Willy Beçak

Cytological evidence of constant tetraploidy in the bisexual South American frog Odontophrynus americanus

Odontophrynus americanus has 2n=44 chromosomes in somatic and gonad cells which can be ordered in 11 groups of homologues. In spermatocytes I they form mostly ring quadrivalents. In metaphase II 22 dyads are present. There is no indication of abnormalities in ♂ and ♀ gonad development.

CLOSE KARYOLOGICAL KINSHIP BETWEEN THE REPTILIAN SUBORDER SERPENTES AND THE CLASS AVES.

SummaryIn contrast to the situation found in two classes of warm-blooded vertebrates, mammals and birds, the class Reptilia is not uniform with regard to total genetic content; rather, it contains two distinct categories. The close cytological kinship between snakes and birds was revealed. Both are almost identical in total genetic content, which is about 50 per cent that of placental mammals. Both have microchromosomes, as well as Z-chromosomes very similar in absolute size, comprising nearly 10 per cent of the homogametic haploid (AZ) set. This leads to the implication that snakes and birds originated from the same lineage, and that their Z-chromosomes have not changed substantially since the Jurassic period of the Mesozoic era, about 180 million years ago.Within the reptilian suborder Serpentes, the step-by-step differentiation from the primitive ZW pair to the grossly heteromorphic ZW pair could be observed. In the ancient family Boidae, the sex chromosomes were still homomorphic to each other. In the family Colubridae, the beginning of heteromorphism was manifested in two ways. In some species, a pericentric inversion on the W caused it to differ from the Z; in others, duplication of the W occurred. In the family Crotalidae, the W had apparently achieved its very specialized status; it was a distinctly smaller element.

Cytotaxonomy and chromosomal evolution in Serpentes

The karyotypes of 15 species of snakes are described: Lachesis muta noctivaga , Micrurus lemniscatus carvalhoi , Philodryas aestivus aestivus , &l

Polyploidy and mechanisms of karyotypic diversification in Amphibia

Polyploid species were described in amphibians of the family Ceratophrydidae (Procoela). Tetraploid (4N = 44) and octoploid (8N = 104) karyotypes resulted apparently by duplication of ancestral genome

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.

The protective effect of ß-carotene on genotoxicity induced by cyclophosphamide

Abstract The influence of s-carotene on the clastogenicity of the indirect-acting mutagen cyclophosphamide (CPA) was investigated in mice, in vivo, for the induction of chromosome aberrations in bone marrow cells (BM). s-Carotene (0.5, 1.0, 2.0, 5.0, 10, 25, 50, 100 and 200 mg/kg) was administered by gavage for 5 consecutive days. 4 h after the last treatment with s-carotene, the mice were injected intraperitoneally with CPA, and the BM cells were fixed after 16, 24 and 32 h for the evaluation of the frequency of chromosome aberrations. The results showed that s-carotene was effective in reducing chromosomal damage induced by CPA with the increase of its concentration up to a level after which this effect was not observed. This anticlastogenicity was better detected when the cells were fixed at 32 h, although a tendency in reducing the CPA clastogenicity was already observed at 16 and 24 h. Our results suggest that s-carotene provides significant protection against the genotoxicity of CPA, although no dose-effect relationship on the frequencies of cells with chromosomal aberrations was observed.

Nucleolar organizer regions and constitutive heterochromatin in polyploid species of the genus Odontophrynus (Amphibia, Anura)

Chromosome banding patterns obtained by ammoniacal silver staining (Ag-AS) and alkaline Giemsa (CBG) have been analysed in several amphibian species of the genus Odontophrynus from South America. Ag-AS bands were found at secondary constrictions, mainly of chromosomes 4 and 11. The CBG technique revealed centromeric and telomeric constitutive heterochromatin on almost all chromosomes of these species. Moreover, intercalary bands were found at particular sites of several chromosomes. Some inter- and intra-population polymorphisms were found for the Ag-AS and C-banding patterns. The species variability in the number and position of the Ag-AS bands, known to be regions of active ribosomal cistrons, as well as the specific sites of intercalary heterochromatin, are used to discuss the possible evolutionary relationships among these species.

Viral DNA sequences in peripheral blood and vertical transmission of the virus: a discussion about BPV-1

This study has detected BPV-1 DNA sequences in wart, blood and plasma samples collected from animals affected by papillomatosis, suggesting viral presence inside the cell. We sellected an animal in which we could detect BPV-1 DNA sequences in wart, blood, placenta and amniotic liquid samples and her offspring which presented BPV-1 DNA sequences in blood sample collected immediately after birth. These results show a possible vertical transmission of BPV-1.

Investigation of the determinants of nuclear pore number

To assess the functional significance of nuclear pore complexes, we have investigated whether the number of pores per nucleus is determined by such factors as the nuclear volume, nuclear surface area, DNA content, or aspects of nuclear activity. Comparisons were made between cell types chosen to permit observation of differences in nuclear pore number as a function of differences in the other qualities measured. The number of nuclear pores was determined by freeze-etching and measurements of nuclear surface and nuclear volume by electron and light microscopy. Pairs of cell strains in culture that contained different numbers of chromosome sets were investigated to examine the relation of pore number to total DNA content. Tetraploid cells of the rat kangaroo (Potorous tridactylus) have almost exactly twice the number of pores found in the parental diploid strain. However, the pore number in diploid grassfrog (Rana pipiens) cells was only 65% greater than in the parental haploid cells. In addition, a polyploid series of nucleated RBC had a 62% pore number increase with each successive increase in ploidy. Diploid cell strains from the canyon mouse (Peromyscus crinitus) and from the cactus mouse (P. eremicus) were compared to test whether a difference reflecting the 36% additional DNA in cells of the latter, associated with extra heterochromatin, existed. Although both were found to have the same number of pores and nuclear surface area, the cells differed in nuclear volume. These observations suggest that the number of nuclear pores is independent of the total amount of nuclear DNA, the nuclear surface area (and, thus, presumably the fraction of DNA that is bound to the nuclear membrane), the nuclear volume, and the size of the genome. Rather, the number of nuclear pores appears to be associated with some aspect of nuclear metabolic activity, e.g., transcriptional capacity or release of products to the cytoplasm. Further evidence for such a view comes from studies of chick embryo erythroblasts. In these, nuclear pore number was found to be lower in associated with the decreasing nuclear transcriptional activity and longer generation times that characterize the successive cell divisions leading to the fully differentiated state. The number of pore complexes reconstructed in the last cell cycles declined in a manner consistent with reutilization of previously formed pores in the absence of new pore synthesis. Challenging this interpretation is the increase in pore number at lower metabolic activity when Xenopus laevis cells are grown at different temperatures. The speculation that pore complexes have a longer half-life in cooler grown Xenopus cells could resolve the discrepancy.

Coturnix coturnix japonica

The materials for the karyograms were prepared from feather pulp and embryonic tissue of coturnix quail secured through the courtesy of Dr. Hans Abplanalp, University of California, Davis. This colony originated from Japan. This species is one of the few among the birds so far described that have metacentric or submetacentric chromosomes recognizable to about chromosome size twenty.