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BBB seminar: Jaakko Saraste

Functional symmetry of endomembranes

Jaakko Saraste
Department of Biomedicine and Molecular Imaging Center, University of Bergen

It has been well documented that the secretory (export) and endocytic (import) transport routes operating in mammalian cells are interconnected and actively exchange components. Extending this view, our earlier results revealed that the intermediate compartment (IC) at the endoplasmic reticulum (ER)-Golgi boundary and the endocytic recycling compartment (ERC) – defined by the GTPases Rab1 and Rab11, respectively – are functionally linked, establishing a novel membrane system around the centrosome. This finding was unexpected, since the IC has been generally regarded as a transient structure. Notably, the pericentrosomal domain of the IC (pcIC) and the ERC maintain their functional connection when cells are treated with brefeldin A (BFA), a compound that disassembles the Golgi stacks, which are thought to mediate the communication between the early secretory (pre-Golgi) and endocytic (post-Golgi) pathways. Thus, these compartments appear to reside at the crossroads of two interconnected membrane networks, which carry out important cellular functions, such as Golgi-independent trafficking of various molecules. Based on these considerations, it was of interest to examine the fate of the IC during cell division, when the Golgi apparatus undergoes physiological disassembly, and to find out whether it retains its connection with the endosomal system throughout the cell cycle. This talk summarizes these results, supporting the existence of a basic cellular endomembrane system that exhibits functional symmetry.

Chairperson: Stein-Ove Døskeland <stein.doskeland@uib.no>, Department of Biomedicine