Regulation of cargo transport during neuronal development and disease

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Project summary Development of highly elaborate and polarized neuronal morphology requires formation of molecularly distinct compartments within neurons and precise subcellular localization of proteins and organelles. Neuronal compartmentalization requires that motors such as kinesin-1 deliver specific cargos to different sites within the neuron. Neurons are especially dependent on diverse and high fidelity cargo transport because of their highly polarized and complex structure. Defects in transport underlie multiple human developmental and neurodegenerative diseases. Kinesin-1 is known to mediate long-distance transport of multiple cargos, but the mechanisms that determine specificity of cargo selection and delivery during development are poorly understood. The cargo-binding kinesin light chain (KLC) subunits of kinesin-1 (encoded by klc1-4 genes) are likely involved in specificity, yet the developmental processes they mediate are not understood. This is a critical knowledge gap, as mutations in human klc2 and klc4 genes cause spastic paraplegia diseases with very early onset. A major challenge to the field and the long term goal of this project is to understand the mechanisms controlling cargo transport and localization as neurons develop in their natural environment, where they must integrate multiple extracellular cues. We established a model in which we can image dynamics of neuronal cargo transport within developing sensory neurons in the intact zebrafish embryo. Vertebrate sensory neurons extend distinct central and peripheral axons to form the sensory circuit. We discovered unique functions for individual KLCs during neural development, including roles in shaping axon arbors, axon branching, guidance and maintenance during development, and roles in circuit function. In Aim 1 we will determine the mechanisms by which KLC4 regulates axon branching and compartmentalization, and the organelle cargos it transports. In Aim 2 we will determine functions of KLC2 in axon development and cargo transport, and mechanisms underlying human SPOAN syndrome. In Aim 3 we will determine which protein domains confer KLC functional specificity and will identify and determine the function of adaptors that interact with individual KLCs. Elucidation of the molecular signals regulating neuronal compartmentalization, cargo selection and transport, and axon growth and branching is critical for understanding human developmental disorders, neurodegenerative disorders, and the conditions under which regeneration after axon injury can occur. Our experiments will uncover such mechanisms and thus may help to identify molecular targets for disease treatment.