Differential crosstalk between P2X7 and arachidonic acid in activation of mitogen-activated protein kinases

Accumulating evidence indicates that astroglial syncytium plays key role in normal and pathological brain functions. Astrocytes both in vitro and in situ respond to extracellular adenine-based nucleotides via the activation of P2 receptors. Massive release of ATP from neurons and glial cells occurs as a result of pathological conditions of the brain leading to neuroinflammation and involving P2X7 receptors. In this study, we investigated whether P2X7 stimulation on cultured cortical astrocytes promoted a differential activation of mitogen-activated protein kinases (MAPKs), and whether the second messenger arachidonic acid (AA), which is also a key modulator of neuroinflammation, affected the P2X7-mediated MAPK phosphorylation. The results show that the synthetic P2X7 receptor agonist 2′,3′-O-(4-benzoyl)benzoyl-ATP (BzATP), induced a concentration-dependent phosphorylation of MAPK ERK1/2, JNK and p38. Stimulation of ERK1/2, JNK and p38 phosphorylation was also obtained by pathophysiological levels of extracellularly applied AA. Interestingly, a robust potentiation of ERK1/2 phosphorylation was elicited by co-application of BzATP and AA, whereas no differences were observed in JNK or p38 phosphosignals. The kinases activation showed a differential dependence on the presence of extracellular Ca²⁺. The potentiation of BzATP-mediated ERK1/2 phosphorylation was also observed in human embryonic kidney cells (HEK293) stably transfected with rat P2X7, but not in HEK cells expressing truncated P2X7 receptor lacking the full cytoplasmic carboxy-terminal or in those carrying the structurally related rat P2X2. AA and BzATP synergism in ERK1/2 activation was abolished by cyclo-oxygenase and lipoxygenase pathway inhibitors.The result that ERK1/2-mediated transduction pathway is synergistically modulated by ATP and AA signalling depicts possible novel pharmacological targets for interfering with pathological activation of astroglial cells.     

The histone LSD1 demethylase in stemness and cancer transcription programs

DNA and histone chromatin modifying enzymes play a crucial role in chromatin remodeling in several biological processes. Lysine-specific demethylase 1 (LSD1), the first identified histone demethylase, is a relevant player in the regulation of a broad spectrum of biological processes including development, cellular differentiation, embryonic pluripotency and cancer. Here, we review recent insights on the role of LSD1 activity in chromatin regulatory complexes, its functional role in the epigenetic changes during embryonic development, in the establishment and maintenance of stemness and during cancer progression.     

Common and specific responses to iron and phosphorus deficiencies in roots of apple tree (Malus × domestica)

Plant Molecular Biology - Iron and phosphorus are abundant elements in soils but poorly available for plant nutrition. The availability of these two nutrients represents a major constraint for...     

Structure-function relationship studies of PTH(1-11) analogues containing sterically hindered dipeptide mimetics.

The N-terminal 1-34 fragment of parathyroid hormone (PTH) is fully active in vitro and in vivo and reproduces all biological responses characteristic of the native intact PTH. In order to develop safer and non-parenteral PTH-like bone anabolic agents, we have studied the effect of introducing conformationally constrained dipeptide mimetics into the N-terminal portion of PTH in an effort to generate miniaturized PTH-mimetics. To this end, we have synthesized and conformationally and biologically characterized PTH(1-11) analogues containing 3R-carboxy-6S-amino-7,5-bicyclic thiazolidinlactam (7,5-bTL), a rigidified dipeptide mimetic unit. The wild type sequence of PTH(1-11) is H-Ser-Val-Ser-Glu-Ile-Gln-Leu-Met-His-Asn-Leu-NH(2). The following pseudo-undecapeptides were prepared: [Ala(1), 7,5-bTL(3, 4), Nle(8), Arg(11)]hPTH(1-11)NH(2) (I); [Ala(1), 7,5-bTL(6, 7), Nle(8), Arg(11)]hPTH(1-11)NH(2) (II); [Ala(1), Nle(8), 7,5-bTL(9, 10), Arg(11)]hPTH(1-11)NH(2) (III). In aqueous solution containing 20% TFE, only analogue I exhibited the typical CD pattern of the alpha-helical conformation. NMR experiments and molecular dynamics calculations located the alpha-helical stretch in the sequence Ile(5)-His(9). The dipeptide mimetic unit 7,5-bTL induces a type III beta-turn, occupying the positions i - 1 and i of the turn. Analogue II exhibited an equilibrium between a type I beta-turn and an alpha-helix, and analogue III did not show any ordered structure. Biological tests revealed poor activity for all analogues (EC(50) > 0.1 mM). Apparently, the relative side-chain orientation of Val(2), Ile(5) and Met(8) can be critical for effective analogue-receptor interaction. Considering helicity as an essential property to obtain active PTH agonists, one must decorate the correctly positioned dipeptide mimetic azabicycloalkane scaffold with substitutions corresponding to the displaced amino acids.     

The Caenorhabditis elegans Elongator Complex Regulates Neuronal α-tubulin Acetylation

Although acetylated α-tubulin is known to be a marker of stable microtubules in neurons, precise factors that regulate α-tubulin acetylation are, to date, largely unknown. Therefore, a genetic screen was employed in the nematode Caenorhabditis elegans that identified the Elongator complex as a possible regulator of α-tubulin acetylation. Detailed characterization of mutant animals revealed that the acetyltransferase activity of the Elongator is indeed required for correct acetylation of microtubules and for neuronal development. Moreover, the velocity of vesicles on microtubules was affected by mutations in Elongator. Elongator mutants also displayed defects in neurotransmitter levels. Furthermore, acetylation of α-tubulin was shown to act as a novel signal for the fine-tuning of microtubules dynamics by modulating α-tubulin turnover, which in turn affected neuronal shape. Given that mutations in the acetyltransferase subunit of the Elongator (Elp3) and in a scaffold subunit (Elp1) have previously been linked to human neurodegenerative diseases, namely Amyotrophic Lateral Sclerosis and Familial Dysautonomia respectively highlights the importance of this work and offers new insights to understand their etiology.     

Fatal Chytridiomycosis in the Tyrrhenian Painted Frog

Batrachochytrium dendrobatidis (Bd), the causative agent of the amphibian disease chytridiomycosis, is an important factor in the global decline of amphibians. Within Europe, animals that exhibit clinical signs of the disease have only been reported in Spain despite the pathogen’s wide, but patchy, distribution on the continent. Recently, another occurrence of chytridiomycosis was reported in Euproctus platycephalus, the Sardinian brook newt, on the Mediterranean island of Sardinia, but without any evidence of fatal disease. We report further evidence of the emergence of Bd on Sardinia and the first evidence of lethal chytridiomycosis outside of Spain. Unusual mortalities of the Tyrrhenian painted frog (Discoglossus sardus) were found at three sites in the Limbara mountains of northern Sardinia. Molecular and histological screens of corpses, frogs, and tadpoles from these sites revealed infection with Bd. Infection and mortality occurred at locations that are unusual in terms of the published habitat requirements of the pathogen. Given the endemicity, the IUCN Red List status of the amphibian species on Sardinia, and the occurrence of infection and mortality caused by chytridiomycosis, there is serious reason for concern for the impact that disease emergence may have on the conservation of the amphibians of the island.     

Causal relationships between frequency bands of extracellular signals in visual cortex revealed by an information theoretic analysis

Characterizing how different cortical rhythms interact and how their interaction changes with sensory stimulation is important to gather insights into how these rhythms are generated and what sensory function they may play. Concepts from information theory, such as Transfer Entropy (TE), offer principled ways to quantify the amount of causation between different frequency bands of the signal recorded from extracellular electrodes; yet these techniques are hard to apply to real data. To address the above issues, in this study we develop a method to compute fast and reliably the amount of TE from experimental time series of extracellular potentials. The method consisted in adapting efficiently the calculation of TE to analog signals and in providing appropriate sampling bias corrections. We then used this method to quantify the strength and significance of causal interaction between frequency bands of field potentials and spikes recorded from primary visual cortex of anaesthetized macaques, both during spontaneous activity and during binocular presentation of naturalistic color movies. Causal interactions between different frequency bands were prominent when considering the signals at a fine (ms) temporal resolution, and happened with a very short (ms-scale) delay. The interactions were much less prominent and significant at coarser temporal resolutions. At high temporal resolution, we found strong bidirectional causal interactions between gamma-band (40–100 Hz) and slower field potentials when considering signals recorded within a distance of 2 mm. The interactions involving gamma bands signals were stronger during movie presentation than in absence of stimuli, suggesting a strong role of the gamma cycle in processing naturalistic stimuli. Moreover, the phase of gamma oscillations was playing a stronger role than their amplitude in increasing causations with slower field potentials and spikes during stimulation. The dominant direction of causality was mainly found in the direction from MUA or gamma frequency band signals to lower frequency signals, suggesting that hierarchical correlations between lower and higher frequency cortical rhythms are originated by the faster rhythms.     

Observations on population structure and reproductive features of <Emphasis Type="Italic">Laetmonice producta</Emphasis> Grube (Polychaeta,Aphroditidae) in Antarctic waters

The large scale-worm Laetmonice producta Grube 1877 is the most abundant aphroditid polychaete in Antarctic coastal waters. We investigated the demographic structure and some reproductive features of different L. producta populations from high-Antarctic (Weddell Sea) and Antarctic Peninsula (King George Island) shelf bottoms, collected in summer 1996 (ANT-XIII/3, EASIZ I cruise) and autumn 2000 (ANT-XVII/3, EASIZ III cruise). L. producta in the studied geographic areas showed a wide bathymetric range (200-850 m depth), and a different size distribution pattern with depth, characterised by a reduction of large specimens in the deepest stations. The species is gonochoric, with females more abundant in specimens of larger sizes. Eggs at different stages of maturation (ranging from 40 to 320 wm in diameter) were examined in 270 individuals from different stations and size classes. Egg size showed a slightly bimodal trend, with largely overlapping egg cohorts, suggesting a continuous reproduction, and a long-lasting gametogenesis. Significant differences (Kolmogorov-Smirnov test, P<0.05) in egg-size frequency distribution were detected only when data of the two geographic areas were compared (Weddell Sea vs King George Island), and not according to stations within each area, and females' size. The two sets of geographic samples were collected in different seasons and therefore it was not possible to assess if differences observed are due to sampling time or to geographic factors. Mature spermatozoa were recognisable only in autumn male specimens from King George Island, and showed a rounded nucleus and a short conical acrosome. Occurrence of an endosymbiont polychaete, Veneriserva pygoclava meridionalis (new sub-species of Dorvilleidae), was recorded in the coelomic cavity of 163 specimens of L. producta, 125 of which were from the deepest station of the Weddell Sea (stn. 14, 850 m depth). L. producta females with and without the endosymbiont did not show differences in egg-size distribution. The reproductive features of L. producta, together with its large size and slow growth, seem typical of a long-living predator species, and uncoupled from the typical summer environmental conditions and the pulsating system of coastal Antarctic waters.