Regulation of mitochondrial morphogenesis by annexin a6.

Mitochondrial homeostasis is critical in meeting cellular energy demands, shaping calcium signals and determining susceptibility to apoptosis. Here we report a role for anxA6 in the regulation of mitochondrial morphogenesis, and show that in cells lacking anxA6 mitochondria are fragmented, respiration is impaired and mitochondrial membrane potential is reduced. In fibroblasts from AnxA6(-/-) mice, mitochondrial Ca(2+) uptake is reduced and cytosolic Ca(2+) transients are elevated. These observations led us to investigate possible interactions between anxA6 and proteins with roles in mitochondrial fusion and fission. We found that anxA6 associates with Drp1 and that mitochondrial fragmentation in AnxA6(-/-) fibroblasts was prevented by the Drp1 inhibitor mdivi-1. In normal cells elevation of intracellular Ca(2+) disrupted the interaction between anxA6 and Drp1, displacing anxA6 to the plasma membrane and promoting mitochondrial fission. Our results suggest that anxA6 inhibits Drp1 activity, and that Ca(2+)-binding to anxA6 relieves this inhibition to permit Drp1-mediated mitochondrial fission

3D reconstruction of antiphase boundaries in Cu3Au from field ion images

International audienceField ion microscopy (FIM) was used to study the atomic level structure of the antiphase boundaries (APBs) in Cu3Au alloys. This technique allows a metallic sample volume to be investigated by using controlled evaporation of atomic layers. We used an emitter shape model from which the APBs can be reconstructed in three dimensions. The approach to the exact spatial arrangement of boundaries in the material volume allows the nature of planes of APBs to be determined. The results corroborate the observations from high resolution electron microscopy technique (HREM), which show that the APBs are mainly located in the cubic planes (001). \textcopyright 1995

3D reconstruction of antiphase boundaries in Cu3Au from field ion images

International audienceField ion microscopy (FIM) was used to study the atomic level structure of the antiphase boundaries (APBs) in Cu3Au alloys. This technique allows a metallic sample volume to be investigated by using controlled evaporation of atomic layers. We used an emitter shape model from which the APBs can be reconstructed in three dimensions. The approach to the exact spatial arrangement of boundaries in the material volume allows the nature of planes of APBs to be determined. The results corroborate the observations from high resolution electron microscopy technique (HREM), which show that the APBs are mainly located in the cubic planes (001). \textcopyright 1995

Intracellular Ca(2+) operates a switch between repair and lysis of streptolysin O-perforated cells

Pore-forming (poly)peptides originating from invading pathogens cause plasma membrane damage in target cells, with consequences as diverse as proliferation or cell death. However, the factors that define the outcome remain unknown. We show that in cells maintaining an intracellular Ca(2+) concentration [Ca(2+)](i) below a critical threshold of 10 microM, repair mechanisms seal off 'hot spots' of Ca(2+) entry and shed them in the form of microparticles, leading to [Ca(2+)](i) reduction and cell recovery. Cells that are capable of preventing an elevation of [Ca(2+)](i) above the critical concentration, yet are unable to complete plasma membrane repair, enter a prolonged phase of [Ca(2+)](i) oscillations, accompanied by a continuous shedding of microparticles. When [Ca(2+)](i) exceeds the critical concentration, an irreversible formation of ceramide platforms within the plasma membrane and their internalisation drives the dying cells beyond the 'point of no return'. These findings show that the extent of [Ca(2+)](i) elevation determines the fate of targeted cells and establishes how different Ca(2+)-dependent mechanisms facilitate either cell survival or death