Increasing the Complexity of Microtubule-based transport: Cargo adaptors and Hitchhiking on Vesicles. - PROJECT SUMMARY
Proper positioning of intracellular cargos (organelles, vesicles, and macromolecules) is critical for cell growth,
maturation, and survival. Eukaryotic cells use the molecular motors dynein and kinesin to transport cargos along
microtubule tracks. Defects in microtubule-based transport and mutations in the motors themselves, are an
underlying feature of many neurodevelopmental and neurodegenerative diseases. Since each type of cargo is
tuned for specific cellular functions, their loading, movement and unloading along microtubules requires
divergent transport mechanisms. How is cargo specificity on microtubules achieved? This proposal will address
this with an in-depth analysis of the two major modes of microtubule-based transport. The canonical view, known
as the cargo adaptor mode, is that each cargo interacts with specific adaptor proteins capable of recruiting
molecular motors. The regulatory mechanisms by which cargos selectively load and unload from these cargo
adaptors are not well understood. One goal of this proposal is to determine how a conserved phosphorylation
site on vesicle-bound Rab GTPases affects interactions with dynein cargo adaptors and ultimately, how these
interactions affect cellular function. Importantly, this Rab phosphorylation site is the predominant target of the
Parkinson’s disease-linked kinase LRRK2. The other mode of transport is called organelle hitchhiking. In
hitchhiking, Rab-vesicles can direct the movement of organelles on microtubules. To accomplish this, organelles
attach to (or ‘hitchhike’ on) motor-driven Rab-vesicles at membrane contact sites. Organelle hitchhiking is a new,
relatively unexplored paradigm of microtubule-based transport, and the underlying molecular mechanisms are
not well understood. What are the molecular linkers, tethers, and regulators of organelle hitchhiking? Is this a
prominent mode of microtubule-based transport? This proposal will use genetics, microscopy, and biochemistry
in both fungal and mammalian model systems to address these questions. Taken together, studying the two
main modes of microtubule-based transport is extremely important, given the critical roles Rabs, vesicles, and
hitchhiking cargos play in development and age-related diseases.
