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 505 records · Page 28Linked to original sources
PubMed2004

The 18S rRNA from Odontophrynus americanus 2n and 4n (Amphibia, Anura) reveals unusual extra sequences in the variable region V2.

The nucleotide sequence of the rDNA 18S region isolated from diploid and tetraploid species of the amphibian Odontophrynus americanus was determined and used to predict the secondary structure of the corresponding 18S rRNA molecules. Comparison of the primary and secondary structures for the 2n and 4n species confirmed that these species are very closely related. Only three nucleotide substitutions were observed, accounting for 99% identity between the 18S sequences, whereas several changes were detected by comparison with the Xenopus laevis 18S sequence (96% identity). Most changes were located in highly variable regions of the molecule. A noticeable feature of the Odontophrynus 18S rRNA was the presence of unusual extra sequences in the V2 region, between helices 9 and 11. These extra sequences do not fit the model for secondary structure predicted for vertebrate 18S rRNA.

Animals↗
PubMed1983

Chromosome pairing in female and male diploid and polyploid anurans (Amphibia) from South America.

Chromosome pairing in females and males of diploid (2n = 22) and tetraploid (2n = 44) Odontophrynus americanus and diploid Ceratophrys cranwelli (2n = 26) and tetraploid C. ornata (2n = 104) showed that diploid females formed more chiasmata per paired arm than diploid males and polyploids of both sexes. There was a reduction in the level of recombination in female polyploids by forming multivalents with terminal chiasmata. The reduction reflected a change in the genetic control of pairing in females after polyploidization.

Animals↗
PubMed1991

A centromeric satellite DNA in the European plethodontid salamanders (Amphibia, Urodela).

A highly repeated satellite DNA (Hy500) located in the centromeric heterochromatin of the European plethodontid salamander Speleomantes (formerly Hydromantes) was studied. The Hy500 family represents about 1% of the Speleomantes supramontis genome and has a major repeating unit of about 500 base pairs, which may have evolved from the progressive amplification of shorter sequences. This centromeric satellite is conserved in all the Speleomantes species, which nevertheless show distinct patterns of chromosomal distribution, which are of relevance as to their phylogenetic relationships.

Animals↗
PubMed1987

Bicarbonate transport by initial collecting tubule of aquatic- and land-phase amphibia.

The rate of bicarbonate reabsorption (JHCO3) by in vitro initial collecting tubules (ICT) from aquatic- and land-phase Ambystoma tigrinum was measured. These animals intrinsically have different levels of plasma bicarbonate, 17.6 and 27.1 mM, respectively. ICT from both phases reabsorbed bicarbonate at 11 pmol X mm-1 X min-1 when perfused in solutions equilibrated with 3% CO2. The induction of metabolic acidosis or alkalosis had no effect on JHCO3 by in vitro ICT. JHCO3 was abolished when ICT from aquatic animals were perfused with solutions equilibrated with 1% CO2 and returned toward the control value when 3% CO2 was reintroduced. The effect of plasma CO2 partial pressure on JHCO3 of the ICT may explain, at least in part, the observed difference in plasma bicarbonate of the aquatic- and land-phase animals. JHCO3 was reduced to 22% of control with amiloride and to 42% of control when a Na+-free perfusate was used, but was insensitive to ethoxzolamide. These data are consistent with the presence of a sodium-proton exchanger on the apical membrane and a carbonic anhydrase-independent mechanism of H+ secretion.

Absorption↗
PubMed2000

Immunocytochemical localization of gonadotropin-releasing hormones in the brain of a viviparous caecilian amphibian, Typhlonectes natans (Amphibia: Gymnophiona).

The molecular forms and brain distribution of gonadotropin-releasing hormone (GnRH) have been well studied in the amphibian orders Urodela (salamanders and newts) and Anura (frogs and toads). In the order Gymnophiona (caecilians), however, few species have been investigated. Antibodies against different molecular forms of GnRH were used to immunohistochemically localize the GnRH-containing neurons in the brain of the caecilian, Typhlonectes natans which differs from most other amphibians in that it is viviparous. An antibody selective for mammalian GnRH recognized cell bodies predominantly in the septo-preoptic area but only with occasional cell bodies in the lateral hypothalamus and ventral thalamic eminence. Thick, prominent fibers in the septal region and fibers within the terminal nerve were also labeled. An antibody selective for chicken-II GnRH labeled a population of cell bodies in the dorsal hypothalamus, ventral thalamus and midbrain tegmentum. Thin fibers projected laterally from these cells. An antibody specific for salmon GnRH did not label cell bodies but did show intense terminal field immunoreactivity. The brain of this caecilian, therefore, contains three antigenically distinct forms of GnRH. The mammalian and chicken-II GnRH peptides have been shown in other amphibians but the distribution of cells and fibers was unique in this caecilian.

Amphibians↗
PubMed1998

Evolution by polyploidy in Amphibia: new insights.

Polyploidy is an important mechanism of evolution in lower vertebrates, resulting in gene duplication and loci duplication evolving to diploidization. In polyploid anurans DNA is increased, but RNA and protein synthesis is kept at the same levels as in their diploid counterparts. Recent cytogenetic findings in Odontophrynus americanus show: (1) amphiplasty and asynchrony of the cell division cycle in 4n and (2) intra- and interindividual alterations of chromosome 4 morphology in 4n and 2n through breaks at secondary constrictions and at/or around the centromeres, followed by the appearance of changes of centromeres position, dicentrics, bisatellited chromosomes, precocious sister-chromatid segregation, and loss or unequal segregation of the chromosomes. This genome instability suggests the presence of chromosomal aberrations with chromodomain alterations at the centromeres affecting the mechanisms ensuring normal segregation of the chromatids in anaphase of mitosis and meiosis. Cell division asynchrony and chromosome abnormalities, novel findings in polyploids, are discussed respectively in function of gene activity and putative translocations producing polymorphisms in nucleolus organizers and secondary constrictions.

Amphibians↗
PubMed2002

Chromosome banding in Amphibia. XXII. Atypical y chromosomes in Gastrotheca walkeri and Gastrotheca ovifera (Anura, Hylidae).

The chromosomes of the rare South American marsupial frogs Gastrotheca walkeri and G. ovifera were extensively reexamined with various banding techniques. The karyotypes of both species are distinguished by a new category of XY female symbol /XX male symbol female sex chromosomes. The unusual Y chromosomes are characterized by containing the least amount of constitutive heterochromatin in the karyotypes. This is in contrast to all previously known amphibian Y chromosomes and does not fit the evolutionary model of early XY differentiation in vertebrates. In male meiosis, the heteromorphic XY chromosomes of both species still exhibit the same pairing configurations as the autosomes. DNA flow cytometric measurements show the nuclear DNA amount of G. walkeri to be 10.90 pg. The significance of the XY/XX sex chromosomes of these marsupial frogs, the various classes of constitutive heterochromatin detected, and the data obtained from meiotic analyses are discussed in detail.

Animals↗
PubMed2002

Distribution of NADPH-diaphorase/nitric oxide synthase in the brain of the caecilian Dermophis mexicanus (amphibia: gymnophiona): comparative aspects in amphibians.

The organization of nitrergic systems in the brains of anuran and urodele amphibians was recently studied and significant differences were noted between both amphibian orders. However, comparable data are not available for the third order of amphibians, the gymnophionans (caecilians). In the present study we have investigated the distribution of neuronal elements that express nitric oxide synthase (NOS) in the brain of the gymnophionan amphibian Dermophis mexicanus by means of immunohistochemistry with specific antibodies against NOS and enzyme histochemistry for NADPH-diaphorase. Both techniques yielded identical results and were equally suitable to demonstrate the nitrergic system. In addition, they were useful tools in the identification of cell groups and brain structures, otherwise indistinct in the brains of caecilians. The distribution of nitrergic structures observed in Dermophis conforms to the overall amphibian pattern but numerous distinct peculiarities were also noted. These included a dense innervation of the olfactory bulbs but a lack of reactivity in olfactory and vomeronasal fibers and glomeruli. A large population of nitrergic cells in the striatum and the presence of thalamic neurons, as well as the specific distribution of nitrergic cells in the isthmic region, are some of the differential features in the gymnophionan brain. Given the variability among species in the same class of vertebrates any discussion including amphibians should also include evidence for gymnophionans.

Amphibians↗
PubMed2002

Chromosome banding in Amphibia. XXV. Karyotype evolution and heterochromatin characterization in Australian Mixophyes (Anura, Myobatrachidae).

The mitotic chromosomes of the Australian ground frogs Mixophyes fasciolatus and M. schevilli were analyzed by means of banding techniques and restriction endonuclease digestions. Chromosomal differentiation in these two species occurred exclusively by considerable changes in the amount of telomeric and centromeric heterochromatin, whereas the sizes and locations of interstitial heterochromatic regions, the sizes of all euchromatic segments as well as the positions of centromeres remained nearly identical during karyotype evolution. The major heterochromatic regions in the karyotypes of M. fasciolatus and M. schevilli amount to 30.2% and 20.7%, respectively. They consist of AT base pair-rich repetitive DNA sequences that are brightly labeled by AT-specific fluorochromes and display quenched fluorescence after staining with GC-specific fluorochromes. The heterochromatic regions can be differentiated by treatment of metaphase chromosomes and interphase cell nuclei with various restriction enzymes which either disclose the complete set of C-band patterns in the karyotypes of both species, or else reveal several subsets of these C-bands.

Animals↗
PubMed2002

Chromosome banding in Amphibia. XXIV. The B chromosomes of Gastrotheca espeletia (Anura, Hylidae).

The mitotic chromosomes of an Ecuadorian population of the marsupial frog Gastrotheca espeletia were analyzed by means of banding techniques and fluorescence in situ hybridization. This species is characterized by unusual supernumerary (B) chromosomes. The maximum number of B chromosomes is 9 and they occur in three different morphological types. Banding analyses show that the B chromosomes are completely heterochromatic, consist of AT base pair-rich repeated DNA sequences, replicate their DNA in very late S-phase of the cell cycle, and are probably derived from a centromeric or paracentromeric region of a standard (A) chromosome. Exceptionally, the B chromosomes carry 18S + 28S ribosomal RNA genes and the conserved vertebrate telomeric DNA sequence appears to be underrepresented. Flow cytometric measurements of the nuclear DNA content differentiate between individuals with different numbers of B chromosomes. Significantly more B chromosomes are present in female than in male animals.

Animals↗
PubMed2002

Chromosome banding in Amphibia. XXVI. Coexistence of homomorphic XY sex chromosomes and a derived Y-autosome translocation in Eleutherodactylus maussi (Anura, Leptodactylidae).

A 15-year cytogenetic survey on one population of the leaf litter frog Eleutherodactylus maussi in northern Venezuela confirmed the existence of multiple XXAA male symbol /XAA(Y) female symbol sex chromosomes which originated by a centric (Robertsonian) fusion between the original Y chromosome and an autosome. 95% of the male individuals in this population are carriers of this Y-autosome fusion. In male meiosis the XAA(Y) sex chromosomes pair in the expected trivalent configuration. In the same population, 5% of the male animals still possess the original, free XY sex chromosomes. In a second population of E. maussi analyzed, all male specimens are characterized by these ancestral XY chromosomes which form normal bivalents in meiosis. E. maussi apparently represents the first vertebrate species discovered in which a derived Y-autosome fusion still coexists with the ancestral free XY sex chromosomes. The free XY sex chromosomes, as well as the multiple XA(Y) sex chromosomes are still in a very primitive (homomorphic) stage of differentiation. With no banding technique applied it is possible to distinguish the Y from the X. DNA flow cytometric measurements show that the genome of E. maussi is among the largest in the anuran family Leptodactylidae. The present study also supplies further data on differential chromosome banding and fluorescence in situ hybridization experiments in this amphibian species.

Animals↗