Controls on gut phosphatisation : the trilobites from the Weeks Formation Lagerstätte (Cambrian; Utah)

Despite being internal organs, digestive structures are frequently preserved in Cambrian Lagerstätten. However, the reasons for their fossilisation and their biological implications remain to be thoroughly explored. This is particularly true with arthropods--typically the most diverse fossilised organisms in Cambrian ecosystems--where digestive structures represent an as-yet underexploited alternative to appendage morphology for inferences on their biology. Here we describe the phosphatised digestive structures of three trilobite species from the Cambrian Weeks Formation Lagerstätte (Utah). Their exquisite, three-dimensional preservation reveals unique details on trilobite internal anatomy, such as the position of the mouth and the absence of a differentiated crop. In addition, the presence of paired pygidial organs of an unknown function is reported for the first time. This exceptional material enables exploration of the relationships between gut phosphatisation and the biology of organisms. Indeed, soft-tissue preservation is unusual in these fossils as it is restricted to the digestive structures, which indicates that the gut played a central role in its own phosphatisation. We hypothesize that the gut provided a microenvironment where special conditions could develop and harboured a source of phosphorus. The fact that gut phosphatization has almost exclusively been observed in arthropods could be explained by their uncommon ability to store ions (including phosphorous) in their digestive tissues. However, in some specimens from the Weeks Formation, the phosphatisation extends to the entire digestive system, suggesting that trilobites might have had some biological particularities not observed in modern arthropods. We speculate that one of them might have been an increased capacity for ion storage in the gut tissues, related to the moulting of their heavily-mineralised carapace

The Osteopontin Level in Liver, Adipose Tissue and Serum Is Correlated with Fibrosis in Patients with Alcoholic Liver Disease

<div><h3>Background</h3><p>Osteopontin (OPN) plays an important role in the progression of chronic liver diseases. We aimed to quantify the liver, adipose tissue and serum levels of OPN in heavy alcohol drinkers and to compare them with the histological severity of hepatic inflammation and fibrosis.</p> <h3>Methodology/Principal Findings</h3><p>OPN was evaluated in the serum of a retrospective and prospective group of 109 and 95 heavy alcohol drinkers, respectively, in the liver of 34 patients from the retrospective group, and in the liver and adipose tissue from an additional group of 38 heavy alcohol drinkers. Serum levels of OPN increased slightly with hepatic inflammation and progressively with the severity of hepatic fibrosis. Hepatic OPN expression correlated with hepatic inflammation, fibrosis, TGFβ expression, neutrophils accumulation and with the serum OPN level. Interestingly, adipose tissue OPN expression also correlated with hepatic fibrosis even after 7 days of alcohol abstinence. The elevated serum OPN level was an independent risk factor in estimating significant (F≥2) fibrosis in a model combining alkaline phosphatase, albumin, hemoglobin, OPN and FibroMeter® levels. OPN had an area under the receiving operator curve that estimated significant fibrosis of 0.89 and 0.88 in the retrospective and prospective groups, respectively. OPN, Hyaluronate (AUROC: 0.88), total Cytokeratin 18 (AUROC: 0.83) and FibroMeter® (AUROC: 0.90) estimated significance to the same extent in the retrospective group. Finally, the serum OPN levels also correlated with hepatic fibrosis and estimated significant (F≥2) fibrosis in 86 patients with chronic hepatitis C, which suggested that its elevated level could be a general response to chronic liver injury.</p> <h3>Conclusion/Significance</h3><p>OPN increased in the liver, adipose tissue and serum with liver fibrosis in alcoholic patients. Further, OPN is a new relevant biomarker for significant liver fibrosis. OPN could thus be an important actor in the pathogenesis of this chronic liver disease.</p> </div

ADCY5 couples glucose to insulin secretion in human islets

Single nucleotide polymorphisms (SNPs) within the ADCY5 gene, encoding adenylate cyclase 5, are associated with elevated fasting glucose and increased type 2 diabetes (T2D) risk. Despite this, the mechanisms underlying the effects of these polymorphic variants at the level of pancreatic β-cells remain unclear. Here, we show firstly that ADCY5 mRNA expression in islets is lowered by the possession of risk alleles at rs11708067. Next, we demonstrate that ADCY5 is indispensable for coupling glucose, but not GLP-1, to insulin secretion in human islets. Assessed by in situ imaging of recombinant probes, ADCY5 silencing impaired glucose-induced cAMP increases and blocked glucose metabolism toward ATP at concentrations of the sugar >8 mmol/L. However, calcium transient generation and functional connectivity between individual human β-cells were sharply inhibited at all glucose concentrations tested, implying additional, metabolism-independent roles for ADCY5. In contrast, calcium rises were unaffected in ADCY5-depleted islets exposed to GLP-1. Alterations in β-cell ADCY5 expression and impaired glucose signaling thus provide a likely route through which ADCY5 gene polymorphisms influence fasting glucose levels and T2D risk, while exerting more minor effects on incretin action

Γ-X mixing in type-II GaAs/AlAs short period superlattices

We have measured the absolute absorption coefficient of optical transitions in type-II short period GaAs/AlAs superlattices, on a broad spectral range, at low temperature. The transmission experiments have been performed in a waveguiding configuration. Photoluminescence excitation experiments show as well the characteristics of the pseudodirect HH1-Xz excitonic transition. Theoretical calculations of the effective dielectric tensor and absorption coefficient in the vicinity of the exciton resonance frequency are presented, taking explicitely into account the Γ-X mixing of electronic states at heteroboundaries. From comparison between the experimental and theoretical values of the absorption coefficients, we have deduced a value of the Γ-X coupling coefficient for the studied superlattices

Anisotropic exciton states in GaAs/AlAs superlattices in zero and non-zero magnetic field

In short period pseudodirect GaAs/AlAs superlattices, the two radiative heavy exciton states exhibit a very small anisotropic splitting due to their coupling with light exciton states. They are dipole-active along the [110] and [1(-1)0] directions in the layer plane. The splitting energy (a few µeV) is obtained from the period of the quantum beats between the two sublevels observed during the time decay of photoluminescence under excitation with light linearly polarized along [101] or circularly polarized. We report here on the variation of the quantum beats in a magnetic field. In a longitudinal field (parallel to the wave vector of light), we measure the splitting between the radiative states and obtain the hole longitudinal g-factor. In a transverse field, we observe two periods for the quantum beats. One corresponds to the splitting between the radiative states and the other to the splitting between the radiative states and the non-radiative ones which become optically allowed in a transverse field. We also discuss the influence of the coupling to light excitons in a transverse field on the hole transverse g-factor

STUDY OF VERTICAL TRANSPORT IN A SUPERLATTICE GaAs/AlAs BY TIME-RESOLVED PHOTOLUMINESCENCE

En mesurant le comportement temporel de la luminescence d'un puits quantique en fonction de l'épaisseur du super-réseau qui le sépare de la surface de l'échantillon, nous déterminons le coefficient de diffusion dans le super-réseau. Nous montrons que les excitations qui diffusent sont des excitons du super-réseau.By measuring the luminescence time behaviour of an enlarged quantum well as a function of the superlattice thickness, we determine the diffusion coefficient in the superlattice. We show that very likely the excitations which diffuse are excitons

Fluorescence yield and lifetime of isolated polydiacetylene chains: Evidence for a one-dimensional exciton band in a conjugated polymer

The fluorescence lifetime tau and quantum yield eta(f) of isolated red polydiacetylene chains dispersed in their monomer single crystal matrix were measured between 10 and 100 K. tau increases up to 120 ps at 40 K, then rapidly decreases at higher T. eta(f) is a continuously decreasing function of T. The radiative lifetime tau(r) is proportional to rootT in the whole T range studied. This is the expected behavior for a purely one-dimensional system without localization, a behavior which is not usually observed even in semiconductor quantum wires. An order of magnitude of the exciton effective mass m*approximate to0.3 is inferred. The nonradiative lifetime tau(nr) is constant up to 50 K, then decreases exponentially, indicating the opening of a thermally activated decay channel