587 research outputs found
Regulation of maize Ac/Ds transposition by replication and DNA methylation
Full text linkIn maize the transposable elements Activator/Dissociation (Ac/Ds) transpose shortly after
replication from one of the two resulting chromatids ("chromatid selectivity"). A model
was suggested that explains this phenomenon as a consequence of different Ac transposase
binding to holo-, hemi- and unmethylated transposon ends (Wang et al., 1996). It assumes
that before replication the element is holomethylated and does not transpose because TPase
can not bind to the transposon ends. Shortly after replication one of the two differentially
hemimethylated daughter transposons should become transposition competent.
However, DNA methylation-mediated replication dependence does not completely explain
the behavior of Ac/Ds transposition. In several studies performed in monocot hosts, it was
found that in a transient assay Ac/Ds element excision from extrachromosomal geminivirus
vectors occurs only during vector replication, although the transfected DNAs were not Cmethylated.
In this work the correlation between Ds transposition, DNA replication and DNA
methylation in the dicot species Petunia hybrida was studied. Ds reporter vectors
harboring TYLCV (Tomato Yellow Leaf Curl Virus) geminivirus replicon sequences and
replicating in transfected petunia cells were constructed. It has been shown that the
transposition of a Ds element from an extrachromosomal vector in petunia cells is
regulated by DNA replication in a methylation-dependent and -independent mode.
Holomethylation completely inhibits Ds excision from a non-replicating plasmid, whereas
Ds transposition is restored by replication. Moreover, Ds elements that are hemimethylated
on one DNA strand transpose in the absence of replication, whereas methylation on the
complementary DNA strand results in at least 6.3-fold reduced excision frequencies. These
data strongly support the transposition model of Wang et al. (1996).
Beyond that, Ds transposition is strongly promoted by replication also in the absence of
methylation. It has been shown that in petunia cells, unlike monocot hosts, replication is
not a prerequisite for Ds transposition, nevertheless it enhances Ds transposition by at least
a factor of 7.5. Moreover, replication promotes the formation of a predominant excision
footprint. Implications on the mechanism and regulation of Ac/Ds transposition are
discussed
EFFECTS OF TRIBUTYLTIN CHLORIDE ON THE EMBRYONIC DEVELOPMENT OF THE SEA URCHIN PARACENTROTUS LIVIDUS (LMK).
No full textTributyltin (TBT) has been used extensively for almost 30 years in marine antifouling paints as a biocide. During this period hazardous levels of TBT and of its less toxic products of degradation, i.e. dibutyltin (DBT) and monobutyltin (MBT), were reached in estuaries and coastal water-sediment ecosystems in various parts of the world. Concern about the negative effects of low concentrations of butyltin compounds in the marine environment, recently as a lot of severe toxic effects on marine invertebrates. These effects were demonstrated mostly in molluscs, in which TBT exposure induced shell thinning, imposex and block of the embryonic development. In tunicates, immunodepression and embryotoxicity were used as indexes of butyltin pollution. Nothing is up to date known about the effects of these compounds on echinoderms. Therefore, we set up a procedure to reveal the effects and the mechanism of action of butyltin compounds on the embryonic development of the sea urchin Paracentrotus lividus. Embryos were obtained in laboratory by cross-fertilization and their development from post-fertilization to pluteus was followed in vivo after incubation with different exposure concentrations (0.1, 0.5, 1, 5, 10 μg l-1). We examined various developmental indexes, i.e. survival, frequency of developmental stages 24 and 48 hs after fertilization, embryonic growth and frequency of larval abnormalities 48 hs after fertilization. Morphological observations were also carried out under light and electron microscopies. Results show that embryotoxic effects occur in the presence of butyltin compounds in a dose-dependent manner. The exposed embryos generally suffer develpmental delay. Growth reduction of plutei, regularly increases as TBT concentration rises and becomes highly significant (p<0.001) at 1 μg l-1. At the same TBT dose plutei exhibit clear disturbance of the skeleton symmetry: the post-oral rods appear particularly short and/or folded. A very significant (p<0.001) interruption at the morula stage is observed begining from 5 μg l-1 TBT. Abnormal morula appear formed by irregular blastomeres from which many cytoplasmatic blisters jut towards a large space between the cells and the fertilization membrane. We suggest an influence of butyltin compounds with calcium homeostasis both in the microtubule polymerization during the cleavage stages and in calcification and organization of pluteus skeleton
Invertebrati marini come bioindicatori di inquinanti stannorganici: studi di embrio- e immunotossicità
No full textNegli ultimi anni i composti stannorganici hanno destato un crescente interesse in campo biologico per gli elevati effetti tossici di cui sono responsabili. Essi vengono utilizzati quali componenti di vernici antivegetative per scafi di imbarcazioni, moli e reti da pesca, e come pesticidi anticercosporiosi della barbabietola da zucchero in agricoltura. Visto il loro uso incontrollato e non regolamentato, la loro presenza nelle acque e nei sedimenti costieri è da ritenersi certa. La stabile presenza di questi composti nell’ecosistema marino rappresenta un elevato fattore di rischio, in quanto essi sono in grado di provocare effetti deleteri negli organismi già a basse concentrazioni e, inoltre, sono soggetti ad un rapido bioaccumulo con effetti tossici a lungo termine. Nei vertebrati gli organi-bersaglio dei butil- e trifenilstannici sono il cervello, il fegato e gli organi linfatici. I molluschi, sia bivalvi che gasteropodi, esposti a queste sostanze subiscono decalcificazione della conchiglia e vanno incontro ad una riduzione della fertilità. Recentemente è stato dimostrato anche un effetto teratogeno di questi composti nei mammiferi e nei pesci. In questo studio sono state utilizzate specie ampiamente diffuse di molluschi (Mytilus galloprovincialis, Tapes philippinarum), ascidiacei (Botryllus schlosseri, Styela plicata) ed echinodermi (Paracentrotus lividus), come bioindicatori di inquinamento da stannorganici nell’ambiente marino costiero con lo scopo di indagare gli effetti immuno- ed embriotossici di tali contaminanti, proponendo anche metodi di indagine facilmente riproducibili. La scelta di queste specie si è basata sull’elevata sensibilità agli stannorganici dimostrata dai tunicati in precedenti ricerche, sull’importanza economica e il rischio per la salute umana relativi ai bivalvi e infine sulla particolare affidabilità e sensibilità dei ricci di mare come modello sperimentale nello studio degli effetti di xenobiotici sula riproduzione e sullo sviluppo. Abbiamo valutato gli effetti immunotossici degli stannorganici su processi quali la fagocitosi (inibizione dell’indice di fagocitosi, del “burst” respiratorio e delle attività enzimatiche associati alla fagocitosi) approntando opportuni saggi in vitro, mentre gli effetti embriotossici (arresto, rallentamenti, anomalie dello sviluppo) sono stati valutati trattando gli embrioni in diversi momenti dello sviluppo, per diversi periodi di tempo e con varie concentrazioni di stannorganici. I risultati ottenuti indicano che gli stannorganici determinano effetti tossici subletali dose- e tempo-dipendenti nonché strettamente correlati alle loro proprietà lipofiliche. Il meccanismo d’azione di tali composti appare complesso. Da un alto, esso comporta una forte interazione con l’omeostasi cellulare del calcio, mediante inibizione dell’attività della Ca2+-ATPasi di membrana calmodulina-dipendente, aumento del calcio intracellulare e depolimerizzazione delle proteine del citoscheletro. Dall’altro lato, il meccanismo d’azione comporta anche un’interazione oligomicina-simile con la fosforilazione ossidativa mitocondriale, mediante inibizione degli enzimi della catena respiratoria osservabile sia dal punto di vista morfologico, come progressivo accumulo di stannorganici sulle creste mitocondriali dei blastomeri embrionali, sia dal punto di vista citochimico e spettrofotometrico, come inibizione della produzione di radicali dell’ossigeno durante la fagocitosi. Si ritiene che questi studi potranno contribuire alla definizione di test biologici affidabili, sensibili e specifici, in grado di essere applicati in ricerche ambientali accanto ai metodi chimici analitici molto precisi e tuttavia costosi che richiedono lunghi e delicati processi preliminari di estrazione
The geostatistical approach for the restoring of pollutant release applied to experimental column data and Monte Carlo numerical tests
No full textTossicità da stannorganici in invertebrati marini
No full textNegli ultimi anni i composti stannorganici hanno destato un crescente interesse in campo biologico per gli elevati effetti tossici di cui sono responsabili. La stabile presenza di questi composti nell'ecosistema marino rappresenta un elevato fattore di rischio, in quanto essi sono in grado di provocare effetti deleteri sugli organismi già a basse concentrazioni e, inoltre, sono soggettti ad un rapido bioaccumulo con effetti tossici a lungo temine. I Molluschi, sia bivalvi che gasteropodi, esposti a queste sostanze subiscono decalcificazione della conchiglia e vanno incontro ad una riduzione della fertilità. Recentemente è stato dimostrato anche un effetto teratogeno di questi composti nei pesci. In questo studio sono state utilizzate specie ampiamente diffuse di molluschi (Mytilus galloprovincialis, Tapes philippinarum), ascidiacei (Botryllus schlosseri, Styela plicata) ed echinodermi (Paracentrotus lividus), come bioindicatori di inquinamento da stannorganici nell'ambiente marino. Abbiamo valutato gli effetti immunotossici degli stannorganici approntando opportuni saggi su emociti in vitro, mentre gli effetti embriotossici (arresto, rallentamenti, anomalie dello sviluppo) sono stati valutati trattando gli embrioni in diversi momenti dello sviluppo, per diversi periodi di tempo e con varie concentrazioni di stannorganici. I risultati ottenuti indicano che gli stannorganici determinano effetti tossici dose- e tempo-dipendenti nonché strettamente correlati alle loro proprietà lipofiliche. Si ritiene che questi studi potranno contribuire alla definizione di test biologici affidabili, sensibili e specifici, in grado di essere applicati in ricerche ambientali accanto a metodi chimici analitici molto precisi e tuttavia costodi che richiedono lunghi e delicati processi preliminari di estazione
Immunotoxic effects of organotin compounds in Tapes philippinarum
No full textSince 1970 in Italy the cultivation of Tapes philippinarum has experienced a rapid expansion in the lagoons and along te coasts of the Northern Adratic Sea, with important economic and social implications. This type of bivalve culture, however, has developed without a precise plan and the necessary technical assistance. Over the past few years, in parallel with the diffusion of this and other types of mollusc cultures the need to acquire a better knowledge and control of the lagoon environment has arisen. A remarkable problem is the superposition of areas with intense maritime activity and agricultural exploitation with those of mollusc cultivation. Among the main pollutants concerning these areas organotin compounds (OTC) represent one of the most harmful group of substances both for mollusc cultivation and human health, since bivalves are filter-feeding organisms which rapidly bioaccumulate the environmental contaminants. With the aim to study the effects of OTC - already reported to be immunotoxic in mammals - in T. philippinarum, we have investigated whether they exert an immunosuppressant role also on in vitro yeast phagocytosis by haemocytes of this species. The phagocytic index is significantly reduced by OTC in an irreversible manner and depends on concentration and lipophilic affinity, but neither cell mortality nor cytolysis occur. For butyltin compounds, which are used as biocides in antifouling paints, the order of inhibition is TBT > DBT > MBT (p TPTA > TPTH (p < 0.05 for 0.01 μM TPTC and for 0.05 μM TPTA and TPTH). As this test is rapid and easily reproducible, it can effectively applied together with other ecotoxicological bioassays in evaluation studies of OTC environmental impact
Competitive Sorption of Metal Ions from Aqueous Solution onto Sand
No full texthe major part of groundwater contaminants strongly interact with soils and aquifer rocks. Therefore sorption processes on porous matrix are of utmost importance in the frame of the nuclear waste disposal. The objectives of this study were to evaluate sorption uptake by silica sand of some safety-relevant metal ions such as Cs+, Sr2+, Cu2+, Ni 2+ and to investigate the existence of competitive sorption processes between these ions. To this aim, kinetic and equilibrium, mono-component and multi-component, batch experiments were carried out in order to study: i) the influence of metal concentration, pH and contact time, on sorption onto silica sand of the above ions in aqueous solution, and ii) the presence of competition phenomena. Sorption data were well fitted by Langmuir and Freundlich models. Multi-component tests show that the uptake of each ion is reduced in presence of other ions in solution with respect to mono-component batch tests results and that competition between species appears influenced by the equilibrium times of the single species in solution and by pH
Unlocking organizational change: a deep dive through a data triangulation in healthcare
Full text linkAdsorption and competitive adsorption of metal ions from aqueous solution onto sand and silica colloids.
No full textEasyLocal++ a 25-year Perspective on Local Search Frameworks
Full text linkEasyLocal++ is a white-box C++ framework for designing local search algorithms. Over the years, it has been successfully used across various domains, such as timetabling, rostering, scheduling, and logistics, and has produced state-of-the-art results in benchmark datasets and competitions. Beyond research, EasyLocal++ has found practical use in real-world and industrial settings, demonstrating the flexibility and adaptability of the framework for different applications. In this paper, we position EasyLocal++ within the existing literature by comparing its capabilities with those of available alternative/similar tools. We then trace its history from its initial design 25 years ago to the current version. Furthermore, we describe its architecture, highlighting its design principles and functionalities. We also discuss the features developed to simplify the design of local search methods and enhance their performance. Lastly, we explore potential future perspectives and developments
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