Cypermethrin induction of DNA damage and oxidative stress in zebrafish gill cells

Cypermethrin (CYP) is a synthetic pyrethroid insecticide, used to control pests in domestic, industrial and agricultural environments. According to recent reports, it is one of the most common contaminants in freshwater aquatic systems. The aim of this study was to evaluate its potential genotoxic effect and the activation of the superoxide dismutase (SOD) and catalase (CAT) systems of adult zebrafish gill cells after in vivo exposure. The comet assay (CA) demonstrated that gill cells are sensitive to DNA damage after in vitro exposure to hydrogen peroxide (H₂O₂), showing a dose-dependent response. We also found an increase in DNA damage of gill cells following a dose- and time-dependent treatment with CYP. Moreover, it was verified that SOD and CAT activities significantly increased after exposure to 0.6 µg/L CYP, both during six and nine days. The same treatment caused a significant up-regulation of the mRNA levels of Mn-sod and cat genes. These data indicate that CYP causes gill cell's DNA damage and oxidative stress, modifying the activities of the enzymes responsible for maintaining ROS balance, as well as in their corresponding gene expression levels.

Cypermethrin: Oxidative stress and genotoxicity in retinal cells of the adult zebrafish

Cypermethrin (CM), widely used for control of indoor and field pests, is one of the most common contaminants in freshwater aquatic systems. We evaluated CM genotoxicity and the activities of superoxide dismutase (SOD) and catalase (CAT) in retinal cells of adult zebrafish. Histological and immunofluorescence techniques show the presence of apoptotic cells in the zebrafish retina after 9 d of treatment with 0.6 μg/L CM. Histone γ-H2AX, a marker of DNA damage, was detected in both outer and inner nuclear layers; caspase-3, an apoptotic marker, was detected in the outer nuclear layer. In the comet assay, the cells were sensitive to hydrogen peroxide-induced DNA damage, showing a dose-dependent response. We observed a positive comet assay response to CM that was dose- and time-dependent. Following exposure to CM, SOD and CAT enzyme activities, and sod and cat mRNA levels, increased. These results indicate that CM causes DNA damage and oxidative stress and can induce apoptosis in retinal cells.

E-cadherin roles in animal biology: A perspective on thyroid hormone-influence

The establishment, remodeling and maintenance of tissular architecture during animal development, and even across juvenile to adult life, are deeply regulated by a delicate interplay of extracellular signals, cell membrane receptors and intracellular signal messengers. It is well known that cell adhesion molecules (cell-cell and cell-extracellular matrix) play a critical role in these processes. Particularly, adherens junctions (AJs) mediated by E-cadherin and catenins determine cell-cell contact survival and epithelia function. Consequently, this review seeks to encompass the complex and prolific knowledge about E-cadherin roles during physiological and pathological states, particularly focusing on the influence exerted by the thyroid hormone (TH).

Isolation and nucleotide sequence analysis of the of Rhinella arenarum β-catenin: an mRNA and protein expression study during the larval stages of the digestive tract development

β-catenin interacts with several proteins mediating key biological processes, such as cadherin-mediated cell-cell adhesion as well as signal transduction. This work was done to establish the molecular basis and regulation of the formation pattern of cadherin/β-catenin-mediated adherens junctions, using an animal model of unknown gene sequence, the toad Rhinella arenarum. A Rhinella arenarum β-catenin homolog was isolated from larval tissue, their sequence compared and analyzed with those of eight other vertebrates using bioinformatics tools. The mRNA and protein expression levels of β-catenin were determined during the development of Rhinella arenarum digestive tract both by Reverse Transcriptase-Polymerase Chain Reaction (RT-PCR) and immunohistochemistry-morphometry respectively. Using Xenopus laevis frog specific primers, a fragment 539 bp of Rhinella arenarum toad β-catenin cDNA was obtained and sequenced. The resulting putative sequence of 177 amino acids showed high similarity at the amino acid level (97%) when compared to other six vertebrates (Xenopus laevis, Xenopus tropicalis, Mus musculus, Rattus norvegicus, Bos taurus and Homo sapiens), with sequences and structural domains characteristic of catenins. Subsequently, using primers specifically designed for Rhinella arenarum nucleotide sequence, β-catenin-mRNA increasing levels were found during the Rhinella arenarum metamorphosis. Finally, increasing β-catenin protein expression during development has confirmed the specificity the detection of Rhinella arenarum β-catenin. Summarizing, we have isolated and sequenced a β-catenin-homologue sequence from the Rhinella arenarum toad, which is highly conserved between species, and following we have detected β-catenin mRNA and protein levels during their digestive tract development.

T3 regulates E-cadherin, and β- and α-catenin expression in the stomach during the metamorphosis of the toad Rhinella arenarum

The metamorphosis of Rhinella arenarum was induced precociously for 5 days, then blocked for 3 months to evaluate the role of thyroid hormones as modulators of morphoregulatory molecules such as E-cadherin, and β- and α-catenin during epithelium remodeling. We then performed an immunohistochemical and morphometric study of these molecules in the larval stomach. We show that 3,5,3'-triiodothyronine exerts a positive regulatory effect on E-cadherin and β- and α-catenin expression in stomach epithelium. This suggests continuous synthesis of E-cadherin, and β- and α-catenin; synthesis essentially is thyroid hormone-independent during premetamorphosis and early prometamorphosis, but it becomes thyroid hormone-dependent during metamorphic climax.

3D automatic quantification applied to optically sectioned images to improve microscopy analysis

New fluorescence microscopy techniques, such as confocal or digital deconvolution microscopy, allow to easily obtain three-dimensional (3D) information from specimens. However, there are few 3D quantification tools that allow extracting information of these volumes. Therefore, the amount of information acquired by these techniques is difficult to manipulate and analyze manually. The present study describes a model-based method, which for the first time shows 3D visualization and quantification of fluorescent apoptotic body signals, from optical serial sections of porcine hepatocyte spheroids correlating them to their morphological structures. The method consists on an algorithm that counts apoptotic bodies in a spheroid structure and extracts information from them, such as their centroids in cartesian and radial coordinates, relative to the spheroid centre, and their integrated intensity. 3D visualization of the extracted information, allowed us to quantify the distribution of apoptotic bodies in three different zones of the spheroid.

Apoptotic cell death in the central nervous system of Bufo arenarum tadpoles induced by cypermethrin

Tadpoles of the toad Bufo arenarum treated with cypermethrin (CY) at concentrations above 39 mug CY/L showed dose-dependent apoptotic cell death in immature cells of the central nervous system as demonstrated by morphometric analysis, the TUNEL method, and DNA fragmentation assay. Light-and electron-microscopic studies showed structural alterations in the intermediate and marginal layers of the brain. Immature cerebral tissue showed cellular shrinkage, nuclear fragmentation and increase of intercellular spaces. In this study we demonstrated high toxicity of CY to larval stages of Bufo arenarum. Our results show that doses lower than those used in routine insecticide applications can cause massive apoptosis in the immature cells of the central nervous system. These results coincide with our previous studies in Physalaemus biligonigerus, confirming the severe toxic effects of CY to the central nervous system of anuran species from Argentina. This may increase the mortality index in wild animals and contribute to the loss of biodiversity in our agroecosystems. We postulate that CY induces apoptosis in central nervous system cells of Bufo arenarum tadpoles by specific neurotoxic mechanisms.

CAS role in the brain apoptosis of Bufo arenarum induced by cypermethrin

CAS might have a key role in the apoptosis induced by toxins, acting as anti-apoptotic factor, stimulating the cellular proliferation and the cell contact stabilization. To start to elucidate their role in the brain apoptosis of Bufo arenarum induced by cypermethrin (CY), the expression patterns of CAS and several cell adhesion molecules (CAMs) were established. Bufo arenarum tadpoles of the control and acute bioassay survival at different doses (39, 156, 625 and 2,500 microg CY/L) and times (24, 48, 72 and 96 h) of CY treatment were fixed in Carnoy, embedded in paraffin and sectioned. CAS and CAMs expression was determined by immunofluorescence and immunohistochemistry, respectively. When the bioassay starts, CAS increases suggesting a proliferative or regenerative effect, but decreases when the doses and/or the biocide exposure time increases, suggesting compromise of the cellular cycle control and trigger of an apoptotic wave. However, these neurotoxic mechanisms should not involve degradation of N-cadherin and alpha-catenin, in contrast of beta-catenin and axonal N-CAM180, at least in the initial apoptotic phase. Additionally, an adhesion compensatory mechanism by N-CAM180 is observed in the neuron cell body. These results suggest a dual role of CAS in the cellular cycle control during the CY-induced apoptosis: induction of cell proliferation and stabilization of the cell-cell junctions by modulating CAMs expression.

Alterations induced by E-cadherin and beta-catenin antibodies during the development of Bufo arenarum (Anura-Bufonidae)

E(epithelial)-cadherin is a member of a calcium-dependent family of cell surface glycoproteins involved in cell-cell adhesion and morphogenesis. Catenins are a large family of proteins that connect the cadherins to the cytoskeleton. They are important for cadherin function and for transducing signals involved in specification of cell fate during embryogenesis. The best characterized catenins include alpha-, beta-, gamma-, and p120-catenin. Using specific antibodies, we studied the expression and distribution of E-cadherin, and alpha- and beta-catenin in developmental stages of Bufo arenarum toad. The three proteins were found co-localized in stages 19 to 41 of development. Surprisingly, E-cadherin was the only of these three proteins found earlier than stage 19. To test whether E-cadherin and beta-catenin have a functional role in Bufo arenarum embryogenesis, stage 17 whole embryos were incubated with anti-E-cadherin and beta-catenin antibodies. Both anti-E-cadherin and anti-beta-catenin antibodies induced severe morphological alterations. However, while alterations produced by the anti-beta-catenin antibody, showed some variability from the most severe (neural tube and notochord duplication) to a simple delay in development, the alterations with anti-E-cadherin were homogeneous. These observations suggest a critical role for E-cadherin and beta-catenin in the early embryonic development of the Bufo arenarum toad. Our results are consistent with the developmental role of these proteins in other species. One of the most surprising findings was the blockage with the anti-beta-catenin antibodies on later embryo stages, and we hypothesize that the partial axes duplication could be mediated by the notochord induction.

Expression of N-CAM-180 and N-cadherin during development in two South-American anuran species (Bufo arenarum and Hyla nana)

Cadherins and N-CAM are Ca++-dependent and Ca++-independent cell adhesion molecules respectively. These molecules play a key role in morphogenesis and histogenesis. We determined the spatiotemporal pattern of N-cadherin and N-CAM-180 kDa expression by immunohistochemistry during development in two South-American anuran species (Bufo arenarum, toad and Hyla nana, frog). Both N-cadherin and N-CAM were not detectable during early developmental stages. Expression of N-cadherin appeared between the inner and the outer ectoderm layers at stages 19-20. At stages 24-25, N-cadherin was expressed in the neural tube and the heart. In early tadpoles, N-cadherin expression increased along with the central nervous system (CNS) morphogenesis, and reached its maximum level at metamorphic climax stage. N-Cadherin expression was not uniformly distributed. At stage 42, olfactory placodes and retina expressed N-cadherin. Contrary to N-CAM, the strongly myelinated cranial nerves were not labeled. N-Cadherin was present in several mesoderm derivatives such as the notochord, heart and skeletal muscle. The non-neural ectoderm and the endoderm were always negative. Expression of N-CAM appeared first in the neural tube at stages 24-25 and the level of expression became uniform from pre-metamorphic to metamorphic climax tadpoles. At this latter stage, a clear N-CAM immunolabeling appeared in the nerve terminals of pharynx and heart. N-Cadherin and N-CAM were found mainly co-expressed in the CNS from early tadpole to metamorphic climax tadpole. Our results show that the expression of N-CAM and N-cadherin is evolutionary conserved. Their increased expression during late developmental stages suggests that N-CAM and N-cadherin are involved in cell contact stabilization during tissue formation.

Expression of polysialic acid, alpha- and beta-cantenins in adult toad testis in hibernation stage and after gonadotrophin--releasing hormone (GnRH) treatment

The Polysialic Acid (PSA), glycosydic moiety of the Neural Cell Adhesion Molecule (N-CAM), and alpha- and beta-Catenins, which mediate interaction between Cadherins and cytoskeletal proteins, participate in cell adhesion phenomena in numerous organs and tissues. We have performed an immunohistochemical analysis, in hibernating toad testis and in GnRH-reactivated hibernating animals. In hibernating toads we could demonstrate PSA-immunoreactivity (PSA-IR) within the seminiferous tubules, in clusters of primary spermatocytes, spermatids and spermatozoa, in follicular and Sertoli cells. PSA-IR was seen in peritubular, Leydig and efferent duct cells. In GnRH-treated toads PSA-IR persists in primary spermatocyte groups. alpha-Catenin is localized in the basal laminae of seminiferous tubules and in Leydig cells of hibernating toads. This did not change after hormonal treatment. In hibernating toads, beta-Catenin was detected only in Leydig cells and within seminiferous tubules on basal spermatocystes and limiting spermatozoa clusters. In GnRH-treated toads, the beta-Catenin-IR was less intense in Leydig cells and vanished within seminiferous tubules.

Paraquat tolerance and alteration of internal gill structure of Scinax nasica tadpoles (Anura: Hylidae)

Paraquat acute tolerance, and histological and ultrastructural response analysis of gills were evaluated in Scinax nasica tadpoles at stages 25-26. The treated tadpoles were able to survive with a mortality rate similar to the controls in media containing 6.48 to 10.80 mg PQ/L. At 18.00 mg PQ/L survival rate was about 85%; at 30.00 and 50.00 mg PQ/L an incremented mortality rate was detected. Their internal gills appear to have a critical role in adaptation to exposure to PQ. The LC-50 values found helped us conclude that increasing time of exposure to PQ produces a decrease of tadpole survival rate. With light microscopy, the apical ramification gill tufts exhibited a dose response increase of the total volume. At the ultrastructural level, an increase in the intercellular spaces and alteration in gill epithelium organization were the most notable changes. Furthermore, the capillaries showed enlarged endothelial cells, irregular nuclei, and numerous cytoplasmatic projections.

Atrial natriuretic factor (ANF)-like immunoreactivity and secretory granules in internal gills tadpoles of South American toad Bufo arenarum (Hensel)

In this study, an ultrastructural and immunohistochemical analysis was carried out on the presence of Atrial Natriuretic Factor-like substance in the internal gills of premetamorphic larval stages of the South American toad. The results of immunohistochemical study indicate that, at larval 27 and following stages, ANF-like immunoreactive cells are seen in internal gills. At electron-microscopy level "secretory granules" similar to those ANF-immunoreactives granules of myoendocrine cells of the same species are seen only in clear cells of gill rakers. Our results reveal the occurrence of ANF-like substance in Bufo arenarum gills and may suggest that "cardiac hormones" might play a paracrine and/or autocrine role in the water and electrolyte balance at internal gills level.

Presence and release of immunoreactive atrial natriuretic peptide (ANP) in Bufo arenarum spermatozoa after HCG treatment

Atrial natriuretic peptide (ANP)-like immunoreactivity has been demonstrated in mature spermatozoa of Bufo arenarum. However, after spermiation induced by Gonadotropin Releasing Hormone (GnRH), no ANP immunoreactivity was detected in testicular spermatozoa. Recently, the presence of GnRH and GnRH receptors in amphibian testes has been demonstrated. To clarify if the loss of ANP-like immunoreactivity in spermatozoa is a direct effect of GnRH or pituitary gonadotropins, a study on Bufo arenarum adult males, has been performed. The in vivo treatment with Human Chorionic Gonadotropin (HCG) induced spermiation and loss of ANP-like immunoreactivity. The in vitro treatment with HCG showed the same results. However, in vitro GnRH treatment failed to cause spermiation and loss of ANP-like immunoreactivity. The present results indicate that ANP from mature spermatozoa is regulated via gonadotropic hormones and may be involved in the spermiation process.

Expression of isoforms of the neural cell adhesion molecule (NCAM) and polysialic acid during the development of the Bufo arenarum olfactory system

The neural cell adhesion molecule (NCAM), a member of the immunoglobulin superfamily that promotes Ca(2+)-independent cell-cell adhesion, is expressed as various isoforms generated by alternative splicing. In this study, the expression of the 180 kDa isoform (180-NCAM), total NCAM (180, 140 and 120 kDa isoforms) and the polysialic acid moiety of NCAM (PSA) were analyzed during the development of the olfactory system of the toad Bufo arenarum using specific antibodies and immunofluorescence light microscopy. NCAM and PSA were not found in the ectodermal thickening corresponding to the olfactory placode at early larval stage (stage 17), but by stage 19, total NCAM, 180-NCAM and PSA were all expressed in the invaginating olfactory placode at the sites of cell-cell contact and in the differentiating olfactory epithelium. Later, NCAM isoforms and PSA were found also in the primary fibers of the olfactory nerve and in the olfactory bulb. However, the expression of 180-NCAM decreased near the end of larval development and was absent in post-metamorphic and adult animals. In contrast, total NCAM (representing 140 and/or 120 kDa isoforms) and PSA continued to be expressed in olfactory tissues of post-metamorphic and adult animals, consistent with the persistent neural plasticity of this tissue. Because 180-NCAM has been associated with non-proliferating neurons, its down-regulation in post-metamorphic and adult olfactory system may be associated with the regenerative capability and continuous cell turnover documented for this region in adult animals.

Demonstration of atrial natriuretic peptide immunoreactivity and ultrastructurally related secretory granules in myoblasts of the chick myotome

In this study, an ultrastructural and immunohistochemical examination was carried out on the presence of an 'atrial-natriuretic-peptide (ANP)-like factor' in the myoblasts of the brachial myotome of chicken embryos at Hamburger and Hamilton stages 17 +/- to 19. The results of the immunohistochemical study indicate that, at these stages of their development, the myoblasts of the brachial myotome show ANP immunoreactivity. The ultrastructural analysis of the myoblasts shows the presence of 'granules' or 'secretory vesicles', similar to the secretory granules which contain natriuretic peptides. The demonstration of immunoreactivity to ANP in the myotome and the specific localization of secretory vesicles in myoblasts, as the first evidence relating ANP with skeletal muscle development, reveal a new site at which an ANP-like factor may be synthesized. The hypothesis of a paracrine and/or autocrine function(s) during myogenesis is suggested.

The presence of atrial natriuretic peptide (ANP) in spermatozoa of Bufo arenarum, and effects of GnRH

Atrial natriuretic peptide (ANP)-like immunoreactivity has been demonstrated in the testes of adult Bufo arenarum. Reaction was limited to the head of mature spermatozoa attached to Sertoli cells, interstitial tissue, and seminiferous tubules walls. An immunohistochemical study of isolated spermatozoa showed the reaction to be limited to the basal area of spermatozoon head. After spermiation induced by GnRH, testicular spermatozoa were not immunoreactive. Neither isolated spermatozoa from homogenized testes nor isolated spermatozoa from urine immunostained. The demonstration of immunoreactive ANP in B. arenarum testes, its specific location in specific regions of spermatozoa, and the absence of immunostaining after GnRH treatment, suggest that the "cardiac" peptide may be involved in testicular function.

Differentiation of endocrine myocardiocytes in the developing heart of the toad (Bufo arenarum Hensel)

The differentiation of endocrine myocardiocytes was investigated in the heart of developing toad Bufo arenarum Hensel, combining ultrastructural and immunocytochemical procedures. The distribution of immuno-reactive atrial natriuretic peptide (ANP) in the whole heart was appraised by light microscopy, applying biotin-streptavidin and immunofluorescence techniques. With the latter procedures ANP was first recognized at embryonic stage 22, in both atrium and ventricle. In the ensuing stages the ANP-reactivity became stronger in the atrium, while it became dimmer in the ventricle. At the end of the larval prometamorphic stage, atrial myocardiocytes acquired almost all the features of adult myoendocrine cells. At electron microscope level, small inclusions, about 110-120 nm in diameter, resembling secretory granules were found in myoendocrine cells beginning at embryonic stage 22. However, no immunogold labeling of ANP occurred until stage 25. The number of secretory granules diminished in the ventricles and increased in the atrium of the larval heart and at the end of the prometamorphic stage the atrial myoendocrine cells presented the ultrastructural characteristics of active secretory cells. The synthesis of ANP in larvae is enhanced at a critical period of development when the developing toad switches from an aquatic environment to terrestrial life. The cardiac hormones seem to play a key role in the regulation of the osmolarity of body fluids at this developmental stage.