy cycles with 5FU have been associated with increased rates of complete response, however these strategies imply significant toxicity. In the last years, epidemiologic findings have demonstrated that metformin is associated with significantly higher rates of pathological complete response to nCRT. Also, pre-clinical studies using cell lines provide evidence for the radiosensitive effect of metformin. However, no studies have been performed using rectal cancer patient samples to test this radiosensitive effect of metformin and compared it to the standard 5FU. Here, we designed an experimental study to compare both radiosensitizers in the zebrafish xenograft model (zAvatar), using rectal cancer surgical specimens and diagnostic biopsies. Patient zAvatars confirmed that metformin has indeed a powerful in vivo radiosensitizer effect, similar to 5FU. Our work confirms that metformin constitutes a promising less toxic alternative to the standard 5FU, which could be game changing in elderly/frail patients to optimize tumor regression.

The Development and Application of Opto-Chemical Tools in the Zebrafish

The zebrafish is one of the most widely adopted animal models in both basic and translational research. This popularity of the zebrafish results from several advantages such as a high degree of similarity to the human genome, the ease of genetic and chemical perturbations, external fertilization with high fecundity, transparent and fast-developing embryos, and relatively low cost-effective maintenance. In particular, body translucency is a unique feature of zebrafish that is not adequately obtained with other vertebrate organisms. The animal's distinctive optical clarity and small size therefore make it a successful model for optical modulation and observation. Furthermore, the convenience of microinjection and high embryonic permeability readily allow for efficient delivery of large and small molecules into live animals. Finally, the numerous number of siblings obtained from a single pair of animals offers large replicates and improved statistical analysis of the results. In this review, we describe the development of opto-chemical tools based on various strategies that control biological activities with unprecedented spatiotemporal resolution. We also discuss the reported applications of these tools in zebrafish and highlight the current challenges and future possibilities of opto-chemical approaches, particularly at the single cell level.

Engraftment of Allotransplanted Tumor Cells in Adult rag2 Mutant Xenopus tropicalis

Simple Summary

While the mouse is without doubt the most studied animal for experimental cancer research, aquatic vertebrates such as zebrafish have also contributed to the field. More recently, thanks to the Nobel-prize winning technology of CRISPR/Cas mediated genomic engineering, the frog Xenopus tropicalis has emerged as an additional powerful model for studying human cancer. Via CRISPR-mediated genome editing, several models for different human cancers have been obtained in this animal. However, what has been lacking in Xenopus is the possibility to transplant tumor cells between different frogs. This is important to allow better characterization of the tumor cells and exploration of therapeutic opportunities. In this paper, we describe the generation of a genetic mutant in Xenopus tropicalis that has a compromised immune system, thereby allowing the grafting and expansion of tumors obtained in this species. In addition, an optimized protocol is provided for the irradiation of wild-type Xenopus frogs that subsequently are temporarily immunocompromised and during that period allow tumor engraftment. This work will expand the toolbox for modeling human cancer in Xenopus tropicalis, thereby further establishing it as a powerful experimental cancer model.

Abstract

Modeling human genetic diseases and cancer in lab animals has been greatly aided by the emergence of genetic engineering tools such as TALENs and CRISPR/Cas9. We have previously demonstrated the ease with which genetically engineered Xenopus models (GEXM) can be generated via injection of early embryos with Cas9 recombinant protein loaded with sgRNAs targeting single or multiple tumor suppressor genes. What has been lacking so far is the possibility to propagate and characterize the induced cancers via transplantation. Here, we describe the generation of a rag2 knockout line in Xenopus tropicalis that is deficient in functional T and B cells. This line was validated by means of allografting experiments with primary tp53^−/− and apc^+/−/tp53^−/− donor tumors. In addition, we optimized available protocols for the sub-lethal irradiation of wild-type X. tropicalis froglets. Irradiated animals also allowed the stable, albeit transient, engraftment of transplanted X. tropicalis tumor cells. The novel rag2^−/− line and the irradiated wild-type froglets will further expand the experimental toolbox in the diploid amphibian X. tropicalis and help to establish it as a versatile and relevant model for exploring human cancer.

Differential proinflammatory activities of Spike proteins of SARS-CoV-2 variants of concern

The coronavirus disease 2019 (COVID-19) pandemic turned the whole world upside down in a short time. One of the main challenges faced has been to understand COVID-19-associated life-threatening hyperinflammation, the so-called cytokine storm syndrome (CSS). We report here the proinflammatory role of Spike (S) proteins from different severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) variants of concern in zebrafish. We found that wild-type/Wuhan variant S1 (S1WT) promoted neutrophil and macrophage recruitment, local and systemic hyperinflammation, emergency myelopoiesis, and hemorrhages. In addition, S1γ was more proinflammatory S1δ was less proinflammatory than S1WT, and, notably, S1β promoted delayed and long-lasting inflammation. Pharmacological inhibition of the canonical inflammasome alleviated S1-induced inflammation and emergency myelopoiesis. In contrast, genetic inhibition of angiotensin-converting enzyme 2 strengthened the proinflammatory activity of S1, and angiotensin (1-7) fully rescued S1-induced hyperinflammation and hemorrhages. These results shed light into the mechanisms orchestrating the COVID-19-associated CSS and the host immune response to different SARS-CoV-2 S protein variants.

Longitudinal investigation of a xenograft tumor zebrafish model using polarization-sensitive optical coherence tomography

Breast cancer is a leading cause of death in female patients worldwide. Further research is needed to get a deeper insight into the mechanisms involved in the development of this devastating disease and to find new therapy strategies. The zebrafish is an established animal model, especially in the field of oncology, which has shown to be a promising candidate for pre-clinical research and precision-based medicine. To investigate cancer growth in vivo in zebrafish, one approach is to explore xenograft tumor models. In this article, we present the investigation of a juvenile xenograft zebrafish model using a Jones matrix optical coherence tomography (JM-OCT) prototype. Immunosuppressed wild-type fish at 1-month post-fertilization were injected with human breast cancer cells and control animals with phosphate buffered saline in the tail musculature. In a longitudinal study, the scatter, polarization, and vasculature changes over time were investigated and quantified in control versus tumor injected animals. A significant decrease in birefringence and an increase in scattering signal was detected in tumor injected zebrafish in comparison to the control once. This work shows the potential of JM-OCT as a non-invasive, label-free, three-dimensional, high-resolution, and tissue-specific imaging tool in pre-clinical cancer research based on juvenile zebrafish models.

Rab35 governs apicobasal polarity through regulation of actin dynamics during sprouting angiogenesis

In early blood vessel development, trafficking programs, such as those using Rab GTPases, are tasked with delivering vesicular cargo with high spatiotemporal accuracy. However, the function of many Rab trafficking proteins remain ill-defined in endothelial tissue; therefore, their relevance to blood vessel development is unknown. Rab35 has been shown to play an enigmatic role in cellular behaviors which differs greatly between tissue-type and organism. Importantly, Rab35 has never been characterized for its potential contribution in sprouting angiogenesis; thus, our goal was to map Rab35’s primary function in angiogenesis. Our results demonstrate that Rab35 is critical for sprout formation; in its absence, apicobasal polarity is entirely lost in vitro and in vivo. To determine mechanism, we systematically explored established Rab35 effectors and show that none are operative in endothelial cells. However, we find that Rab35 partners with DENNd1c, an evolutionarily divergent guanine exchange factor, to localize to actin. Here, Rab35 regulates actin polymerization through limiting Rac1 and RhoA activity, which is required to set up proper apicobasal polarity during sprout formation. Our findings establish that Rab35 is a potent brake of actin remodeling during blood vessel development.

The promiscuous GTPase Rab35 has been shown to be involved in many important cellular functions. In this article, Francis et al. illustrate how Rab35 acts as a critical brake to actin remodeling during sprouting angiogenesis and how it is necessary for proper blood vessel development.

Development of a digital zebrafish phantom and its application to dedicated small-fish PET

Objective. We are developing a small-fish positron emission tomography (PET) scanner dedicated to small aquatic animals relevant for biomedical and biological research, e.g. zebrafish. We plan to use Monte Carlo simulations to optimize its configuration and the required water-filled imaging chambers. Our objectives were: (1) to create a digital 3D zebrafish phantom using conventional micro-CT, (2) include the phantom into a simulated PET environment based on the framework GATE, and (3) investigate the effects of the water environment on the reconstructed images. Approach. To create the phantom, we performed ex vivo measurements of zebrafish specimen using a tabletop micro-CT and compared three methods to fixate the specimen. From segmented micro-CT images we created digital emission and transmission phantoms which were incorporated in GATE via tessellated volumes. Two chamber sizes were considered. For reference, a simulation with the zebrafish in air was implemented. The simulated data were reconstructed using CASToR. For attenuation correction, we used the exact attenuation information or a uniform distribution (only water). Several realizations of each scenario were performed; the reconstructed images were quantitatively evaluated. Main results. Fixation in formalin led to the best soft-tissue contrast at the cost of some specimen deformation. After attenuation correction, no significant differences were found between the reconstructed images. The PET images reflected well the higher uptake simulated in the brain and heart, despite their small size and surrounding background activity; the swim bladder (no activity) was clearly identified. The simplified attenuation map, consisting only of water, slightly worsened the images. Significance. A conventional micro-CT can provide sufficient image quality to generate numerical phantoms of small fish without contrast media. Such phantoms are useful to evaluate in-silico small aquatic animal imaging concepts and develop imaging protocols. Our results support the feasibility of zebrafish PET with an aqueous environment.

One Host-Multiple Applications: Zebrafish (Danio rerio) as Promising Model for Studying Human Cancers and Pathogenic Diseases

In recent years, zebrafish (ZF) has been increasingly applied as a model in human disease studies, with a particular focus on cancer. A number of advantages make it an attractive alternative for mice widely used so far. Due to the many advantages of zebrafish, modifications can be based on different mechanisms and the induction of human disease can take different forms depending on the research goal. Genetic manipulation, tumor transplantation, or injection of the pathogen are only a few examples of using ZF as a model. Most of the studies are conducted in order to understand the disease mechanism, monitor disease progression, test new or alternative therapies, and select the best treatment. The transplantation of cancer cells derived from patients enables the development of personalized medicine. To better mimic a patient's body environment, immune-deficient models (SCID) have been developed. A lower immune response is mostly generated by genetic manipulation but also by irradiation or dexamethasone treatment. For many studies, using SCID provides a better chance to avoid cancer cell rejection. In this review, we describe the main directions of using ZF in research, explain why and how zebrafish can be used as a model, what kind of limitations will be met and how to overcome them. We collected recent achievements in this field, indicating promising perspectives for the future.

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.

Teleost Fish and Organoids: Alternative Windows Into the Development of Healthy and Diseased Brains

The variety in the display of animals’ cognition, emotions, and behaviors, typical of humans, has its roots within the anterior-most part of the brain: the forebrain, giving rise to the neocortex in mammals. Our understanding of cellular and molecular events instructing the development of this domain and its multiple adaptations within the vertebrate lineage has progressed in the last decade. Expanding and detailing the available knowledge on regionalization, progenitors’ behavior and functional sophistication of the forebrain derivatives is also key to generating informative models to improve our characterization of heterogeneous and mechanistically unexplored cortical malformations. Classical and emerging mammalian models are irreplaceable to accurately elucidate mechanisms of stem cells expansion and impairments of cortex development. Nevertheless, alternative systems, allowing a considerable reduction of the burden associated with animal experimentation, are gaining popularity to dissect basic strategies of neural stem cells biology and morphogenesis in health and disease and to speed up preclinical drug testing. Teleost vertebrates such as zebrafish, showing conserved core programs of forebrain development, together with patients-derived in vitro 2D and 3D models, recapitulating more accurately human neurogenesis, are now accepted within translational workflows spanning from genetic analysis to functional investigation. Here, we review the current knowledge of common and divergent mechanisms shaping the forebrain in vertebrates, and causing cortical malformations in humans. We next address the utility, benefits and limitations of whole-brain/organism-based fish models or neuronal ensembles in vitro for translational research to unravel key genes and pathological mechanisms involved in neurodevelopmental diseases.

The MAP3Ks DLK and LZK Direct Diverse Responses to Axon Damage in Zebrafish Peripheral Neurons

Mitogen-activated protein kinase kinase kinases (MAP3Ks) dual leucine kinase (DLK) and leucine zipper kinase (LZK) are essential mediators of axon damage responses, but their responses are varied, complex, and incompletely understood. To characterize their functions in axon injury, we generated zebrafish mutants of each gene, labeled motor neurons (MNs) and touch-sensing neurons in live zebrafish, precisely cut their axons with a laser, and assessed the ability of mutant axons to regenerate in larvae, before sex is apparent in zebrafish. DLK and LZK were required redundantly and cell autonomously for axon regeneration in MNs but not in larval Rohon-Beard (RB) or adult dorsal root ganglion (DRG) sensory neurons. Surprisingly, in dlk lzk double mutants, the spared branches of wounded RB axons grew excessively, suggesting that these kinases inhibit regenerative sprouting in damaged axons. Uninjured trigeminal sensory axons also grew excessively in mutants when neighboring neurons were ablated, indicating that these MAP3Ks are general inhibitors of sensory axon growth. These results demonstrate that zebrafish DLK and LZK promote diverse injury responses, depending on the neuronal cell identity and type of axonal injury.SIGNIFICANCE STATEMENT The MAP3Ks DLK and LZK are damage sensors that promote diverse outcomes to neuronal injury, including axon regeneration. Understanding their context-specific functions is a prerequisite to considering these kinases as therapeutic targets. To investigate DLK and LZK cell-type-specific functions, we created zebrafish mutants in each gene. Using mosaic cell labeling and precise laser injury we found that both proteins were required for axon regeneration in motor neurons but, unexpectedly, were not required for axon regeneration in Rohon-Beard or DRG sensory neurons and negatively regulated sprouting in the spared axons of touch-sensing neurons. These findings emphasize that animals have evolved distinct mechanisms to regulate injury site regeneration and collateral sprouting, and identify differential roles for DLK and LZK in these processes.

Screening of Mineralogenic and Osteogenic Compounds in Zebrafish—Tools to Improve Assay Throughput and Data Accuracy

Bone disorders affect millions of people worldwide and treatments currently available often produce undesirable secondary effects or have limited efficacy. It is therefore of the utmost interest for patients to develop more efficient drugs with reduced off-target activities. In the long process of drug development, screening and preclinical validation have recently gained momentum with the increased use of zebrafish as a model organism to study pathological processes related to human bone disorders, and the development of zebrafish high-throughput screening assays to identify bone anabolic compounds. In this review, we provided a comprehensive overview of the literature on zebrafish bone-related assays and evaluated their performance towards an integration into screening pipelines for the discovery of mineralogenic/osteogenic compounds. Tools available to standardize fish housing and feeding procedures, synchronize embryo production, and automatize specimen sorting and image acquisition/analysis toward faster and more accurate screening outputs were also presented.

A comparative analysis of Danionella cerebrum and zebrafish (Danio rerio) larval locomotor activity in a light-dark test

The genus Danionella comprises some of the smallest known vertebrate species and is evolutionary closely related to the zebrafish, Danio rerio. With its optical translucency, rich behavioral repertoire, and a brain volume of just 0.6 mm³, Danionella cerebrum (Dc) holds great promise for whole-brain in vivo imaging analyses with single cell resolution of higher cognitive functions in an adult vertebrate. Little is currently known, however, about the basic locomotor activity of adult and larval Danionella cerebrum and how it compares to the well-established zebrafish model system. Here, we provide a comparative developmental analysis of the larval locomotor activity of Dc and AB wildtype as well as crystal zebrafish in a light-dark test. We find similarities but also differences in both species, most notably a striking startle response of Dc following a sudden dark to light switch, whereas zebrafish respond most strongly to a sudden light to dark switch. We hypothesize that the different startle responses in both species may stem from their different natural habitats and could represent an opportunity to investigate how neural circuits evolve to evoke different behaviors in response to environmental stimuli.

Dendrite regeneration in the vertebrate spinal cord

Axon regeneration in response to injury has been documented in many animals over several hundred years. In contrast, how neurons respond to dendrite injury has been examined only in the last decade. So far, dendrite regeneration after injury has been documented in invertebrate model systems, but has not been assayed in a vertebrate. In this study, we use zebrafish motor neurons to track neurons after dendrite injury. We address two major gaps in our knowledge of dendrite regeneration: 1) whether post-synaptic dendrites can regenerate and 2) whether vertebrate dendrites can regenerate. We find that motor neurons survive laser microsurgery to remove one or all dendrites. Outgrowth of new dendrites typically initiated one to three days after injury, and a new, stable dendrite arbor was in place by five days after injury. We conclude that zebrafish motor neurons have the capacity to regenerate a new dendrite arbor.

Modeling Spitz melanoma in zebrafish using sequential mutagenesis

Spitz neoplasms are a diverse group of molecularly and histologically defined melanocytic tumors with varying biologic potentials. The precise classification of Spitz neoplasms can be challenging. Recent studies have revealed recurrent fusions involving multiple kinases in a large proportion of Spitz tumors. In this study, we generated a transgenic zebrafish model of Spitz melanoma using a previously identified ZCCHC8-ROS1 fusion gene. Animals developed grossly apparent melanocytic proliferations as early as 3 weeks of age and overt melanoma as early as 5 weeks. By 7 weeks, ZCCHC8-ROS1 induced a histologic spectrum of neoplasms ranging from hyperpigmented patches to melanoma. Given the swift onset of these tumors during development, we extended this approach into adult fish using a recently described electroporation technique. Tissue-specific expression of ZCCHC8-ROS1 in adults led to melanocyte expansion without overt progression to melanoma. Subsequent electroporation with tissue-specific CRISPR, targeting only tp53 was sufficient to induce transformation to melanoma. Our model exhibits the use of sequential mutagenesis in the adult zebrafish, and demonstrates that ZCCHC8-ROS1 induces a spectrum of melanocytic lesions that closely mimics human Spitz neoplasms.

Summary: We describe the first animal model of Spitz neoplasms and demonstrate its use for modeling sequential mutagenesis and its potential for studying melanocyte development in vivo.

Local aberration control to improve efficiency in multiphoton holographic projections

Optical aberrations affect the quality of light propagating through a turbid medium, where refractive index is spatially inhomogeneous. In multiphoton optical applications, such as two-photon excitation fluorescence imaging and optogenetics, aberrations non-linearly impair the efficiency of excitation. We demonstrate a sensorless adaptive optics technique to compensate aberrations in holograms projected into turbid media. We use a spatial light modulator to project custom three dimensional holographic patterns and to correct for local (anisoplanatic) distortions. The method is tested on both synthetic and biological samples to counteract aberrations arising respectively from misalignment of the optical system and from samples inhomogeneities. In both cases the anisoplanatic correction improves the intensity of the stimulation pattern at least two-fold.