Rab complexes and membrane biogenesis in the endocytic pathway: structural imaging of a cell dynamic architecture. Jean Salamero, CNRS UMR 144, Institut Curie The structural and functional properties of the organelles involved in membrane trafficking are defined by molecular and dynamic architectures that permit membranes to fuse with or exit from a given compartment. These architectures must therefore not be distributed randomly, which requires conflicting needs for communication and segregation. Maintenance of segregation between Rab-defined compartments and partition of Rab complexes into membrane subdomains, point to Rab proteins as key players in these processes. However, proximal Rab domains must also “talk to each other” and this might be a generic role for many Rab interacting proteins. Our previous studies revealed the function of Rab11A together with a cohort of Rab11 Interacting Proteins, as membrane organizers in the endosomal pathway, which may lead to biogenesis or maintenance of specialized cellular compartments. The imaging techniques allow to consider the different Rab domains and their progressive conversion as a function of temporally defined multimolecular interactions. We adapted or developed diverse biophotonic approaches aimed to determine the dynamic and topological characterization of multi Rab complexes (Rab11A/Rabin8/Rab8; Rab11A/ RCP/Rab4; Rab6A or A’/Rab6IP1/Rab11A), in living cells.