E-cadherin turnover rates vary in space and fluctuate in time.

<p>(A) Distribution of turnover rates (k_off) of E-cadherin-GFP measured by FRAP at diffraction-limited spots at different junctions across a confluent layer of MDCK cells. For each junction (N = 41) the individual fluorescence recovery curve was fit with an exponential relaxation. The solid curve shows a gaussian fit (average rate 4.8 10^-3 s^-1 and standard deviation 2.5 10^–3 s^-1) of the distribution of the 34 non-outlying values. (B) At each single spot, the turnover rate was measured twice (#1 and #2) with a 45 minutes time interval. (C) For each spot, the temporal variation of the turnover rate is assessed by the ratio of the successive measurements k_off#2/ k_off#1 (iterative FRAP, left panel, red circles). This ensemble of ratios was compared to the similar ensemble obtained after a random permutation of the rates within the first set (#1) (rand. perm., blue squares). Rates were also compared within matched pairs of spots belonging to two different AJs of the same cell (right panel): ratios for matched pairs (green diamonds) were compared to mismatched pairs (random permutations of values, black crosses). No significant correlations were found between rates, neither in time when sampled across a 45 minutes interval, or in space within single cells.</p

E-cadherin turnover rates increase with intercellular tension.

<p>(A-a) A perpendicular force was applied on individual junctions by pulling on the apical surface with a glass micro-pipette. The junctions were then clamped at a stable position approximately 0.5 μm away from the initial one. (A-b) Typical overlay image of a cell before (gray) and after traction (red), with the micro-pipette (dashed line) and the force vector (arrow). Scale bar: 10 μm. (B) FRAP was achieved on MDCK cells expressing E-cadherin-GFP, giving for each AJ a pair of rates (k_off) before (red dots) and after (blue squares) traction (N = 12). (C) For each rate pair, the ratio k_{off "after"}/ k_{off "before"} is shown (blue squares), and compared to control experiments without traction (red dots). Turnover rates increased after tension was applied in all (N = 11) but one case (red line in B).</p

E-cadherin endocytosis rates match across individual unperturbed AJs.

<p>Endocytosis rates of E-cadherin were measured using dual-color FRAP on mature heterochromatic AJs between MDCK cells expressing either E-cadherin-GFP or E-cadherin-DsRed (A, arrows in B). Kinetics were recorded simultaneously but resolved separately on each side of a same junction (A insert). Each measurement led to a pair of rates shown as a point in a biparametric logarithmic plot (k_off^DsRed, k_off^GFP) (C). A linear fit gives a rate ratio k_off^GFP/k_off^DsRed = 1.07 (red line, R = 0.88). The distribution of ratios of rate pairs k_off^GFP /k_off^DsRed (insert, red dots) is compared to what is obtained following a random permutation with the set of k_off^DsRed values (blue squares).</p

Management of alcohol-related liver disease: the French Association for the Study of the Liver and the French Alcohol Society clinical guidelines

International audienceExcessive alcohol consumption is the leading cause of liver diseases in Western countries, especially in France. Alcohol-related liver disease (ARLD) is an extremely broad context and there remains much to accomplish in terms of identifying patients, improving prognosis and treatment, and standardising practices. The French Association for the Study of the Liver wished to organise guidelines together with the French Alcohol Society in order to summarise the best evidence available about several key clinical points in ARLD. These guidelines have been elaborated based on the level of evidence available in the literature and each recommendation has been analysed, discussed and voted by the panel of experts. They describe how patients with ARLD should be managed nowadays and discuss the main unsettled issues in the field

Mechanosensitive Adaptation of E-Cadherin Turnover across adherens Junctions

In the natural and technological world, multi-agent systems strongly depend on how the interactions are ruled between their individual components, and the proper control of timescales and synchronization is a key issue. This certainly applies to living tissues when multicellular assemblies such as epithelial cells achieve complex morphogenetic processes. In epithelia, because cells are known to individually generate actomyosin contractile stress, each individual intercellular adhesive junction line is subjected to the opposed stresses independently generated by its two partner cells. Contact lines should thus move unless their two partner cells mechanically match. The geometric homeostasis of mature epithelia observed at short enough time-scale thus raises the problem to understand how cells, if considered as noisy individual actuators, do adapt across individual intercellular contacts to locally balance their time-average contractile stress. Structural components of adherens junctions, cytoskeleton (F-actin) and homophilic bonds (E-cadherin) are quickly renewed at steady-state. These turnovers, if they depend on forces exerted at contacts, may play a key role in the mechanical adaptation of epithelia. Here we focus on E-cadherin as a force transducer, and we study the local regulation and the mechanosensitivity of its turnover in junctions. We show that E-cadherin turnover rates match remarkably well on either side of mature intercellular contacts, despite the fact that they exhibit large fluctuations in time and variations from one junction to another. Using local mechanical and biochemical perturbations, we find faster turnover rates with increased tension, and asymmetric rates at unbalanced junctions. Together, the observations that E-cadherin turnover, and its local symmetry or asymmetry at each side of the junction, are mechanosensitive, support the hypothesis that E-cadherin turnover could be involved in mechanical homeostasis of epithelia