Colloquium: Mechanical formalisms for tissue dynamics

The understanding of morphogenesis in living organisms has been renewed by tremendous progressin experimental techniques that provide access to cell-scale, quantitative information both on theshapes of cells within tissues and on the genes being expressed. This information suggests that ourunderstanding of the respective contributions of gene expression and mechanics, and of their crucialentanglement, will soon leap forward. Biomechanics increasingly benefits from models, which assistthe design and interpretation of experiments, point out the main ingredients and assumptions, andultimately lead to predictions. The newly accessible local information thus calls for a reflectionon how to select suitable classes of mechanical models. We review both mechanical ingredientssuggested by the current knowledge of tissue behaviour, and modelling methods that can helpgenerate a rheological diagram or a constitutive equation. We distinguish cell scale ("intra-cell")and tissue scale ("inter-cell") contributions. We recall the mathematical framework developpedfor continuum materials and explain how to transform a constitutive equation into a set of partialdifferential equations amenable to numerical resolution. We show that when plastic behaviour isrelevant, the dissipation function formalism appears appropriate to generate constitutive equations;its variational nature facilitates numerical implementation, and we discuss adaptations needed in thecase of large deformations. The present article gathers theoretical methods that can readily enhancethe significance of the data to be extracted from recent or future high throughput biomechanicalexperiments.Comment: 33 pages, 20 figures. This version (26 Sept. 2015) contains a few corrections to the published version, all in Appendix D.2 devoted to large deformation

WSES Guidelines for the management of acute left sided colonic diverticulitis in the emergency setting

Acute left sided colonic diverticulitis is one of the most common clinical conditions encountered by surgeons in acute setting. A World Society of Emergency Surgery (WSES) Consensus Conference on acute diverticulitis was held during the 3rd World Congress of the WSES in Jerusalem, Israel, on July 7th, 2015. During this consensus conference the guidelines for the management of acute left sided colonic diverticulitis in the emergency setting were presented and discussed. This document represents the executive summary of the final guidelines approved by the consensus conference.Peer reviewe

E2A expression stimulates Ig hypermutation.

Ig hypermutation is limited to a region of 2 kb downstream of the transcription start sites of the Ig loci. The process requires transcription and the presence of Ig enhancer sequences, and is initiated by the activation-induced cytidine deaminase (AID)- mediated deamination of cytidine bases. It remains unknown why AID causes mutations selectively in the Ig genes and not in most other transcribed loci of B cells. In this study, we report that the inactivation of the E2A gene strongly reduces the rate of Ig L chain mutations in the chicken B cell line DT40 without affecting the levels of surface Ig or AID expression. The defect is complemented by the expression of cDNAs corresponding to either of the two E2A splice variants E12 or E47. The results suggest that E2A-encoded proteins enhance Ig hypermutation by recruitment of AID to the Ig loci