De Novo Generation of Infectious Prions In Vitro Produces a New Disease Phenotype

Prions are the proteinaceous infectious agents responsible for Transmissible Spongiform Encephalopathies. Compelling evidence supports the hypothesis that prions are composed exclusively of a misfolded version of the prion protein (PrP^Sc) that replicates in the body in the absence of nucleic acids by inducing the misfolding of the cellular prion protein (PrP^C). The most common form of human prion disease is sporadic, which appears to have its origin in a low frequency event of spontaneous misfolding to generate the first PrP^Sc particle that then propagates as in the infectious form of the disease. The main goal of this study was to mimic an early event in the etiology of sporadic disease by attempting de novo generation of infectious PrP^Sc in vitro. For this purpose we analyzed in detail the possibility of spontaneous generation of PrP^Sc by the protein misfolding cyclic amplification (PMCA) procedure. Under standard PMCA conditions, and taking precautions to avoid cross-contamination, de novo generation of PrP^Sc was never observed, supporting the use of the technology for diagnostic applications. However, we report that PMCA can be modified to generate PrP^Sc in the absence of pre-existing PrP^Sc in different animal species at a low and variable rate. De novo generated PrP^Sc was infectious when inoculated into wild type hamsters, producing a new disease phenotype with unique clinical, neuropathological and biochemical features. Our results represent additional evidence in support of the prion hypothesis and provide a simple model to study the mechanism of sporadic prion disease. The findings also suggest that prion diversity is not restricted to those currently known, and that likely new forms of infectious protein foldings may be produced, resulting in novel disease phenotypes.     

Vegetation fluctuation in mediterranean dune ponds in relation to rainfall variation and water extraction

Abstract. The structure of dune ponds hygrophytic vegetation has a spatial organisation in belts around the pond basin, closely related to water level and flooding regime. Doñana National Park has an important representation of temporal dune ponds, which are subjected to rainfall fluctuations and may be suffering the impact of water extraction from the neighbouring tourist resort. Permanent transects in a vegetation complex of five dune ponds have been monitored during a eight year period (1990-1997). This period was characterised by a number of dry years (annual rainfall around 300 mm), located between two wet cycles (800-900 mm). Transects were analysed in 1990 (wet period), 1994 (dry) and 1997 (wet) by hierarchical agglomera-tive clustering. During the dry period hygrophytic species showed regression, with a high mortality of some species like Ulex minor, while the xerophytic species advanced to lower areas. Seedlings of some xerophytic species colonised the dry surface of the pond basin. The lowering of the water table varied in the different ponds, ranging from 312 to 190 cm depending on topography and the distance to the pumping area. The new period of flooding during 1995-96 and 1996-97 cycles provided the opportunity for hygrophytic spe cies to re-establish themselves in their original places. This study suggest that changes in vegetation are caused by the interaction between weather conditions and human disturbance (water extractions). In our example man-made disturbance is more marked during the dry periods while wet periods tend to obscure the effects of water extractions. From a management perspective, long-term monitoring of water table and vegetation structure is revealed as a key procedure to the management of land-water ecotones on pressured areas and threatened habitats.     

Combining molecular dynamics and docking simulations of the cytidine deaminase from Mycobacterium tuberculosis H37Rv

Cytidine Deaminase (CD) is an evolutionarily conserved enzyme that participates in the pyrimidine salvage pathway recycling cytidine and deoxycytidine into uridine and deoxyuridine, respectively. Here, our goal is to apply computational techniques in the pursuit of potential inhibitors of Mycobacterium tuberculosis CD (MtCDA) enzyme activity. Molecular docking simulation was applied to find the possible hit compounds. Molecular dynamics simulations were also carried out to investigate the physically relevant motions involved in the protein-ligand recognition process, aiming at providing estimates for free energy of binding. The proposed approach was capable of identifying a potential inhibitor, which was experimentally confirmed by IC₅₀ evaluation. Our findings open up the possibility to extend this protocol to different databases in order to find new potential inhibitors for promising targets based on a rational drug design process.     

Vegetative innervation of the esophagus. II. Intraganglionic laminar endings.

The intraganglionic laminar endings in the esophagus of the cat and the rhesus monkey show absolute equivalence between the results in both species from the morphological standpoint. The different types of apparatus found are described, with their location in the esophagus and their percentage distribution in relation to the different portions of its wall. The osmium tetroxide-zinc iodide technique gives pictures equivalent to those using silver impregnations, with the added advantage that the former brings out the morphological details more clearly, to the point of showing up the peculiar characteristics of the edges with their thorn-like protrusions. The complete independence of these structures within the ganglion is confirmed, and evidence is provided for rejecting the possibility that they might be dendritic prolongations of the neuronal elements composing the intramural ganglia. A possible afferent function is proposed, which, however, must be considered an open question, pending the results of further experimental investigation.     

Synergistic effects of kinship, sex and rank in the behavioural interactions of captive stump-tailed macaques

In almost all non-human primate species kinship, sex and rank bias the patterning of interactions among subjects, seemingly in a way that favours the individual's fitness. A number of studies have been done in order to study separately the effects of these variables, concluding that an adequate model of interactions cannot be developed assuming preponderance of a single variable. The 'willingness' of one animal to interact with another can be explained as the result of assessing the possible outcomes (proximate and/or ultimate) of the interaction. The interrelationship of variables such as kinship, sex and rank, among others, provides the actors with a basis for deciding their rates of social interactions. The following study was done to assess whether kinship, rank and sex exerted independent, additive effects in the within-group distributions of eight social behaviour categories of captive groups of stump-tailed macaques. We found that the three variables synergistically affected the patterning of all behavioural categories. This suggests that the pay-offs of social interactions do not vary linearly, being intrinsically correlated with the actors' attributes so that uncertainty in the choice of a potential partner is minimized.