Structural characterization of microcin E492 amyloid formation: Identification of the precursors

Microcin E492 is a low-molecular weight, channel-forming bacteriotoxin that generates amyloid structures. Using electron microscopy and image processing techniques several structural conformations can be observed. Prior to the conditions that induce amyloid formation and at its initial stage, microcin E492 molecules can be found in two main types of oligomers: a pentameric, pore-like structure consisting of globular monomers of ～25? diameter, and long filaments made up of stacked pentamers. The equilibrium between these structures depends on the properties of the solvent, because samples kept in methanol mainly show the pentameric structure. Amyloid induction in aqueous solvent reveals the presence, together with the above mentioned structures, of several amyloid structures such as flat and helical filaments. In addition, X-ray diffraction analysis demonstrated that the fibrils formed by microcin E492 presented cross-β structure, a distinctive property of amyloid fibrils. Based on the study of the observed structures we propose that microcin E492 has two conformations: a native one that assembles mainly into a pentameric structure, which functions as a pore, and an amyloid conformation which results in the formation of different types of amyloid filaments.     

Ensayo de formación y cuantificación de biopelículas mixtas de Candida albicans y Staphylococcus aureus

This study quantifies the production of single and mixed biofilms of Candida albicans and Staphylococcus aureus to determine if such mixed biofilms have synergistic effects. Assays were performed using polystyrene microtitre plates of 96 wells, metabolic activity was measured by the enzymatic reduction of a tetrazolium salt (XTT) and colorimetric changes were measured at 490 nm. Confocal scanning laser microscopy was used to visualise the biofilms of each microorganism and its growth kinetics. The highest levels of biofilm formation were observed in mixed biofilms, followed by those of Candida albicans only, with the lowest levels of biofilm formation being detected for Staphylococcus aureus; all together these results suggest a synergistic relationship between the tested microorganisms.     

The importance of defining the geographic distribution of species for conservation: The case of the Bearded Wood-Partridge

Delimitation of the distribution areas of species has fundamental implications for the understanding of biodiversity and for decision-making in conservation. This is illustrated by the case of the Bearded Wood-Partridge (Dendrortyx barbatus), which is endemic to Mexico and was classified as threatened by the IUCN. Recently the discovery of this species in new locations caused an increase in the known distribution area whereupon it was reclassified in a lower risk category. In our study, delimitation and comparison of the Bearded Wood-Partridge distribution area is carried out utilising five different methods: minimum convex polygon; areographic; cartographic; ecological niche modeling; and, “free hand”. A number of locality records are also used to demonstrate the chronological order of appearance. The results show that the size and shape of the distribution area of this species vary depending on the number of records and on their spatial and environmental location, as well as on the particular delimitation method used. However, ecological niche modeling provides the best results in terms of spatial and numerical sensitivity as well as lower values of omission and a moderate extent of predicted areas. We suggest that decisions related to species conservation (categories of risk, areas of endemism, etc.), particularly those species of high geographical restriction, should be contingent on the formalised delimitation of distribution areas based on ecological niche modeling methods.     

Inhibition of Wnt and PI3K Signaling Modulates GSK-3β Activity and Induces Morphological Changes in Cortical Neurons: Role of Tau Phosphorylation

Glycogen synthase kinase GSK-3β has been identified as one of the major candidates mediating tau hyperphosphorylation at the same sites as those present in tau protein in brain from Alzheimer′s disease (AD) patients. However, the signal transduction pathways involved in the abnormal activation of GSK-3β, have not been completely elucidated. GSK-3β activity is repressed by the canonical Wnt signaling pathway, but it is also modulated through the PI3K/Akt route. Recent studies have suggested that Wnt signaling might be involved in the pathophysiology of AD. On the other hand, modulators of the PI3K pathway might be reduced during aging leading to a sustained activation of GSK-3β, which in turn would increase the risk of tau hyperphosphorylation. The role of Wnt and PI3K signaling inhibition on the extent of tau phosphorylation and neuronal morphology has not been completely elucidated. Thus, in the present investigation we analyzed the effects of different negative modulators of the Wnt and the PI3K pathways on GSK-3β activation and phosphorylation of tau at the PHF-1 epitope in cortical cultured neurons and hippocampal slices from adult rat brain. Changes in the microtubule network were also studied. We found that a variety of Wnt and PI3K inhibitors, significantly increased tau phosphorylation at the PHF-1 site, induced the disarrangement of the microtubule network and the accumulation of tau within cell bodies. These changes correlated with alterations in neuronal morphology. Special issue article in honor of Dr. Ricardo Tapia.     

Climatic patterns in the establishment of wintering areas by North American migratory birds

Long‐distance migration in birds is relatively well studied in nature; however, one aspect of this phenomenon that remains poorly understood is the pattern of distribution presented by species during arrival to and establishment of wintering areas. Some studies suggest that the selection of areas in winter is somehow determined by climate, given its influence on both the distribution of bird species and their resources. We analyzed whether different migrant passerine species of North America present climatic preferences during arrival to and departure from their wintering areas. We used ecological niche modeling to generate monthly potential climatic distributions for 13 migratory bird species during the winter season by combining the locations recorded per month with four environmental layers. We calculated monthly coefficients of climate variation and then compared two GLM (generalized linear models), evaluated with the AIC (Akaike information criterion), to describe how these coefficients varied over the course of the season, as a measure of the patterns of establishment in the wintering areas. For 11 species, the sites show nonlinear patterns of variation in climatic preferences, with low coefficients of variation at the beginning and end of the season and higher values found in the intermediate months. The remaining two species analyzed showed a different climatic pattern of selective establishment of wintering areas, probably due to taxonomic discrepancy, which would affect their modeled winter distribution. Patterns of establishment of wintering areas in the species showed a climatic preference at the macroscale, suggesting that individuals of several species actively select wintering areas that meet specific climatic conditions. This probably gives them an advantage over the winter and during the return to breeding areas. As these areas become full of migrants, alternative suboptimal sites are occupied. Nonrandom winter area selection may also have consequences for the conservation of migratory bird species, particularly under a scenario of climate change.     

Reconstructing the Mexican Tropical Dry Forests via an Autoecological Niche Approach: Reconsidering the Ecosystem Boundaries

We used Ecological Niche Modeling (ENM) of individual species of two taxonomic groups (plants and birds) in order to reconstruct the climatic distribution of Tropical Dry Forests (TDFs) in Mexico and to analyze their boundaries with other terrestrial ecosystems. The reconstruction for TDFs’ distribution was analyzed considering the prediction and omission errors based upon the combination of species, obtained from the overlap of individual models (only plants, only birds, and all species combined). Two verifications were used: a primary vegetation map and 100 independent TDFs localities. We performed a Principal Component (PCA) and Discriminant Analysis (DA) to evaluate the variation in the environmental variables and ecological overlap among ecosystems. The modeling strategies showed differences in the ecological patterns and prediction areas, where the “all species combined” model (with a threshold of ≥10 species) was the best strategy to use in the TDFs reconstruction. We observed a concordance of 78% with the primary vegetation map and a prediction of 98% of independent locality records. Although PCA and DA tests explained 75.78% and 97.9% of variance observed, respectively, we observed an important overlap among the TDFs with other adjacent ecosystems, confirming the existence of transition zones among them. We successfully modeled the distribution of Mexican TDFs using a number of bioclimatic variables and co-distributed species. This autoecological niche approach suggests the necessity of rethinking the delimitations of ecosystems based on the recognition of transition zones among them in order to understand the real nature of communities and association patterns of species.     

High-Throughput 3-D Monitoring of Agricultural-Tree Plantations with Unmanned Aerial Vehicle (UAV) Technology

The geometric features of agricultural trees such as canopy area, tree height and crown volume provide useful information about plantation status and crop production. However, these variables are mostly estimated after a time-consuming and hard field work and applying equations that treat the trees as geometric solids, which produce inconsistent results. As an alternative, this work presents an innovative procedure for computing the 3-dimensional geometric features of individual trees and tree-rows by applying two consecutive phases: 1) generation of Digital Surface Models with Unmanned Aerial Vehicle (UAV) technology and 2) use of object-based image analysis techniques. Our UAV-based procedure produced successful results both in single-tree and in tree-row plantations, reporting up to 97% accuracy on area quantification and minimal deviations compared to in-field estimations of tree heights and crown volumes. The maps generated could be used to understand the linkages between tree grown and field-related factors or to optimize crop management operations in the context of precision agriculture with relevant agro-environmental implications.     

Epigenetic and Conventional Regulation Is Distributed among Activators of FLO11 Allowing Tuning of Population-Level Heterogeneity in Its Expression

Epigenetic switches encode their state information either locally, often via covalent modification of DNA or histones, or globally, usually in the level of a trans-regulatory factor. Here we examine how the regulation of cis-encoded epigenetic switches controls the extent of heterogeneity in gene expression, which is ultimately tied to phenotypic diversity in a population. We show that two copies of the FLO11 locus in Saccharomyces cerevisiae switch between a silenced and competent promoter state in a random and independent fashion, implying that the molecular event leading to the transition occurs locally at the promoter, in cis. We further quantify the effect of trans regulators both on the slow epigenetic transitions between a silenced and competent promoter state and on the fast promoter transitions associated with conventional regulation of FLO11. We find different classes of regulators affect epigenetic, conventional, or both forms of regulation. Distributing kinetic control of epigenetic silencing and conventional gene activation offers cells flexibility in shaping the distribution of gene expression and phenotype within a population.     

Protein changes in the shoot-tips of vanilla (<Emphasis Type="Italic">Vanilla planifolia</Emphasis>) in response to osmoprotective treatments

Cryogenic storage of vanilla shoot-tips represents the safest biotechnological strategy for the long-term conservation of the vanilla germplasm, but successful cryopreservation depends on its tolerance to both dehydration stress imposed by cryoprotective treatments and thermal stress produced by immersion in liquid nitrogen. In this work, we evaluated the impact of various osmoprotective treatments on protein expression patterns in vanilla (Vanilla planifolia) shoot-tips subjected to successive dehydration steps prior to cryopreservation. Two-dimensional electrophoretic protein profiles of shoot-tips dissected from in vitro grown plants and preconditioned on semisolid media with 0.3 M sucrose for one day, and shoot-tips preconditioned, loaded with a solution of 0.4 M sucrose and 2 M glycerol, and subsequently exposed to plant vitrification solution 3 (50% (w/v) sucrose and 50% (w/v) glycerol), were compared with non-treated dissected shoot-tips. We observed an increase in the expression level of six protein spots (fold change exceeding 1.5) and a decrease (fold change not exceeding 0.6) of ten protein spots after preconditionig treatment, whereas the profiles after preconditioning, loading and exposure to vitrification solution showed an increase in the expression level of 21 protein spots and a decrease in the expression level of 13. Most proteins identified were down-regulated and belonged to groups of biosynthesis, folding, and protein degradation. Many others were related to energetic metabolism, defense, and cell structure. These preliminary results contribute to knowledge of the proteome of this species and partially clarify its sensitivity to osmotic dehydration treatments.