Browsing by Issue Date, starting with "2011-12"
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- A dual function of Drosophila capping protein on DE-cadherin maintains epithelial integrity and prevents JNK-mediated apoptosisPublication . Jezowska, B.; Fernández, B.G.; Amândio, A.R.; Duarte, P.; Mendes, C.; Brás-Pereira, C.; Janody, F.E-cadherin plays a pivotal role in epithelial cell polarity, cell signalling and tumour suppression. However, how E-cadherin dysfunction promotes tumour progression is poorly understood. Here we show that the actin-capping protein heterodimer, which regulates actin filament polymerization, has a dual function on DE-cadherin in restricted Drosophila epithelia. Knocking down capping protein in the distal wing disc epithelium disrupts DE-cadherin and Armadillo localization at adherens junctions and upregulates DE-cadherin transcription. In turn, DE-cadherin provides an active signal, which prevents Wingless signalling and promotes JNK-mediated apoptosis. However, when cells are kept alive with the Caspase inhibitor P35, the activity of the JNK pathway and of the Yorkie oncogene trigger massive proliferation of cells that fail to stably retain associations with their neighbours. Moreover, loss of capping protein cooperates with the Ras oncogene to induce massive tissue overgrowth. Taken together, our findings argue that in some epithelia, the dual effect of capping protein loss on DE-cadherin triggers the elimination of mutant cells, preventing them from proliferating. However, the appearance of a second mutation that blocks cell death may allow for the development of some epithelial tumours
- Dynamics of Histone H3 Deposition In Vivo Reveal a Nucleosome Gap-Filling Mechanism for H3.3 to Maintain Chromatin IntegrityPublication . Ray-Gallet, Dominique; Woolfe, Adam; Vassias, Isabelle; Pellentz, Céline; Lacoste, Nicolas; Puri, Aastha; Schultz, David C.; Pchelintsev, Nikolay A.; Adams, Peter D.; Jansen, Lars E.T.; Almouzni, GenevièveEstablishment of a proper chromatin landscape is central to genome function. Here, we explain H3 variant distribution by specific targeting and dynamics of deposition involving the CAF-1 and HIRA histone chaperones. Impairing replicative H3.1 incorporation via CAF-1 enables an alternative H3.3 deposition at replication sites via HIRA. Conversely, the H3.3 incorporation throughout the cell cycle via HIRA cannot be replaced by H3.1. ChIP-seq analyses reveal correlation between HIRA-dependent H3.3 accumulation and RNA pol II at transcription sites and specific regulatory elements, further supported by their biochemical association. The HIRA complex shows unique DNA binding properties, and depletion of HIRA increases DNA sensitivity to nucleases. We propose that protective nucleosome gap filling of naked DNA by HIRA leads to a broad distribution of H3.3, and HIRA association with Pol II ensures local H3.3 enrichment at specific sites. We discuss the importance of this H3.3 deposition as a salvage pathway to maintain chromatin integrity.