Mutations in tetrapyrrole biosynthesis pathway uncouple nuclear WUSCHEL expression from de novo shoot development in Arabidopsis

Plant Cell, Tissue and Organ Culture (PCTOC) - The effect of several parameters on trans-resveratrol extracellular production in Vitis vinifera cv Monastrell suspension cultured cells elicited with...     

Cardiovascular and ventilatory interactions in the facultative air-breathing teleost Pangasianodon hypophthalmus

Journal of Comparative Physiology B - All vertebrates possess baroreceptors monitoring arterial blood pressure and eliciting reflexive changes in vascular resistance and heart rate in response to...     

Widening the antimicrobial spectrum of esters of bicyclic amines: In vitro effect on gram-positive Streptococcus pneumoniae and gram-negative non-typeable Haemophilus influenzae biofilms

Antibiotic resistance is a global current threat of increasing importance. Moreover, biofilms represent a medical challenge since the inherent antibiotic resistance of their producers demands the use of high doses of antibiotics over prolonged periods. Frequently, these therapeutic measures fail, contributing to bacterial persistence, therefore demanding the development of novel antimicrobials. Esters of bicyclic amines (EBAs), which are strong inhibitors of Streptococcus pneumoniae growth, were initially designed as inhibitors of pneumococcal choline-binding proteins on the basis of their structural analogy to the choline residues in the cell wall. However, instead of mimicking the characteristic cell chaining phenotype caused by exogenously added choline on planktonic cultures of pneumococcal cells, EBAs showed an unexpected lytic activity. In this work we demonstrate that EBAs display a second, and even more important, function as cell membrane destabilizers. We then assayed the inhibitory and disintegrating activity of these molecules on pneumococcal biofilms. The selected compound (EBA 31) produced the highest effect on S. pneumoniae (encapsulated and non-encapsulated) biofilms at very low concentrations. EBA 31 was also effective on mixed biofilms of non-encapsulated S. pneumoniae plus non-typeable Haemophilus influenzae, two pathogens frequently forming a self-produced biofilm in the human nasopharynx. These results support the role of EBAs as a promising alternative for the development of novel, broad-range antimicrobial drugs encompassing both Gram-positive and Gram-negative pathogens.     

Impact of demography on extinction/fixation events

In this article we consider diffusion processes modeling the dynamics of multiple allelic proportions (with fixed and varying population size). We are interested in the way alleles extinctions and fixations occur. We first prove that for the Wright–Fisher diffusion process with selection, alleles get extinct successively (and not simultaneously), until the fixation of one last allele. Then we introduce a very general model with selection, competition and Mendelian reproduction, derived from the rescaling of a discrete individual-based dynamics. This multi-dimensional diffusion process describes the dynamics of the population size as well as the proportion of each type in the population. We prove first that alleles extinctions occur successively and second that depending on population size dynamics near extinction, fixation can occur either before extinction almost surely, or not. The proofs of these different results rely on stochastic time changes, integrability of one-dimensional diffusion processes paths and multi-dimensional Girsanov’s tranform.

     

The Response to Stimulation in Neurons and Astrocytes

Neurochemical Research - The brain uses mainly glucose as fuel with an index of glucose to oxygen utilization close to 6, the maximal index if all glucose was completely oxidized. However, this...     

Effect of heterochiral inversions on the structure of a β-hairpin peptide

We study computationally a family of β-hairpin peptides with systematically introduced chiral inversions, in explicit water, and we investigate the extent to which the backbone structure is able to fold in the presence of heterochiral perturbations. In contrast to the recently investigated case of a helical peptide, we do not find a monotonic change in secondary structure content as a function of the number of L- to D-inversions. The effects of L- to D-inversions are instead found to be highly position-specific. Additionally, in contrast to the helical peptide, some inversions increase the stability of the folded peptide: in such cases, we compute an increase in β-sheet content in the aqueous solution equilibrium ensemble. However, the tertiary structures of the stable (folded) configurations for peptides for which inversions cause an increase in β-sheet content show differences from one another, as well as from the native fold of the nonchirally perturbed β-hairpin. Our results suggest that although some chiral perturbations can increase folding stability, chirally perturbed proteins may still underperform functionally, given the relationship between structure and function.     

Seasonal variation in migration strategies used to cross ecological barriers in a nearctic migrant wintering in Africa

Ecological barriers such as oceans, mountain ranges or glaciers can have a substantial influence on the evolution of animal migration. Along the migration flyway connecting breeding sites in the North American Arctic and wintering grounds in Europe or Africa, nearctic species are confronted with significant barriers such as the Atlantic Ocean and the Greenland icecap. Using geolocation devices, we identified wintering areas used by ringed plovers nesting in the Canadian High‐Arctic and investigated migration strategies used by these nearctic migrants along the transatlantic route. The main wintering area of the ringed plovers (n = 20) was located in western Africa. We found contrasting seasonal migration patterns, with ringed plovers minimizing continuous flight distances over the ocean in spring by making a detour to stop in Iceland. In autumn, however, most individuals crossed the ocean in one direct flight from southern Greenland to western Europe, as far as southern Spain. This likely resulted from prevailing anti‐clockwise winds associated with the Icelandic low‐pressure system. Moreover, the plovers we tracked largely circumvented the Greenland icecap in autumn, but in spring, some plovers apparently crossed the icecap above the 65°N. Our study highlighted the importance of Iceland as a stepping‐stone during the spring migration and showed that small nearctic migrants can perform non‐stop transatlantic flights from Greenland to southern Europe.     

Melatonin synthesis in the optic lobes and midbrain of the grasshopper Oedipoda caerulescens

The pathways of insect melatonin (MEL) biosynthesis apparently follow the same routes as those identified in vertebrates but information on MEL synthesis variations related with serotonin (5‐HT), 5‐hydroxy‐indole acetic acid (5HIAA), and N‐acetylserotonin (NAS) levels, as well as 5‐HT N‐acetyltransferase (NAT) activity throughout the day, is very limited in the insect nervous system. In the present study, the levels of MEL, metabolites (5‐HT, NAS, and 5‐HIAA) and enzyme NAT were determined in the optic lobes and the midbrain of the grasshopper Oedipoda caerulescens, in conditions of light and darkness. In both tissues, a different pattern of MEL synthesis was observed over the light/dark cycle. Variations in the levels of 5‐HT, NAS and NAT activity related to the synthesis of cerebral MEL follow a pattern very similar to that observed in the pineal of mammals, with a peak of synthesis in the first half of the scotophase. Also, we observed differences in the metabolism of 5‐HT between the optic lobes and the midbrain light/dark‐dependent.