The role of the hypoxic transcription factor gene MGA2 in Kluyveromyces lactis fatty acids metabolism and cell fitness

Kluyveromyces lactis è un lievito non convenzionale ampiamente utilizzato sia nelle applicazioni industriali che nella ricerca di base. Nel nostro laboratorio stiamo studiando il gene KlMGA2, che codifica per un modulatore della risposta all’ipossia. In lavori precedenti, abbiamo mostrato come la delezione del gene KlMGA2 in K. lactis generi un ceppo vitale, ma con difetti di crescita cellulare, alterazione in quantità e composizione degli acidi grassi, respirazione difettosa e morfologia mitocondriale alterata. Con questo lavoro mostriamo come l'assenza del gene KlMGA2 causi, oltre ai fenotipi sopra citati, una maggiore resistenza allo stress ossidativo ed una longevità molto estesa, accompagnati da un aumento dell’espressione genica delle catalasi e delle superossido dismutasi. Questo potrebbe suggerire un coinvolgimento di KlMga2 come mediatore diretto non solo della risposta ipossica, ma anche nella risposta allo stress ossidativo, ipotizzando una correlazione tra ipossia, regolazione del glucosio, biosintesi degli acidi grassi e metabolismo dei ROS. In seconda analisi, con questo lavoro si è cercato di verificare una possibile risposta di K. lactis allo stress luminoso. Negli organismi unicellulari come il lievito, che non presentano tessuti specializzati per contrastare i cambiamenti dell’ambiente esterno, l’esistenza di meccanismi cellulari adattativi alle condizioni di stress risulta essere di fondamentale importanza. Precedenti studi, hanno evidenziato che in Saccharomyces cerevisiae l’impulso luminoso rappresenta una fonte di stress, in quanto provoca l’aumento intracellulare di perossido di idrogeno (H2O2). Visti i nostri studi riguardanti KlMga2 come mediatore di risposta allo stress ossidativo, abbiamo indagato sul suo possibile coinvolgimento nella trasduzione del segnale luminoso. Pertanto, tale studio permetterebbe di esaminare dei meccanismi foto-dipendenti anche in organismi apparentemente privi di domini proteici sensibili alla luce.The yeast Kluyveromyces lactis has been widely used in both industrial applications and basic research. We previously demonstrated that deletion of the KlMGA2, coding for a hypoxic mediator in K. lactis, generated a viable strain, although suffering of several deficiencies. We also showed that glucose signaling and glucose catabolism were involved in KlMga2 regulation. In this work, we showed that, in addition to these defects, the deletion of KlMGA2 also caused increased resistance to oxidative stress and extremely extended lifespan. These phenotypes are associated with increased expression levels of catalase and superoxide dismutase genes. We propose that KlMga2 might act as a direct mediator not only of hypoxic response, but also of oxidative stress response/adaptation, thus revealing connections between hypoxia, glucose signaling, fatty acid biosynthesis and ROS metabolism. Secondly, in this work we wanted to investigate the possible light response in this yeast. In unicellular organisms like yeasts, that cannot utilize specialized tissue for protection against environmental challenges, the presence of cellular mechanisms to respond and adapt to stress conditions is fundamental. Saccharomyces cerevisiae has been reported to respond to light by increasing hydrogen peroxide (H2O2) levels. Therefore, it could be interesting to study the possible role of oxidative stress mediator KlMga2, already studied in our laboratory, in the light response of yeast

The hypoxic transcription factor KlMga2 mediates the response to oxidative stress and influences longevity in the yeast Kluyveromyces lactis

Hypoxia is defined as the decline of oxygen availability, depending on environmental supply and cellular consumption rate. The decrease in O2 results in reduction of available energy in facultative aerobes. The response and/or adaptation to hypoxia and other changing environmental conditions can influence the properties and functions of membranes by modifying lipid composition. In the yeast Kluyveromyces lactis, the KlMga2 gene is a hypoxic regulatory factor for lipid biosynthesis-fatty acids and sterols-and is also involved in glucose signaling, glucose catabolism and is generally important for cellular fitness. In this work we show that, in addition to the above defects, the absence of the KlMGA2 gene caused increased resistance to oxidative stress and extended lifespan of the yeast, associated with increased expression levels of catalase and SOD genes. We propose that KlMga2 might also act as a mediator of the oxidative stress response/adaptation, thus revealing connections among hypoxia, glucose signaling, fatty acid biosynthesis and ROS metabolism in K. lactis

Plasmonic-Solitonic coupling structure

The applications of optics, in particular non-linear optics, have joined the electrical ones in many contexts, often equaling or exceeding them thanks to the characteristics ensured by the physical nature of light such as high speed of propagation and low losses. In recent years, nanotechnologies combined with plasmon propagation are shaping a new development scenario that touches areas such as medicine, robotics or neurobiology. In fact, nano-devices are able to reproduce a very large number of functions ensuring very small dimensions. Among these, the applications of surface plasmon polariton waves are becoming more and more important, thanks to their peculiar behavior both as an electric wave and as a light wave. In this work we present an innovative structure consisting of a nano metallic waveguide on which it is possible to propagate a surface-plasmon- polariton signal at the interface with a photorefractive dielectric material. At the end of the guide, the diffracting light can generate, under suitable conditions, a self-confined light beam (bright-screening-photorefractive soliton). In this way the polariton plasmon waves propagating at the interface are automatically coupled within a soliton-based optical waveguide. By definition, soliton guides have very low propagation losses, opening the possibility of using this type of hybrid interconnection in extended complex circuits, for example as memories, thanks to the intrinsic plasticity of the photorefractive nonlinear refractive index

A study on the compressive strength of thick carbon fibre-epoxy laminates

This paper describes an experimental study that examines the effect of specimen size on the axial compressive strength of IM7/8552 carbon fibre/epoxy unidirectional laminates (UD). Laminate gauge length, width and thickness were increased by a scaling factor of 2 and 4 from the baseline specimen size of 10 mm x 10 mm x 2 mm. In all cases, strength decreased as specimen size increased, with a maximum reduction of 45%; no significant changes were observed for the axial modulus. Optical micrographs show that the failure mechanism is fibre microbuckling accompanied by matrix cracking and splitting. The location of failure in most specimens, especially the thicker ones, is where the tabs terminate and the gauge section begins suggesting that the high local stresses developed due to geometric discontinuity contribute to premature failure and hence reduced compressive strength. Two generic quasi-isotropic multi-directional (MD) lay-ups were also tested in compression, one with blocked plies [45n/90n/-45n/0n]s and the other with distributed plies [45/90/-45/0]ns with n=2, 4 and 8. The material used and test fixture was identical to that of the unidirectional specimens with three different gauge sections (30 mm x 30 mm, 60 mm x 60 mm and 120 mm x 120 mm) to establish any size effects. Strength results showed no evidence of a size effect when the specimens are scaled up using distributed plies and compared to the 2 mm thick specimens. All blocked specimens had similar compressive strengths to the sub-laminate ones apart of the 8 mm specimens that showed a 30% reduction due to extensive matrix cracking introduced during the specimen's cutting process. The calculated unidirectional failure stress (of the 0° ply within the multidirectional laminate) of about 1710 MPa is slightly higher than the average measured value of 1570 MPa of the 2 mm thick baseline unidirectional specimen, suggesting that the reduced unidirectional strength observed for the thicker specimens is a testing artefact. It appears that the unidirectional compressive strength in thicker specimens (>2 mm) is found to be limited by the stress concentration developed at the end tabs and manufacturing induced defects

The human YAE1-ORAOV1 complex of the cytosolic iron-sulfur protein assembly machinery binds a [4Fe-4S] cluster

Abstract Iron-sulfur (Fe-S) clusters are among the most versatile cofactors in biology. Although Fe-S clusters formation can be achieved spontaneously in vitro with inorganic iron and sulfur sources, the in vivo behaviour is more complex and requires the so-called Fe-S biogenesis machineries. In the cytosol, the biogenesis of Fe-S proteins is assisted by the cytosolic Fe-S protein assembly machinery, which comprises at least thirteen known proteins, among which there are human ORAOV1 and YAE1. A hetero-complex formed by the two latter proteins facilitates Fe-S cluster insertion in the human ABC protein ABCE1 within a chain of binding events that are still not well understood. In the present work, ORAOV1 and the YAE1-ORAOV1 complex were produced and their structural and cluster binding properties spectroscopically investigated. It resulted that both ORAOV1 and the YAE1-ORAOV1 complex are characterized by well-structured, α -helical regions and by unstructured, flexible regions, and are both able to bind a [4Fe-4S]2+ cluster. Bioinformatics and site-directed mutagenesis studies indicated that the [4Fe-4S] cluster in ORAOV1 is bound by a conserved cluster binding motif, while YAE1, which does not have a metal-binding consensus motif, is not essential for the [4Fe-4S]2+ cluster binding in the YAE1-ORAOV1 hetero-complex. Overall, these results support a model that the YAE1-ORAOV1 complex might actively participate in the Fe-S cluster insertion into ABCE1 thanks to the [4Fe-4S]2+ cluster binding properties of ORAOV1

CD21-/low B cells: a snapshot of a unique B cell subset in health and disease

B cells represent one of the cellular components of the immune system thatprotects the individual from invading pathogens. In response to the invader,these cells differentiate into plasma cells and produce large amounts of antibodiesthat bind to and eliminate the pathogen. A hallmark of autoimmune diseases isthe production of autoantibodies i.e. antibodies that recognize self. Those that areconsidered pathogenic can damage tissues and organs, either by direct binding orwhen deposited as immune complexes. For decades, B cells have been consideredto play a major role in autoimmune diseases by antibody production. However, aspathogenic autoantibodies appear to derive mainly from T cell dependentresponses, T cells have been the focus for many years. The successful treatment ofpatients with autoimmune diseases with either B cell depletion therapy(rituximab) or inhibition of B cell survival (belimumab), suggested that notonly the autoantibodies but also other B cell features are important. This hascaused a surg e of interest in B cells and their biology resulting in theidentification of various subsets e.g. regulatory B cells, several memory B cellsubsets etc. Also, in other conditions such as chronic viral infect ions and primaryimmunodeficiency, several B cell subsets with unique characteristics have beenidentified. In this review, we will discuss one of these subsets, a subset that isexpanded in conditions characterized by chronic immune stimulation. This B cellsubset lacks, or expresses low, surface levels of the complement receptor 2(CD21) and has therefore been termed CD21-/lowB cell