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The Hitchhikers Guide Through the Cytoplasm

Orateur :

Igor Kulic, Division of Engineering and Applied Sciences, Harvard University, Cambridge, USA

Salle :

des thèses

Sujet :

Cellular cargos are moved by attached molecular motors through the cytoplasm along rigid and immobile microtubules. At least that’s the textbook version of our present understanding of the intracellular transport. However a peculiar but very common phenomenon called ’bidirectional transport’ seems to defy a simple explanation within this textbook framework. This rapid aperiodic back-and-forth direction switching of cellular cargos seems inconsistent with a tug of war of opposite polarity motors kinesin and dynein or any regulated switching process between them.

Starting from this dead end we describe an alternative mechanism called ’hitchhiking’ which results from motor induced longitudinal fluctuations of cytoskeletal microtubules (MT). Those short range fluctuations combined with transient cargo binding to MTs lead to long range transport even for cargos having no molecular motors on them. We present experimental evidence from several organisms indicating that MTs indeed act as nonequilibrium fluctuation reservoirs/transmitters and can drive the motion of vesicles rather than just passively hosting it. From this perspective MTs seem more than just cell’s rigid ’bones’ and immobile ’highways’. In the powerful hands of molecular motors they indeed act as cytoplasmic stirring bars !

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