Differential sensitivity of developmental stages of the South American toad to a fungicide based on fludioxonil and metalaxyl-M

Agricultural fungicide application in Argentina has increased twice since 2008, with Maxim® XL (2.5% fludioxonil +1% metalaxyl-M) as one of the most used fungicide formulation. The toxicity of this pesticide on Rhinella arenarum was assessed by means of continuous (from embryo and larval development) and 24-h pulse exposure standardized bioassays. Lethality was concentration- and exposure time-dependent. Maxim® XL caused a progressive lethal effect along the bioassays with higher toxicity on embryos than larvae, obtaining 50% lethal concentrations at 96, 336, and 504 h of 10.85, 2.89, and 1.71 mg/L for embryos, and 43.94, 11.79, and 5.76 mg/L for larvae respectively. Lethal 504-h no observed effect concentration values for embryos and larvae were 1 and 2.5 mg/L respectively. A stage-dependent toxicity of Maxim® XL was also demonstrated within the embryo development, with early stages more sensitive than the later ones, and blastula as the most sensitive developmental stage. The risk quotients obtained for chronic risk assessment determined a potential threat for the survival and continuity of R. arenarum populations under these conditions. The results indicate that the levels of the fungicide reaching amphibian habitats could be risky for the early development of this amphibian species. This study also emphasizes the necessity to evaluate the chronic effects of fungicides in pesticide risk assessment.

Differential gene expression patterns during embryonic development of sea urchin exposed to triclosan

Triclosan (TCS; 2,4,4'-trichloro-2'-hydroxydiphenyl ether) is a broad-spectrum antibacterial agent used in common industrial, personal care and household products which are eventually rinsed down the drain and discharged with wastewater effluent. It is therefore commonly found in the aquatic environment, leading to the continual exposure of aquatic organisms to TCS and the accumulation of the antimicrobial and its harmful degradation products in their bodies. Toxic effects of TCS on reproductive and developmental progression of some aquatic organisms have been suggested but the underlying molecular mechanisms have not been defined. We investigated the expression patterns of genes involved in the early development of TCS-treated sea urchin Strongylocentrotus nudus using cDNA microarrays. We observed that the predominant consequence of TCS treatment in this model system was the widespread repression of TCS-modulated genes. In particular, empty spiracles homeobox 1 (EMX-1), bone morphogenic protein, and chromosomal binding protein genes showed a significant decrease in expression in response to TCS. These results suggest that TCS can induce abnormal development of sea urchin embryos through the concomitant suppression of a number of genes that are necessary for embryonic differentiation in the blastula stage. Our data provide new insight into the crucial role of genes associated with embryonic development in response to TCS. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 426-433, 2017.

[ENGAGEMENT OF SEROTONIN-MODULATING ANTICONSOLIDATION PROTEIN IN REGULATION OF EMBRYOGENESIS OF LYMNEAE STAGNALIS AND LEWIS SARCOMA IN HYBRID MICE Fl C57B2/6 X DBA]

The article concerns study of the effects of a novel serotonin-modulating anticonsolidation protein (SMAP) being in a linear relationship with serotonin level, on embryogenesis of Lymneae stagnalis and Lewis sarcoma in hybrid mice Fl C57B2/6 X DBA. Inhibition of embryogenesis of Lymneae stagnalis on the stage of four blastomers and late blastula, lack of changes on the stage of trochofora and acceleration of metamorphosis under the effects of SMAP in a dose-dependent manner was observed. Short-term retardation (during the first 10 days) of development of Lewis sarcoma in mice and survival of 25% of transferring animals under high doses of SMAP was revealed. Cytostatic activity for high doses of SMAP and their effects on the duration of single phases of the cell cycle is proposed.

Lethal and sublethal toxicity of the industrial chemical epichlorohydrin on Rhinella arenarum (Anura, Bufonidae) embryos and larvae

Lethal and sublethal toxicity of the major chemical used in epoxide compounds, epichlorohydrin (ECH) was evaluated on the early life cycle of the common South American toad, Rhinella arenarum (Anura, Bufonidae). The stages evaluated were (according to Del Conte and Sirlin): early blastula (S.3-S.4), gastrula (S.10-S.12), rotation (S.15), tail bud (S.17), muscular response (S.18), gill circulation (S.20), open mouth (S.21), opercular folds (S.23) and complete operculum (S.25). The LC50 and EC50 values for lethal and sublethal effects were calculated. The early blastula was the most sensitive stage to ECH both for continuously and pulse-exposures (LC50-24h=50.9 mg L(-1)), while S.20 was the most resistant (LC50-24h=104.9 mg L(-1)). Among sublethal effects, early blastula was also the most sensitive stage (LOEC-48 h=20 mg L(-1)) and it has a Teratogenic Index of 2.5, which indicates the teratogenic potential of the substance. The main abnormalities were persistent yolk plugs, cell dissociation, tumors, hydropsy, oral malformations, axial/tail flexures, delayed development and reduced body size. ECH also caused neurotoxicity including scarce response to stimuli, reduction in the food intake, general weakness, spasms and shortening, erratic or circular swimming. Industrial contamination is considered an important factor on the decline of amphibian populations. Considering the available information about ECH's toxicity and its potential hazard to the environment, this work shows the first results of its developmental toxicity on a native amphibian species, Rhinella arenarum.

Comparative toxicity of antifouling compounds on the development of sea urchin

In the present study, embryotoxicity experiments using the sea urchin Lytechinus variegatus were carried out to better clarify the ecotoxicological effects of tributyltin (TBT) and triphenyltin (TPT) (the recently banned antifouling agents), and Irgarol and Diuron (two of the new commonly used booster biocides). Organisms were individually examined to evaluate the intensity and type of effects on embryo-larval development, this procedure has not been commonly used, however it showed to be a potentially suitable approach for toxicity assessment. NOEC and LOEC were similar for compounds of same chemical class, and IC10 values were very close and showed overlapping of confidence intervals between TBT and TPT, and between Diuron and Irgarol. In addition, IC10 were similar to NOEC values. Regardless of this, the observed effects were different. Embryo development was interrupted at the gastrula and blastula stages at 1.25 and 2.5 μg l(-1) of TBT, respectively, whereas pluteus stage was reached with the corresponding concentrations of TPT. Furthermore, embryos reached the prism and morula stages at 5 μg l(-1) of TPT and TBT, respectively. The effects induced by Irgarol were also more pronounced than those caused by Diuron. Pluteus stage was always reached at any tested Diuron concentration, while embryogenesis was interrupted at blastula/gastrula stages at the highest concentrations of Irgarol. Therefore, this study proposes a complementary approach for interpreting embryo-larval responses that may be employed together with the traditional way of analysis. Consequently, this application leads to a more powerful ecotoxicological assessment tool focused on embryotoxicity.

Paraquat-induced oxidative stress response during amphibian early embryonic development

In addition to the endogenous production of reactive oxygen species (ROS) as a result of normal development, amphibian external development often forces embryos to deal with oxidative stress-producing agents present in the environment. Embryos should therefore develop protective systems to reduce ROS toxicity and achieve successful development. The present work was aimed to characterize the effects produced by the widespread-used ROS-generator pesticide Paraquat during early embryonic development in the toad Chaunus arenarum, as well as to get insights into the defense response elicited by amphibian embryos. The approach consisted in generating a sharp and brief oxidative stress condition early during embryonic development to stimulate the cellular mechanisms involved in ROS-antioxidant response. Results revealed that Paraquat-treatment reduced the ability of embryos to develop normally, leading to arrests of development and severe malformations such as tail abnormalities, abdominal edema, reduced head development and curved dorsal structures. Although Paraquat effects were morphologically evident from gastrula stage on, alterations such as chromatin condensation were observed even at blastula stage by histological examinations. Regarding detoxifying enzymes, a significant induction of Mn-superoxide dismutase activity was detected at stages beyond gastrula in embryos surviving Paraquat treatment, suggesting a major role of this enzyme in the antioxidant response during early embryonic development.

Embryotoxicity and teratogenicity of pesticide indoxacarb to sea urchin (Strongylocentrotus intermedius)

Sperm cell and embryo toxicity tests using the sea urchin Strongylocentrotus intermedius (S. intermedius) were performed to assess the toxicity of indoxacarb, a new widely used insecticide. New toxicity data for indoxacarb expressed as median effective concentration (EC(50)) were reported for the sea urchin species. When sperms and cells were exposed to the pesticide before fertilization, no significant inhibition in the fertilization success of S. intermedius (up to 40 mg/L) was observed. Developmental toxicity of the pesticide displayed a significant dose-related increase of larval malformations and differentiation arrest at concentrations of 0.1 mg/L to 40.0 mg/L at each cleavage, including the 2-cell stage, 4-cell, blastula, gastrula, prism and 4-arm pluteus stages. It seems that 4-arm pluteus is the most sensitive to indoxacarb with the EC(50) of 3.73 mg/L, two times less than that of the first cleavage stage. All these results indicate that more attentions should be paid to the potential marine pollutions caused by this pesticide indoxacarb.

FGF4 regulates blood and muscle specification in Xenopus laevis

BACKGROUND INFORMATION

FGF (fibroblast growth factor) signalling is known to be required for many aspects of mesoderm formation and patterning during Xenopus development and has been implicated in regulating genes required for the specification of both blood and skeletal muscle lineages.

RESULTS

In the present study, we have specifically knocked down the expression of FGF4 using AMO (antisense morpholino oligonucleotide)-mediated inhibition and demonstrate that FGF4 acts in the dorsal marginal zone to restrict blood development and promote the development of skeletal muscle. In addition, we used a drug inhibitor of FGF signalling and an inducible form of FGFR1 (FGF receptor 1) to identify a period of competence during late blastula and gastrula stages when FGF signalling acts to regulate blood versus muscle specification. Notably, we found that it is the dorsal activity of FGF that is required to restrict the expression of SCL (stem cell leukaemia) to the ventral blood island.

CONCLUSIONS

Our data indicate that FGF4 is a key organizer-derived signal involved in the process of dorsoventral patterning of the mesoderm.

Determination of myoseverin embryotoxic potential by using FETAX

BACKGROUND

Since MYS is a microtubular poison with a reversible activity, Xenopus blastulae were exposed to MYS to verify the eventual drug-related developmental suspension and the reversibility of this effect.

METHODS

Lethal and teratogenic effects of myoseverin (MYS) were evaluated using the FETAX. Embryos were exposed to different MYS concentrations from stage 8 to stage 47.

RESULTS

Probit analysis gave 12.14 microM LC50 and 7.67 microM TC50 from which 1.58 T.I. is derived. Several malformations were observed such as facial abnormalities, abnormal tail flexure, heart ventricle chamber enlargement and external appendix. MYS led to an arrest of living embryo development. Before MYS removing, exposed blastulae showed the lack of mitotic spindles along with different nuclei alterations. Living embryos, moved in control solution, mainly died around the hatching showing severe malformations likely ascribable to the altered planes of newly occurring mitosis.

CONCLUSION

In spite of the low T.I, MYS has to be considered a highly teratogenic compound.

Comparison of induction during development between Xenopus tropicalis and Xenopus laevis

Several in vitro systems exist for the induction of animal caps using growth factors such as activin. In this paper, we compared the competence of activin-treated animal cap cells dissected from the late blastulae of Xenopus tropicalis and Xenopus laevis. The resultant tissue explants from both species differentiated into mesodermal and endodermal tissues in a dose-dependent manner. In addition, RT-PCR analysis revealed that organizer and mesoderm markers were expressed in a similar temporal and dose-dependent manner in tissues from both organisms. These results indicate that animal cap cells from Xenopus tropicalis have the same competence in response to activin as those from Xenopus laevis.

Gonadotropin stimulation of steroid synthesis and metabolism in the Rana pipiens ovarian follicle: sequential changes in endogenous steroids during ovulation, fertilization and cleavage stages

Steroid synthesis and metabolism have been followed in Rana pipiens ovarian follicles, denuded oocytes and eggs during ovulation, fertilization and cleavage stages (blastula formation). Under physiological conditions, gonadotropin stimulation of the fully grown follicle leads to progesterone synthesis from [(3)H]acetate as well as formation of much smaller amounts of 17alpha-hydroxyprogesterone, androstenedione, pregnanedione and pregnanediol. Progesterone levels increase during completion of the first meiotic division, but by ovulation progesterone disappears from the egg. Plasma membrane-bound progesterone is taken up into the oocyte cortical granules and is largely metabolized to 5alpha-pregnane-3alphaol,20-one and 5beta-pregnane-3alpha,17alpha,20beta-triol coincident with internalization of 60% of the oocyte surface (and >90% of bound progesterone) by the end of the hormone-dependent period. The principal steroid in the ovulated egg is 5beta-pregnane-3alpha,17alpha,20beta-triol. There is a rapid efflux of 5beta-pregnane-3alpha,17alpha,20beta-triol into the medium immediately following fertilization and residual steroid levels remain low in the developing blastula. Dissociated blastulae cells prepared from stage 9 1/2 embryos concentrate both pregnenolone and progesterone from the medium with minimal metabolism. The results indicate that the ovarian follicle has the ability to synthesize and metabolize progesterone but that this ability disappears in the ovulated egg. The progesterone metabolites formed during meiosis are largely released at fertilization.

Precycle administration of GnRH antagonist and microdose HCG decreases clinical pregnancy rates without affecting embryo quality and blastulation

The outcome of a novel protocol utilizing precycle gonadotrophin-releasing hormone (GnRH) antagonist administration and LH activity support with microdose recombinant human chorionic gonadotrophin (HCG) was compared to GnRH agonist long protocol used in patients undergoing their first ICSI (n=707) or IVF (n=571) cycles, which had resulted in one or two blastocyst transfers. In GnRH antagonist cycles, cetrorelix acetate (3 mg) was administered s.c. 4 days before FSH stimulation and a repeat dose was given when the lead follicular diameter was 13-14 mm. LH support was provided by recombinant HCG (2.5 microg). Embryo progression and blastulation were evaluated using embryo progression indices and blastocyst quality scores. The tested protocol demonstrated reduced implantation and clinical pregnancy rates as compared with GnRH agonist long protocol, although the embryo progression and blastulation parameters and blastocyst quality were comparable among the groups. Logistic regression models further supported the significant negative impact of GnRH antagonist/microdose HCG protocol on clinical pregnancy rates in both ICSI and IVF patients. Assisted reproduction cycles with fresh blastocyst transfers utilizing precycle GnRH antagonist administration and microdose HCG support resulted in lower implantation and clinical pregnancy rates as compared with GnRH agonist cycles, although the embryo progression and blastulation parameters were comparable.

Ethanol exposure affects gene expression in the embryonic organizer and reduces retinoic acid levels

Fetal Alcohol Spectrum Disorder (FASD) is a set of developmental malformations caused by alcohol consumption during pregnancy. Fetal Alcohol Syndrome (FAS), the strongest manifestation of FASD, results in short stature, microcephally and facial dysmorphogenesis including microphthalmia. Using Xenopus embryos as a model developmental system, we show that ethanol exposure recapitulates many aspects of FAS, including a shortened rostro-caudal axis, microcephally and microphthalmia. Temporal analysis revealed that Xenopus embryos are most sensitive to ethanol exposure between late blastula and early/mid gastrula stages. This window of sensitivity overlaps with the formation and early function of the embryonic organizer, Spemann's organizer. Molecular analysis revealed that ethanol exposure of embryos induces changes in the domains and levels of organizer-specific gene expression, identifying Spemann's organizer as an early target of ethanol. Ethanol also induces a defect in convergent extension movements that delays gastrulation movements and may affect the overall length. We show that mechanistically, ethanol is antagonistic to retinol (Vitamin A) and retinal conversion to retinoic acid, and that the organizer is active in retinoic acid signaling during early gastrulation. The model suggests that FASD is induced in part by an ethanol-dependent reduction in retinoic acid levels that are necessary for the normal function of Spemann's organizer.

Effect of human hydrosalpinx fluid on the development of mouse embryos and role of the concentration of growth factors in culture medium with and without hydrosalpinx fluid

The aim of this study was to investigate the effect of human hydrosalpinx fluid (HF) on the development and blastulation of mouse embryos and the role of the concentration of growth factors in culture medium with and without HF. In total, 2100 mouse embryos were cultured. Female mice were induced to superovulate and then mated with males. Two-cell-stage embryos were recovered from the oviduct and cultured in Ham's F-10 medium with bovine serum albumin and HF. Epidermal growth factor (EGF) and insulin-like growth factor-I (IGF-I) were analyzed by quantitative enzyme immunoassay. Mean blastulation index of 1.11, 0.97 and 0.98 was found at HF concentration of 5%, 20% and 30%, respectively (p = 0.8). The mean value of EGF in the control culture medium without HF was 11.2 pg/ml, which was statistically significantly different from that in culture medium containing HF (p < 0.001). The mean value of IGF-I in the control group without HF was 1.30 pg/ml and was not statistically significantly different from that in culture medium containing HF. Development of the two-cell-stage embryos was not affected at low (< 30%) HF concentrations. In conclusion, the present study demonstrates that even apparently normal blastulation is affected by any concentration of HF because of low embryonic EGF.

Cadmium induces the expression of specific stress proteins in sea urchin embryos

Marine organisms are highly sensitive to many environmental stresses, and consequently, the analysis of their bio-molecular responses to different stress agents is very important for the understanding of putative repair mechanisms. Sea urchin embryos represent a simple though significant model system to test how specific stress can simultaneously affect development and protein expression. Here, we used Paracentrotus lividus sea urchin embryos to study the effects of time-dependent continuous exposure to subacute/sublethal cadmium concentrations. We found that, between 15 and 24 h of exposure, the synthesis of a specific set of stress proteins (90, 72-70, 56, 28, and 25 kDa) was induced, with an increase in the rate of synthesis of 72-70 kDa (hsps), 56 kDa (hsp), and 25 kDa, which was dependent on the lengths of treatment. Recovery experiments in which cadmium was removed showed that while stress proteins continued to be synthesized, embryo development was resumed only after short lengths of exposure.

Involvement of nitric oxide duringin vitro fertilization and early embryonic development in mice

Nitric oxide (NO) has emerged as an important intracellular and intercellular messenger, controlling many physiological processes and participating in the fertilization process via the autocrine and paracrine mechanisms. This study investigated whether nitric oxide synthase (NOS) inhibitior (L-NAME) and L-arginine could regulate in vitro fertilization and early embryonic development in mice. Mouse epididymal spermatozoa, oocytes, and embryos were incubated in mediums of variable conditions with and without L-NAME or L-arginine (0.5, 1, 5 and 10 mM). Fertilization rate and early embryonic development were significantly inhibited by treating sperms or oocytes with L-NAME (93. 8% vs 66.3%, 92.1% vs 60.3%), but not with L-arginine. In contrast, fertilization rate and early embryonic development were conspicuously reduced when L-NAME or L-arginine was added to the culture media for embryos. Early embryonic development was inhibited by microinjection of L-NAME into the fertilized embryos in a dose-dependent manner, but only by high concentrations of L-arginine. These results suggest that a moderate amount of NO production is essential for fertilization and early embryo development in mice.

Diterpenes from the roots of Euphorbia kansui and their in vitro effects on the cell division of Xenopus (part 2)

Four new ingenane-type diterpenes, 3-O-(2,3-dimethylbutanoyl)-13-O-dodecanoyl-20-O-acetylingenol (1), 3-O-(2,3-dimethylbutanoyl)-13-O-dodecanoyl-20-deoxyingenol (2), 3-O-(2E,4Z-decadienoyl)-20-deoxyingenol (3), and 3-O-(2E,4E-decadienoyl)-20-deoxyingenol (4), two new jatrophane-type diterpenes, kansuinins D (9) and E (10), and four known ingenane-type diterpenes were isolated from the root of Euphorbia kansui. Their structures were elucidated by spectroscopic and chemical analysis, and individual Xenopus cells at the blastular stage were cultured with the diterpenes to test for biological activity. 20-Deoxyingenol diterpenes 3 and 4 induced the greatest cell cleavage arrest (0.5 micro g/ml of each compound resulted in >75% cleavage arrest), but cell cleavage inhibitory activity became weak when C-16 had an acyl residue. In contrast, the jatrophane diterpene kansuinin D (9) showed no activity.

Monoclonal antibody against dnmt1 arrests the cell division of xenopus early-stage embryos

DNA methylation plays a crucial role in embryogenesis, and Dnmt1 is known to be a key enzyme in the maintenance of DNA methylation. Dnmt1 is highly accumulated in mature oocytes and eggs. To analyze the function of the maternally accumulated Dnmt1, we injected monoclonal antibodies that specifically recognize the amino terminus of Xenopus Dnmt1 into Xenopus laevis embryos. The monoclonal antibodies inhibited the cell division of the embryos before the midblastula transition. Monoclonal antibody neither inhibited DNA methylation activity of Dnmt1 in vitro nor affected its stability in embryos. In addition, injection of alpha-amanitin, an inhibitor of transcription, did not rescue the cell division arrest. The results suggest that the inhibition of cell division by monoclonal antibodies was due neither to the direct inhibition of DNA methylation activity of Dnmt1 nor to aberrant transcription before the midblastula transition. The morphology of chromatin of the arrested cells showed that the cell cycle was arrested at interphase. This was supported by the biochemical analysis in which the arrested cells demonstrated low histone H1 kinase activity, which indicated that the cells had not entered M phase. Dnmt1 may have an important function other than DNA methylation activity for early embryogenesis in Xenopus laevis.

Overexpression of S-adenosylmethionine decarboxylase (SAMDC) in Xenopus embryos activates maternal program of apoptosis as a "fail-safe" mechanism of early embryogenesis

In Xenopus, injection of S-adenosylmethionine decarboxylase (SAMDC) mRNA into fertilized eggs or 2-cell stage embryos induces massive cell dissociation and embryo-lysis at the early gastrula stage due to activation of the maternal program of apoptosis. We injected SAMDC mRNA into only one of the animal side blastomeres of embryos at different stages of cleavage, and examined the timing of the onset of the apoptotic reaction. In the injection at 4- and 8-cell stages, a considerable number of embryos developed into tadpoles and in the injection at 16- and 32-cell stages, all the embryos became tadpoles, although tadpoles obtained were sometimes abnormal. However, using GFP as a lineage tracer, we found that descendant cells of the blastomere injected with SAMDC mRNA at 8- to 32-cell stages are confined within the blastocoel at the early gastrula stage and undergo apoptotic cell death within the blastocoel, in spite of the continued development of the injected embryos. These results indicate that cells overexpressed with SAMDC undergo apoptotic cell death consistently at the early gastrula stage, irrespective of the timing of the mRNA injection. We assume that apoptosis is executed in Xenopus early gastrulae as a "fail-safe" mechanism to eliminate physiologically-severely damaged cells to save the rest of the embryo.

Application of a sea urchin micronucleus assay to monitoring aquatic pollution: influence of sample osmolality

We have improved our sea urchin micronucleus assay for aquatic samples and used it to evaluate marine pollution. We found that the water samples we had collected for 2 years from the Tokyo bay coast near Tokyo, an industrial megalopolis, were positive due to the water samples being hypo-osmotic rather than to chemical pollutants. The evidence was as follows: (i) the osmolality and salinity of the samples were about half that of sea water; (ii) the micronucleus frequency induced in the water sample decreased to the control level when the osmolality was increased to that of sea water; (iii) artificial sea water diluted with distilled water induced micronuclei dilution-dependently. Since micronucleus induction in the sea urchin assay is influenced by sample osmolality, the osmolality must be adjusted to that of sea water for the assay and osmotic pressure must be considered when evaluating water pollution.