Use of the enhanced frog embryo teratogenesis assay-Xenopus (FETAX) to determine chemically-induced phenotypic effects

Ionizing radiation induces neurotoxicity in Xenopus laevis embryos through neuroactive ligand-receptor interaction pathway

Ionizing radiation (IR) poses a significant threat to both the natural environment and biological health. Exposure to specific doses of ionizing radiation early in an organism's development can lead to developmental toxicity, particularly neurotoxicity. Through experimentation with Xenopus laevis (X. laevis), we examined the effects of radiation on early developmental stage. Our findings revealed that radiation led to developmental abnormalities and mortality in X. laevis embryos in a dose-dependent manner, disrupting redox homeostasis and inducing cell apoptosis. Additionally, radiation caused neurotoxic effects, resulting in abnormal behavior and neuron damage in the embryos. Further investigation into the underlying mechanisms of radiation-induced neurotoxicity indicated the potential involvement of the neuroactive ligand-receptor interaction pathway, which was supported by RNA-Seq analysis. Validation of gene expression associated with this pathway and analysis of neurotransmitter levels confirmed our hypothesis. In addition, we further validated the important role of this signaling pathway in radiation-induced neurotoxicity through edaravone rescue experiments. This research establishes a valuable model for radiation damage studying and provides some insight into radiation-induced neurotoxicity mechanisms.

Spirulina (Arthrospira maxima) mitigates the toxicity induced by a mixture of metal and NSAID in Xenopus laevis

Cadmium (Cd) is often detected in the environment due to its wide use in industry; also, NSAIDs are one of the most consumed pharmaceuticals, particularly diclofenac (DCF). Several studies have reported the presence of both contaminants in water bodies at concentrations ranging from ng L-1 to μg L-1; in addition, they have shown that they can induce oxidative stress in aquatic species and disturb signal transduction, cell proliferation, and intercellular communication, which could lead to teratogenesis. Spirulina has been consumed as a dietary supplement; its antioxidant, anti-inflammatory, neuroprotective, and nutritional properties are well documented. This work aimed to evaluate if Spirulina reduces the damage induced by Cd and DCF mixture in Xenopus laevis at early life stages. FETAX assay was carried out: 20 fertilized oocytes were exposed to seven different treatments on triplicate, control, Cd (24.5 μg L-1), DCF (149 μg L-1), Cd + DCF, Cd+DCF+Spirulina (2 mg L-1), Cd+DCF+Spirulina (4 mg L-1), Cd+DCF+Spirulina (10 mg L-1), malformations, mortality, and growth were evaluated after 96 h, also lipid peroxidation, superoxide dismutase and catalase activity were determined after 192 h. Cd increased DCF mortality, Cd and DCF mixture increased the incidence of malformations as well as oxidative damage; on the other hand, the results obtained show that Spirulina can be used to reduce the damage caused by the mixture of Cd and DCF since it promotes growth, reduce mortality, malformations, and oxidative stress in X. laevis.

Toxic effects of long-term dual or single exposure to oxytetracycline and arsenic on Xenopus tropicalis living in duck wastewater

Direct discharge of aquaculture wastewater may have toxic effects, due to the presence of heavy metals, antibiotics, and even resistant pathogens, but little attention has been given. Here, tanks simulating a wild ecosystem were built to study the effects of long-term exposure to duck wastewater containing oxytetracycline (OTC) and/or arsenic (As) on the growth, physiological function, and gut microbiota evolution of Xenopus tropicalis. The results showed that duck wastewater had no apparent impact on X. tropicalis, but the impact increased significantly (P < 0.05) with exposure to OTC and/or As, especially the impact on body weight and growth rate. Biochemical indicators revealed varying degrees of oxidative stress damage, hepatotoxicity (inflammation, necrosis, and sinusoids), and collagen fibrosis of X. tropicalis in all treated groups after 72 days of exposure, which indirectly inhibited X. tropicalis growth. Moreover, 16S rDNA amplicon sequencing results showed that the gut microbiota structure and metabolic function were perturbed after chronic exposure, which might be the leading cause of growth inhibition. Interestingly, the abundance of intestinal resistance genes (RGs) increased with exposure time owing to the combined direct and indirect effects of stress factors in duck wastewater. Moreover, once the RGs were expressed, the resistance persisted for at least 24 days, especially that conferred by tetA. These results provide evidence of the toxic effects of DW containing OTC (0.1-4.0 mg/L) and/or As (0.3-3.5 µg/L) on amphibians and indicate that it is vital to limit the usage of heavy metals and antibiotics on farms to control the biotoxicity of wastewater.

Mortality and malformation effects of acute vanadium (V) exposure on the African clawed frog (Xenopus laevis) embryos

Vanadium (V) is a transition metal that is found in low concentrations in aquatic ecosystems. These levels increase due to anthropogenic activities. The mortality and teratogenicity effects of V remain unexplored in amphibian species. To address this gap in the knowledge base, a standard Frog Embryo Teratogenic Index - Xenopus (FETAX) assessment was conducted. Vanadium pentoxide (V₂O₅) was chosen for its known toxicity in other aquatic biota and its solubility in water. A range-finding test was conducted in two different mediums, V₂O₅ in distilled water (VDH2O) and V₂O₅ in FETAX medium (VMED), to determine concentration ranges where effects occurred. Thereafter, definitive tests were conducted using two separate breeding pairs, with two replicate dishes per concentration containing 15 embryos each. Multiple endpoints were assessed including mortality, malformations, minimum concentration to inhibit growth (MCIG), and the teratogenic index (TI). Mortality and malformation effects occurred at different ranges, and therefore, the exposures were conducted in low dose and high dose ranges. The high dose range for mortality effects was conducted at 0, 10, 20, 40, 80, and 160 mg/L of V. The low dose exposures to assess malformation effects were conducted at 0.0001, 0.00025, 0.0005, 0.00075, and 0.001 mg/L. Binary logistic regression was used to determine the LC50 and EC50 for the two sets of definitive tests. The LC50s were determined to be 46.10 mg/L and 26.91 mg/L for VDH₂O and 34.50 and 25.25 for VMED for the two breeding pairs respectively. The EC50 was calculated as 0.00053 mg/L and 0.00037 mg/L for VDH2O and 0.00036 mg/L and 0.00017 mg/L for VMED for the two definitive tests respectively. The TI was calculated as 86,981 and 72,729 for VDH2O and 95,833 and 148,526 for VMED. Ultimately, there were severe malformation effects in embryos exposed to low doses of V and V was determined to be a very strong teratogen.

Polymethylmethacrylate nanoplastics can cause developmental malformations in early life stages of Xenopus laevis

Polymethylmethacrylate (PMMA) production has increased almost 20% over the last years. With its release into the aquatic environment, its breakdown or degradation to nano dimensions (nanoplastics-NPLs) due to biological and physical/mechanical action is, theoretically, anticipated. The occurrence of PMMA-NPLs in aquatic ecosystems may thus cause adverse effects particularly to early life stages of amphibians, which may be in contact with PMMA-NPLs suspended in the water column or deposited in upper layers of the sediments. Accordingly, this work aimed at assessing the effects of PMMA-NPLs to aquatic early life stages of the model anuran species Xenopus laevis. To attain this objective, two types of toxicity assays were carried out by exposing embryos [Nieuwkoop and Faber (NF) stage 8-11] or tadpoles (NF 45) to three concentrations of PMMA-NPLs (1, 100 and 1000 μg/L): i) 96-h embryo teratogenicity assay, where survival, malformation, and total body length (BL) of embryos were assessed; and ii) 48-h feeding rate assay, where survival, feeding (FR), malformations and growth rates (body weight-BW and BL) of tadpoles were evaluated. PMMA-NPLs exposure had no significant effects on mortality, malformations of X. laevis embryos but BL was lower at 1000 μg PMMA-NPLs/L. In tadpoles, no effects on survival or FR were observed after exposure to PMMA-NPLs, but significant changes occured in BW and BL. Moreover, anatomical changes in the abdominal region (externalization of the gut) were observed in 62.5% of the tadpoles exposed to 1000 μg PMMA-NPLs/L. Despite the lack of knowledge regarding the environmental levels of NPLs, it is expected that sediments constitute a sink for these contaminants, where they can become available for organisms that, like tadpoles, feed on the organic matter at the surface of sediments. Considering the continuous release and subsequent accumulation of PMMA, the malformations obtained in the feeding assays suggest that, in the future, these nano-polymers may constitute a risk for aquatic life stages of amphibians.

Protective effects of Spirulina (Arthrospira maxima) against toxicity induced by cadmium in Xenopus laevis

Spirulina (Arthrospira maxima) has been recognized as a superfood and nutraceutical by its high nutritional value and the benefits of its consumption; it is an important source of lipids, proteins, vitamins, minerals, and antioxidants. It is known that spirulina has positive effects on the toxicity induced by pharmaceuticals and metals. Heavy metals such as cadmium, frequently used in industrial activities, are continuously detected in water bodies and can generate adverse effects on aquatic organisms even at low concentrations. This study aimed to evaluate the protective effect of spirulina (Arthrospira maxima) against the toxic effects induced by cadmium in the early life stages of Xenopus laevis. Twenty Xenopus laevis embryos were exposed to five different treatments on triplicate, control, cadmium (CdCl₂ 24.5 μg L^-1) and three spirulina mixtures Cd + S 1 (24.5 μg L^-1 CdCl₂ + 2 mg L^-1 spirulina), Cd + S 2 (24.5 μg L^-1 CdCl₂ + 2 mg L^-1 spirulina), Cd + S 3 (24.5 μg L^-1 CdCl₂ + 10 mg L^-1 spirulina); after 96 h of exposure: Malformations, mortality and length were evaluated; also, after 192 h, lipid peroxidation (LPX), superoxide dismutase (SOD) and catalase (CAT) were determined. All spirulina treatments decreased mortality from 34 to 50% and reduced malformations on incidence from 36 to 68%. Treatment Cd + S 3 decreased growth inhibition significantly. Spirulina treatment Cd + S 2 decreased lipidic peroxidation and antioxidant activity; these results suggest that spirulina (Arthrospira maxima) can decrease the mortality, frequency of malformations, the severity of malformations, growth inhibition, and oxidative damage induced by cadmium in Xenopus laevis embryos.

Bisphenol A exposure induces apoptosis and impairs early embryonic development in Xenopus laevis

Bisphenol A (BPA), an endocrine-disrupting chemical that is largely produced and used in the plastics industry, causes environmental pollution and is absorbed by humans through consumption of food and liquids in polycarbonate containers. BPA exerts developmental and genetic toxicities to embryos and offsprings, but the embryotoxicity mechanism of this chemical is unclear. This study aimed to explore the toxic effect of BPA on embryonic development and elucidate its toxicity mechanism. Embryos of Xenopus laevis as a model were treated with different concentrations (0.1, 1, 10, and 20 μM) of BPA at the two-cell stage to investigate the developmental toxicity of BPA. Embryonic development and behaviors were monitored 24 h-96 h of BPA exposure. BPA concentrations greater than 1 μM exerted significant teratogenic effects on the Xenopus embryos, which showed short tail axis, miscoiled guts, and bent notochord as the main malformations. The 20 μM BPA-treated embryos were seriously damaged in all aspects and exhibited deformity, impaired behavioral ability, and tissue damage. The DNA integrity and apoptosis of the Xenopus embryos were also investigated. Exposure to BPA concentrations higher than 0.1 μM significantly induced DNA damage (p < 0.05). The 10 and 20 μM BPA-treated embryos exhibited higher levels of cleaved caspase-3 protein than the control. The ratios of bax/bcl-2 mRNA were significantly higher in the 10 μM and 20 μM-treated embryos than the ratio in the control group. Overall, data indicated that BPA can delay the early development, induce DNA damage and apoptosis, and eventually cause multiple malformations in Xenopus embryos.

Potential reproductive toxicity of multi-walled carbon nanotubes and their chronic exposure effects on the growth and development of Xenopus tropicalis

The increasing production and use of multi-walled carbon nanotubes (MWCNTs) will inevitably lead to discharge into the environment and exert negative effects on organisms. Many studies have focused on the toxicity of MWCNTs to aquatic animals, but little is known about their possible potential reproductive toxicity. In this study, 6 sexually mature Xenopus tropicalis were exposed to 0.5 and 2.5 mg/L MWCNTs suspensions for 56 days, and the toxicity of MWCNTs to the growth and reproduction of X. tropicalis were studied. The results showed that MWCNTs could inhibit the growth of body, including the testis, ovaries and fat of X. tropicalis. Histopathological section analysis showed that MWCNTs affected the formation of spermatogonia and oocytes, while had no notable effect on the heart or liver. MWCNTs would be accumulated in lungs of X. tropicalis inducing lung cannons. In addition, MWCNTs changed the microbial community structure and diversity of gut microbiota but did not change its abundance significantly. Moreover, MWCNTs could even decrease the fertilized and survival rate of X. tropicalis embryos. These results indicated that chronic exposure to MWCNTs would not only affect the growth and development of X. tropicalis, but also pose a potential risk on their reproduction.

Accumulation and toxicity of multi-walled carbon nanotubes in Xenopus tropicalis tadpoles

Multi-walled carbon nanotubes (MWCNTs), a common nanomaterial widely used and discharged in environment, might exert toxic effects on aquatic animals. In this paper, filter-feeding tadpole of Xenopus tropicalis was selected as bioindicator to study the exposure effects of MWCNTs suspensions of 0.5, 1, 2, 4 and 8 mg/L for 72 h. The results showed that the tadpoles could remain high survival rate of over 96.7% after 24 h's exposure to MWCNTs, but then decrease considerably, showing a significant time-dependent relationship. The LC₅₀ was 2.53 mg/L for tadpoles exposed to MWCNTs for 72 h, when MWCNTs accumulated in their gills and digestive tracts. Moreover, the enrichment degree of MWCNTs in tadpole was related to exposure density than time. When MWCNTs suspension concentration was not over 1 mg/L, the heart rates increased significantly and then decreased continuously. The survivors from the toxicity test were transferred to fresh filtered water for recovery, but MWCNTs accumulated in the tadpoles' body didn't decrease obviously after 4 days. Although the maximum tadpoles survival rate of 80% was recorded in the exposure group of 0.5 mg/L MWCNTs, only 43.3% of the survivors could recover. Therefore, the final survival rate was negative related to the exposure densities of MWCNTs but positive related to the accumulating degree in tadpoles' body. The results demonstrated that MWCNTs exposure posed potential health risks to filter-feeding organisms by intake and accumulation in organs, which could provide useful information for the reasonable evaluation and scientific management of nanomaterials.

Current understanding of potential ecological risks of retinoic acids and their metabolites in aquatic environments

In animals, retinoic acids (RAs), one of the main derivatives of vitamin A, are crucial for a variety of physiological processes. RAs, including all-trans-RA, 9-cis-RA, 13-cis-RA, and their corresponding metabolites (i.e., all-trans-4-oxo-RA, 9-cis-4-oxo-RA and 13-cis-4-oxo-RA) can be excreted through urination from humans and animals. Sewage treatment plants (STPs) are a significant source of RAs and 4-oxo-RAs into aquatic environments. RAs and 4-oxo-RAs can be identified and quantified by use of liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). RAs and 4-oxo-RAs have been reported in various environmental matrices including rivers, lakes, reservoirs and coastal marine environments as well as in sewage effluents discharged from STPs. Greater concentrations of RAs and 4-oxo-RAs have been observed during blooms of cyanobacteria and microalgae, suggesting that cyanobacteria and microalgae are natural sources of RAs and 4-oxo-RAs in aquatic environments. These potential sources of RAs and 4-oxo-RAs raise concerns about their concentrations and risks in aquatic environments because excessive intake of these chemicals can result in abnormal morphological development in animals. Teratogenic effects were observed in amphibians, fish embryos, gastropods, mammals and birds when exposed to RAs. This review summarizes sources, concentrations, adverse effects and ecological risks of RAs and 4-oxo-RAs in aquatic environments. An interim, predicted no-effect concentration (PNEC) of RAs (in terms of at-RA) for freshwater environments was determined to be 3.93 ng/L at-RA equivalents. Based on limited data on concentrations of RAs in freshwater ecosystems, their hazard quotients were found to range from zero to 16.41, depending on the environmental conditions of receiving waters. Ecological risks of RAs in marine environments are yet to be explored due to the paucity of data related to both their concentrations in marine environment and toxic potencies to marine species. This review updates current knowledge of RAs and 4-oxo-RAs in aquatic environments and calls for more studies on their concentrations and fate in aquatic environments, especially estuarine and coastal marine environments with a view to enabling a comprehensive assessment of their ecological risks around the globe.

Current Status and Future Prognosis of Malaria Vector Control Pesticide Ecotoxicology and Xenopus sp

Anurans from the genus Xenopus have long been used as standard testing organisms and occur naturally in tropical and sub-tropical areas where malaria vector control pesticides are actively used. However, literature on the toxic effects of these pesticides is limited. This review analyses the available data pertaining to both Xenopus and the pesticides used for malaria vector control in order to determine the pesticides that have the greatest potential to influence amphibian health while also identifying gaps in literature that need to be addressed. Amphibian diversity has shown the fastest decline of any group, yet there are still voids in our understanding of how this is happening. The lack of basic toxicity data on amphibians with regard to pesticides is an issue that needs to be addressed in order to improve effectiveness of amphibian conservation strategies. Meta-analyses performed in this review show that, at current usage, with the available acute toxicity literature, the pyrethroid pesticide group could hold the highest potential to cause acute toxicity to Xenopus sp. in relation to the other MVCPs discussed, but the lack of data cripples the efficacy with which meta-analyses can be performed and conclusions made from such analyses. Several studies have shown that DDT accumulates in Xenopus sp. from malaria vector control areas, but accumulation of other MVCPs in frogs is still largely unknown. Through this review we hope to encourage future research into the field of amphibian ecotoxicology and to promote the use of the Xenopus standard model in order to build comprehensive datasets that may be used in amphibian conservation.

The role of pparγ in embryonic development of Xenopus tropicalis under triphenyltin-induced teratogenicity

Evidence has shown that triphenyltin (TPT) triggers severe malformations in Xenopus tropicalis embryos, partly due to activation of PPARγ (peroxisome proliferator activated receptor γ) protein. In the present study, we investigated how abundance of pparγ and TPT exposure interact and affect X. tropicalis embryonic development. We observed pparγ expression signals appeared in the neural crest and neural fold, as well as in the brain, eyes and spinal cord organs. Both pparγ overexpression and its Morpholino (MO) knockdown inhibited pax6 (paired box 6) expression, a marker of eye development, and significantly up- and down-regulated lipid and glucose homeostasis related genes, such as lpl (lipoprotein lipase), slc2a4 (solute carrier family 2 (facilitated glucose transporter), member 4) and pck1 (phosphoenolpyruvate carboxykinase 1, cytosolic), thus inducing eye phenotypes. Overexpression of pparγ induced small eye phenotype, while pparγ MO induced small eye plus turbid eye lens microencephaly and enlarged trunk. In contrast, 5-20μgSn/L (stannum/L) TPT exposure reversed some impacts induced by pparγ overexpression, i.e., no small eye, up-regulation of pax6 and down-regulation of pparγ, lpl, slc2a4 and pck1. Meanwhile, microinjection of pparγ MO combined with exposure to 20μgSn/L TPT caused 85% mortality. In brief, our work clearly indicates that pparγ is essential to eye development and inhibition of its expression combined with TPT exposure can be extremely harmful to X. tropicalis embryo.

Microplastics in Small Waterbodies and Tadpoles from Yangtze River Delta, China

Although microplastic (MP) pollution in freshwater systems is gaining attention, our knowledge of its distribution in small waterbodies is scarce. Small waterbodies are freshwater habitats to many species, including amphibians, that are vulnerable to MP pollution. This study analyzed the distribution and characteristics of MPs in 25 small waterbodies from the Yangtze River Delta, China. MPs were detected in surface water, sediment, and tadpoles with abundances ranging from 0.48 to 21.52 items L^-1, 35.76 to 3185.33 items kg^-1, and 0 to 2.73 items individual^-1 (0 to 168.48 items g^-1), respectively. The dominant shape and polymer of MPs in water and tadpole samples were polyester (PES) fibers, and polypropylene (PP) fibers and fragments were dominant in sediment samples. In addition, MPs were primarily <0.5 mm in length in all samples. Tadpole length was positively correlated to the number of MPs detected. The abundance, shape, and polymer distribution of MPs in tadpoles resembled that of water rather than sediment, suggesting that tadpoles likely take up MPs from the surrounding water. This study demonstrated that MPs are abundant in these small waterbodies and are ingested by resident tadpoles. This may suggest a pathway of MP entry into aquatic and terrestrial food webs.

Single and mixture toxicity of strobilurin and SDHI fungicides to Xenopus tropicalis embryos

The decline in amphibian populations is a critical threat to global biodiversity, and pesticide pollution is considered as one of the major factors. Although effects of single pesticides on amphibians have been documented, toxicological interactions prevailing in mixtures of pesticides have not been well elucidated. Strobilurin and succinate dehydrogenase inhibitor (SDHI) fungicides are new types of commonly used pesticides. In this study, effects of three strobilurins (pyraclostrobin, trifloxystrobin and azoxystrobin), two SDHIs (isopyrazam and bixafen), and their mixtures on X. tropicalis embryos were fully investigated. Results showed that exposure to individual fungicides induced lethal and teratogenetic effects; and malformed embryos displayed similar phenotypes including microcephaly, hypopigmentation, somite segmentation and narrow fin. Exposure to two strobilurins or two SDHIs at equitoxic concentrations caused additive or synergetic effects at environmentally relevant concentrations. TU for mixtures of isopyrazam and bixafen was 0.53 and 0.30 for lethal and teratogenic toxicity, respectively. Finally, binary mixtures of strobilurins and SDHIs also exhibited additive or synergetic effects on amphibian embryos. Overall, these results reveal that the mixtures of multiple fungicides caused a higher incidence of lethality and teratogenicity of amphibian embryos, compared to a single fungicide at the corresponding doses. Our findings provide important data about the ecotoxicology of agricultural fungicides on non-target organisms, which is useful for guiding management practices for pesticides.

Responses of growth, malformation, and thyroid hormone-dependent genes expression in Bufo gargarizans embryos following chronic exposure to Pb2

The aim of this study was to examine the adverse effects of lead (Pb) exposure on Bufo gargarizans embryos. The 96 h-LC₅₀ of Pb²⁺ for B. gargarizans embryos was determined to be 26.6 mg L^-1 after an acute test. In the chronic test, B. gargarizans embryos at Gosner stage 3 were exposed to 10~2000 μg Pb²⁺ L^-1 during embryogenesis. Total length, weight, developmental stage, and malformation were monitored. In addition, the transcript levels of type II and type III iodothyronine deiodinase (Dio2 and Dio3) and thyroid hormone receptors (TRα and TRβ) were determined to assess the thyroid-disrupting effects of Pb²⁺. Slightly increased growth and development of B. gargarizans embryos were observed at low concentrations of Pb²⁺ (10, 50, and 100 μg L^-1), while retarded growth and development were found at high concentrations of Pb²⁺ (1000 and 2000 μg L^-1). In addition, Pb²⁺ exposure induced morphological abnormalities, which were characterized by edema at tail, wavy fin, abdominal edema, stunted growth, hyperplasia, and axial flexures in B. gargarizans embryos. Furthermore, our results showed that exposure to 2000 μg Pb²⁺ L^-1 decreased the transcript levels of Dio2, TRα, and TRβ, but it increased Dio3 mRNA level. In contrast, exposure to 50 μg Pb²⁺ L^-1 increased TRα mRNA level and decreased Dio3 mRNA level. These results suggested that Pb²⁺ might have thyroid-disrupting effects, leading to the disruption of growth and development in B. gargarizans embryos.

Retinoid-like compounds produced by phytoplankton affect embryonic development of Xenopus laevis

Teratogenic effects, which were remarkably similar to those induced by retinoic acids, have been seen in wild frogs indicating possible source of retinoids in the environment. Recent studies indicate that some cyanobacterial species can contain teratogenic retinoic acids (RAs) and their analogues. Retinoids are known to regulate important processes such as differentiation, development, and embryogenesis. The study investigated the effects of exudates (extracellular compounds) of two cyanobacteria species with retinoic-like activity and one algae species on embryonic development of amphibians. The retinoid-like activity determined by in vitro reporter gene assay reached 528ng retinoid equivalents (REQ)/L and 1000ng REQ/L in exudates of Cylindrospermopsis raciborskii and Microcystis aeruginosa, respectively, while algal exudates showed no detectable activity. Total mean of retinoid-like copounds into exudate was 35.6ng ATRA/mil.cells for M.aeruginosa and 6.71ng ATRA/mil.cells for C.raciborskii, respectively. Toxicity tests with amphibian embryos up to 96h of development were carried out according to the standard guide for the Frog Embryo Teratogenesis Assay Xenopus. Lowest observed effect concentrations (LOEC) of malformations (2.5-2.6µg/L REQ) were two times lower than LOEC for ATRA (5µg/L). The exudates of both cyanobacteria were indeed provoking diverse teratogenic effects (e.g. tail, gut and eyes deformation) and interference with growth in frogs embryos, while such effects were not observed for the algae. Xenopus embryos were also exposed to all-trans retinoic acid (ATRA) in concentration range (1-40µg/L) equivalent to the REQs detected in cyanobacterial exudates. ATRA (10µg/L) caused similar teratogenic phenotypes at corresponding REQs as cyanobacterial exudates. The study confirms the ability of some species of cyanobacteria to produce retinoids naturally and excrete them directly into the environment at concentrations which might have adverse influence on the development of amphibians.

The unexpected teratogenicity of RXR antagonist UVI3003 via activation of PPARγ in Xenopus tropicalis

The RXR agonist (triphenyltin, TPT) and the RXR antagonist (UVI3003) both show teratogenicity and, unexpectedly, induce similar malformations in Xenopus tropicalis embryos. In the present study, we exposed X. tropicalis embryos to UVI3003 in seven specific developmental windows and identified changes in gene expression. We further measured the ability of UVI3003 to activate Xenopus RXRα (xRXRα) and PPARγ (xPPARγ) in vitro and in vivo. We found that UVI3003 activated xPPARγ either in Cos7 cells (in vitro) or Xenopus embryos (in vivo). UVI3003 did not significantly activate human or mouse PPARγ in vitro; therefore, the activation of Xenopus PPARγ by UVI3003 is novel. The ability of UVI3003 to activate xPPARγ explains why UVI3003 and TPT yield similar phenotypes in Xenopus embryos. Our results indicate that activating PPARγ leads to teratogenic effects in Xenopus embryos. More generally, we infer that chemicals known to specifically modulate mammalian nuclear hormone receptors cannot be assumed to have the same activity in non-mammalian species, such as Xenopus. Rather they must be tested for activity and specificity on receptors of the species in question to avoid making inappropriate conclusions.

Uptake, accumulation and elimination of polystyrene microspheres in tadpoles of Xenopus tropicalis

Microplastic is an emerging contaminant affecting freshwater and marine ecosystem across the globe. In the present study, the filter feeding tadpoles of Xenopus tropicalis were exposed to polystyrene microspheres (1 and 10 μm) for 48 h. Microspheres were observed in gills and digestive tract of tadpoles within 1 h after exposure as well as in feces 6 h after exposure. The accumulation of microspheres in the tadpoles were concentration dependent (Univariate ANOVA, p < 0.001), but no time dependent accumulation of microspheres was observed in tadpoles 48 h after exposure (Univariate ANOVA, p > 0.05). After the exposed tadpoles were transferred to clean water, the number of microspheres in the tadpoles decreased dramatically after 1 d and continued to decrease gradually afterwards. The absorbed polystyrene particles in unfed tadpoles was significantly higher than those in the fed tadpoles at 12 and 24 h after exposure. After transfer to clean water, the fed tadpoles showed a significant decrease in the amount of absorbed polystyrene particles, while the unfed tadpoles showed no significant change in the amount of absorbed polystyrene particles. Our results suggested that microspheres were likely to be ingested and egested relatively fast by tadpoles. Our results indicated that aquatic vertebrate organisms might ingest more microplastics if the abundance of microplastics continues to increase while the available food becomes less.

Strong lethality and teratogenicity of strobilurins on Xenopus tropicalis embryos: Basing on ten agricultural fungicides

Agricultural chemical inputs have been considered as a risk factor for the global declines in amphibian populations, yet the application of agricultural fungicides has increased dramatically in recent years. Currently little is known about the potential toxicity of fungicides on the embryos of amphibians. We studied the effects of ten commonly used fungicides (four strobilurins, two SDHIs, two triazoles, fludioxonil and folpet) on Xenopus tropicalis embryos. Lethal and teratogenic effects were respectively examined after 48 h exposure. The median lethal concentrations (LC50s) and the median teratogenic concentrations (TC50s) were determined in line with actual exposure concentrations. These fungicides except two triazoles showed obvious lethal effects on embryos; however LC50s of four strobilurins were the lowest and in the range of 6.81-196.59 μg/L. Strobilurins, SDHIs and fludioxonil induced severe malformations in embryos. Among the ten fungicides, the lowest TC50s were observed for four strobilurins in the range of 0.61-84.13 μg/L. The teratogenicity shared similar dose-effect relationship and consistent phenotypes mainly including microcephaly, hypopigmentation, somite segmentation and narrow fins. The findings indicate that the developmental toxicity of currently-used fungicides involved with ecologic risks on amphibians. Especially strobilurins are highly toxic to amphibian embryos at μg/L level, which is close to environmentally relevant concentrations.