0218: Comparison of transvenous versus surgical implantation of left ventricular lead for cardiac resynchronization therapy

BackgroundApproximately 1% of the adult population have heart failure with reduced ejection fraction. Since the 1980s, therapeutic advances in this field have been significant, particularly through the development of cardiac resynchronization therapy (CRT). However, transvenous implantation of the left ventricular (LV) lead is unsuccessful in 5 - 15% of patients. For this group, surgical placement of LV lead is an alternative.ObjectiveCompare the effects of transvenous versus surgical implantation of the LV lead in CRT.MethodsWe included 100 consecutive patients who had received CRT in our centre between January 2008 and July 2012 in a retrospective observational study. Twelve patients who had failed transvenous implantation of LV lead had a surgical placement.ResultsPopulation characteristics were a mean age of 66±11 years, 16% female, New York Heart Association class 2.9±0.5, 45% ischemic cardiomyopathy, left ventricular ejection fraction (LVEF) 24±7%, QRS width 165±23ms. There were no major difference in preoperative variables between two groups except sex category (12.5% female in transvenous group versus 42% in surgical group, p=0.022). During a mean follow-up of 508±429 days, the improvements seen in all variables showed no difference between the groups. At six months, 77% of patients had improved at least one class of their dyspnea stage, LVEF improved significantly (24±7% versus 36±10% at six months).ConclusionsSurgical placement of LV lead offers similar benefits as compared with transvenous implantation

Cortical localization of maternal embryonic leucine zipper kinase (MELK) implicated in cytokinesis in early xenopus embryos

MELK has been implicated in a large variety of functions. Because its level is elevated in cancer tissues and it is involved in cell proliferation, MELK is considered as a potential therapeutic target for cancers. In a recent, study we have shown that MELK is involved in cytokinesis in early Xenopus laevis embryos. MELK dynamically accumulates at the cell cortex including a narrow band corresponding to the presumptive division furrow shortly before cytokinesis onset. MELK co-localizes and interacts with anillin an important regulator of cytokinesis. In addition, MELK overexpression interferes with accumulation at the cleavage furrow of activated Rho GTPase another crucial regulator of cytokinesis. Interestingly, our study also revealed that a transition implying a change in the direction of asymmetric furrow ingression occurs during early development. After this transition, MELK, as well as other proteins involved in cytokinesis, do not localize anymore as a band at the equatorial cortex but still localizes at the cell cortex. Our results indicate that cortical localization is an important feature of MELK in X. laevis embryos

Adherens junctions are involved in polarized contractile ring formation in dividing epithelial cells of Xenopus laevis embryos

International audienceCells dividing in the plane of epithelial tissues proceed by polarized constriction of the actomyosin contractile ring, leading to asymmetric ingression of the plasma mem brane. Asymmetric cytokinesis results in the apical positioning of the actomyosin contractile ring and ultimately of the midbody. Studies have indicated that the contractile ring is associated with adherens junctions, whose role is to maintain epithelial tissue cohesion. However, it is yet unknown when the contractile ring becomes associated with adherens junctions in epithelial cells. Here, we examined contractile ring formation and activation in the epithelium of Xenopus embryos and explored the implication of adherens junctions in the contractile ring formation. We show that accumulation of proteins involved in contractile ring formation and activation is polarized, starting at apical cell-cell contacts at the presumptive division site and spreading within seconds towards the cell basal side. We also show that adherens junctions are involved in the kinetics of contractile ring formation. Our study reveals that the link between the adherens junctions and the contractile ring is established from the onset of cytokinesis

Tight junction-associated protein GEF-H1 in the neighbours of dividing epithelial cells is essential for adaptation of cell-cell membrane during cytokinesis

International audienceAnimal cells divide by a process called cytokinesis which relies on the constriction of a contractile actomyosin ring leading to the production of two daughter cells. Cytokinesis is an intrinsic property of cells which occurs even for artificially isolated cells. During division, isolated cells undergo dramatic changes in shape such as rounding and membrane deformation as the division furrow ingresses. However, cells are often embedded in tissues and thus are surrounded by neighbouring cells. How these neighbours might influence, or might themselves be influenced by, the shape changes of cytokinesis is poorly understood in vertebrates. Here, we show that during cytokinesis of epithelial cells in the Xenopus embryo, lateral cell-cell contacts remain almost perpendicular to the epithelial plane. Depletion of the tight junction-associated protein GEF-H1 leads to a transient and stereotyped deformation of cell-cell contacts. Although, this deformation occurs only during cytokinesis, we show that it originates from immediate neighbours of the dividing cell. Moreover, we show that exocyst and recycling endosome regulation by GEF-H1 are involved in adaptation of cell-cell contacts to deformation. Our results highlight the crucial role of tight junctions and GEF-H1 in cell-cell contact adaptation when cells are exposed to a mechanical stress such as cytokinesis

Tight junctions negatively regulate mechanical forces applied to adherens junctions in vertebrate epithelial tissue

International audienceEpithelia are layers of polarised cells tightly bound to each other by adhesive contacts. Epithelia act as barriers between an organism and its external environment. Understanding how epithelia maintain their essential integrity while remaining sufficiently plastic to allow events such as cytokinesis to take place is a key biological problem. In vertebrates, the remodelling and reinforcement of adherens junctions maintains epithelial integrity during cytokinesis. The involvement of tight junctions in cell division, however, has remained unexplored. Here, we examine the role of tight junctions during cytokinesis in the epithelium of the Xenopus laevis embryo. Depletion of the tight junction-associated proteins ZO-1 and GEF-H1 leads to altered cytokinesis duration and contractile ring geometry. Using a tension biosensor, we show that cytokinesis defects originate from misregulation of tensile forces applied to adherens junctions. Our results reveal that tight junctions regulate mechanical tension applied to adherens junctions, which in turn impacts cytokinesis

Epithelial cell division in the Xenopus laevis embryo during gastrulation

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Maternal embryonic leucine zipper kinase is stabilized in mitosis by phosphorylation and is partially degraded upon mitotic exit.

International audienceMELK (maternal embryonic leucine zipper kinase) is a cell cycle dependent protein kinase involved in diverse cell processes including cell proliferation, apoptosis, cell cycle and mRNA processing. Noticeably, MELK expression is increased in cancerous tissues, upon cell transformation and in mitotically-blocked cells. The question of how MELK protein level is controlled is therefore important. Here, we show that MELK protein is restricted to proliferating cells derived from either cancer or normal tissues and that MELK protein level is severely decreased concomitantly with other cell cycle proteins in cells which exit the cell cycle. Moreover, we demonstrate in human HeLa cells and Xenopus embryos that approximately half of MELK protein is degraded upon mitotic exit whereas another half remains stable during interphase. We show that the stability of MELK protein in M-phase is dependent on its phosphorylation state

Asymmetries in Cell Division, Cell Size, and Furrowing in the Xenopus laevis Embryo

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A functional analysis of MELK in cell division reveals a transition in the mode of cytokinesis during Xenopus development.

International audienceMELK is a serine/threonine kinase involved in several cell processes, including the cell cycle, proliferation, apoptosis and mRNA processing. However, its function remains elusive. Here, we explored its role in the Xenopus early embryo and show by knockdown that xMELK (Xenopus MELK) is necessary for completion of cell division. Consistent with a role in cell division, endogenous xMELK accumulates at the equatorial cortex of anaphase blastomeres. Its relocalization is highly dynamic and correlates with a conformational rearrangement in xMELK. Overexpression of xMELK leads to failure of cytokinesis and impairs accumulation at the division furrow of activated RhoA - a pivotal regulator of cytokinesis. Furthermore, endogenous xMELK associates and colocalizes with the cytokinesis organizer anillin. Unexpectedly, our study reveals a transition in the mode of cytokinesis correlated to cell size and that implicates xMELK. Collectively, our findings disclose the importance of xMELK in cytokinesis during early development and show that the mechanism of cytokinesis changes during Xenopus early development