An innovative continuous flow system for monitoring heavy metal pollution in water using transgenic Xenopus laevis tadpoles

Ecotoxicological perspectives of microplastic pollution in amphibians

Microplastics (MPs) are contaminants widely distributed in the environment and biota. Previously, most studies focused on identifying and characterizing microplastics in the marine environment, while their impact on freshwater ecosystems remains to be determined. This review summarizes recent findings regarding MPs physiological, immunological, and genetic effects on amphibians based upon the biological relevance of this species as indicators of freshwater pollution. Data demonstrated that MPs contamination may potentially alter various physiological processes in aquatic animals, mainly in the embryonic stages. It is worthwhile noting that adverse effects might be enhanced in synergy with other pollutants. However, amphibians might counteract the effect of MPs and other pollutants through microbiota present both in the intestine and on the skin. In addition, amphibian microbial composition might also be altered by MPs themselves in a manner that leads to unpredicted health consequences in amphibians.

High-throughput screening paradigms in ecotoxicity testing: Emerging prospects and ongoing challenges

The rapidly increasing number of new production chemicals coupled with stringent implementation of global chemical management programs necessities a paradigm shift towards boarder uses of low-cost and high-throughput ecotoxicity testing strategies as well as deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity that can be used in effective risk assessment. The latter will require automated acquisition of biological data, new capabilities for big data analysis as well as computational simulations capable of translating new data into in vivo relevance. However, very few efforts have been so far devoted into the development of automated bioanalytical systems in ecotoxicology. This is in stark contrast to standardized and high-throughput chemical screening and prioritization routines found in modern drug discovery pipelines. As a result, the high-throughput and high-content data acquisition in ecotoxicology is still in its infancy with limited examples focused on cell-free and cell-based assays. In this work we outline recent developments and emerging prospects of high-throughput bioanalytical approaches in ecotoxicology that reach beyond in vitro biotests. We discuss future importance of automated quantitative data acquisition for cell-free, cell-based as well as developments in phytotoxicity and in vivo biotests utilizing small aquatic model organisms. We also discuss recent innovations such as organs-on-a-chip technologies and existing challenges for emerging high-throughput ecotoxicity testing strategies. Lastly, we provide seminal examples of the small number of successful high-throughput implementations that have been employed in prioritization of chemicals and accelerated environmental risk assessment.

Recent progress in cytometric technologies and their applications in ecotoxicology and environmental risk assessment

Environmental toxicology focuses on identifying and predicting impact of potentially toxic anthropogenic chemicals on biosphere at various levels of biological organization. Presently there is a significant drive to gain deeper understanding of cellular and sub-cellular mechanisms of ecotoxicity. Most notable is increased focus on elucidation of cellular-response networks, interactomes, and greater implementation of cell-based biotests using high-throughput procedures, while at the same time decreasing the reliance on standard animal models used in ecotoxicity testing. This is aimed at discovery and interpretation of molecular pathways of ecotoxicity at large scale. In this regard, the applications of cytometry are perhaps one of the most fundamental prospective analytical tools for the next generation and high-throughput ecotoxicology research. The diversity of this modern technology spans flow, laser-scanning, imaging, and more recently, Raman as well as mass cytometry. The cornerstone advantages of cytometry include the possibility of multi-parameter measurements, gating and rapid analysis. Cytometry overcomes, thus, limitations of traditional bulk techniques such as spectrophotometry or gel-based techniques that average the results from pooled cell populations or small model organisms. Novel technologies such as cell imaging in flow, laser scanning cytometry, as well as mass cytometry provide innovative and tremendously powerful capabilities to analyze cells, tissues as well as to perform in situ analysis of small model organisms. In this review, we outline cytometry as a tremendously diverse field that is still vastly underutilized and often largely unknown in environmental sciences. The main motivation of this work is to highlight the potential and wide-reaching applications of cytometry in ecotoxicology, guide environmental scientists in the technological aspects as well as popularize its broader adoption in environmental risk assessment.

Generation of mt:egfp transgenic zebrafish biosensor for the detection of aquatic zinc and cadmium

Zebrafish embryo toxicity testing has become a popular method for detecting environmental pollutions. However, the present research showed that zebrafish embryos exhibited no visible paramorphia, malformation, or mortality when exposed to heavy metals in a range above environmental standard limits, indicating that zebrafish embryos are an imprecise model for monitoring environmental heavy metals concentrations above regulatory limits. Aiming to obtain a biosensor for aquatic heavy metals, a metal-sensitive vector including zebrafish metallothionein (MT) promoter and enhanced green fluorescent protein (EGFP) was reconstructed and microinjected into 1-cell stage zebrafish embryos. The authors obtained an mt:egfp transgenic zebrafish line sensitive to aquatic zinc and cadmium. A quantitative experiment showed that zinc and cadmium treatment significantly induced the expression of EGFP in a dose- and time-dependent manner. In particular, EGFP messenger RNA levels increased remarkably when exposed to heavy metals above the standard limits. The results suggest that the transgenic zebrafish is a highly sensitive biosensor for detecting environmental levels of zinc and cadmium. Environ Toxicol Chem 2016;35:2066-2073. © 2016 SETAC.

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.

Towards a humanized PPARγ reporter system for in vivo screening of obesogens

Overeating and lack of exercise are major contributors to the current obesity epidemic, but environmental contaminants, or obesogens, are also considered to be potential actors. A common obesogen target is the Peroxisome Proliferator Activated Receptor Gamma (PPARγ). Screening for exogenous obesogens requires in vivo systems as many xenobiotics exert their effects through metabolites. We thus developed a humanized in vivo PPARγ reporter model, using Xenopus laevis larvae, a species possessing metabolic capacities comparable to mammals. A somatic transgenesis approach was used to co-express an expression vector for the human PPARγ protein simultaneously with one of a series of reporter vectors, each containing a PPARγ Response Element (PPRE)-eGFP sequence. Treatment of tadpoles with PPARγ agonists, antagonists or candidate obesogens, significantly modulated eGFP expression. Thus, the system provides a promising proof of principle for a sensitive and reliable humanized in vivo tool to screen both novel PPARγ drug ligands and potential endocrine disruptors or obesogens targeting this receptor.

Fountain flow cytometry

Fountain Flow Cytometry (FFC) is a simple and inexpensive technology that is adaptable to situations requiring detection and enumeration of cells/organisms at low concentrations, but is limited to particles of relatively high fluorescence intensity. This work presents the basic physics behind the novel scheme Fountain Flow Cytometry employs for the detection of target particles, a hybrid of conventional flow cytometry and video epifluorescence microscopy. The method is based on LED-induced fluorescence of labeled particles and requires no filtration step. Unlike conventional flow cytometry, the resulting fluorescence is measured with a digital camera as the measured sample flows toward the camera along the optical axis. An automated target particle recognition and enumeration computer program, Biocount, is used to count particles. FFC allows for detection of target particles in transparent and translucent fluids, such as environmental water, blood, and beverages. In addition, FFC can be used for detection of target particles in the presence of high photometric background, including unbound fluorescent dye. This facilitates use of the technique in situations where cells are unwashed. Current applications extend, but are not limited to, particles from µm-size bacteria to multi-millimeter-sized multicellular organisms.

Generation of fluorescent zebrafish to study endocrine disruption and potential crosstalk between thyroid hormone and corticosteroids

Several environmental chemicals disrupt thyroid function, a key regulator of normal development involved in many physiological processes in fish. We studied the effects of such chemicals in vivo using transient transgenic zebrafish (Danio rerio), expressing Green Fluorescent Protein (GFP) under the control of a TH/bZIP promoter from Xenopus laevis. Exposure to thyroid hormone (T3) at 10(-8)M increased GFP fluorescence in F0 embryos and larvae. Transient transgenic embryos were exposed to a T3 signaling agonist (TRIAC) or antagonists (NH(3) or NaClO(4)), or to the endocrine disruptor Bisphenol A (BPA). When tested alone, TRIAC increased fluorescence, confirming the specificity of our model. Exposure to NH(3) or NaClO(4) decreased fluorescence, reflecting inhibition of thyroid function. When tested alone, BPA did not modify fluorescence, but when tested with T3, it significantly reduced T3-induced fluorescence, suggesting disruption of the thyroid function by BPA. The expression of genes involved in the TH axis (TR-alpha, TR-beta, TSH) and the corticoid axis (GR and MR) was followed by q-PCR after T3 or BPA exposure (24 or 48h) and at different developmental stages (0, 1, or 5 days post-fertilization). Expression of TR-alpha, TR-beta, and TSH genes increased after 48h T3 exposure in 1-day-old larvae. When tested alone, BPA only slightly affected gene expression. When applied with T3, BPA decreased expression of all candidate genes in 1-day-old embryos compared to the T3 treated group, in agreement with data obtained with the TH/bZIP-eGFP zebrafish model. Finally, we show that T3 exposure leads to up-regulation of MR and GR genes. This study provides a new rapid diagnostic tool for characterizing the disrupting effects of toxicants on thyroid function and suggests possible crosstalk between the TR and Corticoid Signaling system.

Wormometry-on-a-chip: Innovative technologies for in situ analysis of small multicellular organisms

Small multicellular organisms such as nematodes, fruit flies, clawed frogs, and zebrafish are emerging models for an increasing number of biomedical and environmental studies. They offer substantial advantages over cell lines and isolated tissues, providing analysis under normal physiological milieu of the whole organism. Many bioassays performed on these alternative animal models mirror with a high level of accuracy those performed on inherently low-throughput, costly, and ethically controversial mammalian models of human disease. Analysis of small model organisms in a high-throughput and high-content manner is, however, still a challenging task not easily susceptible to laboratory automation. In this context, recent advances in photonics, electronics, as well as material sciences have facilitated the emergence of miniaturized bioanalytical systems collectively known as Lab-on-a-Chip (LOC). These technologies combine micro- and nanoscale sciences, allowing the application of laminar fluid flow at ultralow volumes in spatially confined chip-based circuitry. LOC technologies are particularly advantageous for the development of a wide array of automated functionalities. The present work outlines the development of innovative miniaturized chip-based devices for the in situ analysis of small model organisms. We also introduce a new term "wormometry" to collectively distinguish these up-and-coming chip-based technologies that go far beyond the conventional meaning of the term "cytometry."