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At least 1,369 records · Page 76Linked to original sources
PubMed2001

Distribution of blue-sensitive photoreceptors in amphibian retinas.

Previously, we reported that an opsin (Rc-MS) belonging to the SWS2 group opsins is expressed in bullfrog green rods [Hisatomi, O. et al., FEBS Lett., 1999, 447, 44-48]. An anti-Rc-MS antiserum recognized the cones of the Japanese common newt, Cynops pyrrhogaster, which has no green rods. We isolated a cDNA encoding an SWS2 group opsin (Cp-SWS2) from this newt and found that Cp-SWS2 is expressed in a small population of the cones. Our results suggest that SWS2 opsins can be expressed in either green rods or cones of caudata. It seems reasonable to suppose that green rods arose before amphibia were divided into caudata and anura.

Amino Acid Sequence↗
PubMed1986

Pathways for the movements of ions during calcium-free perfusion and the induction of the 'calcium paradox'.

The intracellular sodium content of cardiac cells in fish and amphibia, measured with either an isotope technique or with sodium-sensitive micro-electrodes, rises steeply from around 15 mmol/l in calcium-containing solution to as much as 70 mmol/l, during exposure to a Ca2+-free solution. This increase is associated with the development of spontaneous and prolonged action potentials so that the membrane may stabilise around -20 mV. On reperfusion with calcium-containing medium the membrane repolarises before a strong contracture develops. Inhibition of the Na-pump increases both the sodium gain and the subsequent calcium re-admission tension. A number of agents e.g. divalent cations, anti-arrhythmic drugs, local anaesthetics and Ca-channel blockers are able to prevent the development of the contracture but only if they are present during the calcium-free perfusion. They also inhibit the development of spontaneous electrical activity and the rise in Nai. The calcium re-admission contracture can be blocked in amphibian preparations voltage clamped around the resting potential during low calcium perfusion. From the known pharmacological action of these agents and the voltage and time dependence of the calcium channel, it is concluded that during calcium depletion, the prolongation of the action potentials is associated with a sustained entry of Na+ via the Ca-channels which leads to the rise in Nai. Once Nai has risen, these agents with the exception of Mn2+, a known inhibitor of the Na/Ca exchange, are unable to prevent the development of the contracture. This suggests that the re-admission contracture follows calcium uptake by way of the Na/Ca exchange.

Action Potentials↗
PubMed1984

Osmium ferricyanide fixation improves microfilament preservation and membrane visualization in a variety of animal cell types.

Using a fixation formula which includes adding potassium ferricyanide (K3Fe(CN)6) to the osmium step and an en bloc aqueous uranyl acetate step before dehydration we have looked at cells from mammals, birds, amphibia, algae, and higher plants and we have collaborated in fixing cells of teleost fish. In every cell type except the algae and higher plants the final EM image was improved by the OsFeCN-uranium method. The most common improvement was an increase in the membrane contrast but more significantly, some cells show improved preservation of microfilaments. We conclude that the OsFeCN adds contrast to all classes of membrane and does not destroy microfilaments to the extent that osmium alone does. Adding uranyl acetate to the cells may protect delicate filamentous structures from collapse during dehydration and embedding. We have preliminary evidence in PtK1 cells that addition of tannic acid after OsFeCN may function in a similar manner. This method is recommended for any animal cell type where improved visualization of membranes and filaments is required.

Animals↗
PubMed2003

Ultrastructure of developing tooth plates in the Australian lungfish, Neoceratodus forsteri (Osteichthyes: Dipnoi).

While the lungfish dentition is partially understood as far as morphology and light microscopic structure is concerned, the ultrastructure is not. Each tooth plate is associated with a dental lamina that develops from the inner layer of endodermal cells that form the oral epithelium. Dentines, bone and cartilage of the jaws differentiate from mesenchyme cells aggregating beneath the oral endothelium. Enamel, in the developing and in the mature form, has similarities to that of other early vertebrates, but unusual characters appear as development proceeds. Ameloblasts are capable of secreting enamel, and, with mononuclear osteoclasts, of remodelling the bone below the tooth plate. The forms of dentine, all based largely on an extracellular matrix of collagen and mineralised with biological apatite, differ from each other and from the underlying bone in the ultrastructure of associated cells and in the mineralised extracellular matrices produced. Cell processes emerging from the odontoblasts and from the osteoblasts vary in length, degree of branching and of anastomoses between the processes, although all of the cell types have large amounts of rough endoplasmic reticulum. Mineralisation of the extracellular matrices varies among the enamel, dentines and bone in the tooth plate. In addition, the development of the hard tissues of the tooth plates indicates that many of the similarities in fine structure of the dentition in lungfish, to tissues in other fish and amphibia, apparent early in development, disappear as the dentition matures.

Animals↗
PubMed1993

Intermediate filaments and ATPase activity in the vascular wall of vertebrates.

The vascular wall of aorta and vena cava was examined for adenosine triphosphatase (ATPase) activity and cytoskeletal intermediate filaments (IF) in different representatives of vertebrates. Enzyme activity was studied by the modified method of Padykula and Herman. A streptavididin-biotin immunohistochemical method was applied to reveal desmin (D) and vimentin (V) IF. Endothelial cells of all vessels were V-positive and D-negative and exhibit high ATPase activity. Vascular smooth muscle cells (SMC) in lower vertebrates (pisces and amphibia) were also V-positive and D-negative, but showed low ATPase activity. SMC were D-positive and V-negative and possessed high enzyme activity in aves and mammals, similar to that of the endothelium. In cow vascular wall D-reactivity and high ATPase activity were mostly expressed in bundles of mosaically arranged thick SMC fibres of the outer aortic media as well as in the longitudinal fibres in the inferior vena cava. In higher vertebrates SMC of vasa vasorum were both V- and D-positive and showed high enzyme activity. The results demonstrate that D-immunoreactivity is mostly expressed in SMC of layers of high functional activity, which correlates with the intense ATPase reaction in these cells.

Adenosine Triphosphatases↗
PubMed1999

Lectin binding patterns in amphibian skin epithelium.

Seven lectins (PNA, DBA, WGA, UEA-I, RCA, SBA, Con A) were used to localize glycoconjugates in the skin of 10 species of Amphibia, 7 anurans (Bufo marinus, Bufo bufo, Rana ridibunda, Rana pipiens, Hyla arborea, Pelobates syriacus and Xenopus laevis) and 3 urodeles (Salamandra salamandra, Triturus vulgaris and Ambystoma mexicanum). It was found that every lectin has a specific binding pattern in the skin of each species. No common pattern could be established, either among frogs or toads, nor for a particular lectin. Each lectin bound specifically and selectively to a particular epithelial component, which differed from one species to the other. A number of lectins showed selective binding to mitochondria-rich cells, but, again, a pattern in positivity could not be found. It is concluded that lectin histochemistry does correlate with cellular function. Our data can be applied in studies of epithelium and skin development, and of changes that occur during adaptation to the environment by amphibian species.

Animals↗
PubMed1999

The anterior margin of the mammalian gastrula: comparative and phylogenetic aspects of its role in axis formation and head induction.

Recent findings on morphology and gene expression in several mammalian embryos suggest that there is a new landmark and possibly a center with organizer activity in the anterior margin of the embryo at the onset of gastrulation. This review compiles morphological variations and similarities found among mammals during gastrulation stages and, at the same time, stresses the common aspects, at the morphological and the molecular level, of setting up the body plan with regard to axis formation and head induction. Both morphological and functional aspects are then used to draw comparisons with equivalent developmental stages in lower vertebrate species, such as birds, amphibia, and bony fish. Finally, a suggestion is made as to how gastrulation may have evolved in the vertebrate phylum.

Animals↗
PubMed2001

Initiation and early patterning of the endoderm.

We review the early stages of endoderm formation in the major animal models. In Amphibia maternal molecules are important in initiating endoderm formation. This is followed by successive signaling events that establish and then pattern the endoderm. In other organisms there are differences in endodermal development, particularly in the initial, prephylotypic stages. Later many of the same key families of transcription factors and signaling cassettes are used in all animals, but more work will be needed to establish exact evolutionary homologies.

Amphibians↗
PubMed1985

Ribocharin: a nuclear Mr 40,000 protein specific to precursor particles of the large ribosomal subunit.

Using a monoclonal antibody (No-194) we have identified, in Xenopus laevis and other amphibia, an acidic protein of Mr 40,000 (ribocharin) which is specifically associated with the granular component of the nucleolus and nucleoplasmic 65S particles. These particles contain the nuclear 28S rRNA and apparently represent the precursor to the large ribosomal subunit in nucleocytoplasmic transit. By immunoelectron microscopy ribocharin has been localized in the granular component of the nucleolus and in interchromatin granules. During mitosis ribocharin-containing particles are associated with surfaces of chromosomes and are recollected in the reconstituting nucleoli in late telophase. We suggest that ribocharin is a specific component of precursor particles of the large ribosomal subunit, which dissociates from the 65S particle before passage through the nuclear envelope, and is reutilized in ribosome biogenesis.

Animals↗
PubMedDate not supplied

Phosphatidylserine expression on apoptotic lymphocytes of Xenopus laevis, the South African clawed toad, as a signal for macrophage recognition.

Inflammation is avoided in apoptosis by early removal of dying cells by macrophages (MOs). In mammalian cells, an early aspect of apoptosis is the translocation of phosphatidylserine (PS) from the inner leaflet of the cell membrane to the surface. PS recognition can serve as a signal for triggering removal of dying cells. PS expression on splenocytes and thymocytes of Xenopus laevis was quantified using FITC-Annexin and flow cytometry following exposure in vitro to several known apoptogens for this species. All apoptogens used induced PS expression. Dose dependency and the kinetics of PS expression following exposure to the calcium ionophore, A23187, were also examined. Peritoneal exudate cells (PEC's) were cultured with A23187-treated thymocytes to test MO capacity for recognition of PS. MO binding to apoptotic thymocytes was reduced following exposure of PEC's to a water soluble analogue of PS, phospho-L-serine. The presence of a phagocytic PS-dependent recognition system in amphibia is supportive of the evolutionary conservation of this function in mammals that is crucial in limiting inflammation induced by dying cells.

Animals↗
PubMedDate not supplied

Noradrenergic and peptidergic innervation of the amphibian spleen: comparative studies.

Spleens from representatives of the three amphibian orders were examined using sucrose-potassium phosphate-glyoxylic acid (SPG) histofluorescence to detect catecholamines and immunocytochemistry to detect several neural antigens. Nerve fibers are scattered throughout the spleens of adult salamanders (Taricha torosa, Notophthalmus viridescens, and Ambystoma mexicanum). A less abundant but similarly diffuse pattern of innervation characterizes the spleen of the caecilian, Typhlonectes sp. The spleen of the adult frog, Xenopus laevis, is separated into clearly defined compartments of red pulp and white pulp, much as is seen in the mammalian spleen. As in mammals, sympathetic innervation of the Xenopus spleen is noradrenergic (NA) and confined to the white pulp. The white pulp of Xenopus spleen also contains fibers which stain for neuropeptide Y and substance P. The spleen of the anuran, Rana pipiens, is also highly compartmentalized, with tyrosine hydroxylase positive fibers in proximity to blood vessels. These findings provide an anatomical substrate for neural-immune interactions in the Amphibia.

Amphibians↗
PubMed1999

Odorant receptors: a plethora of G-protein-coupled receptors.

Odorant receptors (ORs) comprise the largest family of G-protein-coupled receptors (GPCRs). They are located in the nasal epithelium, at the ciliated surface of olfactory sensory neurones, where the initial steps of the olfactory transduction cascade occur. ORs are encoded by a large and diverse multi-gene family, which has been characterized in cyclostomes, teleosts, amphibia, birds and mammals, as well as in Drosophila and Caenorhabditis elegans. Here, the range of diversity in OR and chemoreceptor structure is examined, noting that their functions are fundamentally similar to those of many neurotransmitter or neurohormone receptors. It is argued that ORs have emerged directly from other GPCRs independently in many species. According to this view, there is no structural prerequisite for OR identity and any GPCR has the potential to be or become an OR at a given point in evolution.

Animals↗
PubMed2002

Frogs and toads in front of a mirror: lateralisation of response to social stimuli in tadpoles of five anuran species.

Tadpoles of five anuran species were tested for preferences in the use of the eyes during inspection of their own visual image in a mirror. When tested in a tank with several small mirrors, tadpoles of five different species (Bufo bufo, Bufo viridis, Rana temporaria, Rana esculenta, Bombina variegata) preferentially approached and positioned themselves with the mirror located on their left side, thus looking at the image with the monocular field of their left eye. Similar results were obtained with tadpoles of R. temporaria tested in a simple task in which they had to choose approaching one or other of two large mirrors located on their left and right side. Control experiment showed that the behavioural asymmetry was not due to motor preferences and that it was independent of morphological asymmetries in the positions of the spiracles. This is the first demonstration of a functional visual lateralisation among juvenile amphibia before metamorphosis.

Animals↗
PubMed1999

Structure of the Xenopus laevis TFF-gene xP4.1, differentially expressed to its duplicated homolog xP4.2.

TFF-peptides (formerly P-domain peptides, trefoil factors) represent major secretory products of mucous epithelia in mammals and amphibia. The nucleotide sequence of a large portion of a gene encoding the TFF-peptide xP4.1 from Xenopus laevis and its genomic organization were determined in the present study. The peptide xP4.1 containing four TFF-domains is thought to represent the functional frog homolog of human TFF2 (formerly hSP). The xP4.1 gene analyzed spans a region of about 7 kb and consists of six exons. Each TFF-domain is encoded by a single exon flanked by type 1 introns typical of shuffled modules. The 5'-upstream region contains a TATA-box, and potential binding sites for hepatocyte nuclear factor 3 and AP-1. Furthermore, the cDNA sequence of a transcript named xP4.2 with 91% similarity to xP4.1 is presented. RT-PCR analysis revealed that xP4.1 and xP4.2 genes are differentially expressed. xP4.1 transcripts are detectable only in the stomach, but not in the esophagus, whereas xP4.2 transcripts are found both in the esophagus and in the stomach with a descending gradient from fundus to antrum.

Amino Acid Sequence↗
PubMed1999

Head in the WNT: the molecular nature of Spemann's head organizer.

Formation of the head during vertebrate embryogenesis has been one of the most-studied topics in development, probably because we are such cephalized beings ourselves. Early experimenters found that the head is induced during gastrulation by Spemann's organizer. In 1999 we celebrate the 75th anniversary of the discovery of the organizer by Spemann and Mangold, a group of cells in amphibia that secretes powerful signalling molecules. Recently, advances have been made in identifying candidate head inducers. Not surprisingly, these inducers act in familiar molecular pathways, namely transforming growth factor beta (TGF-beta) and WNT signalling.

Animals↗
PubMed2000

Structure-function relationships in bombinins H, antimicrobial peptides from Bombina skin secretions.

Skin secretions of amphibia of the Bombina genus contain two families of antimicrobial peptides, the bombinins (bombinin-like peptides) and the bombinins H (H for hydrophobic and hemolytic). The latter family includes a number of peptides containing a D-amino acid in the second position, in addition to their corresponding all L-isomers. The antimicrobial activity of three pairs of bombinin H isomers, H2/H4, H6/H7 and GH-1D/GH-1L, has been investigated. The first two pairs of peptides were actually isolated from the secretion, whereas the third was synthesized according to the sequence deduced from a gene coding for a bombinin-like peptide in Bombina orientalis.

Amino Acids↗
PubMed2002

Ecological risk assessment and testing for endocrine disruption in the aquatic environment.

Field observations of endocrine disruption (ED) in fish and other aquatic species have contributed to a global effort to establish test methods for detecting ED effects in wildlife species. For ecological risk assessment, validated tests are needed for Amphibia, fish and aquatic invertebrates, supported by a tiered approach incorporating mechanistic data and exposure characterisation. The potential for extrapolation of ED data from mammalian to aquatic species may be limited, however, due to significant physiological differences in function and regulation of hormone systems in (aquatic) lower vertebrates and invertebrates. Presently, the OECD is considering a tiered approach for ED risk assessment, incorporating a fish 14-day screening assay (Tier 1); fish development and reproduction tests (both Tier 2); and a fish full life-cycle test (Tier 3). For detection of (anti-)oestrogens, the yolk-precursor protein vitellogenin is an ideal biomarker of exposure and functionally equivalent biomarkers are being sought for (anti-)androgens in fish. At the two higher tiers, impacts are assessed in terms of apical endpoints (e.g. development, breeding behaviour and fecundity) and also gonadal histopathology. Validation of these higher tier tests should include comparison of sensitivity of biochemical and apical endpoints to optimise the value of biomarkers for predicting adverse health effects (e.g. impaired reproduction). The specificity of future OECD fish and amphibian test guidelines for endocrine disrupters needs further consideration through inclusion of mechanistic endpoints based on state-of-the-art molecular endocrinology.

Amphibians↗
PubMed1998

Use of explant cultures of peripheral nerves of adult vertebrates to study axonal regeneration in vitro.

Explanted preparations of peripheral nerves with attached dorsal root ganglia of adult mammals and amphibia survive for several days in serum-free medium and can be used to study axonal regeneration in vitro. This review outlines the methods which we routinely use and how they may be applied to study different aspects of axonal regeneration. When the peripheral nerves are crushed in vitro, axons regenerate through the crush site into the distal stump within 1 day (mouse) or 3 days (frog). The outgrowth distance of the leading sensory axons can be determined with the use of a simple method based on axonal transport of labelled proteins. A compartmentalised system permits selective application of drugs and other agents to either ganglia or peripheral nerve containing the regenerating axons and has been used to study selected aspects of regeneration including influence of non-neuronal cells, retrograde signalling, axonal release of proteins during regeneration and the role of phospholipase A2 activity. Explanted preparations may also be cultured in a layer of extracellular matrix material (matrigel), in which spontaneous outgrowth of a large number of naked axons from the cut ends of nerves starts within 1 day and continues for several days. This provides an opportunity to study the direct effects of different agents on axonal elongation. Preparations cultured in collagen gels show sparse spontaneous axonal growth, but this can be increased by addition of certain growth factors. The phenotype of the regenerating axons can be studied using immunohistochemical methods.

Animals↗