Gating of miRNA movement at defined cell-cell interfaces governs their impact as positional signals

Mobile small RNAs serve as local positional signals in development and coordinate stress responses across the plant. Despite its central importance, an understanding of how the cell-to-cell movement of small RNAs is governed is lacking. Here, we show that miRNA mobility is precisely regulated through a gating mechanism polarised at defined cell-cell interfaces. This generates directional movement between neighbouring cells that limits long-distance shoot-to-root trafficking, and underpins domain-autonomous behaviours of small RNAs within stem cell niches. We further show that the gating of miRNA mobility occurs independent of mechanisms controlling protein movement, identifying the small RNA as the mobile unit. These findings reveal gate-keepers of cell-to-cell small RNA mobility generate selectivity in long-distance signalling, and help safeguard functional domains within dynamic stem cell niches while mitigating a 'signalling gridlock' in contexts where developmental patterning events occur in close spatial and temporal vicinity

Toxicity Associated with Stavudine Dose Reduction from 40 to 30 mg in First-Line Antiretroviral Therapy

To compare the incidence and timing of toxicity associated with the use of a reduced dose of stavudine from 40 to 30 mg in first-line antiretroviral therapy (ART) for HIV treatment and to investigate associated risk factors

Transcriptional dynamics during cell wall removal and regeneration reveals key genes involved in cell wall development in rice

Efficient and cost-effective conversion of plant biomass to usable forms of energy requires a thorough understanding of cell wall biosynthesis, modification and degradation. To elucidate these processes, we assessed the expression dynamics during enzymatic removal and regeneration of rice cell walls in suspension cells over time. In total, 928 genes exhibited significant up-regulation during cell wall removal, whereas, 79 genes were up-regulated during cell wall regeneration. Both gene sets are enriched for kinases, transcription factors and genes predicted to be involved in cell wall-related functions. Integration of the gene expression datasets with a catalog of known and/or predicted biochemical pathways from rice, revealed metabolic and hormonal pathways involved in cell wall degradation and regeneration. Rice lines carrying Tos17 mutations in genes up-regulated during cell wall removal exhibit dwarf phenotypes. Many of the genes up-regulated during cell wall development are also up-regulated in response to infection and environmental perturbations indicating a coordinated response to diverse types of stress

Comperative study of a multi-storey steel building for different bracing systems

239 σ.Στην παρούσα διπλωματική εργασία γίνεται η στατική και δυναμική ανάλυση ενός επταώροφου κτιρίου γραφείων που κατασκευάστηκε κατά την περίοδο των Ολυμπιακών Αγώνων του 2004 (κέντρο τύπου MPC), εξετάζοντας διάφορα συστήματα παραλαβής οριζοντίων δυνάμεων. Ο φέρων οργανισμός του κτιρίου είναι μεταλλικός με στατικό σύστημα διπλής πλαισιακής λειτουργίας με έκκεντρους συνδέσμους δυσκαμψίας, συνδεδεμένους με άκαμπτες συνδέσεις πλήρους αντοχής. Γίνεται η διερεύνηση εναλλακτικών στατικών συστημάτων με στόχο να εξετασθεί η επιρροή των συστημάτων δυσκαμψίας στην δυναμική απόκριση της κατασκευής και η σύγκριση αυτών. Πιο συγκεκριμένα, στα κεφάλαια 1 έως 8 δίνονται κάποια εισαγωγικά στοιχεία, περιγράφεται το προσομοίωμα του φορέα, υπολογίζονται όλα τα φορτία της κατασκευής αναλυτικά, περιγράφονται οι συνδυασμοί φόρτισης και υπολογίζεται με λεπτομέρεια η σύμμικτη πλάκα της κατασκευής καθώς και οι δοκοί με πολυγωνικά ανοίγματα στον κορμό τους. Ακολουθεί μια γενική περιγραφή των συστημάτων δυσκαμψίας καθώς και των επιμέρους απαιτήσεων του EC8 για τον σχεδιασμό απόσβεσης ενέργειας κάθε συστήματος. Στα κεφάλαια 9 έως 12 γίνεται ο υπολογισμός της μεταθετότητας, η ανάλυση των δοκών, υποστυλωμάτων και των συστημάτων δυσκαμψίας, ο σχεδιασμός απόσβεσης ενέργειας και οι ικανοτικοί έλεγχοι, η παρουσίαση των βασικών δυναμικών χαρακτηριστικών, της συνολικής μάζας και των πινάκων με τις χρησιμοποιούμενες διατομές για κάθε ένα από τα ακόλουθα συστήματα: a. Χωρικά πλαίσια ροπής (MRF) b. Συνδυασμός πλαισίων ροπής με αρθρωτούς έκκεντρους συνδέσμους (MRF + EBF) c. Έκκεντροι σύνδεσμοι δυσκαμψίας (EBF) d. Κεντρικοί σύνδεσμοι δυσκαμψίας τύπου Λ και V (CBF) Τέλος ακολουθούν τα συμπεράσματα και η σύγκριση των παραπάνω συστημάτων στο κεφάλαιο 13 και η βιβλιογραφία στο κεφάλαιο 14.The present thesis essentially includes the static and dynamic analysis of a seven-storey office building, designed for the Olympic Games Athens 2004 (Media Press Center, MPC), testing different bracing systems for the horizontal actions. The building is constructed as a steel structure with moment resisting frames to its two directions and eccentric bracing systems, connected with rigid full strength joints. It is a comparative study of alternative static systems in order to examine the influence of several bracing systems at the dynamic response of the structure. More specifically, in the chapters 1 to 8 it is presented some introductive data, described the model of the structure, calculated all the loads of the structure analytically, presented the load combinations and calculated in detail the composite slab and, in addition, the castellated beams which are the secondary ones. We continue with a general description of the used bracing systems and the special demands of EC8 that has to do with the design of energy dissipation of each bracing system. The chapters 9 to 12, deal with the calculations of sway or non-sway behavior, the analysis of the beams, the columns and the bracing systems, the energy dissipation design and the capacity design checks, the basic dynamic characteristics of the structure, and finally the total mass and tables of the used cross sections for each one of the following bracing systems : a. Moment Resisting Frames (MRF) b. Combination of moment resisting frames with pinned eccentrically braced frames (MRF + EBF) c. Eccentrically braced frames (EBF) d. Concentrically braced frames of V bracing type (CBF) The dissertation ends with the conclusions and the comparison of the previous bracing systems in chapter 13 and the bibliography in chapter 14.Απόστολος Π. ΟικονόμουΑργύριος Σ. Σκοπελίτη

Modulation of higher-plant NAD(H)-dependent glutamate dehydrogenase activity in transgenic tobacco via alteration of beta subunit levels

Glutamate dehydrogenase (GDH; EC 1.4.1.2-1.4.1.4) catalyses in vitro the reversible amination of 2-oxoglutarate to glutamate. In vascular plants the in vivo direction(s) of the GDH reaction and hence the physiological role(s) of this enzyme remain obscure. A phylogenetic analysis identified two clearly separated groups of higher-plant GDH genes encoding either the alpha- or beta-subunit of the GDH holoenzyme. To help clarify the physiological role(s) of GDH, tobacco (Nicotiana tabacum L.) was transformed with either an antisense or sense copy of a beta-subunit gene, and transgenic plants recovered with between 0.5- and 34-times normal leaf GDH activity. This large modulation of GDH activity (shown to be via alteration of beta-subunit levels) had little effect on leaf ammonium or the leaf free amino acid pool, except that a large increase in GDH activity was associated with a significant decrease in leaf Asp (similar to 51%, P=0.0045). Similarly, plant growth and development were not affected, suggesting that a large modulation of GDH beta-subunit titre does not affect plant viability under the ideal growing conditions employed. Reduction of GDH activity and protein levels in an antisense line was associated with a large increase in transcripts of a beta-subunit gene, suggesting that the reduction in beta-subunit levels might have been due to translational inhibition. In another experiment designed to detect post-translational up-regulation of GDH activity, GDH over-expressing plants were subjected to prolonged dark-stress. GDH activity increased, but this was found to be due more likely to resistance of the GDH protein to stress-induced proteolysis, rather than to post-translational up-regulation

Boundary Formation through a Direct Threshold-Based Readout of Mobile Small RNA Gradients

Summary Small RNAs have emerged as a new class of mobile signals. Here, we investigate their mechanism of action and show that mobile small RNAs generate sharply defined domains of target gene expression through an intrinsic and direct threshold-based readout of their mobility gradients. This readout is highly sensitive to small RNA levels at the source, allowing plasticity in the positioning of a target gene expression boundary. Besides patterning their immediate targets, the readouts of opposing small RNA gradients enable specification of robust, uniformly positioned developmental boundaries. These patterning properties of small RNAs are reminiscent of those of animal morphogens. However, their mode of action and the intrinsic nature of their gradients distinguish mobile small RNAs from classical morphogens and present a unique direct mechanism through which to relay positional information. Mobile small RNAs and their targets thus emerge as highly portable, evolutionarily tractable regulatory modules through which to create pattern