Motors and Adaptors : Transport Regulation within Neurons

Abstract

Human thoughts and behavior are the outcome of communication between neurons in our brains. There is an entire world inside each of these neurons where transactions are established and meeting points are set. By using molecular motors to transport proteins and organelles along cytoskeletal tracks, neurons create the internal order of the bustling community of macromolecules. Given the challenging geometry of the neuron, the mechanisms that deliver fuel and materials to sustain the distant synapses are extremely important and not surprisingly, defects in intracellular transport are increasingly linked to neuropathologies. The work presented in this thesis describes novel regulatory mechanisms of the complex neuronal transport system. First we examined the trafficking rules that govern polarized transport in neurons. Specific types of microtubule-based motor proteins facilitate the sorting of cargo between the axon and the dendrites. By developing a new trafficking assay in hippocampal neurons to selectively probe specific motor protein activity, we investigated the contribution of dynein motors to neuronal polarity. Our findings highlight the interplay between microtubules and motors for the initial polarized sorting of neuronal cargos between axons and dendrites. Second, we examined the regulation of transport on the level of cargo-motor interaction by studying adaptor proteins and mitochondrial transport. Mitochondria, cellular power plants, are produced within the cell body and are needed throughout the neuron. We show how two homologous adaptor proteins utilize two different transport machineries to steer mitochondria into axons and dendrites. Third, we studied how transport is regulated on the level of motor-microtubule binding. We found an unusual type of kinesin motor regulator that blocks the microtubule binding of kinesin motors and thereby regulating transport of synaptic vesicle precursors by kinesin-3. Finally, in addition to regulatory transport mechanisms, the role of a recently discovered class of non-coding miRNAs in crucial neuronal processes was studied by using the primary hippocampal neuron culture system. Specific miRNAs expression profiles correlated with changes in neuronal development and neuronal activity. The experiments described in this thesis represent a considerable step towards understanding the complex trafficking process in neurons, and provide the basis for future study of brain function and brain pathology.