Showing papers by "National University of Cuyo published in 2007"

Induction of autophagy promotes fusion of multivesicular bodies with autophagic vacuoles in k562 cells.

Abstract: Morphological and biochemical studies have shown that autophagosomes fuse with endosomes forming the so-called amphisomes, a prelysosomal hybrid organelle. In the present report, we have analyzed this process in K562 cells, an erythroleukemic cell line that generates multivesicular bodies (MVBs) and releases the internal vesicles known as exosomes into the extracellular medium. We have previously shown that in K562 cells, Rab11 decorates MVBs. Therefore, to study at the molecular level the interaction of MVBs with the autophagic pathway, we have examined by confocal microscopy the fate of MVBs in cells overexpressing green fluorescent protein (GFP)–Rab11 and the autophagosomal protein red fluorescent protein–light chain 3 (LC3). Autophagy inducers such as starvation or rapamycin caused an enlargement of the vacuoles decorated with GFP–Rab11 and a remarkable colocalization with LC3. This convergence was abrogated by a Rab11 dominant negative mutant, indicating that a functional Rab11 is involved in the interaction between MVBs and the autophagic pathway. Interestingly, we presented evidence that autophagy induction caused calcium accumulation in autophagic compartments. Furthermore, the convergence between the endosomal and the autophagic pathways was attenuated by the Ca2+ chelator acetoxymethyl ester (AM) of the calcium chelator 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (BAPTA), indicating that fusion of MVBs with the autophagosome compartment is a calcium-dependent event. In addition, autophagy induction or overexpression of LC3 inhibited exosome release, suggesting that under conditions that stimulates autophagy, MVBs are directed to the autophagic pathway with consequent inhibition in exosome release.

The autophagic pathway is actively modulated by phase II Coxiella burnetii to efficiently replicate in the host cell.

Abstract: The etiologic agent of Q fever Coxiella burnetii, is an intracellular obligate parasite that develops large vacuoles with phagolysosomal characteristics, containing multiple replicating bacteria. We have previously shown that Phase II C. burnetii replicative vacuoles generated after 24-48 h post infection are decorated with the autophagic protein LC3. The aim of the present study was to examine, at earlier stages of infection, the distribution and roles of the small GTPases Rab5 and Rab7, markers of early and late endosomes respectively, as well as of the protein LC3 on C. burnetii trafficking. Our results indicate that: (i) Coxiella phagosomes (Cph) acquire the two Rab proteins sequentially during infection; (ii) overexpression of a dominant negative mutant form of Rab5, but not of Rab7, impaired Coxiella entry, whereas both Rab5 and Rab7 dominant negative mutants inhibited vacuole formation; (iii) Cph colocalized with the protein LC3 as early as 5 min after infection; acquisition of this protein appeared to be a bacterially driven process, because it was inhibited by the bacteriostatic antibiotic chloramphenicol and (iv) C. burnetii delayed the arrival of the typical lysosomal protease cathepsin D to the Cph, which delay is further increased by starvation-induced autophagy. Based on our results we propose that C. burnetii transits through the normal endo/phagocytic pathway but actively interacts with autophagosomes at early times after infection. This intersection with the autophagic pathway delays fusion with the lysosomal compartment possibly favouring the intracellular differentiation and survival of the bacteria.

Proposed macro-model for the analysis of infilled frame structures

Abstract: Reinforced concrete frames infilled with masonry panels constitute an important part of the high-risk structures in different regions of high seismicity. In some developing countries, they are still used as main structural system for low to medium rise buildings. Consequently, reliable methods to analyse infilled frames are required in order to reduce the loss of life and property associated with a possible structural failure. The equivalent strut model, proposed in the 1960s, is a simple procedure to represent the effect of the masonry panel. Several improvements of the original model have been proposed, as a result of a better understanding of the behaviour of these structures and the development of computer software. This paper presents a new macro-model for the evaluation of the global response of the structure, which is based on a multi-strut formulation,. The model, implemented as 4-node panel element, accounts separately for the compressive and shear behaviour of masonry using a double truss mechanism and a shear spring in each direction. The principal premises in the development of the model are the rational consideration of the particular characteristics of masonry and the adequate representation of the hysteretic response. Furthermore, the model is able to represent different modes of failure in shear observed for masonry infills. The comparison of analytical results with experimental data showed that the proposed model, with a proper calibration, is able to represent adequately the in-plane response of infilled frames.

Protective role of autophagy against Vibrio cholerae cytolysin, a pore-forming toxin from V. cholerae.

Abstract: Autophagy is the unique, regulated mechanism for the degradation of organelles. This intracellular process acts as a prosurvival pathway during cell starvation or stress and is also involved in cellular response against specific bacterial infections. Vibrio cholerae is a noninvasive intestinal pathogen that has been studied extensively as the causative agent of the human disease cholera. V. cholerae illness is produced primarily through the expression of a potent toxin (cholera toxin) within the human intestine. Besides cholera toxin, this bacterium secretes a hemolytic exotoxin termed V. cholerae cytolysin (VCC) that causes extensive vacuolation in epithelial cells. In this work, we explored the relationship between the vacuolation caused by VCC and the autophagic pathway. Treatment of cells with VCC increased the punctate distribution of LC3, a feature indicative of autophagosome formation. Moreover, VCC-induced vacuoles colocalized with LC3 in several cell lines, including human intestinal Caco-2 cells, indicating the interaction of the large vacuoles with autophagic vesicles. Electron microscopy analysis confirmed that the vacuoles caused by VCC presented hallmarks of autophagosomes. Additionally, biochemical evidence demonstrated the degradative nature of the VCC-generated vacuoles. Interestingly, autophagy inhibition resulted in decreased survival of Caco-2 cells upon VCC intoxication. Also, VCC failed to induce vacuolization in Atg5−/− cells, and the survival response of these cells against the toxin was dramatically impaired. These results demonstrate that autophagy acts as a cellular defense pathway against secreted bacterial toxins.

On the killing of mycobacteria by macrophages.

Abstract: Summary Both pathogenic and non-pathogenic mycobacteria are internalized into macrophage phagosomes. Whereas the non-pathogenic types are invariably killed by all macrophages, the pathogens generally survive and grow. Here, we addressed the survival, production of nitrogen intermediates (RNI) and intracellular trafficking of the non-pathogenic Mycobacterium smegmatis, the pathogen-like, BCG and the pathogenic M. bovis in different mouse, human and bovine macrophages. The bacteriocidal effects of RNI were restricted for all bacterial species to the early stages of infection. EM analysis showed clearly that all the mycobacteria remained within phagosomes even at late times of infection. The fraction of BCG and M. bovis found in mature phagolysosomes rarely exceeded 10% of total, irrespective of whether bacteria were growing, latent or being killed, with little correlation between the extent of phagosome maturation and the degree of killing. Theoretical modelling of our data identified two different potential sets of explanations that are consistent with our results. The model we favour is one in which a small but significant fraction of BCG is killed in an early phagosome, then maturation of a small fraction of phagosomes with both live and killed bacteria, followed by extremely rapid killing and digestion of the bacteria in phago-lysosomes.

A new Cretaceous terrestrial ecosystem from Gondwana with the description of a new sauropod dinosaur

Abstract: A unique site at the northern area of Patagonia (Neuquen, Argentina) reveals a terrestrial ecosystem preserved in a detail never reported before in a Late Cretaceous deposit. An extraordinary diversity and abundance of fossils was found concentrated in a 0.5 m horizon in the same quarry, including a new titanosaur sauropod, Futalognkosaurus dukei n.gen., n.sp, which is the most complete giant dinosaur known so far. Several plant leaves, showing a predominance of angiosperms over gymnosperms that likely constituted the diet of F. dukei were found too. Other dinosaurs (sauropods, theropods, ornithopods), crocodylomorphs, pterosaurs, and fishes were also discovered, allowing a partial reconstruction of this Gondwanan continental ecosystem.

Enhanced at puberty 1 (EAP1) is a new transcriptional regulator of the female neuroendocrine reproductive axis

Abstract: The initiation of mammalian puberty and the maintenance of female reproductive cycles are events controlled by hypothalamic neurons that secrete the decapeptide gonadotropin-releasing hormone (GnRH). GnRH secretion is, in turn, controlled by changes in neuronal and glial inputs to GnRH-producing neurons. The hierarchical control of the process is unknown, but it requires coordinated regulation of these cell-cell interactions. Here we report the functional characterization of a gene (termed enhanced at puberty 1 [EAP1]) that appears to act as an upstream transcriptional regulator of neuronal networks controlling female reproductive function. EAP1 expression increased selectively at puberty in both the nonhuman primate and rodent hypothalamus. EAP1 encoded a nuclear protein expressed in neurons involved in the inhibitory and facilitatory control of reproduction. EAP1 transactivated genes required for reproductive function, such as GNRH1, and repressed inhibitory genes, such as preproenkephalin. It contained a RING finger domain of the C3HC4 subclass required for this dual transcriptional activity. Inhibition of EAP1 expression, targeted to the rodent hypothalamus via lentivirus-mediated delivery of EAP1 siRNAs, delayed puberty, disrupted estrous cyclicity, and resulted in ovarian abnormalities. These results suggest that EAP1 is a transcriptional regulator that, acting within the neuroendocrine brain, contributes to controlling female reproductive function.

Effect of cooking on garlic (Allium sativum L.) antiplatelet activity and thiosulfinates content.

Abstract: The raw form of garlic and some of its preparations are widely recognized as antiplatelet agents that may contribute to the prevention of cardiovascular disease. Herein, we examined the in-vitro antiaggregatory activity (IVAA) of human blood platelets induced by extracts of garlic samples that were previously heated (in the form of crushed versus uncrushed cloves) using different cooking methods and intensities. The concentrations of allicin and pyruvate, two predictors of antiplatelet strength, were also monitored. Oven-heating at 200 degrees C or immersing in boiling water for 3 min or less did not affect the ability of garlic to inhibit platelet aggregation (as compared to raw garlic), whereas heating for 6 min completely suppressed IVAA in uncrushed, but not in previously crushed, samples. The latter samples had reduced, yet significant, antiplatelet activity. Prolonged incubation (more than 10 min) at these temperatures completely suppressed IVAA. Microwaved garlic had no effect on platelet aggregation. However, increasing the concentration of garlic juice in the aggregation reaction had a positive IVAA dose response in crushed, but not in uncrushed, microwaved samples. The addition of raw garlic juice to microwaved uncrushed garlic restored a full complement of antiplatelet activity that was completely lost without the garlic addition. Garlic-induced IVAA was always associated with allicin and pyruvate levels. Our results suggest that (1) allicin and thiosulfinates are responsible for the IVAA response, (2) crushing garlic before moderate cooking can reduce the loss of activity, and (3) the partial loss of antithrombotic effect in crushed-cooked garlic may be compensated by increasing the amount consumed.

Acrosomal exocytosis, a special type of regulated secretion.

Abstract: The acrosome is a single secretory granule present in the head of mammalian--and other animal groups--sperm. Secretion of this granule is an absolute requirement for physiological fertilization. Acrosome exocytosis is a synchronized and tightly regulated all-or-nothing process, with no recycling of membranes. In the last few years, it has been shown that acrosomal exocytosis is mediated by a molecular mechanism that is homologous to that reported in the secretion of neuroendocrinal cells. Moreover, because of its particular characteristics, acrosomal exocytosis is a unique mammalian model for the study of the different steps of the membrane fusion cascade. Combining results in intact and permeabilized sperm, the following sequence of events has been proposed. In resting sperm, SNARE proteins are locked in inactive cis complexes. Sperm activation causes a calcium increase in the cytoplasm that promotes the production of cAMP and activates Rab3A. Afterwards, NSF and alphaSNAP disassemble cis complexes and the free SNAREs are then able to reassemble in loose trans complexes. Membrane fusion is arrested at this stage until calcium is released from inside the acrosome by inositol 1,4,5-trisphosphate-sensitive calcium channels to trigger the final steps of membrane fusion, which require fully assembled trans SNARE complexes and the calcium sensor synaptotagmin. This working model is still incomplete and tentative. Its improvement will be important to share light on this and other processes of regulated exocytosis. Moreover, it will bring new perspectives into the field of sperm-related fertility and sterility.

Exogenous Abscisic Acid Increases Carbohydrate Accumulation and Redistribution to the Grains in Wheat Grown Under Field Conditions of Soil Water Restriction

Abstract: This work investigates the effects of abscisic acid (ABA) on physiologic parameters related to yield in wheat (Triticum aestivum) grown under field conditions with water restriction ranging between 457% and 495% of field capacity during anthesis and postanthesis ABA (300 mg L−1) was sprayed onto the plants at the beginning of shoot lengthening which significantly promoted leaf area and higher concentrations of chlorophylls and carotenoids in flag leaf at anthesis ABA also increased soluble carbohydrates in shoots at anthesis, which were then re-exported to the grains at maturity This correlated with a yield increase that was achieved by a higher number and weight of grains per spike, but protein content was not significantly affected

Characterisation of Lymnaea cubensis, L. viatrix and L. neotropica n. sp., the main vectors of Fasciola hepatica in Latin America, by analysis of their ribosomal and mitochondrial DNA.

Abstract: Although, in the endemic areas throughout the world, human fascioliasis presents varying patterns in its epidemiology, the species of lymnaeid snail that act as intermediate hosts and vectors are always crucial in the transmission of the causative parasites. Species in the Galba/Fossaria group of snails, such as Lymnaea cubensis, L. viatrix var. A ventricosa, L. viatrix var. B elongata and Galba truncatula, appear to be frequently involved in the transmission of Fasciola hepatica in Central and South America, although specific classification within this morphologically and anatomically confusing group is often very difficult. To explore the potential use of molecular analyses in the identification of vector snails, regions of the ribosomal DNA - the small subunit (18S) gene and internal transcribed spacers (ITS-2 and ITS-1) - and of the mitochondrial DNA - the cytochrome c oxidase subunit I (COI) - of wild-caught lymnaeid snails of L. cubensis, L. viatrix var. A ventricosa, L. viatrix var. B elongata and G. truncatula have been sequenced. The samples of the Latin American species included specimens from the respective type localities. The genetic distances observed and the results of phylogenetic analyses demonstrate that two different species exist within L. viatrix. Lymnaea neotropica n. sp. (=L. viatrix var. B elongata) is here proposed for specimens from Lima, Peru, and is differentiated from L. viatrix (=L. viatrix var. A ventricosa), L. cubensis and G. truncatula. The data collected on the 18S ribosomal-RNA gene indicate that the snails investigated may cover more than one supraspecific taxon. The ITS-2, ITS-1 and COI nucleotide sequences are clearly useful markers for the differentiation of these morpho-anatomically similar lymnaeid species. The numerous microsatellite repeats found within ITS-2 are potential tools for differentiation at population level.

Basal cerebral glucose distribution in long-term post-traumatic stress disorder

Abstract: The purpose of this investigation was to study basal cerebral glucose absorption patterns associated to long-term post-traumatic stress disorder. Fluorodeoxyglucose positron emission tomography (FDG-PET) and statistic parametric mapping (SPM) were used to compare regional cerebral glucose absorption between 15 war veterans (Hispanic men, aged 39-41 (M = 39.5, SD = 0.84)) diagnosed with post-traumatic stress disorder (PTSD) based on DSM-IV criteria, and a matching control group of six asymptomatic veterans. This study was conducted 20 years after the traumatic events. PTSD patients presented relatively diminished activity (P<0.005) in: cingulate gyri, precuneus, insula, hippocampus; frontal, pre-frontal and post-central regions; lingual, calcarine, occipital medial and superior gyri, and verbal and paraverbal areas. Relativeley augmented activity (P<0.005) was observed in PTSD patients in: fusiform, temporal superior, medial, and inferior gyri; occipital medial, inferior and lingual gyri; precuneus, and cerebellum. The amygdala and the thalamus showed normal metabolic activity. Various brain regions that showed diminished activity (limbic, frontal and prefrontal cortex, multimodal parieto-occipital areas and verbal and paraverbal areas) have evolved lately, and sub-serve highly complex cognitive and behavioural functions. Metabolic activity patterns are comparable to those observed in personality disorders of the borderline type.

Cytotoxicity is predicted by unbound and not total bilirubin concentration.

Abstract: Although it has been suggested that the unbound, free, (Bf) rather than total (BT) bilirubin level correlates with cell toxicity, direct experimental evidence supporting this conclusion is limited. In addition, previous studies never included a direct measurement of Bf, using newer, accurate methods. To test “the free bilirubin hypothesis”, in vitro cytotoxicity was assessed in four cell lines exposed to different Bf concentrations obtained by varying BT/Albumin ratio, using serum albumins with different binding affinities, and/or displacing unconjugated bilirubin (UCB) from albumin with a sulphonamide. Bf was assessed by the modified, minimally diluted peroxidase method. Cytotoxicity varied among cell lines but was invariably related to Bf and not BT. Light exposure decreased toxicity parallel to a decrease in Bf. In the absence of albumin, no cytotoxicity was found at a Bf of 150 nM whereas in the presence of albumin a similar Bf resulted in a 40% reduction of viability indicating the importance of total cellular uptake of UCB in eliciting toxic effect. In the presence of albumin-bound UCB, bilirubin-induced cytotoxicity in a given cell line is accurately predicted by Bf irrespective of the source and concentration of albumin, or total bilirubin level.

Biochemical-molecular markers in unilateral ureteral obstruction.

Abstract: Congenital obstructive nephropathy is the primary cause of end-stage renal disease in children. Rapid diagnosis and initiation of the treatment are vital to preserve function and/or to slow down renal injury. Obstructive uropathy effects -decline in the plasmatic renal flow and glomerular filtration rate, interstitial infiltrate of leukocytes, significant decrease of the urine concentration, loss of the capacity to concentrate urine as well as fibrosis and apoptosis- are a consequence of a variety of factors that work in complex ways and are still not fully understood. Mediators as angiotensin II, transforming growth factor-beta (TGF-beta) and nitric oxide (NO) have been implicated in congenital obstructive nephropathy. The renin-angiotensin system is regulated in different ways, affecting both renal structure and function, and that it in turn depends upon the duration of the obstruction. On the other hand, the role of nitric oxide in renal injury remains somewhat controversial due to the fact that it can exert opposite effects such as cytoprotective and prooxidant / proapoptotic efects as well as proinflammatory and anti-inflammatory effects. In addition, reactive oxidative species (ROS) might contribute to the progression of renal disease. During unilateral ureteral obstruction induced uncoordinated and aberrant growth may lead to the loss of cellular phenotype and apoptosis. Promoting inflammatory responses, the oxidizers can regulate the adherence of certain molecules and proinflammatory mediators, transcription factors and fibrogenic cytokines, that are clearly involved in the progression of renal disease. The congenital obstructive nephropathy is characterized by tubular atrophy, cellular proliferation, apoptosis and fibrosis; immature kidney is more susceptible than adult kidney to showing the above mentioned alterations. Apoptosis seems to be the principal mechanism that leads to tubular atrophy during the neonatal unilateral ureteral obstruction (UUO). Considering the significant role of the apoptosis in UUO, we believe of big interest the study of the regulatory factors of apoptosis in the renal obstruction neonatal. The complex biochemical and molecular events during the development, maintenance and progression of the renal injury in unilateral ureteral obstruction require further major studies to better understand the alterations mentioned above.

Autophagy: a pathogen driven process

Abstract: Host cell recognition and eradication of invading pathogens is crucial for the control of microbial infections. However, several microorganisms develop tactics that allow them to survive intracellularly. Autophagy, a process involved in protein turnover and in charge of the removal of aged organelles by degradation of engulfed cytoplasmic portions, was recently shown to play a clear role in the detection and elimination of intracellular pathogens. Yet, some pathogens employ elegant strategies to elude entrapment in autophagosomes, and thus to avoid lysosomal degradation, whereas others utilize the autophagy pathway for their own benefit. In this review some recent findings on the relationship between microorganisms and autophagy are summarized, the underlying assumption being that intracellular infection models may contribute to the understanding of the molecular mechanisms involved in the autophagic process.

Magnetism of manganite nanotubes constituted by assembled nanoparticles

Abstract: We present a study on the magnetic properties of manganite ultrafine grains assembled in nanotubes of $800\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ of external diameter and $6--8\phantom{\rule{0.3em}{0ex}}\ensuremath{\mu}\mathrm{m}$ length. The study includes two homogeneous ferromagnetic compounds, ${\mathrm{La}}_{0.67}{\mathrm{Ca}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$ and ${\mathrm{La}}_{0.67}{\mathrm{Sr}}_{0.33}\mathrm{Mn}{\mathrm{O}}_{3}$, and one exhibiting ferromagnetic and charge-ordered phase coexistence, ${\mathrm{La}}_{0.325}{\mathrm{Pr}}_{0.300}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$. From magnetic measurements, we conclude that the grains behave as single magnetic domains. Observations of dipolar interactions between magnetic grains are evidenced by isothermal remanent magnetization and direct current demagnetization experiments. These experiments suggest that the grain magnetic moments should be arranged in a fanning configuration at $H=0$. Also, a uniaxial shape anisotropy was observed on previously aligned ferromagnetic nanotubes by ferromagnetic-resonance experiences. In ${\mathrm{La}}_{0.325}{\mathrm{Pr}}_{0.300}{\mathrm{Ca}}_{0.375}\mathrm{Mn}{\mathrm{O}}_{3}$, we observe distinctive features related to its inhomogeneous character as compared with the ferromagnetic homogeneous nanotubes.

Effects of chronic exposure to cadmium on prostate lipids and morphology.

Abstract: Cadmium is an environmental toxic metal implicated in human prostate carcinogenesis. The mechanism of its toxicity is not fully understood. Previously, we showed that cadmium exposure induces oxidative stress, especially lipid peroxidation. This study evaluates the effect of chronic exposure to 0.886 mM of cadmium (Cd) per liter in the drinking water on prostate lipid content and metabolism in Wistar rats. We determined the lipid profile and measured the expression of lipogenic enzymes: FAS, GPAT, LPL, DGAT-1, DGAT-2, ACO, CPT-1 and CT, and of certain factors involved in lipid regulation and fatty acid transporters: FAT/CD36, E-FABP, SREBP-2, PPAR-gamma and PPAR-alpha by RT-PCR. Ultrastructure was analyzed by electron microscopy and, as prostate is an androgen controlled gland, AR expression was measured by RT-PCR and Western blot. Cd altered the prostatic lipid profile. Triglycerides (TG) and esterified cholesterol (EC) decreased, free cholesterol (FC) and phospholipids (PL) increased and total cholesterol (TC) did not change. FAS, MDH and IDH activities did not vary but G6PDH decreased significantly in Cd group. Regarding TG synthesis, DGAT-1 decreased while GPAT increased and FAS, LPL and DGAT-2 remained unchanged. Regarding beta oxidation, CPT-1 increased while ACO expression decreased in Cd group. In the PL pathway, CT expression was increased. All these results would justify the decrease of TG in Cd group when compared to control. In the cholesterol metabolic pathway, HMGCoAR and SREBP-2 increased. PPAR-alpha increased but PPAR-gamma did not change. Regarding fatty acid transporters, FAT/CD36 decreased, while E-FABP increased. AR mRNA and protein expression decreased. Ultrastructural analysis showed a decrease in lipid droplets and signs of cellular damage in the Cd group. Cadmium exposure induces important changes in prostatic lipid profile and metabolism, confirmed by the morphology analyses, which also showed signs of cellular damage. These results could be important to further understanding the complex mechanism of cadmium toxicity in prostate and in the development of better treatments for people and animals exposed to the heavy metal.

Apoptosis and blood–testis barrier during the first spermatogenic wave in the pubertal rat

Abstract: This research explores the initial assembly of the blood-testis barrier (BTB) during puberty, when a massive physiological apoptosis in the first spermatogenic wave takes place. Fragments of testis from 14- to 20-day-old rats were studied by conventional transmission electron microscopic techniques. Lanthanum hydroxide was used as an intercellular tracer. Light microscopy was used to confirm apoptotic death when paraffin-embedded sections were studied by TUNEL analysis. When the seminiferous cords reached the zygotene-pachytene spermatocyte level, they exhibited abundant apoptotic figures, whereas the remaining segments showed sporadic apoptosis. We found a BTB not yet assembled in the cords with zygotene-pachytene spermatocytes and abundant apoptosis. The observed apoptosis frequency diminished drastically when BTB was organized, as confirmed by the use of the tracer. Our conclusion is that the massive apoptosis found in the zygotene-pachytene spermatocytes between days 14 and 20 coincides with an open BTB. The absence of BTB could be one of the factors causing massive apoptosis of zygotene-pachytene spermatocytes, at least within the time span analyzed. The zygotene-pachytene spermatocytes are left exposed in an open environment instead of being isolated in the adluminal compartment to which they are destined.

The neuronal Arf GAP centaurin α1 modulates dendritic differentiation

Abstract: Centaurin α1 is an Arf GTPase-activating protein (GAP) that is highly expressed in the nervous system. In the current study, we show that endogenous centaurin α1 protein is localized in the synaptosome fraction, with peak expression in early postnatal development. In cultured dissociated hippocampal neurons, centaurin α1 localizes to dendrites, dendritic spines and the postsynaptic region. siRNA-mediated knockdown of centaurin α1 levels or overexpression of a GAP-inactive mutant of centaurin α1 leads to inhibition of dendritic branching, dendritic filopodia and spine-like protrusions in dissociated hippocampal neurons. Overexpression of wild-type centaurin α1 in cultured hippocampal neurons in early development enhances dendritic branching, and increases dendritic filopodia and lamellipodia. Both filopodia and lamellipodia have been implicated in dendritic branching and spine formation. Following synaptogenesis in cultured neurons, wild-type centaurin α1 expression increases dendritic filopodia and spine-like protrusions. Expression of a GAP-inactive mutant diminishes spine density in CA1 pyramidal neurons within cultured organotypic hippocampal slice cultures. These data support the conclusion that centaurin α1 functions through GAP-dependent Arf regulation of dendritic branching and spines that underlie normal dendritic differentiation and development.

Molecular mechanisms of membrane fusion during acrosomal exocytosis.

Abstract: Sperm are attractive cells. Understanding their physiology has motivated researchers from all over the globe for decades. Initially came the description of sperm's overall shape and properties, together with their genesis and development in the testis. Later, the study of exocytosis took off owing to ultrastructural analysis that achieved exquisite levels of detail. Biochemical analysis ensued, identifying ligands and signalling pathways whose end point was exocytosis. Somehow, the unveiling of the molecular mechanisms involved in membrane fusion itself lagged behind all this progress. The picture changed dramatically in the last few years, due to an explosion in our knowledge of the many proteins required for exocytosis and its regulation, and the discovery that very similar versions of these proteins play the same roles in virtually all membrane fusion models. Luckily, sperm are not the exception to this rule. For instance, fusion of the outer acrosomal to the plasma membrane depends on Rab3 activation, alpha-SNAP/NSF, synaptotagmin, and SNAREs; it also requires an efflux of calcium from the acrosomal lumen. Convergence of Rab- and toxin-sensitive SNARE-dependent pathways is a hallmark of the acrosome reaction that makes it an attractive mammalian model to study the different phases of the membrane fusion cascade. Finally, because nature has endowed sperm with a cellular specialization that gives them a single, irreversible chance to fertilise an egg, the acrosome reaction is more straightforward to dissect than fusion in other cell types, where the same substances are secreted again and again, requiring the membranes and fusion machinery to recycle multiple times.

Linking small desert mammal distribution to habitat structure in a protected and grazed landscape of the Monte, Argentina

Abstract: Interpretation of landscape patterns from the perspective of different species allows knowing the way in which they perceive landscape, and how their perception varies with scale. We examined distribution of four small mammal species at different scales over a landscape including protected and grazed areas, and associated species distribution with landscape structure. The study was conducted in the central Monte Desert (Reserve of Nacunan). Trap grids were set in both areas at two scales, varying their grain and extent. To determine whether spatial patterns are random, clumped or regular, we used a point pattern analysis. Logistic regressions were performed to relate the presence-absence of small mammals to environmental variables. Intensity of the point pattern was not constant, either in the Reserve or the grazed area. Small mammal abundance exhibited a heterogeneous distribution, and the existence of a first-order effect was detected for all species. No second-order effects were detected, the point pattern was random for all species in both areas. Both areas were differently perceived by rodent species. Habitat structure in both conditions and its variations with scale appear to be important factors affecting distribution patterns.

Stability of Jahn Teller distortion in LaMnO3 under pressure: An x-ray absorption study

Abstract: The local environment of manganese atoms in $\mathrm{La}\mathrm{Mn}{\mathrm{O}}_{3}$ under pressure up to $15.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ has been studied by x-ray absorption spectroscopy. For pressures below $8\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, no change is detected within the $\mathrm{Mn}{\mathrm{O}}_{6}$ octahedra. Above this pressure a continuous reduction of the long Mn-O distance takes place, however, the octahedral distortion persists over the whole pressure range. At $15.3\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$ the average Jahn-Teller splitting of the distances is reduced by about one-third, indicating that a total removal of the local Jahn-Teller distortion would occur only for pressures around $30\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$, where metallization is reported to take place. A hysteresis in the long distance reduction is observed down to ambient pressure, suggesting the coexistence of $\mathrm{Mn}{\mathrm{O}}_{6}$ distorted and undistorted units.

Notas sobre el clientelismo político en la Ciudad de México

Abstract: Este ensayo aborda el intercambio de favores por votos entre los pobres del sector urbano y los partidos politicos en la ciudad de Mexico. Basado en un trabajo etnografico realizado en una colonia popular, se estudian las condiciones sociales de las practicas clientelares y las interpretaciones elaboradas por los propios “clientes” y “mediadores” a fin de clarificar las relaciones de poder, la distribucion de recursos, el papel del lider y las alternativas de accion de los habitantes pobres del sector urbano. Se analizan los cambios operados en las practicas clientelares a partir del aumento de la competencia electoral, las alianzas y compromisos resultantes, la relacion entre necesidades, politica y legitimidad, y las posibilidades de autonomia de los colonos

Magnetic behavior of superconductor/ferromagnet superlattices

Abstract: A study of the electromagnetic response of superconductor/ferromagnet $\mathrm{Nb}∕\mathrm{Co}$ superlattices is presented. The dc magnetization is measured as a function of Co layer thickness, applied field ${H}_{a}$, and temperature. For very thin Co layers, no ferromagnetism is detected and the observed response is essentially that of a collection of uncoupled Nb layers. When the Co layer is thick enough for ferromagnetism to be established, prior to the field-cooled magnetization measurements, the Co layers are magnetically saturated in the parallel or antiparallel directions to ${H}_{a}$. In this case, the magnetic response of the otherwise uncoupled Nb layers is found to depend on both ${H}_{a}$ and the stray fields.

Allopregnanolone modulates striatal dopamingergic activity of rats under different gonadal hormones conditions.

Abstract: Objectives: Progesterone modulates dopamine (DA) release in corpus striatum. Our objective was to evaluate the effect of the i.c.v injection of the neurosteroid allopregnanolone (ALL), a progesterone metabolite on dopaminergic activity in the corpus striatum of rats under different gonadal hormonal conditions. Methods: We have measured the concentrations of DOPA, DA and DOPAC (main metabolite of DA) in the corpus striatum in estrus and diestrus rats and in ovariectomized rats without hormonal replacement (OVX group) and primed with estrogen and progesterone (OVXi group). Additionally, we have used the aromatic acid decarboxylase inhibitor NSD in order to evaluate the function of tyrosine hydroxylase (TH), the rate-limiting enzyme of dopamine synthesis. Results: ALL significantly decreased the striatal concentrations of both DA and DOPAC in the estrus. On the other hand, ALL increased significantly the levels of DA in the OVXi group. The DOPA accumulation in OVXi after NSD treatment in the ALL-tre...