Muscle development and differentiation in the urodele Ambystoma mexicanum.

Skeletal muscle in vertebrates is the most representative tissue and it is composed by different types of fibers which differ for anatomical and physiological features. These traits permit to distinguish them basing on the speed of twitch and the load resistance. The characteristics of a fiber depend on the amount of glycogen and mitochondria in their cytoplasm, as well as by the presence of glycolitic and oxidative enzymes. In particular, slow fibers are specific for a long-lasting contraction, they express a MyHC isoform having an ATPase activity at acidic pH (pH 4.0) and an aerobic oxidative metabolism. In contrast, fast fibers are larger in size, with few mitochondria. They are specialized in rapid and short-lasting contractions and express a MyHC isoform, having an ATPase activity at basic pH (pH 10.0) and an anaerobic glycolitic metabolism. These different types of fibers, both in amniotes and in lower vertebrates such as fish and anuran amphibians s come from distinct populations of myoblasts which appear in the somites during the embryonic development. Even if substantial data concerning the muscle differentiation and the characterization of the different types of fibers in zebrafish and Xenopus are available, nothing is still known about the mechanisms regulating these processes in amphibian urodeles. Since these animals present some anatomical features and life style between fish and anurans, the study of myogenic processes in these animals could be useful to clarify the evolutionary changes which lead to the formation of skeletal muscle in the trunk of land vertebrates. To shed light on the myogenic processes in urodele amphibians we focused our studies on the axolotl Ambystoma mexicanum and we analysed several embryonic stages of this amphibian in order to identify the different types of fibers and their pattern of distribution during the myogenic process. Using morphological analysis, enzymatic hystochemistry and immunohystochemistry we showed that in A. mexicanum, as in zebrafish, the first differentiating fibers are the slow ones deriving from myoblasts localized close to the notochord. These fibers then migrate towards the somitic surface and here they give rise to a uperficial layer of slow fibers, while the myoblasts forming the medial part of the somite differentiate into fast fibers. Further, in order to evaluate the possible involvement of muscle-specific transcriptional factors and protein signalling in the regulation of myogenic process of this amphibian, we used molecular biological approaches to identify and clone the muscle-specific transcriptional factor (Myf5) and the Sonic hedgehog signalling protein, known to regulate the muscle development and differentiation both in amniotes and lower vertebrates

Shock waves in the magnetized cosmic web: the role of obliquity and cosmic-ray acceleration

Structure formation shocks are believed to be the largest accelerators of cosmic rays in the Universe. However, little is still known about their efficiency in accelerating relativistic electrons and protons as a function of their magnetization properties, i.e. of their magnetic field strength and topology. In this work, we analyzed both uniform and adaptive mesh resolution simulations of large-scale structures with the magnetohydrodynamical grid code Enzo, studying the dependence of shock obliquity with different realistic scenarios of cosmic magnetism. We found that shock obliquities are more often perpendicular than what would be expected from a random three-dimensional distribution of vectors, and that this effect is particularly prominent in the proximity of filaments, due to the action of local shear motions. By coupling these results to recent works from particle-in-cell simulations, we estimated the flux of cosmic-ray protons in galaxy clusters, and showed that in principle the riddle of the missed detection of hadronic gamma-ray emission by the Fermi-LAT can be explained if only quasi-parallel shocks accelerate protons. On the other hand, for most of the cosmic web the acceleration of cosmic-ray electrons is still allowed, due to the abundance of quasi-perpendicular shocks. We discuss quantitative differences between the analyzed models of magnetization of cosmic structures, which become more significant at low cosmic overdensities.Comment: Accepted for publication in MNRAS, 20 pages, 32 figure

On the alignment of haloes, filaments and magnetic fields in the simulated cosmic web

The continuous flow of gas and dark matter across scales in the cosmic web can generate correlated dynamical properties of haloes and filaments (and the magnetic fields they contain). With this work, we study the halo spin properties and orientation with respect to filaments, and the morphology of the magnetic field around these objects, for haloes with masses in the range 1e8-1e14 Msun and filaments up to 8 Mpc long. Furthermore, we study how these properties vary in presence, or lack thereof, of different (astro)physical processes and with different magnetic initial conditions. We perform cosmological magnetohydrodynamical simulations with the Eulerian code Enzo and we develop a simple and robust algorithm to study the filamentary connectivity of haloes in three dimensions. We investigate the morphological and magnetic properties and focus on the alignment of the magnetic field along filaments: our analysis suggests that the degree of this alignment is partially dependent on the physical processes involved, as well as on magnetic initial conditions. We discuss the contribution of this effect on a potential attempt to detect the magnetic field surrounding these objects: we find that it introduces a bias in the estimation of the magnetic field from Faraday rotation measure techniques. Specifically, given the strong tendency we find for extragalactic magnetic fields to align with the filaments axis, the value of the magnetic field can be underestimated by a factor 3, because this effect contributes to making the line-of-sight magnetic field (for filaments in the plane of the sky) much smaller than the total one.Comment: 16 pages, 21 figure

Macroscopic and microscopic aspects of particle acceleration by cosmic shocks

Cosmic collisionless shocks are highly energetic phenomena in which different non-thermal processes take place. Above all, particle acceleration is arguably the most important, and observations of its signatures can be a powerful tool to constrain the local plasma and magnetic properties at the acceleration site. Within large-scale structures, the presence of cosmic rays can be revealed by means of different detection approaches: relativistic electrons can emit in radio via synchrotron radiation (radio relics), while energetic protons can interact with thermal protons of the intracluster medium and emit in the gamma-ray band. Both electrons and protons should in principle be accelerated by the first order Fermi acceleration mechanism known as diffusive shock acceleration: however, only evidence of cosmic-ray electrons has been detected so far in galaxy clusters, while no signatures of cosmic-ray proton have been reported. With a comprehensive analysis from 'macroscopic' to 'microscopic' scales, I address the missing gamma-ray issue by means of advanced numerical simulations, in which extragalactic magnetic fields are evolved together with the dynamics of large-scale structures. The primary factor at play is obliquity, the angle between the shock propagation direction and the magnetic field. I first determine the distribution of obliquity in cosmological simulations as a function of the medium in which the shock takes place. Then, I detect a pattern in the arrangement of the magnetic field around filaments and perform a quantitative study of the topological properties of the magnetic field surrounding the cosmic web. Finally, shocks in filaments are more closely investigated with new particle-in-cell simulations on much smaller scales, where the actual acceleration efficiency by realistic shocks can be measured. The new insights obtained from these numerical simulations provide a tool for the correct interpretation of observations and to estimate the magnetic properties that can be inferred, e.g. from Faraday rotation measurements

Photodynamic therapy for the eradication of biofilms formed by catheter associated Pseudomonas aeruginosa strains

Pseudomonas aeruginosa has emerged as a major opportunistic pathogen causing catheter-associated urinary tract infections (CA-UTIs) associated with high mortality and morbidity. In this study 18 P. aeruginosa isolates from urine of catheterized patients were evaluated for in vitro biofilm formation.All the tested strains showed the ability to form biofilm more thicker than those formed by a cohort of 29 blood culture strains belonging to the same species. Photodynamic antimicrobial chemotherapy (PACT) is a novel antimicrobial treatment that exploits a photosensitizer (PS) and visible light to induce lethal oxidative damages in bacterial cells and could be used as local antimicrobial approach in CA-UTIs. Here we tested the susceptibility of planktonic and sessile cultures of P. aeruginosa strains, the model strain PAO1 and CA-UTI isolates, to photodynamic inactivation with a di cationic porphyrinic photosensitizer, the 5, 15-di (N-benzyl-4-pyridynium)-porphyrin di chloride.Although Pseudomonas aeruginosa is regarded as a difficult target for antimicrobial chemotherapy, satisfactory bactericidal activities on both planktonic and biofilm cultures were observed

Extraction of antibacterial active compounds from dry leaves of African plants of the Combretaceae family

The dry leaves of two African plants of the Combretaceae family, furnished by the botanist of the St. Jean de Dieu hospital of Tangueita (Benin, central Africa),were extracted with a sequence of 5 solvents with increasing polarity (from cyclohexane to water).The raw materials, obtained from these extractions following solvent evaporations, were tested for antibiotic activity against gram negative and gram positive bacterial strains. According to the results of a modified Kirby-Bauer test, no promising effect was obtained against Gram negative bacteria while interesting dose-effect activities were observed against Gram positive strains. In particular, from G. senegalensis active compounds were found in the low polarity extract (dichloromethane) which, at a concentration of 800 μg/disk (13 mm diameter disk), resulted in a grow inhibition crown of 4.7 mm and 2.6 mm on Enterococcus faecalis and Staphylococcus aureus MSSA, respectively. An higher amount of the aqueous extract (4760 μg/disk) also produced a good result as 5.7 mm and 5.0 mm crowns were observed. The extracts from C. micranthum showed an inhibiting effect in the more polar extracts (i.e. from ethanol and water) which gave 1 mm of grow inhibition crown on both strains at a concentration of 1000 μg/disk. The most promising extract from each plant was partially purified and then tested on some clinical relevant bacterial strains: S. aureus MRSA, Clostridium difficile, Streptococcus pyogenes, Streptococcus pneumoniae, Corynebacterium striatum, Neisseria gonorrhoeae, Haemophylus influenzae, Escherichia coli, obtaining a good killing effects on the Gram positive bacteria of the panel

Identification, Isolation and Expansion of Myoendothelial Cells Involved in Leech Muscle Regeneration

Adult skeletal muscle in vertebrates contains myoendothelial cells that express both myogenic and endothelial markers, and which are able to differentiate into myogenic cells to contribute to muscle regeneration. In spite of intensive research efforts, numerous questions remain regarding the role of cytokine signalling on myoendothelial cell differentiation and muscle regeneration. Here we used Hirudo medicinalis (Annelid, leech) as an emerging new model to study myoendothelial cells and muscle regeneration. Although the leech has relative anatomical simplicity, it shows a striking similarity with vertebrate responses and is a reliable model for studying a variety of basic events, such as tissue repair. Double immunohistochemical analysis were used to characterize myoendothelial cells in leeches and, by injecting in vivo the matrigel biopolymer supplemented with the cytokine Vascular Endothelial Growth Factor (VEGF), we were able to isolate this specific cell population expressing myogenic and endothelial markers. We then evaluated the effect of VEGF on these cells in vitro. Our data indicate that, similar to that proposed for vertebrates, myoendothelial cells of the leech directly participate in myogenesis both in vivo and in vitro, and that VEGF secretion is involved in the recruitment and expansion of these muscle progenitor cells

Biosignatures in atmosfere di super Terre attorno a stelle M

L'elaborato si occupa dell'analisi delle potenziali biosignatures riscontrabili in atmosfere di super Terre attorno a stelle di tipo spettrale M: è quindi stata condotta un'indagine sulle atmosfere che potrebbero ospitare forme di vita e sui metodi di identificazione di queste caratteristiche spettrali. Particolare attenzione è stata rivolta all'esperimento "atmosfere in provetta" in corso di svolgimento dall'Osservatorio Astronomico e dall'Università di Padov

Circumstellar Dust Distribution in Systems with Two Planets in Resonance.

Protoplanetary discs are the fundamental channel to peer into both star formation and planet formation: their study through the combination of theory, observations and numerical simulations is essential to unveil still unanswered questions about their structure and the processes that rule them. ALMA and SPHERE are among the most powerful instrumentation for observations of the cold universe, which open up the opportunity of studying objects like dust discs surrounding young stars. This new generation of imaging has led to major changes in the understanding of protoplanetary discs, which are now acknowledged to have different, complex structures. The mutual interaction between gas, dust, planets and their surroundings leads to deviations from axisymmetric shapes, like gaps, spirals and warps. In my thesis I investigated via numerical simulations the effects of two giant planets locked in resonance on the dust distribution of the circumstellar disc around a young star, in order to gather if such systems are able to leave peculiar features such as a common gap, which is an essential requirement for outward migration — invoked to explain the observed position of several giant exoplanets with respect to their host star (Walsh et al. 2011). In my work I tested the outcome of the variations of some parameters, i.e. the eccentricity of the planets, the scale height of the disc and the equation of state: in particular, I aimed to show the differences produced by the inclusion of viscous heating and radiative transfer. I used the tridimensional code PLUTO (Mignone et al. 2007) and tested its efficiency in simulating the gaseous and dusty components of the disc. The main results I obtained are that gaps in both gas and dust are more easily formed in a locally isothermal disc with a lower scale height and with planets on eccentric orbits: radiative transfer acts as an obstruction for gap forming and dust accretion

ANGPTL8 has both endocrine and autocrine effects on substrate utilization

The angiopoietin-like protein ANGPTL8 (A8) is one of 3 ANGPTLs (A8, A3, A4) that coordinate changes in triglyceride (TG) delivery to tissues by inhibiting lipoprotein lipase (LPL), an enzyme that hydrolyzes TG. Previously we showed that A8, which is expressed in liver and adipose tissue, is required to redirect dietary TG from oxidative to storage tissues following food intake. Here we show that A8 from liver and adipose tissue have different roles in this process. Mice lacking hepatic A8 have no circulating A8, high intravascular LPL activity, low plasma TG levels, and evidence of decreased delivery of dietary lipids to adipose tissue. In contrast, mice lacking A8 in adipose tissue have higher postprandial TG levels and similar intravascular LPL activity and plasma A8 levels and higher levels of plasma TG. Expression of A8, together with A4, in cultured cells reduced A4 secretion and A4-mediated LPL inhibition. Thus, hepatic A8 (with A3) acts in an endocrine fashion to inhibit intravascular LPL in oxidative tissues, whereas A8 in adipose tissue enhances LPL activity by autocrine/paracrine inhibition of A4. These combined actions of A8 ensure that TG stores are rapidly replenished and sufficient energy is available until the next meal