1,720,966 research outputs found
Stress, transposons and genome evolution
Full text linkAfter Darwin's book on the origin of species by the natural selection, the theory of his precursor Lamarck was never completely abandoned. Over time, the observation of strange natural phenomena has occasionally resurrected the concept of the heredity of acquired characters. To explain, in Darwinian sense, some of the apparent Lamarckian-like phenomena, Waddington elaborated the “canalization and assimilation” concepts (Waddington, 1959). He observed that some phenotypic traits induced in Drosophila pupae by heat shock treatment and selected for a number of generations in the presence of the same stress, became heritable, thereby showing that an induced phenotypic trait could be inherited trough the germ line. Waddington hypothesized the existence of a cryptic genetic variation that is maintained hidden due to the robustness of the developmental process that he indicated as “canalization”. If an environmental stress is strong enough to overcome this robustness, the development pathway can change because of the expression of a cryptic genetic variant. Then, this variant can be selected and become heritable by an “assimilation” process. During the last few years, data supporting this view and providing possible molecular explanations were published. Rutheford and Lindquist (1998) showed that, in Drosophila, impairment of Hsp90 function induces morphogenetic variants that occasionally became fixed and stably transmitted. The interpretation was that Hsp90 is a capacitor of morphological evolution and buffers a pre-existing genetic variation that is not expressed and accumulates in neutral conditions. The stress sensitive storage and release of genetic variation by Hsp90 would favour adaptive evolution. However, our recent study has suggested a different explanation of these results (Specchia et al., 2010). It has been demonstrated that Hsp90 is involved in repression of transcription and mobilization of transposable elements in germ cells by affecting piRNA biogenesis. The reduction of HSP90 causes stress response-like activation and transposition of mobile elements along with a wide range of phenotypic variants due to the transposon insertions to the corresponding genes. On the basis of these observations, we have suggested that Hsp90, rather than functioning as a capacitor, acts, when absent, as a mutator, capable of causing activation and transposition of mobile elements through impairment of piRNAi silencing. Consequently, we propose that stress causes the activation of transposons that would induce de novo gene mutations, affecting development pathways; mutations can be expressed and fixed across subsequent generations by an assimilation process consisting of a co-selection of a somatic and a germinal event giving the same phenotype. This view implies that transposon activation is a major reaction of genomes to environmental stresses and represents a powerful adaptive response
Heterochromatin protein 1 (HP1) is intrinsically required for post-transcriptional regulation of Drosophila Germline Stem Cell (GSC) maintenance
Full text linkA very important open question in stem cells regulation is how the fine balance between GSCs self-renewal and differentiation is orchestrated at the molecular level. In the past several years much progress has been made in understanding the molecular mechanisms underlying intrinsic and extrinsic controls of GSC regulation but the complex gene regulatory networks that regulate stem cell behavior are only partially understood. HP1 is a dynamic epigenetic determinant mainly involved in heterochromatin formation, epigenetic gene silencing and telomere maintenance. Furthermore, recent studies have revealed the importance of HP1 in DNA repair, sister chromatid cohesion and, surprisingly, in positive regulation of gene expression. Here, we show that HP1 plays a crucial role in the control of GSC homeostasis in Drosophila. Our findings demonstrate that HP1 is required intrinsically to promote GSC self-renewal and progeny differentiation by directly stabilizing the transcripts of key genes involved in GSCs maintenanc
Drosophilidae monitoring in Apulia (Italy) reveals Drosophila suzukii as one of the four most abundant species
No full textThe knowledge of the endemic drosophilid assemblage is a useful reference to study population dynamics when new species are introduced in a geographical area. The introduction of invasive species can change the structure of the drosophilid community; hence, the distribution data for endemic species are also essential to support efficient pest management. We provide the first description of the natural drosophilid populations (Diptera Drosophilidae) recorded in Apulia, in Southern Italy. The flies, which were collected in a field survey throughout a year, were classified by morphological and molecular analyses by sequencing the barcode fragment of the COI mtDNA gene. The identified species show a distribution of frequencies that varies throughout the year, reflecting a seasonal life cycle peculiar to each species. Among the recorded drosophilids, the potential pest species Drosophila suzukii represents one of the four most abundant species
Hsp90 and its interacting partners in the piRNAs pathway
No full textHsp90 is a molecular chaperone stabilizing many key regulatory proteins. Recently it was shown that the functional alteration of Hsp90 causes activation of transposons in Drosophila germ cells due to alterations in the piRNA pathway. This disfunction results in the induction of a series of phenotypic variants. Therefore Hsp90 works as suppressor of variability that can be generated by the movement of transposons.
Preliminary experiments show that the "heat shock" treatment activates the movement of transposons in Drosophila thus suggesting that stress may trigger a functional shift of Hsp90.
To address this point, we performed experiments whose results strongly suggest that a functional shift of Hsp90 induced by stress could be related to the involvement of Hsp90 in complexes that are different in normal and stress conditions. In other words, Hsp90 functions in piRNA pathway in absence of stress, but under stress conditions, its role changes by its interaction with different factors.
A further result obtained in this work is the involvement of GW182 in piRNA pathway. GW182 interact with Hsp90 and localizes in nuage where piRNA biogenesis occurs. In addition, Hsp90 disfunction causes GW182 and Vasa delocalization from nuage. Therefore we can speculate that, in piRNA pathway, the functions of these three proteins are interconnected
Canalization by selection of de novo-induced mutations
No full textOne of the most fascinating scientific problems, a subject of intense debate, is that of the mechanisms of biological evolution. In this context, Waddington elaborated the concepts of "canalization and assimilation" to explain how an apparently somatic variant induced by stress could become heritable through the germline in Drosophila. He resolved this seemingly Lamarckian phenomenon by positing the existence of cryptic mutations that can be expressed and selected under stress. To investigate the relevance of such mechanisms, we performed experiments following the Waddington procedure, then isolated and fixed three phenotypic variants along with another induced mutation that was not preceded by any phenocopy. All the fixed mutations we looked at were actually generated de novo by DNA deletions or transposon insertions, highlighting a novel mechanism for the assimilation process. Our study shows that heat-shock stress produces both phenotypic variants and germline mutations, and suggests an alternative explanation to that of Waddington for the apparent assimilation of an acquired character. The selection of the variants, under stress, for a number of generations allows for the co-selection of newly induced corresponding germline mutations, making the phenotypic variants appear heritable
WiFi related radiofrequency electromagnetic fields promote transposable element dysregulation and genomic instability in Drosophila melanogaster
Full text linkExposure to artificial radio frequency electromagnetic fields (RF-EMFs) has greatly increased in recent years, thus promoting a growing scientific and social interest in deepening the biological impact of EMFs on living organisms. The current legislation governing the exposure to RF-EMFs is based exclusively on their thermal effects, without considering the possible non-thermal adverse health effects from long term exposure to EMFs. In this study we investigated the biological non-thermal effects of low-level indoor exposure to RF-EMFs produced byWiFi wireless technologies, using Drosophila melanogaster as the model system. Flies were exposed to 2.4 GHz radiofrequency in a
Transverse Electromagnetic (TEM) cell device to ensure homogenous controlled fields. Signals were continuously monitored during the experiments and regulated at non thermal levels. The results of this study demonstrate that WiFi electromagnetic radiation causes extensive heterochromatin decondensation and thus a general loss of transposable elements epigenetic silencing in both germinal and neural tissues. Moreover, our findings provide evidence that WiFi related radiofrequency electromagnetic fields can induce reactive oxygen species (ROS) accumulation, genomic instability, and behavioural abnormalities. Finally, we demonstrate that WiFi radiation can synergize with RasV12 to drive tumor progression and invasion. All together, these data indicate that radiofrequency
radiation emitted fromWiFi devices could exert genotoxic effects in Drosophila and set the stage to further explore the biological effects ofWiFi electromagnetic radiation on living organisms
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
Appropriate 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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