The chromosomal localisation of satellite DNA in Ptyas mucosus (Ophidia, Colubridae)

Differential repetitive DNA composition in the centromeric region of chromosomes of Amazonian lizard species in the family Teiidae

Differences in heterochromatin distribution patterns and its composition were observed in Amazonian teiid species. Studies have shown repetitive DNA harbors heterochromatic blocks which are located in centromeric and telomeric regions in Ameiva ameiva (Linnaeus, 1758), Kentropyx calcarata (Spix, 1825), Kentropyx pelviceps (Cope, 1868), and Tupinambis teguixin (Linnaeus, 1758). In Cnemidophorus sp.1, repetitive DNA has multiple signals along all chromosomes. The aim of this study was to characterize moderately and highly repetitive DNA sequences by C ot1-DNA from Ameiva ameiva and Cnemidophorus sp.1 genomes through cloning and DNA sequencing, as well as mapping them chromosomally to better understand its organization and genome dynamics. The results of sequencing of DNA libraries obtained by C ot1-DNA showed that different microsatellites, transposons, retrotransposons, and some gene families also comprise the fraction of repetitive DNA in the teiid species. FISH using C ot1-DNA probes isolated from both Ameiva ameiva and Cnemidophorus sp.1 showed these sequences mainly located in heterochromatic centromeric, and telomeric regions in Ameiva ameiva, Kentropyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin chromosomes, indicating they play structural and functional roles in the genome of these species. In Cnemidophorus sp.1, C ot1-DNA probe isolated from Ameiva ameiva had multiple interstitial signals on chromosomes, whereas mapping of C ot1-DNA isolated from the Ameiva ameiva and Cnemidophorus sp.1 highlighted centromeric regions of some chromosomes. Thus, the data obtained showed that many repetitive DNA classes are part of the genome of Ameiva ameiva, Cnemidophorus sp.1, Kentroyx calcarata, Kentropyx pelviceps, and Tupinambis teguixin, and these sequences are shared among the analyzed teiid species, but they were not always allocated at the same chromosome position.

Characteristic features of the sonicated DNA of Agama agama agama L. (Reptilia, Agamidae) on hydroxyapatite columns, using mouse DNA as a reference

Hydroxyapatite column chromatography has been used to study some properties of the extensively sheared DNA of the Rainbow lizard, Agama agama agama. Reassociation studies show that the genome has a Cot1/2 of 370. Approximately 15% of the genome is highly repetitive in nature. This repetitive fraction is resolved into thermally stable and less stable fractions. The stable fraction has a base composition of 47% GC, higher than the 40.2% GC for the native DNA. This stable fraction is believed to be of recent origin. Chromatography of the total DNA of the lizard with linear gradients of phosphate buffer containing 1 M urea resolves it into two components which were shown by thermal fractionation, also in the presence of 1 M urea, to vary in base composition. This behaviour may be characteristic of reptilian genomes and may be used as a basis for studying the structural organisation of the reptilian genome.

Chromosomal localization of 18S + 28S and 5S Ribosomal RNA genes in evolutionarily diverse anuran amphibians

The chromosomal locations of the 18S + 28S and 5S ribosomal RNA genes have been analyzed by in situ hybridization in ten anuran species of different taxonomic positions. The chosen species belong to both primitive and evolved families of the present day Anura. Each examined species has 18s + 28S rRNA genes clustered in one locus per haploid chromosome set: this locus is placed either in an intercalary position or proximal to the centromere, or close to the telomere. The 5S rRNA genes are arranged in clusters which vary in number from one to six per haploid set. The 5S rDNA sites are found in intercalary positions, at the telomeres, and at, or close to, the centromeres. Microchromosomes and small chromosomes in primitive karyotypes have been found to carry 5S rDNA sequences. The results are discussed in relation to ideas on the karyological evolution of Amphibia.

Cytological studies of heterochromatin function in the Drosophila melanogaster male: autosomal meiotic paring

In Drosophila melanogaster it is now documented that the different satellite DNA sequences make up the majority of the centromeric heterochromatin of all chromosomes. The most popular hypothesis on this class of DNA is that satellite DNA itself is important to the pairing processes of chromosomes. Evidence in support of such a hypothesis is, however, circumstantial. This hypothesis has been evaluated by direct cytological examination of the meiotic behaviour of heterochromatically and/or euchromatically rear-ranged autosomes in the male. It was found that neither substantial deletions nor rearrangements of the autosomal heterochromatin cause any disruption of meiotic pairing. Autosomal pairing depends on homologs retaining sufficient euchromatic homology. This is the first clear demonstration that the highly repeated satellite DNA sequences in the heterochromatin of the second, third and fourth chromosomes are not important in meiotic pairing, but rather than some euchromatic homology in the autosome is essential to ensure a regular meiotic process. These results on the autosomes, when taken in conjunction with our previous studies on sex chromosome pairing, clearly indicate that satellite DNA is not crucial for male meiotic chromosome pairing of any member of the D. melanogaster genome.

Effect of different denaturing agents on the detectability of specific DNA sequences of various base compositions by in situ hybridisation

In situ hybridisation of certain AT rich and GC rich satellite DNA complementary RNAs (cRNAs) to their homologous chromosomes at their respective optimal rate temperatures (TOPTS) after denaturation with various reagents (0.2 N HCl, 0.07 N NaOH, 90% formamide and heat) led to the following conclusions. -- Heat denaturation of chromosomal DNA in 0.1 X SSC at 100 degrees C gives significantly higher grain counts regardless of DNA base composition, HCl denaturation discriminates markedly against GC rich DNA. Chromosome morphology is best preserved after HCl and heat denaturation.

Base composition of DNA from some reptiles

The DNA base composition was studied in 9 reptilian species (4 chelonians, 3 saurians, and 2 ophidians) by the thermal denaturation method. This preliminary investigation has brought to light differences in GC percentages and in the shape of melting curves between chelonian DNA and that from saurians and ophidians.