Reactive oxygen species and anti-oxidant defenses in tail of tadpoles, Xenopus laevis

Nitric Oxide Function and Nitric Oxide Synthase Evolution in Aquatic Chordates

Nitric oxide (NO) is a key signaling molecule in almost all organisms and is active in a variety of physiological and pathological processes. Our understanding of the peculiarities and functions of this simple gas has increased considerably by extending studies to non-mammal vertebrates and invertebrates. In this review, we report the nitric oxide synthase (Nos) genes so far characterized in chordates and provide an extensive, detailed, and comparative analysis of the function of NO in the aquatic chordates tunicates, cephalochordates, teleost fishes, and amphibians. This comprehensive set of data adds new elements to our understanding of Nos evolution, from the single gene commonly found in invertebrates to the three genes present in vertebrates.

Impact of soil from monoculture pine plantations on two anuran species from the Atlantic Forest: Odontophrynus reigi and Leptodactylus luctator

Monoculture tree plantations reduces landscape heterogeneity and the number and diversity of habitats available for species. Physical-chemical changes in soil may affect the ponds where tadpoles develop. This work aimed to study the effect on tadpoles of two species of frogs, Leptodactylus luctator (Ll) and Odontophrynus reigi (Or) exposed to soils from a pine plantation (PP), which were compared to tadpoles exposed to soils from Atlantic Forest, the native forest (NF). The impact of soils from both places on growth, development, antioxidant system and genetic damage of Ll and Or tadpoles were observed. A composite sample (5 kg) of soil was taken from the top 10 cm stratum in a 200 m transect in each site, with random plots of 50x50cm. In collected soil samples Organic Matter (OM), Organic Carbon (OC), and Total Nitrogen (TN) were determined. We conducted laboratory experiments, from 23 until 38 Gosner stages. During the experiment, pH and ammonium in the water were determined. Soil from NF presented higher content of OM, OC and TN, and water pH in PP was 0.2 units lower than in NF. Both species showed ≈60 % increase of catalase activity in PP, and ≈40 % increase of lipid peroxidation in NF. Ll tadpoles presented 10 times higher protein oxidation in PP than in NF, but Gosner stage was higher in NF. In NF the higher OM and OC in both species causes the increase of lipid peroxidation; and Ll responds to a stressor in PP that in Or is not observed. Or presented lower stress response towards PP soils, which indicates a tolerance towards this soil. The changes observed in soil chemistry, although not big from a physical-chemical point of view, affects the growth, development and oxidative stress of two species of anuran tadpoles from the NF, which can affect future populations and anuran diversity.

Protein S-nitrosylation: Nitric oxide signalling during anuran tail regression

Tail regression is a remarkable process where a complex organ like the tail is completely resorbed by cell death during anuran metamorphosis. Nitric oxide is a signalling molecule involved in various physiological processes and along with reactive nitrogen species induces apoptosis. The present study describes the contribution of nitric oxide and reactive nitrogen species (nitrosative stress) during tail regression in the tadpoles of Indian tree frog, Polypedates maculatus. Spectrophotometric estimation revealed significantly higher levels of nitrite, nitrate and peroxynitrite in the regressing tails of the late climactic stages as compared to the early climactic stages and pre-regressing tails. S-nitrosylated proteins were detected in the apoptotic cells of epidermis and muscle, denervated and fragmented myofibres, outer notochordal sheath of the degenerating notochord, endothelium of blood vessels, blood cells and spinal cord of the regressing tail of the late climactic stages using fluorescent detection methods. Thus, a higher level of nitrosative stress in the late climactic stages is suggested to cause S-nitrosylation of proteins and subsequent apoptosis in the tail tissues. Macrophages were found engulfing the apoptotic cells and cell debris at the distal end of the regressing tail. Interestingly, macrophages were always found to be associated with melanocytes suggesting a close association for clearing cell debris by phagocytosis.

Effects of Desiccation on Metamorphic Climax in Bombina variegata: Changes in Levels and Patterns of Oxidative Stress Parameters

Simple Summary

Global warming alters patterns of precipitation and drought, which are important factors in the survival of amphibian populations. Metamorphosis is affected by environmental changes; this is especially true of metamorphic climax, the crucial stage of amphibian development that is accompanied by significant morphological, physiological and behavioral adaptations necessary for the transition to a terrestrial habitat. This study investigated naturally occurring changes in the cellular oxidative status (antioxidant system and oxidative damage) of yellow-bellied toad larvae during this phase, and how exposure to exogenous factors such as desiccation affected them. Our results revealed clear changes in the antioxidant system’s (AOS) response and the levels of oxidative damage during metamorphic climax, with the highest response and damage observed at the end stage. Decreasing water levels during larval development altered the components of the AOS and increased oxidative damage, resulting in increased oxidative stress. The knowledge gained from this study could contribute to a better understanding of the oxidative stress that larvae experience during this critical stage of development, and the consequences of global warming—such as water loss—on amphibians.

Abstract

In this paper, we examined how the oxidative status (antioxidant system and oxidative damage) of Bombina variegata larvae changed during the metamorphic climax (Gosner stages: 42—beginning, 44—middle and 46—end) and compared the patterns and levels of oxidative stress parameters between individuals developing under constant water availability (control) and those developing under decreasing water availability (desiccation group). Our results revealed that larvae developing under decreasing water availability exhibited increased oxidative damage in the middle and end stages. This was followed by lower levels of glutathione in stages 44 and 46, as well as lower values of catalase, glutathione peroxidase, glutathione S-transferase and sulfhydryl groups in stage 46 (all in relation to control animals). Comparison between stages 42, 44 and 46 within treatments showed that individuals in the last stage demonstrated the highest intensities of lipid oxidative damage in both the control and desiccation groups. As for the parameters of the antioxidant system, control individuals displayed greater variety in response to changes induced by metamorphic climax than individuals exposed to desiccation treatment. The overall decrease in water availability during development led to increased oxidative stress and modifications in the pattern of AOS response to changes induced by metamorphic climax in larvae of B. variegata.

An integrated approach to assess the sublethal effects of colloidal gold nanorods in tadpoles of Xenopus laevis

Gold nanorods (AuNR) have been explored for many applications, including innovative nanomedicines, which also might contribute to its increase in the environment, namely due to inadequate disposable of wastes into aquatic environments. Early-life stages of amphibians are usually aquatic and sensitive to chemical contamination. Accordingly, this study aimed to determine the sublethal effects of CTAB functionalized AuNR on Xenopus laevis tadpoles. As such, tadpoles were exposed to serial concentrations of AuNR for 72 h. A reduction in the rate of feeding (EC₅₀ = 4 μg.L^-1), snout to vent growth (EC₅₀ = 5 μg.L^-1) and weight gain (EC₅₀ = 6 μg.L^-1), was observed for AuNR-exposed tadpoles. Also, tadpoles actively avoided concentrations ≥ 4 μg.L^-1 of AuNR, after 12 h of exposure. At the biochemical level, AuNR caused impairments in antioxidant and nervous system related enzymes. Exposure to CTAB alone caused a high mortality. Results indicated that CTAB functionalized AuNR may induce several sublethal effects that may compromise the organism's fitness. Avoidance behavior (which corresponds to the disappearance of organisms, thus, similar to their death), observed at concentrations matching those inducing sublethal effects, suggest that it should be considered in the risk assessment for amphibians.

Water mould exposure induces enzymatic antioxidant defences in embryos of the Two-colored Oval Frog (Elachistocleis bicolor) (Anura: Microhylidae)

Water moulds are pathogens of amphibian eggs and embryos. However, little is known about oxidant or antioxidant status of amphibians in response to stress caused by water moulds. We exposed embryo stages of Two-colored Oval Frogs (Elachistocleis bicolor (Guérin-Méneville, 1838)) to a Saprolegnia-like species of water mould to explore homeostatic adjustments by the shifting of oxidative stress markers. We also tested whether water mould infection affected survivorship, hatching time, and morphology of hatching embryos. We found that the Saprolegnia-like species is a genuine stressor and substantially altered the physiological state of E. bicolor embryos. Among antioxidant defences, superoxide dismutase (SOD) and glutathione S-transferase (GST) activities increased in embryos exposed to the Saprolegnia-like species. However, no difference in lipid peroxidation levels was found between treatments, which might indicate that SOD and GST activations could be enough to prevent oxidative damage. Finally, we found higher mortality and number of malformations in the water mould treatment. We showed the stressful effect of water moulds on amphibian embryos, evidenced by the activation of their antioxidant system, and reveal the importance of considering physiological stress markers as key information when studying the potential consequences of disease outbreaks in the ecology and conservation of amphibians.

Endocrine regulation of regeneration: Linking global signals to local processes

Regeneration in amphibians and reptiles has been explored since the early 18th century, giving us a working in vivo model to study epimorphic regeneration in vertebrates. Studies aiming to uncover primary mechanisms of regeneration have predominantly focused on genetic pathways regulating specific stages of the regeneration process: wound healing, blastema formation and growth, and pattern formation. However, studies across organisms show that environmental conditions and physiological state of the animal can affect the rate or quality of regeneration, and endocrine signals are likely the mediators of these effects. Endocrine signals working/acting directly on receptors expressed in the structure or via neuroendocrine pathways can affect regeneration by modulating immune response to injury, allocation of energetic resources, or by enhancing or inhibiting proliferation and differentiation pathways in regenerating tissue. This review discusses the cumulative knowledge known about endocrine regulation of regeneration and important future research directions of interest to both ecological and biomedical research.

Enantioselective Bioaccumulation, Tissue Distribution, and Toxic Effects of Myclobutanil Enantiomers in Pelophylax nigromaculatus Tadpole

Research on the enantioselective behavior of chiral pesticides on amphibians has received growing attention, because amphibians are experiencing a population decline and amphibian metamorphosis shares many similarities with human fetal development. In this study, the enantioselective behavior of myclobutanil on Pelophylax nigromaculatus tadpole was studied. The antioxidant enzyme (SOD, GST) activities and malondialdehyde (MDA) content were investigated to assess the different toxic effects when tadpoles were exposed to myclobutanil enantiomers for 96 h. In the chronic exposure experiment, the bioaccumulation concentration of (-)-myclobutanil in tadpoles is significantly higher than that of (+)-myclobutanil, and the concentration of myclobutanil in tadpole intestine and liver was higher compared with other tissues. During the elimination experiment, about 95% of myclobutanil in tadpoles was eliminated within only 24 h. On the basis of these data, the enantiomeric differences should be taken into consideration in the risk assessment of myclobutanil.

Comprehensive and Quantitative Proteomic Analysis of Metamorphosis-Related Proteins in the Veined Rapa Whelk, Rapana venosa

Larval metamorphosis of the veined rapa whelk (Rapana venosa) is a pelagic to benthic transition that involves considerable structural and physiological changes. Because metamorphosis plays a pivotal role in R. venosa commercial breeding and natural populations, the endogenous proteins that drive this transition attract considerable interest. This study is the first to perform a comprehensive and quantitative proteomic analysis related to metamorphosis in a marine gastropod. We analyzed the proteomes of competent R. venosa larvae and post-larvae, resulting in the identification of 5312 proteins, including 470 that were downregulated and 668 that were upregulated after metamorphosis. The differentially expressed proteins reflected multiple processes involved in metamorphosis, including cytoskeleton and cell adhesion, ingestion and digestion, stress response and immunity, as well as specific tissue development. Our data improve understanding of the physiological traits controlling R. venosa metamorphosis and provide a solid basis for further study.

A Label-Free Proteomic Analysis on Competent Larvae and Juveniles of the Pacific Oyster Crassostrea gigas

Current understandings on the molecular mechanisms underlying bivalve metamorphosis are still fragmentary, and a comprehensive description is required. In this study, using a large-scale label-free proteomic approach, we described and compared the proteomes of competent larvae (CL) and juveniles (JU) of the Pacific oyster, Crassostrea gigas. A total of 788 proteins were identified: 392 in the CL proteome and 636 in the JU proteome. Gene Ontology analysis of the proteome from each sample revealed active metabolic processes in both stages. Further quantitative analyses revealed 117 proteins that were differentially expressed between the two samples. These proteins were divided into eight groups: cytoskeleton and cell adhesion, protein synthesis and degradation, immunity and stress response, development of particular tissues, signal regulation, metabolism and energy supply, transport, and other proteins. A certification experiment using real-time PCR assay confirmed 20 of 30 examined genes exhibited the same trends at the mRNA and protein levels. The differentially expressed proteins may play roles in tissue remodeling, signal transduction, and organ development during and after metamorphosis. Novel roles were proposed for some differentially expressed proteins, such as chymotrypsin. The results of this work provide an overview of metamorphosis and post-metamorphosis development of C. gigas at the protein level. Future studies on the functions of the differentially expressed proteins will help to obtain a more in-depth understanding of bivalve metamorphosis.

Changes in hormone and stress-inducing activities of municipal wastewater in a conventional activated sludge wastewater treatment plant

Conventional municipal wastewater treatment plants do not efficiently remove contaminants of emerging concern, and so are primary sources for contaminant release into the aquatic environment. Although these contaminants are present in effluents at ng-μg/L concentrations (i.e. microcontaminants), many compounds can act as endocrine disrupting compounds or stress-inducing agents at these levels. Chemical fate analyses indicate that additional levels of wastewater treatment reduce but do not always completely remove all microcontaminants. The removal of microcontaminants from wastewater does not necessarily correspond to a reduction in biological activity, as contaminant metabolites or byproducts may still be biologically active. To evaluate the efficacy of conventional municipal wastewater treatment plants to remove biological activity, we examined the performance of a full scale conventional activated sludge municipal wastewater treatment plant located in Guelph, Ontario, Canada. We assessed reductions in levels of conventional wastewater parameters and thyroid hormone disrupting and stress-inducing activities in wastewater at three phases along the treatment train using a C-fin assay. Wastewater treatment was effective at reducing total suspended solids, chemical and biochemical oxygen demand, and stress-inducing bioactivity. However, only minimal reduction was observed in thyroid hormone disrupting activities. The present study underscores the importance of examining multiple chemical and biological endpoints in evaluating and monitoring the effectiveness of wastewater treatment for removal of microcontaminants.