1,721,011 research outputs found
The role of the diamond gene in the control of Drosophila genome stability
No full textDiamond (dind) is an essential Drosophila gene identified by five mutant alleles induced by EMS. Larvae homozygous for these mutations die at the third instar stage due to extensive defects in chromosome structure and mitosis. Cytological analysis of DAPI stained larval brains revealed that in dind mutants dividing cells are arrested in metaphase and exhibit a severe pleiotropic phenotype. 50% of metaphases are aneuploid or polyploid, 2% are endoreduplicated, 65% exhibit irregularly condensed chromosome and 33% contain broken chromosomes. In addition, in dind brains immunostained for tubulin, we consistently observed diploid cells with defective spindles and anaphase-like figures that contain chromosomes with unseparated sister chromatids. The latter defect does not appear to be due to kinetochore defects, as the localization of several kinetochore components is regular in brain cells of dind mutants. Nevertheless, loss of Dind severely compromises chromosome biorentation and segregation. In dind metaphase figures the Spindle Assembly Checkpoint (SAC) component Zw10 accumulates at the kinetochores and does not ‘‘stream’’ along the spindle microtubules, suggesting a failure to satisfy the SAC. Immunostaining of larval brains for the centrosomal and centriolar markers DSpd-2 and Asterless (Asl) revealed that dind mutants exhibit fragmented centrioles surrounded by pericentriolar material (PCM). These centriole-containing centrosomal fragments give rise to aberrant numbers of microtubule organizing centers (MTOCs) that lead to the assembly of disorganized spindles. Analysis of male germline cells revealed that dind mutant spermatogonia and spermatocytes exhibit most of the phenotypic traits observed in somatic cells, pointing to a pleiotropic role of dind in both mitotic and meiotic divisions.
The lethality and the complex mitotic and meiotic phenotypes elicited by dind mutations are completely rescued by the expression of GFP-tagged dind transgenes. The analysis of GFP-Dind and Dind-GFP expressing brains stained with anti-GFP antibodies revealed that Dind has a diffuse localization in both interphase and mitotic cells, with no detectable signal accumulation in any intracellular structure. The same pattern was observed in wild type larval brains immunostained with an anti-Dind antibody. However, Western blotting on larval cell extracts obtained by separation of cytoplasmic, nucleoplasmic and chromatin fractions showed that Dind is present in the fraction deriving from the pelleted nuclear material, suggesting that at least part of the Dind protein is associated with the chromatin throughout most of the cell cycle. We thus investigated possible interactions between Dind and chromosomal proteins whose loss leads to defects similar to those observed in dind mutants such as Separase (Sse) and Topoisomerase 2 (Top2). Both Sse and Top2 levels resulted significantly reduced in brain extracts from dind mutants. Strikingly, also the amount of Dind was lowered in extracts from both Sse and Top2 mutants, pointing to a mutual dependence between Dind and these two chromosomal proteins.
To the best of our knowledge, dind is the first Drosophila gene so far identified specified by mutations that cause the variety of phenotypic traits described here: defects in chromosome condensation, CABs, metaphase arrest, centriole fragmentation, polyploidy, aneuploidy and endoreduplication. The defects in chromosome morphology and integrity might be explained by assuming that loss of Dind alters the chromatin structure, preventing proper recruitment and stability of Sse and Top2, whose loss would in turn destabilize Dind. On the other hand, the metaphase arrest phenotype, the formation of aneuploid and polyploid cells and centriole fragmentation are more difficult to reconcile with a single chromatin-related function of dind. We thus speculate that the unique pleiotropic phenotype of dind mutants is due to the “moonlighting” functions of the Dind protein, which might be able to perform different roles in different contexts. Further experiments will help to verify this hypothesis and elucidate the Dind functions at the molecular level
Genetic determinants of Glutamine Synthetase in Drosophila melanogaster: role of the 10B8-11 region
No full textGoing 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
Shielding Performance of an Expanded Copper Foil over a Wide Frequency Range
No full textThe shielding effectiveness of an expanded copper foil was tested with three different methods in order to investigate the behavior of the material in different electromagnetic environments over a wide frequency range. The scope of the tests was to better understand and model the shielding performances of materials when used in non conventional environments and situations, including aeronautic applications
Genetic determinants of Glutamine Synthetase in Drosophila melanogaster: A gene for Glutamine Synthetase I resides in the 21B5-6 region
No full textAppropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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