Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Amphibia”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,243 records · Page 69Linked to original sources
PubMed1985

Evolution of the single copy alpha A-crystallin gene: differently sized mRNAs of mammals and birds show homology in their 3' non-coding regions.

alpha A-Crystallin, a major structural polypeptide of the vertebrate eye lens, is evolutionarily highly conserved. We have analyzed the corresponding nucleic acid sequences in both genomic DNA digests as well as in lens cytoplasmic RNA preparations from a wide variety of vertebrates by blot hybridization with cloned rat alpha A2-crystallin cDNA probes. The probes are not able to hybridize under any conditions to RNA and DNA derived from fishes and amphibia, but do show substantial homology with the sequences of mammals, birds and reptiles. The alpha A-crystallin gene, which has been isolated from a hamster gene library occurs only once in the haploid genome. Coding and 3'-untranslated regions of alpha A2-crystallin mRNA are conserved among all mammals and birds examined. However, the regions comprising the conserved sequences are differently represented in the ultimate mRNA. The alpha A2-mRNA 3'-non-coding regions of reptiles and birds are 300-550 bases longer than those of mammals. Some rodents produce next to the alpha A2-mRNA another messenger that encodes the alpha AIns-polypeptide possessing an insertion of 22/23 amino acid residues between positions 63 and 64 of the alpha A2-polypeptide chain. alpha A2 and alpha AIns-mRNA are generated from a single gene as major and minor species, respectively, in a proportion which is similar to the ratio of the polypeptides found in vivo and in vitro. The size heterogeneity of the alpha A2-mRNA from most mammals examined is due to the variable size of the poly(A) tail.

Animals↗
PubMedDate not supplied

Evolution of the mechanisms of connection between neurons: electrical, mixed, and chemical synapses.

Investigation of the mechanisms of transmission of stimuli in synapses of isolated perfused spinal cord of cyclostomes, amphibia, reptiles, and mammals demonstrated that the ratio between electrical and chemical synapses decreased progressively in favor of the latter in the transition from primitive toward more highly developed forms. Electrical transmission was not detected in synapses of spinal cords of reptiles and mammals. On the basis of the data, the result of analysis of elementary synaptic processes in synapses uniting electrical and chemical mechanisms of transmission and dendrodendrite electronic interdependences of the motor neurons, a hypothesis is formulated that the number of electrical connections characterizes the union of similar neurons, while in a sequential union of nerve cells of various functions and origins, there are mixed or chemical synapses. The possible cellular mechanisms which are the basis of this phenomenon are discussed.

Afferent Pathways↗
PubMed1982

Responses in the optic tectum of the salamander Hydromantes italicus to moving prey stimuli.

In the tectum opticum of Hydromantes italicus neurons were recorded extracellularly which responded selectively to moving visual stimuli. Part of the recorded cells were marked iontophoretically by means of alcian-blue dye for anatomical localization. Out of a total of 110 neurons six groups could be distinguished which preferred the square stimulus but differed strongly in their responses to rectangles oriented either vertically or horizontally. Two of these groups showed stimulus preference inversion if the stimulus velocity was changed. These response patterns displayed characteristic differences with those known in other amphibia, well corresponding to differences in the prey catching behaviors.

Animals↗
PubMed1982

Triiodothyronine induces an increase in cyclic GMP in bullfrog tadpole tissues.

Cyclic GMP (cGMP) and cyclic AMP (cAMP) were determined in bullfrog tadpole liver and tail fin using 125I-RIA. cGMP increased approx. 100% 1-6 h after the injection of T3 (3 X 10(-10) mol/g body wt.). Reducing the dose of T3 to 1, 3, and 10 X 10(-11) mol/g body wt. provided increases in cGMP of 50-100% above the control value after 2 h. In contrast, only small increases (less than 20%) in cAMP were observed 2-24 h after T3 injection. We conclude that T3 produces a rapid and significant increase in cGMP in the liver and tail fins of premetamorphic tadpoles. These results suggest that thyroid hormones in amphibia may not be an exclusively nucleus-mediated hormone.

Animals↗
PubMed1987

Polypeptide YY- and neuropeptide Y-immunoreactive cells and nerves in the endocrine and exocrine pancreas of some vertebrates: an onto- and phylogenetic study.

The occurrence of polypeptide YY- and neuropeptide Y-immunoreactive cells and nerves in the pancreas of some species from all the eight main vertebrate groups (cyclostomes, cartilaginous fish, bony fish, amphibia, reptiles, birds, and mammals) was investigated. In addition, an ontogenetic study of these neurohormonal peptides was performed, using the rat pancreas. The distribution of these two peptides was compared with that of the structurally closely related pancreatic polypeptide. Polypeptide YY-immunoreactive cells were found to occur in the endocrine pancreas and neuropeptide Y-immunoreactivity was observed both in neurons and nerve fibres. The polypeptide YY-immunoreactive cells were limited to mammals and reptiles only. Neuropeptide Y-immunoreactive neurons and nerves were observed in reptiles, birds, and mammals only. One reptilian species (out of three) and one mammalian (out of six) failed to show any kind of immunoreactivity for the polypeptide or neuropeptide. Pancreatic polypeptide-immunoreactive cells were found in all the species examined except in the hagfish islet. In rat foetuses, polypeptide YY-immunoreactive cells and neuropeptide Y-immunoreactive nerve elements were first demonstrated at the seventeenth day of gestation, whereas pancreatic peptide-immunoreactive cells did not appear until postnatally, namely in two day-old rats. The polypeptide-containing cells, a new cell type in the endocrine pancreas, are rare. In contrast to the pancreatic peptide cells, they do not seem to have any kind of regional distribution.

Animals↗
PubMed1987

Action potentials in epithelial taste receptor cells induced by mucosal calcium.

Chemosensory cells in the taste bud of the tongue of Necturus generate action potentials in response to electrical stimulation through a microelectrode, as recently described by Roper (Science, 220: 1311-1312, 1983). We report that the epithelial receptor cells also respond to 10 mM CaCl2, applied to the mucosal surface, with a depolarization which elicits action potentials when a threshold of -50 mV is reached. Since CaCl2 is one of the taste stimuli in amphibia, the firing of action potentials by chemoreceptor cells may be part of the signal chain in gustatory reception of Ca ions.

Action Potentials↗
PubMed1984

Inverse relationship between melanogenesis and endogenous hydroquinone.

Inhibition or stimulation of melanogenesis have been found to occur as a result of the alteration of hydroquinone levels in the body. Substances which stimulate melanogenesis are found to lower the level of hydroquinone in amphibia, and evidence for the relationship is also given by mammalian experiments.

Animals↗
PubMed1996

The molecular evolution of vertebrate growth hormones: a pattern of near-stasis interrupted by sustained bursts of rapid change.

It has been demonstrated previously that in mammals the evolution of pituitary growth hormone shows an unusual pattern, with an underlying slow rate and at least two sustained bursts of rapid evolution (in the artiodactyls and primates), during which the rate increased at least 25-fold. It is demonstrated here that a similar pattern applies for growth hormone evolution throughout the vertebrates, with a basal rate similar to that seen in mammals, but bursts of rapid evolution in the amphibia and the elasmobranchs, and several bursts in the teleosts. The placental growth-hormone-like proteins of primates show a similar pattern. It is argued that the bursts of evolution seen for growth hormone are a consequence of selection and that this may reflect changes in the functions of the hormone additional to its basic growth-promoting actions.

Animals↗
PubMed2003

Altered impedance during pigment aggregation in Xenopus laevis melanophores.

Melanophores are dark-brown pigment cells located in the skin of amphibia, fish and many invertebrates. The skin colour of these organisms is regulated by the translocation of pigment organelles, and the pigment distribution can be altered by external stimuli. The ability to change colour in response to stimuli makes these cells of interest for biosensing applications. It was investigated whether pigment aggregation in Xenopus laevis melanophores can be detected by impedance measurements performed in transparent microvials. The results show that cell attachment, cell spreading and pigment aggregation all resulted in impedance changes, seen particularly at the highest frequency tested (10 kHz). The mechanisms behind the impedance changes were investigated by the addition of latrunculin or melatonin, both of which cause pigment aggregation. The latrunculin-induced aggregation was associated with cell area decrease and filamentous actin (F-actin) breakdown, processes that can influence the impedance. Lack of F-actin breakdown and an increase in cell area during melatonin-induced aggregation suggest that some other intracellular process also contributes to the impedance decrease seen for melatonin. It was shown that impedance measurements reflect not only cell attachment and cell spreading, but also intracellular events.

Animals↗
PubMed1997

An essay on the similarities and differences between inductive interactions in anuran and urodele embryos.

As a first step towards providing a conceptual approach to understanding similarities and differences in the mechanisms which guide inductive interactions among related organisms (e.g. various amphibia), a set of five principles is offered here. These principles were formulated by analyzing literature examples of classical embryological phenomena and by performing experiments with activin, a peptide growth factor which is currently suspected to play for a role in mesoderm induction. Mechanisms which account, at least in part, for the observed differences between anuran and urodele inductive processes can be derived from these principles.

Animals↗
PubMed2001

Vision in the ultraviolet.

Sensitivity to ultraviolet light (UV) is achieved by photoreceptors in the eye that contain a class of visual pigments maximally sensitive to light at wavelengths <400 nm. It is widespread in the animal kingdom where it is used for mate choice, communication and foraging for food. UV sensitivity is not, however, a constant feature of the visual system, and in many vertebrate species, the UV-sensitive (UVS) pigment is replaced by a violet-sensitive (VS) pigment with maximal sensitivity between 410 and 435 nm. The role of protonation of the Schiff base-chromophore linkage and the mechanism for tuning of pigments into the UV is discussed in detail. Amino acid sequence analysis of vertebrate VS/UVS pigments indicates that the ancestral pigment was UVS, with loss of UV sensitivity occurring separately in mammals, amphibia and birds, and subsequently regained by a single amino acid substitution in certain bird species. In contrast, no loss of UV sensitivity has occurred in the UVS pigments of insects.

Animals↗
PubMed1998

The molecular clock runs at different rates among closely related members of a gene family.

The serum albumin gene family is composed of four members that have arisen by a series of duplications from a common ancestor. From sequence differences between members of the gene family, we infer that a gene duplication some 580 Myr ago gave rise to the vitamin D-binding protein (DBP) gene and a second lineage, which reduplicated about 295 Myr ago to give the albumin (ALB) gene and a common precursor to alpha-fetoprotein (AFP) and alpha-albumin (ALF). This precursor itself duplicated about 250 Myr ago, giving rise to the youngest family members, AFP and ALF. It should be possible to correlate these dates with the phylogenetic distribution of members of the gene family among different species. All four genes are found in mammals, but AFP and ALF are not found in amphibia, which diverged from reptiles about 360 Myr ago, before the divergence of the AFP-ALF progenitor from albumin. Although individual family members display an approximate clock-like evolution, there are significant deviations-the rates of divergence for AFP differ by a factor of 7, the rates for ALB differ by a factor of 2.1. Since the progenitor of this gene family itself arose by triplication of a smaller gene, the rates of evolution of individual domains were also calculated and were shown to vary within and between family members. The great variation in the rates of the molecular clock raises questions concerning whether it can be used to infer evolutionary time from contemporary sequence differences.

Albumins↗
PubMed1999

Characterization of the Hydra lamin and its gene: A molecular phylogeny of metazoan lamins.

We report sequences for nuclear lamins from the teleost fish Danio and six invertebrates. These include two cnidarians (Hydra and Tealia), one priapulid, two echinoderms, and the cephalochordate Branchiostoma. Combining these results with earlier data on Drosophila, Caenorhabditis elegans, and various vertebrates, the following conclusions on lamin evolution can be drawn. First, all invertebrate lamins resemble in size the vertebrate B-type lamin. Second, all lamins described previously for amphibia, birds and mammals as well as the first lamin of a fish, characterized here, show a cluster of 7 to 12 acidic residues in the tail domain. Since this acidic cluster is absent from all invertebrate lamins including that of the cephalochordate Branchiostoma, it was acquired with the vertebrate lineage. The larger A-type lamin of differentiated cells must have arisen subsequently by gene duplication and insertion of an extra exon. This extra exon of the vertebrate A-lamins is the only major change in domain organization in metazoan lamin evolution. Third, the three introns of the Hydra and Priapulus genes correspond in position to the last three introns of vertebrate B-type lamin genes. Thus the entirely different gene organization of the C. elegans and Drosophila Dmo genes seems to reflect evolutionary drift, which probably also accounts for the fact that C. elegans has the most diverse lamin sequence. Finally we discuss the possibility that two lamin types, a constitutively expressed one and a developmentally regulated one, arose independently on the arthropod and vertebrate lineages.

Amino Acid Sequence↗
PubMed2003

Early human development: new data raise important embryological and ethical questions relevant for stem cell research.

Recent research has considerably changed our views about the developmental biology of early mammalian embryos compared with the ideas that were predominant throughout the previous 30 years or so. New data obtained recently suggest that the mammalian embryo uses traits of axes determination mechanisms that are not too different from the modes used by other vertebrates. In particular, it appears that asymmetry cues derived from the oocyte cytoplasm and modified/specified during sperm penetration appear to be crucial in normal embryogenesis, rather than the environmental influences exerted, e.g. at embryo implantation in the uterus. On the other hand, recent advances in research on the equivalents of a Spemann-Mangold organizer in species other than amphibia (including mammals) provide a background for new discussions of early embryonic patterning (axis formation) processes in the embryonic disc. In combination, these new views appear to be of considerable interest in the debate on the developmental properties and the ethical status of embryonic stem cells. The present review focuses specifically on the new aspects of axis determination and pattern formation processes in early mammalian embryos and relates this to questions about the developmental potential of embryonic stem cells (totipotency vs pluripotency/omnipotency), i.e. facts that appear to be worth considering in the recent debate about the ontological status of the early human embryo as well as of human embryonic stem cells.

Animals↗
PubMed2000

Apical nonspecific cation channels in everted collecting tubules of potassium-adapted ambystoma.

We observed intermediate conductance channels in approximately 20% of successful patch-clamp seals made on collecting tubules dissected from Ambystoma adapted to 50 mm potassium. These channels were rarely observed in collecting tubules taken from animals which were maintained in tap water. Potassium-adaptation either leads to an increase in the number of channels present or activates quiescent channels. In cell-attached patches the conductance averaged 30.3 +/- 2.4 (9) pS. Since replacement of the chloride in the patch pipette with gluconate did not change the conductance, the channel carries cations, not anions. Notably, channel activity was observed at both positive and negative pipette voltages. When the pipette was voltage clamped at 0 mV or positive voltages, the current was directed inward, consistent with the movement of sodium into the cell. The pipette voltage at which the polarity of the current reversed (movement of potassium into the pipette) was -29.6 +/- 6.5(9) mV. Open probability at 0 mV pipette voltage was 0.08 +/- 0.03 and was unaffected when the apical membrane was exposed to either 2 x 10(-6) or 2 x 10(-5) m of amiloride. Exposure of the basolateral surface of the tubule to a saline containing 15 mm potassium caused a significant increase (P less than 0.001) in the open probability of these channels to 0.139 +/- 0.002 without affecting the conductance of the apical channel. These data illustrate the presence of an intermediate conductance, poorly selective, amiloride-insensitive cation channel in native vertebrate collecting tubule. We postulate that, at least in amphibia, this channel may be used to secrete potassium.

Ambystoma↗
PubMed2003

Five hundred sixty-five triples of chicken, human, and mouse candidate orthologs.

The Human Genome Project has provided abundant gene sequence information on human and important model organisms. The chicken is well positioned from an evolutionary standpoint to serve as a link between higher and lower organisms, particularly mammals, and amphibia and fish. In this study we used stringent criteria to select 565 triples of chicken, human, and mouse candidate orthologs. We analyze the sequences with respect to nucleotide and amino acid similarities. This analysis also allows measurement of evolutionary distances of different proteins. We found that chicken-human and chicken-mouse sequence identities are highly correlated; similarly for chicken-human and chicken-mouse evolutionary distances. With chicken as the out-group, we found that mouse has a higher substitution rate than human, supporting the generation-time effect hypothesis. We also described the transversion bias, which is the preference for some transversions than others in nucleotide substitutions. We demonstrated that there are statistically significant properties in the differences of orthologous sequences. The differential patterns, in combination with sequence similarity analysis, may lead to the identification of genes that are very divergent from the mammalian orthologs.

Animals↗
PubMed2004

Biosensors of inorganic lead exposure and effect in an adult amphibian.

Lead (Pb) is a ubiquitous environmental pollutant, widely distributed, representing a high toxicological and ecotoxicological risk. Several morphological, functional, and biochemical parameters have been proposed as biomarkers of effect and exposure to Pb. The information related to adverse effects of Pb is not abundant for adult amphibians. These animals are of interest, because during their development they move from aquatic to terrestrial habitats, which may be polluted by the metal since they are receptors of products generated by anthropogenic activities. Previous studies carried out on the adult South American toad Bufo arenarum (Amphibia, Anura) showed that it has a high tolerance to lead and studied the effect of sublethal doses of the metal on the erythrocyte osmotic fragility and delta-ALAD activity. It was also shown that after a single injection of Pb, a significant increase in the number of reticulocytes was produced, suggesting the suitability of those cell counts as a biomarker of exposure to the metal; its impact on the immune system of the toads was also studied. In this work we extend our early studies on the same species evaluating the chronic effect of sublethal Pb (equivalent to 5.6% of the 120-h LD-50) on free erythrocyte protoporphyrin (FEP) and blood Pb and delta-ALAD activity; blood lead was positively associated with a significant decrease in the enzyme activity and to an increase in the FEP level. Pb concentration in target organs (liver, spleen, femur, and kidney) and the total cumulated amount as well as its impact over the mass of those organs were also determined. In addition, the magnitude of the possible depuration through urine and intestine was evaluated. Our results showed that FEP, delta-ALAD, and blood Pb are reliable biosensors of chronic metal intoxication, the former being the marker with the highest sensitivity.

Animals↗