Calcium metabolism and cardiovascular function after spaceflight.

To determine the influence of dietary calcium on spaceflight-induced alterations in calcium metabolism and blood pressure (BP), 9-wk-old spontaneously hypertensive rats, fed either high- (2%) or low-calcium (0.02%) diets, were flown on an 18-day shuttle flight. On landing, flight animals had increased ionized calcium (P < 0.001), elevated parathyroid hormone levels (P < 0.001), reduced calcitonin levels (P < 0.05), unchanged 1,25(OH)(2)D(3) levels, and elevated skull (P < 0.01) and reduced femur bone mineral density. Basal and thrombin-stimulated platelet free calcium (intracellular calcium concentration) were also reduced (P < 0.05). There was a tendency for indirect systolic BP to be reduced in conscious flight animals (P = 0.057). However, mean arterial pressure was elevated (P < 0.001) after anesthesia. Dietary calcium altered all aspects of calcium metabolism (P < 0.001), as well as BP (P < 0.001), but the only interaction with flight was a relatively greater increase in ionized calcium in flight animals fed low- compared with high-calcium diets (P < 0.05). The results indicate that 1) flight-induced disruptions of calcium metabolism are relatively impervious to dietary calcium in the short term, 2) increased ionized calcium did not normalize low-calcium-induced elevations of BP, and 3) parathyroid hormone was paradoxically increased in the high-calcium-fed flight animals after landing.     

Metabarcoding for the parallel identification of several hundred predators and their prey: Application to bat species diet analysis

Assessing diet variability is of main importance to better understand the biology of bats and design conservation strategies. Although the advent of metabarcoding has facilitated such analyses, this approach does not come without challenges. Biases may occur throughout the whole experiment, from fieldwork to biostatistics, resulting in the detection of false negatives, false positives or low taxonomic resolution. We detail a rigorous metabarcoding approach based on a short COI minibarcode and two‐step PCR protocol enabling the “all at once” taxonomic identification of bats and their arthropod prey for several hundreds of samples. Our study includes faecal pellets collected in France from 357 bats representing 16 species, as well as insect mock communities that mimic bat meals of known composition, negative and positive controls. All samples were analysed using three replicates. We compare the efficiency of DNA extraction methods, and we evaluate the effectiveness of our protocol using identification success, taxonomic resolution, sensitivity and amplification biases. Our parallel identification strategy of predators and prey reduces the risk of mis‐assigning prey to wrong predators and decreases the number of molecular steps. Controls and replicates enable to filter the data and limit the risk of false positives, hence guaranteeing high confidence results for both prey occurrence and bat species identification. We validate 551 COI variants from arthropod including 18 orders, 117 family, 282 genus and 290 species. Our method therefore provides a rapid, resolutive and cost‐effective screening tool for addressing evolutionary ecological issues or developing “chirosurveillance” and conservation strategies.     

The utility of wing morphometrics for assigning type specimens to cryptic bumblebee species

Since the beginning of taxonomy, species have been described based on morphology, but the advent of using semio-chemicals and genetics has led to the discovery of cryptic species (i.e. morphologically similar species). When a new cryptic species is described, earlier type specimens have to be re-evaluated, although this process can be challenging as only nondestructive methods ought to be used in order to preserve the integrity of the type specimens. Methods should allow comparison with recently collected specimens clustered based on chemical, ethological and/or genetic traits with old specimens (i.e. type specimens) where only morphological traits are available. Here we develop a method based on geometric morphometric analyses of wing shape for a taxonomically challenging group of bumblebees, the subgenus Alpinobombus Skorikov. We consider nine monophyletic taxa (including several cryptic species) to assess the accuracy of this method to discriminate the taxa based on their wing shape and then to attribute type specimens using a leave-one-out cross-validation procedure. We show that, for these bees, wing shape is taxon-specific, except for two sister taxa for which the species status is still debated. Moreover, for most of the taxa, type specimens were correctly attributed with high posterior probabilities of attribution, except for a few type specimens corresponding to the same two sister taxa where taxa delimitation based on wing shape was previously the subject of discussion. Our study highlights the potential of geometric morphometric analyses to help in the re-attribution of type specimens when the existence of cryptic species is revealed.     

Identification of functional PDZ domain binding sites in several human proteins

TIP-15 was previously identified as a cellular protein that can bind to the C-terminal end of the HTLV-1 Tax protein via its two PDZ domains. The sequence of the N-terminal part of TIP-15 is identical to that of the synaptic protein PSD-95. Both proteins are likely to be produced from the same gene by alternative splicing. Whereas expression of the PSD-95 mRNA was detected only with brain RNAs, that of TIP-15 was detected with RNAs from thymus, brain, skeletal muscle and Jurkat cells. The TIP-15 protein exhibits an apparent molecular weight of 40 kD and is weakly expressed in T cell lines. A two-hybrid screen performed with TIP-15 as bait revealed the presence of a PDZ binding site (PDZ-BS) in the following proteins: Lysyl tRNA synthetase, 6-phosphogluconolactonase (6-GPL), Stress-activated protein kinase 3 (SAPK3), NET-1, Diacylglycerol kinase zeta, MTMR1, MCM7, and hSec8. The sequence at the C-terminal ends of these proteins matches the X-S/T-X-V-COOH consensus previously defined for PDZ-BSs, with the exception of 6-GPL and SAPK3 which include a leucine as the C-terminal residue. For Lysyl tRNA synthetase, NET1, MTMR1 and hSec8, binding to TIP-15 was confirmed by co-immunoprecipitation experiments performed with the extracts of transfected COS7 cells. These results show the existence of functional PDZ-BSs in these proteins, but future studies will be necessary to establish whether or not TIP-15 represents a physiological partner. The significance of the presence of a PDZ-BS in these various proteins is discussed with respect to their function.     

A similar defect in UV-induced mutagenesis conferred by the rad6 and rad18 mutations of Saccharomyces cerevisiae

The single rad6 and rad18 yeast mutants share a number of physiological and biochemical properties related to DNA repair, suggesting that they affect closely related steps. However, it has been reported that UV-induced mutagenesis is considerably more depressed in rad6 than it is in rad18 cells. In an attempt to better understand the role of these genes, a genetic system believed to differentiate between targeted and untargeted events was used. The data are interpreted to mean that both mutations prevent the occurrence of targeted events, as if they prevent error-prone replication in front of pyrimidine dimers. The number of non-targeted mutants per survivor in each mutant was increased by UV irradiation. This may correspond to a stimulation of the error-prone replication.     

A computational model for understanding the micro-mechanics of collagen fiber network in the tunica adventitia

Abdominal aortic aneurysm is a prevalent cardiovascular disease with high mortality rates. The mechanical response of the arterial wall relies on the organizational and structural behavior of its microstructural components, and thus, a detailed understanding of the microscopic mechanical response of the arterial wall layers at loads ranging up to rupture is necessary to improve diagnostic techniques and possibly treatments. Following the common notion that adventitia is the ultimate barrier at loads close to rupture, in the present study, a finite element model of adventitial collagen network was developed to study the mechanical state at the fiber level under uniaxial loading. Image stacks of the rabbit carotid adventitial tissue at rest and under uniaxial tension obtained using multi-photon microscopy were used in this study, as well as the force–displacement curves obtained from previously published experiments. Morphological parameters like fiber orientation distribution, waviness, and volume fraction were extracted for one sample from the confocal image stacks. An inverse random sampling approach combined with a random walk algorithm was employed to reconstruct the collagen network for numerical simulation. The model was then verified using experimental stress–stretch curves. The model shows the remarkable capacity of collagen fibers to uncrimp and reorient in the loading direction. These results further show that at high stretches, collagen network behaves in a highly non-affine manner, which was quantified for each sample. A comprehensive parameter study to understand the relationship between structural parameters and their influence on mechanical behavior is presented. Through this study, the model was used to conclude important structure–function relationships that control the mechanical response. Our results also show that at loads close to rupture, the probability of failure occurring at the fiber level is up to 2%. Uncertainties in usually employed rupture risk indicators and the stochastic nature of the event of rupture combined with limited knowledge on the microscopic determinants motivate the development of such an analysis. Moreover, this study will advance the study of coupling microscopic mechanisms to rupture of the artery as a whole.

     

The Effects of l-Azetidine-2-Carboxylic Acid (Analogue of Proline) on Dental Cytodifferentiations in vitro

The action of t-azetidine-2-carboxylic acid (an analogue of proline) on the cytodifferentiation of odontoblasts and ameloblasts of mouse tooth buds cultivated In vitro has been studied. The results of our morphological, cytological and functional investigations suggest that the expression of differentiation of ameloblasts is partially conditioned by collagen and/or associated mucopolysaccharides contained in predentin.     

A glimpse on the pattern of rodent diversication: a phylogenetic approach

ABSTRACT: BACKGROUND: Development of phylogenetic methods that do not rely on fossils for the study of evolutionary processes through time have revolutionized the eld of evolutionary biology and resulted in an unprecedented expansion of our knowledge about the tree of life. These methods have helped to shed light on the macroevolution of many taxonomic groups such as the placentals (Mammalia). However, despite the increase of studies addressing the diversication patterns of organisms, no synthesis has addressed the case of the most diversied mammalian clade: the Rodentia. RESULTS: Here we present a rodent maximum likelihood phylogeny inferred from a molecular supermatrix. It is based on 11 mitochondrial and nuclear genes that covers 1,265 species, i.e., respectively 56 % and 81 % of the known specic and generic rodent diversity. The inferred topology recovered all Rodentia clades proposed by recent molecular works. A relaxed molecular clock dating approach provided a time framework for speciation events. We found that the Myomorpha clade shows a greater degree of variation in diversication rates than Sciuroidea, Caviomorpha, Castorimorpha and Anomaluromorpha. We identied a number of shifts in diversication rates within the major clades: two in Castorimorpha, three in Ctenohystrica, 6 within the squirrel-related clade and 24 in the Myomorpha clade. The majority of these shifts occurred within the most recent familial rodent radiations: the Cricetidae and Muridae clades. Using the topological imbalances and the time line we discuss the potential role of different diversication factors that might have shaped the rodents radiation. CONCLUSIONS: The present glimpse on the diversication pattern of rodents can be used for further comparative meta-analyses. Muroid lineages have a greater degree of variation in their diversication rates than any other 1rodent group. Different topological signatures suggest distinct diversication processes among rodent lineages. In particular, Muroidea and Sciuroidea display widespread distribution and have undergone evolutionary and adaptive radiation on most of the continents. Our results show that rodents experienced shifts in diversication rate regularly through the Tertiary, but at different periods for each clade. A comparison between the rodent fossil record and our results suggest that extinction led to the loss of diversication signal for most of the Paleogene nodes.