Mapeamento físico de sequências repetitivas de DNA em cromossomos mitóticos e micronúcleos de Hoplosternum littorale (Callichthyidae, Siluriformes) provenientes de ambientes antropizados e não antropizados de Manaus, AM

Abstract

Several studies have shown that adaptive processes are associated with genetic variability found in regions of repetitive DNAs, and this genomic portion may be largely responsible for the adaptability of amazonian fishes in several natural and anthropogenic aquatic environments. Hoplosternum littorale, known as tamoatá fish, is found in polluted and unpolluted environments as in rivers, streams and floodplains, which is showing its great adaptability. Thus, the main goal of this work has been mapped DNAs repetitive sequences in mitotic chromosomes and micronuclei as like as differential banding and to measure the possibility of genotoxic actions of these environments. Seventy-two individuals were collected for micronuclei analysis which were 16 from Catalão lake and 16 from Marchantaria lake; these environments were chosen because they presented a large parcel of water which contribute to not display detectable chemical pollutants. Still, 25 from Mindu stream and 15 from Quarenta stream were identified as most critical points of environmental pollution in Manaus, Amazonas. Were cytogenetically analyzed 40 individuals to the total, which five males and five females from each locality. Mitotic chromosomes were obtained from kidney cells, detection of heterochromatin by action of barium hydroxide and nucleolus organizer regions (NORs) by silver nitrate stain. Fluorescent in situ hybridization (FISH) was performed with 18S rDNA probes, 5S rDNA Rex 3 and telomeric sequences. Both individuals of polluted and unpolluted environments had diploid number as 2n= 60 chromosomes (4m + 4sm + 52a). Simple NORs were localized in the short arms of pair 5 which is in the same localization of 18 rDNA sites. However, 5S rDNA sites were localized in pericentromeric regions of the pairs 23 and 27 with a fifth additional mark in interstitial region of one of homologue pair 8 for individuals from unpolluted environments. Interstitial telomeric sites were not showed. As to as heterochromatin markings were found in the centromeric region, and pericentromeric terminal of the chromosomes with more conspicuous blocks in individuals from polluted environment. As for heterochromatin, markings were found in the centromeric region, and pericentromeric terminal of the chromosomes, with more conspicuous blocks in individuals of polluted environment. The retroelement Rex 3 showed dispersed up in the chromosomes of individuals from unpolluted environment and compartmentalized in individuals from polluted environment. The micronucleus test revealed no significant differences in comparisons pair-to-pair between environments and sampling locations. The mapping of repetitive DNA sequences revealed that the micronuclei have differential composition, intra and inter individuals. These data indicate that the environment is promoting a differential genome organization, where different portions are lost in micronucleus formation and there is no single fragile region suffering breaks, although involving of repetitive DNA elements in this process.