Karyotype differentiation and cytotaxonomic considerations in species of Serrasalmidae (Characiformes) from the Amazon basin

Six species of Serrasalmidae from the central Amazon, representatives of the genera Serrasalmus (S. elongatus, S. maculatus, S. cf. rhombeus, and S. rhombeus), Pygocentrus (P. nattereri), and Colossoma (C. macropomum), were analyzed regarding the distribution of the Ag-NORs, C-positive heterochromatin and 18S and 5S rRNA genes on the chromosomes. All specimens had 2n = 60 chromosomes, except S. cf. rhombeus, with 2n = 58, and C. macropomum with 2n = 54 chromosomes. The Ag-NORs were multiple and located on the short arms of subtelo-acrocentric chromosomes in all Serrasalmus species and in P. nattereri, but were found on metacentric chromosomes in C. macropomum. The 18S rDNA sites were usually coincident with Ag-NORs, although some species had a higher number and/or a distinct localization of these sites. C-positive heterochromatin was preferentially situated in centromeric regions, remarkably on metacentric pair number 7 in all Serrasalmus species and number 3 in P. nattereri, which beared a conspicuous proximal C-band on the long arms. The 5S rDNA sites were detected in a single chromosomal pair in all species. In Serrasalmus and P. nattereri, this pair was the number 7 and 3, respectively, thereby revealing its co-localization with the conspicuous heterochromatic band. However, in C. macropomum, only one homologue (probably belonging to pair number 12) exhibited 5S rDNA sites on the short arms, close to the centromere. The present data revealed reliable cytotaxonomic markers, enabling the evaluation of karyotype differentiation and interrelationships among Serrasalmidae, as well as the probable occurrence of a species complex in S. rhombeus.

Conserved Cytogenetic Features in the Amazonian Arapaima, Arapaima gigas (Schinz 1822) from Jamari River, Rondônia–Brazil

Specimens of Arapaima gigas from Jamari River (RO) were cytogenetically analyzed. A diploid number of 2n=56 chromosomes was found (28m-sm + 28st-a). Secondary constrictions were observed on the short arms of chromosome 3. Nucleolar Organizer Regions (NORs) were detected at the subterminal region on short arms of the third chromosomal pair by both silver nitrate staining and FISH with 45S rDNA probe, being equivalent to secondary constrictions. The ribosomal sites were also characterized by size heteromorphism and presence of CMA3+/DAPI- blocks. The constitutive heterochromatin was located at pericentromeric region of some chromosomes. After sequential Cbanding and base-specific fluorochromes staining, most of the heterochromatins proved to be neutral, i.e., with similar amounts of AT and GC bases. Nonetheless, some heterochromatic regions were marked by GC-specific fluorochromes in one chromosomal pair and by AT-specific fluorochrome staining on two pairs. The present data are in agreement with previous reports in populations from Araguaya River, indicating that conserved cytogenetic features are present in this important fish species.

Cytogenetic characterization of Aloysia virgata Ruiz and Pavan (Verbenaceae)

Since previous cytogenetic reports of Aloysia have only described the meiotic behavior and chromosomal number of some species, the aim of this work was to provide detailed cytogenetic description of Aloysia virgata that would contribute to the understanding of the taxonomical organization of the Verbenaceae. Aloysia virgata had a karyotype with 2n = 36 metacentric chromosomes, all with similar size. The large amount of heterochromatin seen after Giemsa staining was confirmed by C-banding. Four nucleolar organizer regions (NORs) were detected with an rDNA 45S probe in two homologous pairs and two sites of 5S rDNA located on one chromosomal pair were detected by fluorescence in situ hybridization. The interphase nucleus was classified as semi-reticulate. Meiotic analysis showed a normal chromosomal behavior, with 18 bivalents in some parts of prophase I and in metaphase I. The number of chromosomes, NORs and 5S rDNA segments did not exclude a possible polyploid origin.

Cytogenetic analysis of Astyanax laticeps (Cope, 1894) (Ostariophysi: Characidae) from the laguna dos Patos system

The genus Astyanax is prominent among Characiformes, due to the large number of species found and its wide geographic distribution. In this work, Astyanax laticeps specimens from the laguna dos Patos system were cytogenetically analyzed. A diploid number of 2n = 50 chromosomes distributed into 6m+16sm+16st+12a (FN = 88) was found, without differences between males and females. A few small heterochromatin blocks were observed, besides three more conspicuous C-bands, corresponding to NORs, as confirmed by silver nitrate and CMA3 staining, FISH, and DAPI negative staining. These regions were located in a medium-sized subtelocentric and in a large subtelocentric chromosomal pair, probably because of a deletion of this region in one homologous chromosome, or due to a transposition event between them.

Hyperbaric oxygen therapy of angiopathic changes in patients with inherited gene imbalance

Introduction Phenotype match inherited by genes is in most cases present in monozygotic twins. Their phenotypic resemblance is unfortunately characterized by strong susceptibility for the development of chronic non-infectious diseases. One of the most common non-infectious chronic diseases that are phenotipically represented in twins is diabetes mellitus. Genetic imbalance is, in most cases, placed in 2, 3, 7, 8, 11, 12, 19 and 20 chromosomal pair of the human genome. CASE OUTLINE This study describes a pair of monozygotic twins, aged 54, who were diagnosed for diabetes type 2 ten years earlier. The first patient had trophic changes of muscles and skin tissues of the lower limb, and a necrotic wound on his right leg tibial region with the claudication distance of 50 m. After arteriography, he was referred by a vascular surgeon for hyperbaric oxygen therapy (HBO). HBO protocol implied 70 min. application of 100% oxygen at 2.5 absolute atmospheres. After the first series of HBO therapies consisting of 20 HBO treatments, claudication was eliminated and the necrotic wound healed. Next, surgical aortofemoral bypass was done. During the second HBO treatment, his monozygotic twin brother presented with angiopathic changes due to diabetes. In both patients, biochemical parameters corresponded to the expected level for diabetes type 2 imbalance, and the localization of the chromosomal defect (placed on 3, 11 and 19 chromosomal pair) was also in accordance with the respective disorder. After they were included into next 10 HBO treatments, Doppler imaging of the major arteries of limbs revealed normal findings. Conclusion Identical genetic impairment in monozygotic twins can lead to identical somatic changes with resultant consequences. HBO treatment of such patients associated with other therapeutic procedures (conducted by diabetologist, vascular surgeon and physiatrist) can postpone or prevent irreversible changes occurring due to blood vessel disorders.

Sequence Differentiation Associated With an Inversion on the Neo-X Chromosome of Drosophila americana

Sex chromosomes originate from pairs of autosomes that acquire controlling genes in the sex-determining cascade. Universal mechanisms apparently influence the evolution of sex chromosomes, because this chromosomal pair is characteristically heteromorphic in a broad range of organisms. To examine the pattern of initial differentiation between sex chromosomes, sequence analyses were performed on a pair of newly formed sex chromosomes in Drosophila americana. This species has neo-sex chromosomes as a result of a centromeric fusion between the X chromosome and an autosome. Sequences were analyzed from the Alcohol dehydrogenase (Adh), big brain (bib), and timeless (tim) gene regions, which represent separate positions along this pair of neo-sex chromosomes. In the northwestern range of the species, the bib and Adh regions exhibit significant sequence differentiation for neo-X chromosomes relative to neo-Y chromosomes from the same geographic region and other chromosomal populations of D. americana. Furthermore, a nucleotide site defining a common haplotype in bib is shown to be associated with a paracentric inversion [In(4)ab] on the neo-X chromosome, and this inversion suppresses recombination between neo-X and neo-Y chromosomes. These observations are consistent with the inversion acting as a recombination modifier that suppresses exchange between these neo-sex chromosomes, as predicted by models of sex chromosome evolution.

Reduced Sequence Variability on the NeoY Chromosome of Drosophila americana americana

Sex chromosomes are generally morphologically and functionally distinct, but the evolutionary forces that cause this differentiation are poorly understood. Drosophila americana americana was used in this study to examine one aspect of sex chromosome evolution, the degeneration of nonrecombining Y chromosomes. The primary X chromosome of D. a. americana is fused with a chromosomal element that was ancestrally an autosome, causing this homologous chromosomal pair to segregate with the sex chromosomes. Sequence variation at the Alcohol Dehydrogenase (Adh) gene was used to determine the pattern of nucleotide variation on the neo-sex chromosomes in natural populations. Sequences of Adh were obtained for neo-X and neo-Y chromosomes of D. a. americana, and for Adh of D. a. texana, in which it is autosomal. No significant sequence differentiation is present between the neo-X and neo-Y chromosomes of D. a. americana or the autosomes of D. a. texana. There is a significantly lower level of sequence diversity on the neo-Y chromosome relative to the neo-X in D. a. americana. This reduction in variability on the neo-Y does not appear to have resulted from a selective sweep. Coalescent simulations of the evolutionary transition of an autosome into a Y chromosome indicate there may be a low level of recombination between the neo-X and neo-Y alleles of Adh and that the effective population size of this chromosome may have been reduced below the expected value of 25% of the autosomal effective size, possibly because of the effects of background selection or sexual selection.

Synaptonemal complex analysis of mole rats (Spalax ehrenbergi): unusual polymorphisms of chromosome

Two unusual structural polymorphisms in the largest chromosomal pair of the Israeli mole rat, Spalax ehrenbergi, were analyzed from surface-spread and silver-stained preparations of synaptonemal complexes. A C-band negative polymorphism for the length of the 1p arm was visible as axial length differences during late zygonema and early pachynema. This region underwent synaptic adjustment resulting in a fully paired, mid-pachytene synaptonemal complex with equalized axial lengths. The somatically variable and nonargentophilic secondary constriction in the 1q arm was evident as a distinct silver-stained thickening along the synaptonemal complex. Presence of this structure on the synaptonemal complex varied both among individuals and among cells within individuals. The intraindividual variation of this region is hypothesized to represent differential biochemical activity with its cellular visualization being regulated in a manner similar to that of nucleolus organizer regions.Key words: mole rats, synaptonemal complex, chromosomal polymorphism.

CONTRIBUTION A L'ETUDE CYTOTAXONOMIQUE D'ESPECES MEDITERRANEENNES D'ANEMONE ET DE LEURS HYBRIDES

Statistical comparison of the caryotypes of the four Mediterranean Anemone species: A. palmata L., A. coronaria L., A. pavonina Lamk. and A. hortensis L., is based on the dispersion areas of the T/Θ and L/C parameters estimated for each chromosomal pair. Chromosome alteration has been observed in both interspecific hybrids obtained. These alterations are more marked when the genome is transferred into an alien cytoplasm. The F1 hybrid A. pavonina × A. hortensis is fertile with some meiotic abnormalities. Sterility of the A. pavonina × A. coronaria F1 hybrid is caused by the failure of pairing. Chromosomal doubling by colchicine restored fertility. Phylogenic relations as established by morphological, biochemical and caryotypic characters, as well as by meiotic behavior of interspecific hybrids, are in good agreement. The lack of introgression of new characters into the cultivated species A. coronaria is due to interspecific sterility barriers. Nevertheless, the introduction of the coronaria genome into the cytoplasm of pavonina would be a source of male-sterility at the tetraploid level.