1,720,985 research outputs found
Cytogenetic and molecular studies in a lungfish, Protopterus annectens (Osteichthyes, Dipnoi)
No full textA neontological approach to the problem of the origin of tetrapods consists in the examination of the available cytological and molecular data on the genome of these vertebrates. Dipnoans are a group of osteichthyian fishes, the evolutionary relationships of which with tetrapods have been disputed since their discovery. In the past, they were variously considered as being related to actinistians, tetrapods, and lower actinopterygians, though nowadays they are considered a monophyletic group, the sister group of crossopterygians. Dipnoans first appeared in the geologic record in the Early Devonian with 50 extinct genera, surviving up to date, with only three genera: Lepidosiren, Neoceratodus and Protopterus, including only six recognized species. Nothing is known of the genome of the early tetrapods, except that they and the Choanoichthyes exhibited a remarkable interspecific variability of the karyotype and of DNA content. These characteristics are often found in dipnoans and in the extant lissamphibians. Very little is known about the evolutionary karyology in the four Protopterus species and in the dipnoan clade in general. In this paper, we karyotyped ten male and female specimens of P. annectens (2n=34) from Nigeria. Moreover, we localized heterochromatin and nucleolar organizer regions by using base-specific fluorochromes and detected the human telomeric (TTAGGG)n sequences on all the telomeric sites of P. annectens chromosomes. DNA was also extracted and digested with seven restriction enzymes, which revealed the probable presence of almost three different families of satellite DNA. Nuclear DNA content was identified from blood samples by flow cytometry. New genomic and karyological data were compared and discussed with those on closer genera and taxa available in literature. © 2002 Published by Elsevier Science B.V
Karyotype and genome characterization in four cartilaginous fishes
No full textDifferent approaches can be used to elucidate the unsolved questions concerning taxonomic evolution in cartilaginous fish. The study of the karyological characteristics of these vertebrates by combining molecular and traditional techniques of chromosome preparation and banding has been demonstrated to be a very effective method. In this paper we studied the localization and the composition of the constitutive heterochromatin by using C- and restriction endonuclease-banding in four selachian species, belonging to two of the four superorders. We also characterized two different types of repetitive genomic sequences in these species: satellite DNA and (TTAGGG)n telomeric sequences. Finally, we analysed the nuclear ribosomal gene to determine the number of the nucleolar organizers and their position on chromosomes by using silver staining, chromomycin A3, and FISH (fluorescent in situ hybridization). The results showed a prevailingly telomeric localization of constitutive heterochromatin in the Galeomorphii, the presence of additional nucleolar organizer sites in Raja asterias, an exclusively telomeric localization of the (TTAGGG)n sequences in Scyliorhinus stellaris and both telomeric and interstitial in Taeniura lymma. These data, together with those concerning the conservation of the satellite DNA, seem to support the hypothesis that Chondrichthyes have an evolutionary history leading them to the acquisition of large genomes rich in highly repeated sequences and subjected to some selective pressures favoring the conservation of this DNA fraction. © 2002 Published by Elsevier Science B.V
Assessment of environmental stress by the micronucleus test and the Comet assay on the genome of teleost populations from two natural environments
No full textThe aim of the present paper was to assess the biological damage caused by exposure of the test organism (Gambusia holbrooki: Cyprinodontiformes, Poecilidae) to various mutagenic agents present in the polluted waters of the Sarno River. For this purpose, we performed a micronuclei (MN) test and single cell gel electrophoresis (the Comet assay), testing DNA migration in an electrophoretic field using erythrocytes of G. holbrooki specimens both from the Sarno River and from the waters of the crater of the Astroni natural reserve as negative controls. The results indicate statistically higher values for both MN and DNA migration in the samples from the Sarno River compared with those from Astroni and point to a strong genotoxic action of the mixture of pollutants present in the Sarno River. These data were compared with the values found in the G. holbrooki specimens from the Sarno River kept under laboratory conditions for 100 days in clean water. © 2003 Elsevier Science (USA). All rights reserved
Polypteridae (Actinopterygii: Cladistia) and DANA-SINEs insertions. Mar. Genomics.
No full textSINE sequences are interspersed throughout virtually all eukaryotic genomes and greatly outnumber the other repetitive elements. These sequences are of increasing interest for phylogenetic studies because of their diagnostic power for establishing common ancestry among taxa, once properly characterized. We identified and characterized a peculiar family of composite tRNA-derived short interspersed SINEs. DANA-SINEs, associated with mutational activities in Danio rerio, in a group of species belonging to one of the most basal bony fish families, the Polypteridae, in order to investigate their own inner specific phylogenetic relationships. DANA sequences were identified, sequenced and then localized, by means of fluorescent in situ hybridization (FISH), in six Polypteridae species (Polyptents delhezi, P. ornatipinnis, P. palmas, P. buettikoferi P. senegalus and Erpetoichthys calabaricus) After cloning, the sequences obtained were aligned for phylogenetic analysis, comparing them with three Dipnoan lungfish species (Protopterus annectens, P. aethiopicus, Lepidosiren paradoxa), and Lethenteron reissneri (Petromyzontidae)was used as outgroup. The obtained overlapping MP, ML and NJ tree clustered together the species belonging to the two taxonomically different Osteichthyans groups: the Polypteridae, by one side, and the Protopteridae by the other, with the monotypic genus Erpetoichthys more distantly related to the Polypterus genus comprising three distinct groups: P. palmas and P. buettikoferi, P. delhezi and P. ornatipinnis and P. senegalus. In situ hybridization with DANA probes marked along the whole chromosome arms in the metaphases of all the Polypteridae species examined. (C) 2010 Elsevier B.V. All rights reserved
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