Adaptive molecular evolution of the Major Histocompatibility Complex genes, DRA and DQA, in the genus Equus

<p>Abstract</p> <p>Background</p> <p>Major Histocompatibility Complex (MHC) genes are central to vertebrate immune response and are believed to be under balancing selection by pathogens. This hypothesis has been supported by observations of extremely high polymorphism, elevated nonsynonymous to synonymous base pair substitution rates and trans-species polymorphisms at these loci. In equids, the organization and variability of this gene family has been described, however the full extent of diversity and selection is unknown. As selection is not expected to act uniformly on a functional gene, maximum likelihood codon-based models of selection that allow heterogeneity in selection across codon positions can be valuable for examining MHC gene evolution and the molecular basis for species adaptations.</p> <p>Results</p> <p>We investigated the evolution of two class II MHC genes of the Equine Lymphocyte Antigen (ELA), <it>DRA </it>and <it>DQA</it>, in the genus <it>Equus </it>with the addition of novel alleles identified in plains zebra (<it>E. quagga</it>, formerly <it>E. burchelli</it>). We found that both genes exhibited a high degree of polymorphism and inter-specific sharing of allele lineages. To our knowledge, <it>DRA </it>allelic diversity was discovered to be higher than has ever been observed in vertebrates. Evidence was also found to support a duplication of the <it>DQA </it>locus. Selection analyses, evaluated in terms of relative rates of nonsynonymous to synonymous mutations (<it>d</it>_N<it>/d</it>_S) averaged over the gene region, indicated that the majority of codon sites were conserved and under purifying selection (<it>d</it>_N<<it>d</it>_S). However, the most likely evolutionary codon models allowed for variable rates of selection across codon sites at both loci and, at the <it>DQA</it>, supported the hypothesis of positive selection acting on specific sites.</p> <p>Conclusions</p> <p>Observations of elevated genetic diversity and trans-species polymorphisms supported the conclusion that balancing selection may be acting on these loci. Furthermore, at the <it>DQA</it>, positive selection was occurring at antigen binding sites, suggesting that a few selected residues may play a significant role in equid immune function. Future studies in natural equid populations will be valuable for understanding the functional significance of the uniquely diverse <it>DRA </it>locus and for elucidating the mechanism maintaining diversity at these MHC loci.</p

Liquid-process production of composite-materials with aluminum-based matrix reinforced by fibers of carbon or silicon-carbide

International audienc

Liquid-process production of composite-materials with aluminum-based matrix reinforced by fibers of carbon or silicon-carbide

International audienc

The K2ZrF6 wetting process: Effect of surface chemistry on the ability of a SiC-Fiber preform to be impregnated by aluminum

International audienceSiC-ceramic materials, either as flat substrates or porous fiber preforms, are spontaneously wetted by aluminum at 700 °C to 800 °C when they have been pretreated with an aqueous solution of K2ZrF6. The wetting enhancement effect results from exothermic chemical reactions occurring at the SiC/Al interface. The first phenomenon thought to occur is a disruption of the alumina film covering liquid aluminum due to a reaction of A12O3 with K2ZrF6. Then alumina is totally dissolved at low temperatures by potassium/aluminum mixed fluorides, giving rise to a very fluid cryolitic liquid spreading out on the surface of liquid aluminum and to the true SiC/Al interface. Simultaneously, a large evolution of heat occurs, mainly due to the reduction of K2ZrF6 by aluminum and the formation of Al3Zr. The impregnation of 2D-SiC/SiC preforms by aluminum is modeled, and the effect of both the contact angle decrease and local temperature rise on the impregnation of the preforms, e.g., by gravity casting, is established

Relationships between visual and tactile features and biophysical parameters in human facial skin

Background/purpose: Skin properties, such as colour, hydration and texture, can be studied on a qualitative basis by a clinical assessment or on a quantitative basis using techniques that measure biophysical properties of the skin. The aim of this study was to explore the links between facial skin features and a range of skin biophysical parameters using multivariate methods. Methods: A study was conducted on 256 female volunteers from Ile-de-France with apparent healthy skin, aged between 20 and 50, under controlled environmental conditions (mean ± standard deviation: room temperature 22.9 ± 0.3°C; relative humidity 48.5 ± 2.3%). The study included a medical questionnaire and a clinical examination of the skin performed by a dermatologist, and a biophysical evaluation of the skin properties. Seventy visual and tactile skin features were assessed on the forehead and the cheek using ordinal variables illustrated by photographic scales. Twenty-eight biophysical measurements were taken in the same areas using the following equipment: Chromameter®, Evaporimeter®, Corneometer®, Skicon®, Sebumeter®, Sebutape®, skin thermometer, skin pH-meter and Silflo®. In order to group the variables illustrating a same unimodal phenomenon, a typology of the skin features and a typology of the biophysical parameters were carried out using a clustering method. Then, the relationships between each group of clinical features and each group of biophysical parameters were studied using a series of partial least squares (PLS) regressions. Results: From eight groups of clinical features and three groups of biophysical parameters that were identified, 12 significant PLS regression models were built. Our findings suggest that differences in chromametric measurements express not only differences in skin colour but also differences in skin surface properties, such as skin vascularity status, thickness, and existence of wrinkles, and also demonstrate that the level of sebum excretion can affect other aspects of the skin surface. Conclusion: Some skin features assessed clinically do not appear to be linked to any biophysical parameter. This finding confirms that certain phenomena evaluated on the basis of visual or tactile skin features are not assessed on the basis of the biophysical properties of the skin measured by our bioengineering techniques. Indeed, visual skin features mainly appreciate the skin surface aspect, contrary to some biophysical surrogate markers known to provide information on underlying epidermal structures. Therefore, both clinical and biophysical assessments must be associated to supply a relevant and accurate approach for skin aspect characterisation. © 2007 Blackwell Munksgaard.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Ventilatory response to a hyperoxic test is related to the frequency of short apneic episodes in late preterm Neonates

International audienceChemoreception is frequently involved in the processes underlying apnea in premature infants. Apnea could result from a decrease in carotid body effectiveness. However, increased carotid body activity could also initiate apnea through hypocapnia following hyperventilation when the receptors are stimulated. The aim of this study was to analyze the relationship between carotid body effectiveness and short apneic episodes in older preterm neonates. Carotid body effectiveness was assessed at thermoneutrality in 36 premature neonates (2.07 +/- 0.26 kg) by performing a 30-s hyperoxic test during sleep, the oxygen inhalation involving a ventilation decrease. Blood O-2 saturation (Sp(o2)) and ventilatory parameters were monitored before and during the hyperoxic test. Short episodes of apnea (frequency and mean duration) were recorded during the morning's 3-h interfeeding interval. Pretest SRo2 was not related to any of the measured respiratory parameters. A higher frequency of short apneic episodes was linked to a greater ventilation decrease in response to the hyperoxic test (p = -0.32; p = 0.01). Increased carotid body response is correlated with greater apneic episodes frequency, even in the absence of concomitant oxygen desaturation. Fetal or early postnatal hypoxemia could have increased peripheral chemoreceptor activity, which could initiate a "overshoot/undershoot" situation, which in turn could induce a critical P-o2/P-co2 combination and apne