Zebrafish Entrapment By Restriction Array (ZEBRA) device: a low-cost, agarose-free zebrafish mounting technique for automated imaging

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.

Fish Capsules: A System for High-Throughput Screening of Combinatorial Drugs

Large-scale screening of molecules heavily relies on phenotyping of small living organisms during preclinical development. However, deep profiling candidate therapeutics on whole animals typically requires laborious manipulations and anesthetic treatment using traditional techniques or automated tools. Here, a novel fish capsule system that combines automated zebrafish encapsulating technology and droplet microarray strategy for in vivo functional screening of mono/polytherapies is described. This platform enables automated, rapid zebrafish orientation and immobilization in agarose to generate large-scale fish capsules by using a microfluidic device. Based on the effect of discontinuous dewetting, the prompt trapping of fish capsules in the aqueous arrays is successfully demonstrate. This system provides the capability to integrate pharmaceutical treatments with real-time multispectral microscopic imaging in a simple, pipetting-free and highly parallel manner. Coupling with machine learning algorithms, a small library of compounds is screened and analyzed, and clues about how to exploit compound combinations as therapeutic candidates are obtained. It is believed that this proposed strategy can be readily applied to multiple fields and is especially useful in the exploration of combinatorial drugs with limited amounts of samples and resources to accelerate the identification of novel therapeutics for precision medicines.

Zebrafish Bioassay for Screening Therapeutic Candidates Based on Melanotrophic Activity

In this study, we used the zebrafish animal model to establish a bioassay by which physiological efficacy differential of alpha-melanocyte-stimulating hormone (α-MSH) analogues could be measured by melanosome dispersion in zebrafish larvae. Brain-skin connection research has purported the interconnectedness between the nervous system and skin physiology. Accordingly, the neuropeptide α-MSH is a key regulator in several physiological processes, such as skin pigmentation in fish. In mammals, α-MSH has been found to regulate motivated behavior, appetite, and emotion, including stimulation of satiety and anxiety. Several clinical and animal model studies of autism spectrum disorder (ASD) have already demonstrated the effectiveness of α-MSH in restoring the social deficits of autism. Therefore, we sought to analyze the effect of synthetic and naturally-occurring α-MSH variants amongst different species. Our results showed that unique α-MSH derivatives from several fish species produced differential effects on the degree of melanophore dispersion. Using α-MSH human form as a standard, we could identify derivatives that induced greater physiological effects; particularly, the synthetic analogue melanotan-II (MT-II) exhibited a higher capacity for melanophore dispersion than human α-MSH. This was consistent with previous findings in an ASD mouse model demonstrating the effectiveness of MT-II in improving ASD behavioral symptoms. Thus, the melanophore assay may serve as a useful screening tool for therapeutic candidates for novel drug discovery.

An improved automated zebrafish larva high-throughput imaging system

As a typical multicellular model organism, the zebrafish has been increasingly used in biological research. Despite the efforts to develop automated zebrafish larva imaging systems, existing ones are still defective in terms of reliability and automation. This paper presents an improved zebrafish larva high-throughput imaging system, which makes improvements to the existing designs in the following aspects. Firstly, a single larva extraction strategy is developed to make larva loading more reliable. The aggregated larvae are identified, classified by their numbers and patterns, and separated by the aspiration pipette or water stream. Secondly, the dynamic model of larva motion in the capillary is established and an adaptive robust controller is designed for decelerating the fast-moving larva to ensure the survival rate. Thirdly, rotating the larva to the desired orientation is automated by developing an algorithm to estimate the larva's initial rotation angle. For validating the improved larva imaging system, a real-time heart rate monitoring experiment is conducted as an application example. Experimental results demonstrate that the goals of the improvements have been achieved. With these improvements, the improved zebrafish larva imaging system remarkably reduces human intervention and increases the efficiency and success/survival rates of larva imaging.

Modeling Inflammation in Zebrafish for the Development of Anti-inflammatory Drugs

Dysregulation of the inflammatory response in humans can lead to various inflammatory diseases, like asthma and rheumatoid arthritis. The innate branch of the immune system, including macrophage and neutrophil functions, plays a critical role in all inflammatory diseases. This part of the immune system is well-conserved between humans and the zebrafish, which has emerged as a powerful animal model for inflammation, because it offers the possibility to image and study inflammatory responses in vivo at the early life stages. This review focuses on different inflammation models established in zebrafish, and how they are being used for the development of novel anti-inflammatory drugs. The most commonly used model is the tail fin amputation model, in which part of the tail fin of a zebrafish larva is clipped. This model has been used to study fundamental aspects of the inflammatory response, like the role of specific signaling pathways, the migration of leukocytes, and the interaction between different immune cells, and has also been used to screen libraries of natural compounds, approved drugs, and well-characterized pathway inhibitors. In other models the inflammation is induced by chemical treatment, such as lipopolysaccharide (LPS), leukotriene B4 (LTB4), and copper, and some chemical-induced models, such as treatment with trinitrobenzene sulfonic acid (TNBS), specifically model inflammation in the gastro-intestinal tract. Two mutant zebrafish lines, carrying a mutation in the hepatocyte growth factor activator inhibitor 1a gene (hai1a) and the cdp-diacylglycerolinositol 3-phosphatidyltransferase (cdipt) gene, show an inflammatory phenotype, and they provide interesting model systems for studying inflammation. These zebrafish inflammation models are often used to study the anti-inflammatory effects of glucocorticoids, to increase our understanding of the mechanism of action of this class of drugs and to develop novel glucocorticoid drugs. In this review, an overview is provided of the available inflammation models in zebrafish, and how they are used to unravel molecular mechanisms underlying the inflammatory response and to screen for novel anti-inflammatory drugs.

A non-invasive acoustic-trapping of zebrafish microfluidics

Zebrafish is an emerging alternative model in behavioral and neurological studies for pharmaceutical applications. However, little is known regarding the effects of noise exposure on laboratory-grown zebrafish. Accordingly, this study commenced by exposing zebrafish embryos to loud background noise (≥200 Hz, 80 ± 10 dB) for five days in a microfluidic environment. The noise exposure was found to affect the larvae hatching rate, larvae length, and swimming performance. A microfluidic platform was then developed for the sorting/trapping of hatched zebrafish larvae using a non-invasive method based on light cues and acoustic actuation. The experimental results showed that the proposed method enabled zebrafish larvae to be transported and sorted into specific chambers of the microchannel network in the desired time frame. The proposed non-invasive trapping method thus has potentially profound applications in drug screening.

A Microfluidic System for Stable and Continuous EEG Monitoring from Multiple Larval Zebrafish

Along with the increasing popularity of larval zebrafish as an experimental animal in the fields of drug screening, neuroscience, genetics, and developmental biology, the need for tools to deal with multiple larvae has emerged. Microfluidic channels have been employed to handle multiple larvae simultaneously, even for sensing electroencephalogram (EEG). In this study, we developed a microfluidic chip capable of uniform and continuous drug infusion across all microfluidic channels during EEG recording. Owing to the modular design of the microfluidic channels, the number of animals under investigation can be easily increased. Using the optimized design of the microfluidic chip, liquids could be exchanged uniformly across all channels without physically affecting the larvae contained in the channels, which assured a stable environment maintained all the time during EEG recording, by eliminating environmental artifacts and leaving only biological effects to be seen. To demonstrate the usefulness of the developed system in drug screening, we continuously measured EEG from four larvae without and with pentylenetetrazole application, up to 60 min. In addition, we recorded EEG from valproic acid (VPA)-treated zebrafish and demonstrated the suppression of seizure by VPA. The developed microfluidic system could contribute to the mass screening of EEG for drug development to treat neurological disorders such as epilepsy in a short time, owing to its handy size, cheap fabrication cost, and the guaranteed uniform drug infusion across all channels with no environmentally induced artifacts.

Discovery of Novel Therapeutics for Muscular Dystrophies using Zebrafish Phenotypic Screens

The recent availability and development of mutant and transgenic zebrafish strains that model human muscular dystrophies has created new research opportunities for therapeutic development. Not only do these models mimic many pathological aspects of human dystrophies, but their small size, large clutch sizes, rapid ex utero development, body transparency, and genetic tractability enable research approaches that would be inconceivable with mammalian model systems. Here we discuss the use of zebrafish models of muscular dystrophy to rapidly screen hundreds to thousands of bioactive compounds in order to identify novel therapeutic candidates that modulate pathologic phenotypes. We review the justification and rationale behind this unbiased approach, including how zebrafish screens have identified FDA-approved drugs that are candidates for treating Duchenne and limb girdle muscular dystrophies. Not only can these drugs be re-purposed for treating dystrophies in a fraction of the time and cost of new drug development, but their identification has revealed novel, unexpected directions for future therapy development. Phenotype-driven zebrafish drug screens are an important compliment to the more established mammalian, target-based approaches for rapidly developing and validating therapeutics for muscular dystrophies.

Extended culture and imaging of normal and regenerating adult zebrafish hearts in a fluidic device

Myocardial infarction and heart failure are leading causes of death worldwide, in large part because adult human myocardium has extremely limited regeneration capacity. Zebrafish are a powerful model for identifying new strategies for human cardiac repair because their hearts regenerate after relatively severe injuries. Zebrafish are also relatively scalable and compatible with many genetic tools. However, characterizing the regeneration process in live adult zebrafish hearts has proved challenging because adult fish are opaque, preventing live imaging in vivo. An alternative strategy is to explant and culture intact adult zebrafish hearts and investigate them ex vivo. However, explanted hearts maintained in conventional culture conditions experience rapid declines in morphology and physiology. To overcome these limitations, we designed and fabricated a fluidic device for culturing explanted adult zebrafish hearts with constant media perfusion that is also compatible with live imaging. We then compared the morphology and calcium activity of hearts cultured in the device, hearts cultured statically in dishes, and freshly explanted hearts. After one week of culture, hearts in the device experienced significantly less morphological degradation compared to hearts cultured in dishes. Hearts cultured in devices for one week also maintained capture rates similar to fresh hearts, unlike hearts cultured in dishes. We then cultured explanted injured hearts in the device and used live imaging techniques to continuously record the myocardial revascularization process over several days, demonstrating how our device is compatible with long-term live imaging and thereby enables unprecedented visual access to the multi-day process of adult zebrafish heart regeneration.

Microfluidic devices for embryonic and larval zebrafish studies

Zebrafish or Danio rerio is an established model organism for studying the genetic, neuronal and behavioral bases of diseases and for toxicology and drug screening. The embryonic and larval stages of zebrafish have been used extensively in fundamental and applied research due to advantages offered such as body transparency, small size, low cost of cultivation and high genetic homology with humans. However, the manual experimental methods used for handling and investigating this organism are limited due to their low throughput, labor intensiveness and inaccuracy in delivering external stimuli to the zebrafish while quantifying various neuronal and behavioral responses. Microfluidic and lab-on-a-chip devices have emerged as ideal technologies to overcome these challenges. In this review paper, the current microfluidic approaches for investigation of behavior and neurobiology of zebrafish at embryonic and larval stages will be reviewed. Our focus will be to provide an overview of the microfluidic methods used to manipulate (deliver and orient), immobilize and expose or inject zebrafish embryos or larvae, followed by quantification of their responses in terms of neuron activities and movement. We will also provide our opinion in terms of the direction that the field of zebrafish microfluidics is heading toward in the area of biomedical engineering.

Microstructured Devices for Optimized Microinjection and Imaging of Zebrafish Larvae

Zebrafish have emerged as a powerful model of various human diseases and a useful tool for an increasing range of experimental studies, spanning fundamental developmental biology through to large-scale genetic and chemical screens. However, many experiments, especially those related to infection and xenograft models, rely on microinjection and imaging of embryos and larvae, which are laborious techniques that require skill and expertise. To improve the precision and throughput of current microinjection techniques, we developed a series of microstructured devices to orient and stabilize zebrafish embryos at 2 days post fertilization (dpf) in ventral, dorsal, or lateral orientation prior to the procedure. To aid in the imaging of embryos, we also designed a simple device with channels that orient 4 zebrafish laterally in parallel against a glass cover slip. Together, the tools that we present here demonstrate the effectiveness of photolithographic approaches to generate useful devices for the optimization of zebrafish techniques.

Milling Positive Master for Polydimethylsiloxane Microfluidic Devices: The Microfabrication and Roughness Issues

We provide a facile and low-cost method (F-L) to fabricate a two-dimensional positive master using a milling technique for polydimethylsiloxane (PDMS)-based microchannel molding. This method comprises the following steps: (1) a positive microscale master of the geometry is milled on to an acrylic block; (2) pre-cured PDMS is used to mold the microscale positive master; (3) the PDMS plate is peeled off from the master and punctured with a blunt needle; and (4) the PDMS plate is O₂ plasma bonded to a glass slide. Using this technique, we can fabricate microchannels with very simple protocols quickly and inexpensively. This method also avoids breakage of the end mill (ϕ = 0.4 mm) of the computerized numerical control (CNC) system when fabricating the narrow channels (width < 50 µm). The prominent surface roughness of the milled bottom-layer could be overcomed by pre-cured PDMS with size trade-off in design. Finally, emulsion formation successfully demonstrates the validity of the proposed fabrication protocol. This work represents an important step toward the use of a milling technique for PDMS-based microfabrication.

Microstructured Surface Arrays for Injection of Zebrafish Larvae

Microinjection of zebrafish larvae is an essential technique for delivery of treatments, dyes, microbes, and xenotransplantation into various tissues. Although a number of casts are available to orient embryos at the single-cell stage, no device has been specifically designed to position hatching-stage larvae for microinjection of different tissues. In this study, we present a reusable silicone device consisting of arrayed microstructures, designed to immobilize 2 days postfertilization larvae in lateral, ventral, and dorsal orientations, while providing maximal access to target sites for microinjection. Injection of rhodamine dextran was used to demonstrate the utility of this device for precise microinjection of multiple anatomical targets.

Manipulation of zebrafish's orientation using artificial cilia in a microchannel with actively adaptive wall design

The zebrafish is a powerful genetic model organism especially in the biomedical chapter for new drug discovery and development. The genetic toolbox which this vertebrate possesses opens a new window to investigate the etiology of human diseases with a high degree genetic similarity. Still, the requirements of laborious and time-consuming of contemporary zebrafish processing assays limit the procedure in carrying out such genetic screen at high throughput. Here, a zebrafish control scheme was initiated which includes the design and validation of a microfluidic platform to significantly increase the throughput and performance of zebrafish larvae manipulation using the concept of artificial cilia actuation. A moving wall design was integrated into this microfluidic platform first time in literature to accommodate zebrafish inside the microchannel from 1 day post-fertilization (dpf) to 6 dpf and can be further extended to 9 dpf for axial orientation control in a rotational range between 0 to 25 degrees at the minimum step of 2-degree increment in a stepwise manner. This moving wall feature was performed through the deflection of shape memory alloy wire embedded inside the microchannel controlled by the electrical waveforms with high accuracy.

zWEDGI: Wounding and Entrapment Device for Imaging Live Zebrafish Larvae

Zebrafish, an established model organism in developmental biology, is also a valuable tool for imaging wound healing in space and time with cellular resolution. However, long-term imaging of wound healing poses technical challenges as wound healing occurs over multiple temporal scales. The traditional strategy of larval encapsulation in agarose successfully limits sample movement but impedes larval development and tissue regrowth and is therefore not amenable to long-term imaging of wound healing. To overcome this challenge, we engineered a functionally compartmentalized device, the zebrafish Wounding and Entrapment Device for Growth and Imaging (zWEDGI), to orient larvae for high-resolution microscopy, including confocal and second harmonic generation (SHG), while allowing unrestrained tail development and regrowth. In this device, larval viability was maintained and tail regrowth was improved over embedding in agarose. The quality of tail fiber SHG images collected from larvae in the device was similar to fixed samples but provided the benefit of time lapse data collection. Furthermore, we show that this device was amenable to long-term (>24 h) confocal microscopy of the caudal fin. Finally, the zWEDGI was designed and fabricated using readily available techniques so that it can be easily modified for diverse experimental imaging protocols.

A Novel Long-term, Multi-Channel and Non-invasive Electrophysiology Platform for Zebrafish

Zebrafish are a popular vertebrate model for human neurological disorders and drug discovery. Although fecundity, breeding convenience, genetic homology and optical transparency have been key advantages, laborious and invasive procedures are required for electrophysiological studies. Using an electrode-integrated microfluidic system, here we demonstrate a novel multichannel electrophysiology unit to record multiple zebrafish. This platform allows spontaneous alignment of zebrafish and maintains, over days, close contact between head and multiple surface electrodes, enabling non-invasive long-term electroencephalographic recording. First, we demonstrate that electrographic seizure events, induced by pentylenetetrazole, can be reliably distinguished from eye or tail movement artifacts, and quantifiably identified with our unique algorithm. Second, we show long-term monitoring during epileptogenic progression in a scn1lab mutant recapitulating human Dravet syndrome. Third, we provide an example of cross-over pharmacology antiepileptic drug testing. Such promising features of this integrated microfluidic platform will greatly facilitate high-throughput drug screening and electrophysiological characterization of epileptic zebrafish.

Fish-on-a-chip: microfluidics for zebrafish research

High-efficiency zebrafish (embryo) handling platforms are crucially needed to facilitate the deciphering of the increasingly expanding vertebrate-organism model values. However, the manipulation platforms for zebrafish are scarce and rely mainly on the conventional "static" microtiter plates or glass slides with rigid gel, which limits the dynamic, three-dimensional (3D), tissue/organ-oriented information acquisition from the intact larva with normal developmental dynamics. In addition, these routine platforms are not amenable to high-throughput handling of such swimming multicellular biological entities at the single-organism level and incapable of precisely controlling the growth microenvironment by delivering stimuli in a well-defined spatiotemporal fashion. Recently, microfluidics has been developed to address these technical challenges via tailor-engineered microscale structures or structured arrays, which integrate with or interface to functional components (e.g. imaging systems), allowing quantitative readouts of small objects (zebrafish larvae and embryos) under normal physiological conditions. Here, we critically review the recent progress on zebrafish manipulation, imaging and phenotype readouts of external stimuli using these microfluidic tools and discuss the challenges that confront these promising "fish-on-a-chip" technologies. We also provide an outlook on future potential trends in this field by combining with bionanoprobes and biosensors.

Autonomous system for cross-organ investigation of ethanol-induced acute response in behaving larval zebrafish

Ethanol is widely consumed and has been associated with various diseases in different organs. It is therefore important to study ethanol-induced responses in living organisms with the capability to address specific organs in an integrative manner. Here, we developed an autonomous system based on a series of microfluidic chips for cross-organ investigation of ethanol-induced acute response in behaving larval zebrafish. This system enabled high-throughput, gel-free, and anesthetic-free manipulation of larvae, and thus allowed real-time observation of behavioral responses, and associated physiological changes at cellular resolution within specific organs in response to acute ethanol stimuli, which would otherwise be impossible by using traditional methods for larva immobilization and orientation. Specifically, three types of chips ("motion," "lateral," and "dorsal"), based on a simple hydrodynamic design, were used to perform analysis in animal behavior, cardiac, and brain physiology, respectively. We found that ethanol affected larval zebrafish in a dose-dependent manner. The motor function of different body parts was significantly modulated by ethanol treatment, especially at a high dose of 3%. These behavioral changes were temporally associated with a slow-down of heart-beating and a stereotyped activation of certain brain regions. As we demonstrated in this proof-of-concept study, this versatile Fish-on-Chip platform could potentially be adopted for systematic cross-organ investigations involving chemical or genetic manipulations in zebrafish model.

Microfluidics for High-Throughput Quantitative Studies of Early Development

Developmental biology has traditionally relied on qualitative analyses; recently, however, as in other fields of biology, researchers have become increasingly interested in acquiring quantitative knowledge about embryogenesis. Advances in fluorescence microscopy are enabling high-content imaging in live specimens. At the same time, microfluidics and automation technologies are increasing experimental throughput for studies of multicellular models of development. Furthermore, computer vision methods for processing and analyzing bioimage data are now leading the way toward quantitative biology. Here, we review advances in the areas of fluorescence microscopy, microfluidics, and data analysis that are instrumental to performing high-content, high-throughput studies in biology and specifically in development. We discuss a case study of how these techniques have allowed quantitative analysis and modeling of pattern formation in the Drosophila embryo.

Automation of Technology for Cancer Research

Zebrafish embryos can be obtained for research purposes in large numbers at low cost and embryos develop externally in limited space, making them highly suitable for high-throughput cancer studies and drug screens. Non-invasive live imaging of various processes within the larvae is possible due to their transparency during development, and a multitude of available fluorescent transgenic reporter lines.To perform high-throughput studies, handling large amounts of embryos and larvae is required. With such high number of individuals, even minute tasks may become time-consuming and arduous. In this chapter, an overview is given of the developments in the automation of various steps of large scale zebrafish cancer research for discovering important cancer pathways and drugs for the treatment of human disease. The focus lies on various tools developed for cancer cell implantation, embryo handling and sorting, microfluidic systems for imaging and drug treatment, and image acquisition and analysis. Examples will be given of employment of these technologies within the fields of toxicology research and cancer research.

Micromilling: a method for ultra-rapid prototyping of plastic microfluidic devices

This tutorial review offers protocols, tips, insight, and considerations for practitioners interested in using micromilling to create microfluidic devices. The objective is to provide a potential user with information to guide them on whether micromilling would fill a specific need within their overall fabrication strategy. Comparisons are made between micromilling and other common fabrication methods for plastics in terms of technical capabilities and cost. The main discussion focuses on "how-to" aspects of micromilling, to enable a user to select proper equipment and tools, and obtain usable microfluidic parts with minimal start-up time and effort. The supplementary information provides more extensive discussion on CNC mill setup, alignment, and programming. We aim to reach an audience with minimal prior experience in milling, but with strong interests in fabrication of microfluidic devices.

Light-addressable measurement of in vivo tissue oxygenation in an unanesthetized zebrafish embryo via phase-based phosphorescence lifetime detection

We have developed a digital light modulation system that utilizes a modified commercial projector equipped with a laser diode as a light source for quantitative measurements of in vivo tissue oxygenation in an unanesthetized zebrafish embryo via phase-based phosphorescence lifetime detection. The oxygen-sensitive phosphorescent probe (Oxyphor G4) was first inoculated into the bloodstream of 48 h post-fertilization (48 hpf) zebrafish embryos via the circulation valley to rapidly disperse probes throughout the embryo. The unanesthetized zebrafish embryo was introduced into the microfluidic device and immobilized on its lateral side by using a pneumatically actuated membrane. By controlling the illumination pattern on the digital micromirror device in the projector, the modulated excitation light can be spatially projected to illuminate arbitrarily-shaped regions of tissue of interest for in vivo oxygen measurements. We have successfully measured in vivo oxygen changes in the cardiac region and cardinal vein of a 48 hpf zebrafish embryo that experience hypoxia and subsequent normoxic conditions. Our proposed platform provides the potential for the real-time investigation of oxygen distribution in tissue microvasculature that relates to physiological stimulation and diseases in a developing organism.

Biochemical characterization of three BLT receptors in zebrafish

The leukotriene B₄ (LTB₄) receptor 1 (BLT1) is a high affinity receptor for LTB₄, a chemotactic and inflammatory eicosanoid. The LTB₄ receptor 2 (BLT2) was originally identified as a low affinity receptor for LTB₄, and, more recently, as a high affinity receptor for 12-hydroxyheptadecatrienoic acid (12-HHT). The zebrafish BLT receptors have not been previously identified and the in vivo functions of these receptors have been unknown. In this paper, we describe one zebrafish BLT1-like receptor, Blt1, and two zebrafish BLT2-like receptors, Blt2a and Blt2b. Cells expressing Blt1 exhibited LTB₄-induced intracellular [Ca²⁺] increases, inhibition of cAMP production, ligand-dependent [³⁵S]GTPγS binding, and transforming growth factor-α (TGFα) shedding activity in a dose-dependent manner, similar to human BLT1. Cells expressing Blt2a and Blt2b exhibited 12-HHT- and LTB₄-induced intracellular [Ca²⁺] increases, inhibition of cAMP production, [³⁵S]GTPγS binding, and TGFα shedding activity, with a dose-dependency similar to human BLT2. Reverse transcription (RT)-PCR analysis and whole-mount in situ hybridization revealed that blt1, blt2a, blt2b, zebrafish LTA₄ hydrolase (lta4h), and zebrafish 5-lipoxiganase (5lo) are expressed in zebrafish embryos. Knockdown of blt1 by morpholino antisense oligonucleotides resulted in delayed epiboly at gastrulation. Consistently, knockdown of lta4h, an enzyme mediating LTB₄ production, induced a phenotype similar to knockdown of blt1. These results suggest that the LTB₄-BLT1 axis is involved in epiboly in zebrafish development.

Successes and future outlook for microfluidics-based cardiovascular drug discovery

INTRODUCTION

The greatest advantage of using microfluidics as a platform for the assessment of cardiovascular drug action is its ability to finely regulate fluid flow conditions, including flow rate, shear stress and pulsatile flow. At the same time, microfluidics provide means for modifying the vessel geometry (bifurcations, stenoses, complex networks), the type of surface of the vessel walls, and for patterning cells in 3D tissue-like architecture, including generation of lumen walls lined with cells and heart-on-a-chip structures for mimicking ventricular cardiomyocyte physiology. In addition, owing to the small volume of required specimens, microfluidics is ideally suited to clinical situations whereby monitoring of drug dosing or efficacy needs to be coupled with minimal phlebotomy-related drug loss.

AREAS COVERED

In this review, the authors highlight potential applications for the currently existing and emerging technologies and offer several suggestions on how to close the development cycle of microfluidic devices for cardiovascular drug discovery.

EXPERT OPINION

The ultimate goal in microfluidics research for drug discovery is to develop 'human-on-a-chip' systems, whereby several organ cultures, including the vasculature and the heart, can mimic complex interactions between the organs and body systems. This would provide in vivo-like pharmacokinetics and pharmacodynamics for drug ADMET assessment. At present, however, the great variety of available designs does not go hand in hand with their use by the pharmaceutical community.

High-throughput mapping of brain-wide activity in awake and drug-responsive vertebrates

The reconstruction of neural activity across complete neural circuits, or brain activity mapping, has great potential in both fundamental and translational neuroscience research. Larval zebrafish, a vertebrate model, has recently been demonstrated to be amenable to whole brain activity mapping in behaving animals. Here we demonstrate a microfluidic array system ("Fish-Trap") that enables high-throughput mapping of brain-wide activity in awake larval zebrafish. Unlike the commonly practiced larva-processing methods using a rigid gel or a capillary tube, which are laborious and time-consuming, the hydrodynamic design of our microfluidic chip allows automatic, gel-free, and anesthetic-free processing of tens of larvae for microscopic imaging with single-cell resolution. Notably, this system provides the capability to directly couple pharmaceutical stimuli with real-time recording of neural activity in a large number of animals, and the local and global effects of pharmacoactive drugs on the nervous system can be directly visualized and evaluated by analyzing drug-induced functional perturbation within or across different brain regions. Using this technology, we tested a set of neurotoxin peptides and obtained new insights into how to exploit neurotoxin derivatives as therapeutic agents. The novel and versatile "Fish-Trap" technology can be readily unitized to study other stimulus (optical, acoustic, or physical) associated functional brain circuits using similar experimental strategies.

A microfluidic system for studying the behavior of zebrafish larvae under acute hypoxia

Oxygen is essential for metabolism of animals and is a vital component of their natural habitats. Hypoxic conditions in tissue, when oxygen levels are lower than normal, change a variety of cellular processes, while environmental hypoxia can have physiological and behavioral effects on the whole animal. Larval zebrafish respond to oxygen deprivation with a characteristic set of physiological changes and motor behaviors, making them a convenient vertebrate model to study hypoxia responses. However, to date, hypoxia studies in zebrafish are limited by the existing experimental setups, which only impose hypoxia on a scale of minutes to hours. Here, we present a microfluidic system, which makes it possible to expose spatially confined unanesthetized zebrafish larvae to a broad range of hypoxic and normoxic conditions and to switch between different oxygen concentrations in the medium around the larvae on a 2 second timescale. We used the system to observe different behavioral responses of zebrafish larvae to three levels of rapidly imposed hypoxia. Larvae increased their rate of body movements in response to the strongest hypoxia and increased their rate of pectoral fin beats in response to all levels of hypoxia. Importantly, the behavior of the larvae changed within 15 seconds of the changes in the oxygen content of the medium. The proposed experimental system can be used to study the behavior of zebrafish larvae or other aquatic organisms exposed to other water-dissolved gasses or to different temporal patterns of oxygen concentration. This system can also potentially be used for testing the effects of genetic modifications and small molecule drugs and for probing neural mechanisms underlying various behaviors.

Fishing on chips: up-and-coming technological advances in analysis of zebrafish and Xenopus embryos

Biotests performed on small vertebrate model organisms provide significant investigative advantages as compared with bioassays that employ cell lines, isolated primary cells, or tissue samples. The main advantage offered by whole-organism approaches is that the effects under study occur in the context of intact physiological milieu, with all its intercellular and multisystem interactions. The gap between the high-throughput cell-based in vitro assays and low-throughput, disproportionally expensive and ethically controversial mammal in vivo tests can be closed by small model organisms such as zebrafish or Xenopus. The optical transparency of their tissues, the ease of genetic manipulation and straightforward husbandry, explain the growing popularity of these model organisms. Nevertheless, despite the potential for miniaturization, automation and subsequent increase in throughput of experimental setups, the manipulation, dispensing and analysis of living fish and frog embryos remain labor-intensive. Recently, a new generation of miniaturized chip-based devices have been developed for zebrafish and Xenopus embryo on-chip culture and experimentation. In this work, we review the critical developments in the field of Lab-on-a-Chip devices designed to alleviate the limits of traditional platforms for studies on zebrafish and clawed frog embryo and larvae. © 2014 International Society for Advancement of Cytometry.

Microfluidics expands the zebrafish potentials in pharmaceutically relevant screening

The objective of this study is to enlarge the impact of microfluidics on the pharmaceutical industry by highlighting the reported scientific work on the synergistic relationship between zebrafish and microfluidics, and furthering that effort to shed light on how microfluidics can facilitate the use of zebrafish as a gene screening tool. Zebrafish is ranked the third most important animal model after rats and mice, according to a National Institutes of Health (NIH) announcement in 2003. It has become a staple for scientists to examine and subsequently begin to unravel the mystery of human diseases, and is increasingly used in toxicological studies for new drug development. The unique characteristics that this tiny fish possesses, including rapid growth rate, prodigious numbers of offspring, and eggs that develop outside the body, make it an invaluable genetic tool. Evidently, these advantages can be broadened with the addition of a properly designed microfluidic circuit. By means of the presented illustrations and demonstrated applications, the goal is to spark interest in the development of more novel microfluidic platform designs that can leverage the attributes of zebrafish and quickly come to commercial fruition.

Zebrafish on a chip: a novel platform for real-time monitoring of drug-induced developmental toxicity

Pharmaceutical safety testing requires a cheap, fast and highly efficient platform for real-time evaluation of drug toxicity and secondary effects. In this study, we have developed a microfluidic system for phenotype-based evaluation of toxic and teratogenic effects of drugs using zebrafish (Danio rerio) embryos and larvae as the model organism. The microfluidic chip is composed of two independent functional units, enabling the assessment of zebrafish embryos and larvae. Each unit consists of a fluidic concentration gradient generator and a row of seven culture chambers to accommodate zebrafish. To test the accuracy of this new chip platform, we examined the toxicity and teratogenicity of an anti-asthmatic agent-aminophylline (Apl) on 210 embryos and 210 larvae (10 individuals per chamber). The effect of Apl on zebrafish embryonic development was quantitatively assessed by recording a series of physiological indicators such as heart rate, survival rate, body length and hatch rate. Most importantly, a new index called clonic convulsion rate, combined with mortality was used to evaluate the toxicities of Apl on zebrafish larvae. We found that Apl can induce deformity and cardiovascular toxicity in both zebrafish embryos and larvae. This microdevice is a multiplexed testing apparatus that allows for the examination of indexes beyond toxicity and teratogenicity at the sub-organ and cellular levels and provides a potentially cost-effective and rapid pharmaceutical safety assessment tool.

Low-cost silicone imaging casts for zebrafish embryos and larvae

Due to their size and optical clarity, zebrafish embryos have long been appreciated for their usefulness in time-lapse confocal microscopy. Current methods of mounting zebrafish embryos and larvae for imaging consist mainly of mounting in low percentage, low melting temperature agarose in a Petri dish. Whereas imaging methods have advanced greatly over the last two decades, the methods for mounting embryos have not changed significantly. In this article, we describe the development and use of 3D printed plastic molds. These molds can be used to create silicone casts and allow embryos and larvae to be mounted with a consistent and reproducible angle, and position in X, Y, and Z. These molds are made on a 3D printer and can be easily and cheaply reproduced by anyone with access to a 3D printer, making this method accessible to the entire zebrafish community. Molds can be reused to create additional casts, which can be reused after imaging. These casts are compatible with any upright microscope and can be adapted for use on an inverted microscope, taking the working distance of the objective used into account. This technique should prove to be useful to any researcher imaging zebrafish embryos.

Animal microsurgery using microfluidics

Small multicellular genetic organisms form a central part of modern biological research. Using these small organisms provides significant advantages in genetic tractability, manipulation, lifespan and cost. Although the small size is generally advantageous, it can make procedures such as surgeries both time consuming and labor intensive. Over the past few years there have been dramatic improvements in microfluidic technologies that enable significant improvements in microsurgery and interrogation of small multicellular model organisms.