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PubMed1995

Ty1-copia group retrotransposon sequences in amphibia and reptilia.

We have isolated sequences belonging to Ty1-copia group retrotransposons from the genomes of an amphibian (Pyxicephalus adspersa) and three reptiles (Conolophus subscristatus, Amblyrynchus cristatus and Pytas mucosus). Two different sequences were found in the amphibian (Tpa1 and Tpa2). Each is present in several copies per genome and absent from the genomes of two other amphibian species. The C. subcristatus sequence Tcs1 is present in multiple copies in both its host genome (Galapagos land iguana) and the genome of the related Galapagos marine iguana (A. cristatus). There is little or no polymorphism in Tcs1 insertions between different individual animals, suggesting that this sequence is not transposing rapidly in either iguana genome. The P. mucosus sequence Tpm1 shows a discontinuous distribution in snake species, suggesting that it has either been lost from many lineages during vertical germline transmission or has been transferred horizontally in some snake species. Phylogenetic comparisons of all these sequences with each other and with other members of this retrotransposon group from other animals and plants show that sequences within a particular vertebrate species are most closely related to each other, consistent with a vertical transmission model for their evolution.

Amino Acid Sequence↗
PubMed1980

Chromosome banding in amphibia. IV. Differentiation of GC- and AT-rich chromosome regions in Anura.

The chromosomes of 26 species of Anura from variously highly envolved groups were analysed with the fluorescent GC-specific antibiotics mithramycin and chromomycin A3 as well as with the AT-specific quinacrine. The mithramycin- and chromomycin A3-stainings generally resulted in a pattern of the constitutive heterochromatin opposite to the one obtained with quinacrine stain. The weaker a heterochromatic region fluoresces with quinacrine, the stronger is the intensity of the fluorescence achieved with mithramycin and chromomycin A3. Some of the telomeric and interstitial heterochromatic regions, however, exhibit no enhanced fluorescence with any of the fluorochromes. The nucleolar constrictions of the nucleolus organizer regions (NORs) displayed the brightest mithramycin- and chromomycin A3-fluorescence in the karyotypes and interphase nuclei of all species examined. The contrast of the brightly fluorescing GC-rich heterochromatin and of the NORs is considerably enhanced, when the non-fluorescent AT-specific oligopeptide distamycin A is employed as a counterstain. No banding patterns were observed with the fluorochromes in the euchromatic regions of the metaphase chromosomes; this attributed to the strong spiralization of the anuran chromosomes. A cytochemical classification of the various chromatin types in the anuran chromosomes is discussed on the basis of the differential labelings found on the constitutive heterochromatin by means of the fluorochromes.

Amphibians↗
PubMed1979

On the arrangement of chromosomes in the elongated sperm nuclei of Anura (Amphibia).

The position of specific constitutive heterochromatic chromosome regions within the elongated sperm nuclei of eight species of Anura was examined with Q- and C-banding. These species differ widely with regard to the number, size and position of the brightly fluorescing heterochromatic regions. The empirical frequency distributions determined for the heterochromatic regions relative to the longitudinal axis of the sperm nuclei were compared with random frequency distributions calculated on the basis of two spatial models. None of the specifically stained heterochromatic regions occupy any definite preferential position within the sperm nuclei. In two instances, a specific sequence of the heterochromatic regions within the sperm nuclei could be excluded. The type of chromosomal arrangement within the elongated sperm nuclei of Anura is discussed on the basis of the distribution patterns obtained.

Amphibians↗
PubMed1978

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela).

The mitotic chromosomes of six specimens from Triturus vulgaris meridionalis have been examined by both in situ hybridization with 3H 18S + 28S rRNA and AS-SAT staining method. The results of these two sets of experiments can be summarized as follows: 1) in each specimen the NORs and the additional ribosomal sites, which react positively to in situ hybridization with 3H 18S + 28S rRNA, are also stained by silver; 2) other chromosomal regions, which do not hybridize in situ with 3H 18S + 28S rRNA, are on the other hand stained by the AS-SAT method. These latter AG-positive sites show a species-specific pattern of chromosomal distribution.

Animals↗
PubMed1977

Chromosome location of the ribosomal RNA genes in Triturus vulgaris meridionalis (Amphibia, Urodela). II. Intraspecific variability in number and position of the chromosome loci for 18S + 28S ribosomal RNA.

Ribosomal genes have been localized on mitotic and lampbrush chromosomes of 20 specimens of Triturus vulgaris meridionalis by in situ hybridization with 3H 18S + 28S rRNA. The results may be summarized as follows: 1) each individual shows positive in situ hybridization at the nucleolus organizing region (NOR) on chromosome XI; 2) in addition, many specimens exhibit a positive reaction in chromosomal sites other than the NOR (additional ribosomal sites); 3) the chromosomal distribution of the additional sites appears to be identical in different tissues from the same specimen and to follow a specific individual pattern; 4) the additional ribosomal sites are preferentially found at the telomeric, centromeric or C-band regions of the chromosomes involved.

Animals↗
PubMed1988

Heterochromatic DNA in Triturus (Amphibia, Urodela) II. A centromeric satellite DNA.

The MspI family of highly repeated sequences is a centromeric satellite DNA representing about 1% of the genome of the Italian smooth newt, Triturus vulgaris meridionalis. We have studied the structure, genomic organization, chromosomal localization and conservation across species of this family. MspI sequences are around 197 bp long, as shown by sequencing of three cloned units. The family is organized in large clusters of tandemly arrayed units, present at almost all the centromeres of T.v. meridionalis, and is well conserved in the T.v. vulgaris subspecies. Conserved MspI sequences are also present in the related species T. helveticus, where they appear to be clustered at the centromeres of only a few chromosomes. MspI sequences are not found in other Triturus species analysed. The correlation of these sequences with the overall distribution pattern of heterochromatin and the extent of their conservation within the genus Triturus, are discussed.

Animals↗
PubMed1987

Chromosome banding in amphibia. XI. Constitutive heterochromatin, nucleolus organizers, 18S + 28S and 5S ribosomal RNA genes in Ascaphidae, Pipidae, Discoglossidae and Pelobatidae.

The karyotypes of 14 species of Anura from 9 genera of the suborders Amphicoela, Aglossa, Opisthocoela and Anomocoela were analysed with various banding techniques and conventional cytogenetic methods. The 18S + 28S and 5S ribosomal RNA genes were localized by means of in situ hybridization. No Q-, R- and G-banding patterns in the euchromatic segments of the metaphase chromosomes could be demonstrated in any of the species; this does not seem to be caused by a higher degree of spiralization of the amphibian chromosomes, but by the special DNA organization in these organisms. In most karyotypes, constitutive heterochromatin is present at centromeres, telomeres and nucleolus organizer regions (NORs), but rarely in interstitial positions. The heterochromatic regions are either quinacrine positive and mithramycin negative or vice versa. All species examined possess only one homologous pair of NORs: these display the brightest mithramycin fluorescence in the karyotypes. Many specimens exhibited unequal labelling of the two NORs both after silver and mithramycin staining as well as after in situ hybridization with 3H-18S + 28S rRNA. In four species, between one and six chromosome pairs with homologous 5S rRNA sites could be identified. The 5S rRNA genes and the 18S + 28S rRNA genes are closely linked in two species. In the male meiosis of the Amphicoela and Opisthocoela, there are intersitial, subterminal and terminal chiasmata in the bivalents, whereas only terminal chiasmata are observed in the bivalents of the Aglossa and Anomocoela. No heteromorphic sex-specific chromosomes could be demonstrated in any of the species. The differential staining techniques revealed that the chromosomal structure in these four suborders is largely the same as in the highly evolved anuran suborders Procoela and Diplasiocoela.

Amphibians↗
PubMed1995

Adaptations of the reed frog Hyperolius viridiflavus (Amphibia, Anura, Hyperoliidae) to its arid environment. VII. The heat budget of Hyperolius viridiflavus nitidulus and the evolution of an optimized body shape.

Estivating reed frogs of the superspecies Hyperolius viridiflavus are extraordinarily resistant to the highly adverse climatic conditions prevailing in their African savanna habitats during dry season (air temperature up to 45 degrees C, solar radiation load up to 1000 W.m-2, no water replenishment possible for up to 3 months). They are able to withstand such climatic stress at their exposed estivation sites on dry plants without evaporative cooling. We developed a heat budget model to understand the mechanisms of how an anuran can achieve this unique tolerance, and which allows us to predict the anuran's core and surface temperature for a given set of environmental parameters, to within 4% of the measured values. The model makes it possible to quantify some of the adaptive mechanisms for survival in semiarid habitats by comparing H. viridiflavus with anurans (H. tuberilinguis and Rana pipiens) of less stressful habitats. To minimize heat gain and maximize heat loss from the frog, the following points were important with regard to avoiding lethal heat stress during estivation: 1) solar heat load is reduced by an extraordinarily high skin reflectivity for solar radiation of up to 0.65 under laboratory and even higher in the field under dry season conditions. 2) The half-cylindrical body shape of H. viridiflavus seems to be optimized for estivation compared to the hemispheroidal shape usually found for anurans in moist habitats. A half-cylinder can be positioned relative to the sun so that large surface areas for conductive and convective heat loss are shielded by a small area exposed to direct solar radiation. 3) Another important contribution of body shape is a high body surface area to body mass ratio, as found in the estivating subadult H. viridiflavus (snout-vent lengths of 14-20 mm and body weights of 350-750 mg) compared to adult frogs (24-30 mm, 1000-2500 mg) which have never been observed to survive a dry season. 4) These mechanisms strongly couple core temperature to air temperature. The time constant of the core temperature is 29 +/- 10 s. Since air temperature can be 43-45 degrees C, H. viridiflavus must have a very unusual tolerance to transient core temperatures of 43-45 degrees C. 5) If air temperature rises above this lethal limit, the estivating frog would die despite all its optimizations, but moving from an unsuited to a more favorable site during estivation can be extremely costly in terms of unavoidably high evaporative water loss. Therefore, H. viridiflavus must have developed behavioral strategies for reliably choosing estivation sites with air temperature staying on average within the vital range during the whole dry season.

Acclimatization↗
PubMed1980

Neural crest replaced by gastrula ectoderm in amphibia. Effect on neurulation, CNS, gills and limbs.

Early Axolotl gastrula ectoderm was grafted into early Triturus neural stages in place of excised neural folds at the gill and anterior trunk level. Macroscopically the young graft behaves like normal neural fold material: it follows the closing host neural plate to the dorsal midline, folds into the host's interior and, especially in the gill region, moves ventrad beneath the host's epidermis. These movements cannot be interpreted as active migration. They are the result of passive displacements by morphogenetic forces inside the embryo. Histologically the graft differentiates into neural and neural crest tissue, the quantitative relation depending on the host's region. At the gill level the graft forms mesenchyme and other neural crest elements and hardly any neural structures. In the trunk about one half of the graft forms a secondary, surplus CNS. Problems of induction, differences between gill and trunk region and between graft and normal fold behaviour are discussed. Limbs develop normally. The dorsal layer of the blastema is furnished by graft cells. Host and graft tissue can stay separate or form a combined blastema.

Ambystoma↗
PubMed1994

Comparative study of immature erythroid cells of the diploid Bufo ictericus and the tetraploid Odontophrynus americanus (Amphibia, Anura): ultrastructural cytochemical detection of nucleic acids and polysaccharides, and mapping of the element phosphorus.

In the present study, we used ultrastructural cytochemistry to analyze the distribution of nuclear and cytoplasmic nucleic acids and polysaccharides, and electron spectroscopic imaging to map the element phosphorus in immature erythroid cells taken from two amphibians, the diploid Bufo ictericus and the tetraploid Odontophrynus americanus. In the cytoplasm of cells from the tetraploid species, we detected numerous inclusions containing a material that was similar to the dispersed chromatin seen in the nucleus of these cells. The RNase-gold complex labeled both the dispersed nuclear chromatin and the cytoplasmic inclusions. The Thiéry technique showed that glycoconjugates were present in all the membranous complexes of the erythroid cells of both types of amphibians under study, although they were absent within or around the cytoplasmic RNA inclusions. Electron spectroscopic imaging revealed the presence of phosphorus in these inclusions. These data suggest that an increase in RNA synthesis occurs in tetraploid amphibian cells, probably as a result of an alteration in the mechanisms of gene regulation.

Animals↗
PubMed1975

Neural crest and early fore limb development in amphibia.

Anterior trunk neural folds were exchanged between neurula stages 15 to 16 (Harrison) of several Triturus species and Ambystoma mexicanum. Donor neural crest cells migrated ventrad before and during initial bud formation. They lined the early lumb epidermis and became incorporated into the young blastema. Donor melanophores and non-melanophores contributed substantially to host limb buds.

Ambystoma↗
PubMed1977

Artificial neural induction in amphibia. I. Sandwich explants.

1. Embryonic tissues (ectoderm, neural plate) of Ambystoma mexicanum and Tritus were killed with hot water and implanted into ectoderm sandwiches. They induced the ectoderm to form neural tissue, lentoids and unspecialized epidermis. Neural tissue always showed retina character. Egg pigment was eliminated and gathered at the outer retinal surface or in the centre of rosettes. Neural crest cells like mesenchyme or melanophores were completely lacking, retinal pigment did not develop. 2. The thus induced living retina tissue was reimplanted into fresh ectoderm after 2 days. It continued histogenetic and morphogenetic differentiation and formed ocular vesicles with numerous eye cups. It induced the enveloping ectoderm to again form retina, lentoids and unspecialized epidermis without neural crest derivatives or RPE. 3. This inductive process can be reproduced several times.

Ambystoma↗