1,720,965 research outputs found
Co-localization of ribosomal and telomeric sequences in Leptynia (Insecta: Phasmatodea)
No full textStick insects have been studied mainly for non-conventional reproduction modes, such as parthenogenesis, hybridogenesis and androgenesis. Parallel karyological investigations have evidenced extensive numerical and structural chromosome re-patterning, particularly evident in hybrid parthenogenetic taxa. Chromosome sets of bisexual Leptynia (Pantel) species show an evolutionary trend from 40 to 36 chromosomes and are characterized by cytological atellites of variable size and localization. We performed fluorescence in situ hybridization (FISH) analysis using 45S ribosomal genes and pentameric (TTAGG)n telomere sequences as probes in two strictly related but karyotypically distinct species, L. montana Scali (2n = 38/37; XX/XO) and L. attenuata Pantel (2n = 36). L. attenuata has recently been split into three subspecies (L. attenuata attenuata, L. attenuata iberica and L. attenuata algarvica), and found to share an XX/XY sex chromosome formula, unusual for stick insects. FISH by 45S rDNA sequences consistently labelled the short arm of the 4th chromosome pair, often of a variable size. Silver staining showed that nucleolar organizer regions (NORs) are active. FISH of the telomeric repeats, besides ordinary telomeres, also labelled the short arm of this same pair. The use of both probes in double FISH analysis fully confirmed the co-localization of ribosomal and telomeric
highly repeated sequences. Since it is increasingly emerging that the co-localization of NORs and telomeric sequences appears to be a feature shared by evolutionarily distant animals, its possible role is discussed
Comparative cytogenetics of six Indo-Pacific moray eels (Anguilliformes: Muraenidae) by chromosomal banding and fluorescence in situ hybridization
No full textA comparative cytogenetic analysis, using both conventional staining techniques and fluorescence in situ hybridization, of six Indo-Pacific moray eels from three different genera (Gymnothorax fimbriatus, Gymnothorax flavimarginatus, Gymnothorax javanicus, Gymnothorax undulatus, Echidna nebulosa and Gymnomuraena zebra), was carried out to investigate the chromosomal differentiation in the family Muraenidae. Four species displayed a diploid chromosome number 2n = 42, which is common among the Muraenidae. Two other species, G. javanicus and G. flavimarginatus, were characterized by different chromosome numbers (2n = 40 and 2n = 36). For most species, a large amount of constitutive heterochromatin was detected in the chromosomes, with species-specific C-banding patterns that enabled pairing of the homologous chromosomes. In all species, the major ribosomal genes were localized in the guanine-cytosine-rich region of one chromosome pair, but in different chromosomal locations. The (TTAGGG)n telomeric sequences were mapped onto chromosomal ends in all muraenid species studied. The comparison of the results derived from this study with those available in the literature confirms a substantial conservation of the diploid chromosome number in the Muraenidae and supports the hypothesis that rearrangements have occurred that have diversified their karyotypes. Furthermore, the finding of two species with different diploid chromosome numbers suggests that additional chromosomal rearrangements, such as Robertsonian fusions, have occurred in the karyotype evolution of the Muraenidae
Cytogenetic features of the invasive crayfish Procambarus clarkii (GIRARD, 1852) and comparison with other crustacean decapods
No full textThe Louisiana crayfish Procambarus clarkii (Girard, 1852) is an invasive freshwater crustacean species present in several European countries. Within the last years, P. clarkii has been successfully established in various sites of Sardinian basins. Although their economic and ecological value, the cytogenetics of crustacean decapods is poorly studied. This is principally due to technical constraints in obtaining good chromosomal preparations as well as the features of the chromosome complement. In many species a high number (generally more than 100) of little sized chromosomes are present, and the highest number among Metazoa, 2n=376, belongs to the Astacidae Pacifastacus leniusculus trowbridgii; as a result, different authors’ data concerning the decapod karyotypes differ significantly. Moreover, modern molecular cytogenetic techniques, such as Fluorescence In Situ Hybridization, have been applied to a few species of decapods. With the aim to shed light on the data reported by different authors, here we examine the cytogenetic features of P. clarkii. Chromosome preparations were obtained by the air drying method from testicular and somatic tissues of males captured in Sardinian basins, C-banding and FISH were performed to localize the heterochromatin and ribosomal and telomeric sequences, respectively. Our results confirmed the 2n=188, and pointed out the presence of A-T rich heterochromatic blocks. By FISH mapping, the major ribosomal genes were localized on four chromosome pairs and the telomeric repeat (TTAGG)n, besides the chromosomal ends, was detected in interstitial position of a large chromosome pair; the presence of two pairs of close ITS signals may be due to a telomeric association. Data obtained have been compared with other decapods with the aim to provide chromosome markers useful for cytotaxonomic analyses. This study was supported by the Fondazione di Sardegna (year 2016) and Regione Sardegna (LR 7/2007) for the project: Impact of Invasive Alien Species on Sardinian ecosystems
Karyotype, ribosomal genes, and telomeric sequences in the crayfish Procambarus clarkii (Decapoda: Cambaridae)
No full textMitotic and meiotic chromosomes of the crayfish Procambarus clarkii (Girard, 1852) were characterized by means of heterochromatin staining techniques (C-, DAPI- and CMA(3)-bandings), and FISH of major ribosomal genes and telomeric pentameric repeat (TTAGG)(n). Nucleolar organizer regions have been located on four chromosome pairs. GC-rich heterochromatin was mostly associated with NORs, and brightly fluorescent centromeric/pericentromeric AT-rich bands were present in most chromosomes. Telomeric pentameric repeats (TTAGG)(n), occurred in all the P. clarkii telomeres and in the interstitial region of the largest chromosome pair, not co-located to ribosomal genes; as possible explanation of the origin of this chromosome, a fusion event was hypothesized
INTERSTITIAL TELOMERIC SITES IN NATIVE AND INVASIVE SPECIES OF CRUSTACEA DECAPODA
No full textBy definition, telomeric sequences are located at the chromosomal ends. Several eukaryotic species also show telomeric repeats in non-terminal regions, called interstitial telomeric sequences (ITSs). They might originate from ancestral intrachromosomal rearrangements, differential crossing-over or from the repair of double-strand break during evolution. ITSs could play a significant role in genome instability and evolution, they also might be hotspots of chromosome breakage, rearrangement and amplification sites. Crustacea Decapoda includes species of highly economical value, like lobsters, and of ecological interest such as the Louisiana crayfish, species became invasive in European freshwaters. Although a lot of genetic studies are available on this taxon, many phylogenetic and taxonomic aspects are still unclear. Cytogenetics, and in particular the localization of the telomeric sequence, could provide useful cytotaxonomic data, but very few species have been studied. Here, we examine the chromosomal location of telomeric repeats in 10 species of decapods belonging to different families in order to analyze the extent of ITSs occurrence in the chromosomes of representatives of this taxon. TTAGG telomeric repeat and 45S rDNA have been mapped by fluorescence in situ hybridization (FISH) on mitotic and meiotic chromosomes obtained from gonads and hepatopancreas of males by the air-drying technique. Beside terminal signals, detected in all species, in four of them several interstitial telomeric sites were present. These ITSs varied among different species in number and position and in some case were coincident with major ribosomal genes. Additionally, the invasive Louisiana crayfish Procambarus clarkii (Girard, 1852) presented two conspicuous and adjacent ITSs in one chromosome pair. It is remarkable the presence of ITs in almost 40% of the decapods studied, that suggests a intense chromosome dymanism in this group. In fact, ITs could be the remnant of chromosomal rearrangements, like tandem chromosome fusions, or might be associated with rDNA, satellite DNAs or transpsons, which could explain the interstitial distribution. Our results give new insights both for karyological comparative and cytogenomic analyses in crustacean decapods, underlying the relevance of this approach within this taxon.
Study supported by the Fondazione di Sardegna (year 2016) and Regione Sardegna (LR 7/2007) for the project: Impact of Invasive Alien Species on Sardinian ecosystems
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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