How to be in a good shape? The influence of clone morphology on cell competition

Cell competition is a conserved mechanism where slow proliferating cells (so called losers) are eliminated by faster proliferating neighbors (so called winners) through apoptosis.(1) It is an important process which prevents developmental malformations and maintains tissue fitness in aging adults.(2) Recently, we have shown that the probability of elimination of loser cells correlates with the surface of contact between losers and winners in Myc-induced competition.(3) Moreover, we have characterized an active mechanism that increases the surface of contact between losers and winners, hence accelerating the elimination of loser cells. This is the first indication that cell shape and mechanics can influence cell competition. Here, we will discuss the consequence of the relationship between shape and competition, as well as the relevance of this model for other modes of competition

Unipolar distributions of junctional Myosin II identify cell stripe boundaries that drive cell intercalation throughout Drosophila axis extension.

Convergence and extension movements elongate tissues during development. Drosophila germ-band extension (GBE) is one example, which requires active cell rearrangements driven by Myosin II planar polarisation. A combinatorial code of Toll receptors downstream of pair-rule genes contributes to this polarization via local cell-cell interactions. We developed novel computational methods to analyse the spatiotemporal dynamics of Myosin II. We show that initial Myosin II bipolar cell polarization gives way to unipolar enrichment at parasegmental boundaries and two further boundaries within each parasegment, concomitant with a doubling of cell number as the tissue elongates. These boundaries are the primary sites of cell intercalation, behaving as mechanical barriers and providing a mechanism for how cells remain ordered during GBE. Enrichment at parasegment boundaries during GBE is independent of Wingless signaling, suggesting pair-rule gene control. We propose an updated cell-cell interaction model for Myosin II polarization that we tested in a vertex-based simulation

Multi-center evaluation of the hepatitis B surface antigen (HBsAg) assay and HbsAg confirmatory assay for the family of Access immunoassay systems

BACKGROUND: Accurate detection of Hepatitis B Surface Antigen (HBsAg) is an important aid in the diagnosis of patients infected with the hepatitis B virus (HBV). A multi-center study was conducted to characterize the performance of the HBsAg assay on the family of Access immunoassay systems from Beckman Coulter. METHODS: The Access HBsAg assay was characterized in a multi-center study and compared to the Abbott AxSYM* and PRISM* HBsAg assays. The bioMérieux VIDAS* assay was used to resolve discrepant results. Reproducibility studies (intra-assay, inter-assay and inter-lot) were performed with pooled serum samples (negative sample, close to cut off, low, medium and high positive samples). Analytical sensitivity, subtype and genotype detection were studied with various commercial panels (SFTS panel, WHO 80/549, WHO 00/588, Teragenix HBV Genotype panel). A panel of recombinant HBsAg mutant proteins was tested to investigate reactivity towards genetic mutations. Clinical sensitivity was verified with seroconversion panels and samples from subjects with known HBV infection. Analytical specificity was studied with samples from patients with potential cross-reactive infections. Clinical specificity was validated among blood donors and a hospitalized population. RESULTS: The imprecision was < 10%. Analytical sensitivity was < or = 0.1 ng/mL (SFTS panel), 0.020 PEI Units/mL (ad panel), 0.024 PEI Units/mL (ay panel), 0.092 IU/mL with WHO 80/549 and 0.056 IU/mL with WHO 00/588. All genotype samples and HBsAg mutants were reactive with the Access HBsAg assay. Seroconversion panels tested showed no significant difference with the reference method. Sensitivity for subjects with known HBV infection was 100%. No interference with potentially cross-reactive infections was observed after confirmatory testing. Specificity was 99.96% (100% after confirmatory testing) in a blood donor population and 99.5% (100% after confirmatory testing) in a hospitalized population. Excellent separation of positive and negative populations was observed. CONCLUSIONS: The Access HBsAg and HBsAg Confirmatory assays meet all clinical and analytical performance requirements of assays for the detection of HBsAg

A revised method for estimating hepatitis B virus transfusion residual risk based on antibody to hepatitis B core antigen incident cases

BACKGROUND: To take into account the transient nature of hepatitis B virus (HBV) antigenemia, the calculation of HBV residual risk (RR), based on the incidence/window period model, is adjusted by a correction factor that adds uncertainty to the RR estimates. STUDY DESIGN AND METHODS: This new method to estimate the RR for HBV is a weighted sum of the RR derived from hepatitis B surface antigen (HBsAg) incident cases and the one derived from antibody hepatitis B core antigen (HBc) incident cases. An anti-HBc incident case was defined as a donation from a blood donor who had made at least one anti-HBc–negative donation followed by a donation that was found positive with two different assays within a 3-year period and positive for at least one of the following markers: 1) antibody to hepatitis B e antigen or hepatitis B e antigen, 2) anti-HBc immunoglobulin M, 3) HBV DNA, 4) hepatitis B surface antibody without HBV vaccination history, or 5) HBV DNA retrospectively found in the previous donation. Five overlapping 3-year study periods between 2000 and 2006 were analyzed. RESULTS: The HBV RR estimated with the classical method ranged from 1.51 (2000-2002) to 0.69 per million donations in 2004 through 2006 with a decrease in 2002 through 2004 due to only two HBsAg incident cases reported in this period. By applying the revised model, the HBV RR ranged from 1.06 (2000-2002) to 0.49 per million donations (2004-2006), with a regular decrease. CONCLUSION: The new presented model provides HBV RR estimates that do not statistically differ from those obtained with the classical model; however, it provides more accurate data, especially in low endemic areas where the HBsAg incidence is low

Coordinated waves of actomyosin flow and apical cell constriction immediately after wounding

© 2013 Antunes et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).Epithelial wound healing relies on tissue movements and cell shape changes. Our work shows that, immediately after wounding, there was a dramatic cytoskeleton remodeling consisting of a pulse of actomyosin filaments that assembled in cells around the wound edge and flowed from cell to cell toward the margin of the wound. We show that this actomyosin flow was regulated by Diaphanous and ROCK and that it elicited a wave of apical cell constriction that culminated in the formation of the leading edge actomyosin cable, a structure that is essential for wound closure. Calcium signaling played an important role in this process, as its intracellular concentration increased dramatically immediately after wounding, and down-regulation of transient receptor potential channel M, a stress-activated calcium channel, also impaired the actomyosin flow. Lowering the activity of Gelsolin, a known calcium-activated actin filament-severing protein, also impaired the wound response, indicating that cleaving the existing actin filament network is an important part of the cytoskeleton remodeling process.info:eu-repo/semantics/publishedVersio

Reversal of contractility as a signature of self-organization in cytoskeletal bundles.

Funder: FP7 People: Marie-Curie Actions; FundRef: http://dx.doi.org/10.13039/100011264; Grant(s): PCIG12-GA-2012-334053Bundles of cytoskeletal filaments and molecular motors generate motion in living cells, and have internal structures ranging from very organized to apparently disordered. The mechanisms powering the disordered structures are debated, and existing models predominantly predict that they are contractile. We reexamine this prediction through a theoretical treatment of the interplay between three well-characterized internal dynamical processes in cytoskeletal bundles: filament assembly and disassembly, the attachement-detachment dynamics of motors and that of crosslinking proteins. The resulting self-organization is easily understood in terms of motor and crosslink localization, and allows for an extensive control of the active bundle mechanics, including reversals of the filaments' apparent velocities and the possibility of generating extension instead of contraction. This reversal mirrors some recent experimental observations, and provides a robust criterion to experimentally elucidate the underpinnings of both actomyosin activity and the dynamics of microtubule/motor assemblies in vitro as well as in diverse intracellular structures ranging from contractile bundles to the mitotic spindle

A Dual Function for Prickle in Regulating Frizzled Stability during Feedback-Dependent Amplification of Planar Polarity

The core planar polarity pathway coordinates epithelial cell polarity during animal development, and loss of its activity gives rise to a range of defects, from aberrant morphogenetic cell movements to failure to correctly orient structures, such as hairs and cilia. The core pathway functions via a mechanism involving segregation of its protein components to opposite cells ends, where they form asymmetric intracellular complexes that couple cell-cell polarity. This segregation is a self-organizing process driven by feedback interactions between the core proteins themselves. Despite intense efforts, the molecular pathways underlying feedback have proven difficult to elucidate using conventional genetic approaches. Here we investigate core protein function during planar polarization of the Drosophila wing by combining quantitative measurements of protein dynamics with loss-of-function genetics, mosaic analysis, and temporal control of gene expression. Focusing on the key core protein Frizzled, we show that its stable junctional localization is promoted by the core proteins Strabismus, Dishevelled, Prickle, and Diego. In particular, we show that the stabilizing function of Prickle on Frizzled requires Prickle activity in neighboring cells. Conversely, Prickle in the same cell has a destabilizing effect on Frizzled. This destabilizing activity is dependent on the presence of Dishevelled and blocked in the absence of Dynamin and Rab5 activity, suggesting an endocytic mechanism. Overall, our approach reveals for the first time essential in vivo stabilizing and destabilizing interactions of the core proteins required for self-organization of planar polarity

Dynamic microtubules produce an asymmetric E-cadherin-Bazooka complex to maintain segment boundaries.

Distributing junctional components around the cell periphery is key for epithelial tissue morphogenesis and homeostasis. We discovered that positioning of dynamic microtubules controls the asymmetric accumulation of E-cadherin. Microtubules are oriented preferentially along the dorso-ventral axis in Drosophila melanogaster embryonic epidermal cells, and thus more frequently contact E-cadherin at dorso-ventral cell-cell borders. This inhibits RhoGEF2, reducing membrane recruitment of Rho-kinase, and increasing a specific E-cadherin pool that is mobile when assayed by fluorescence recovery after photobleaching. This mobile E-cadherin is complexed with Bazooka/Par-3, which in turn is required for normal levels of mobile E-cadherin. Mobile E-cadherin-Bazooka prevents formation of multicellular rosette structures and cell motility across the segment border in Drosophila embryos. Altogether, the combined action of dynamic microtubules and Rho signaling determines the level and asymmetric distribution of a mobile E-cadherin-Bazooka complex, which regulates cell behavior during the generation of a patterned epithelium

Dynamic myosin phosphorylation regulates contractile pulses and tissue integrity during epithelial morphogenesis

Apical constriction is a cell shape change that promotes epithelial bending. Activation of nonmuscle myosin II (Myo-II) by kinases such as Rho-associated kinase (Rok) is important to generate contractile force during apical constriction. Cycles of Myo-II assembly and disassembly, or pulses, are associated with apical constriction during Drosophila melanogaster gastrulation. It is not understood whether Myo-II phosphoregulation organizes contractile pulses or whether pulses are important for tissue morphogenesis. Here, we show that Myo-II pulses are associated with pulses of apical Rok. Mutants that mimic Myo-II light chain phosphorylation or depletion of myosin phosphatase inhibit Myo-II contractile pulses, disrupting both actomyosin coalescence into apical foci and cycles of Myo-II assembly/disassembly. Thus, coupling dynamic Myo-II phosphorylation to upstream signals organizes contractile Myo-II pulses in both space and time. Mutants that mimic Myo-II phosphorylation undergo continuous, rather than incremental, apical constriction. These mutants fail to maintain intercellular actomyosin network connections during tissue invagination, suggesting that Myo-II pulses are required for tissue integrity during morphogenesis.National Institute of General Medical Sciences (U.S.) (Transgenic RNAi Project at Harvard Medical School, (R01-GM084947)