This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. The goal of this project is to understand the mechanisms for the coordination between microtubule (MT)-dependent and actin filament (AF) transport using fish melanophores as an experimental system. The only function of these large cells is fast and synchronous redistribution of thousands of membrane-bounded organelles, pigment granules, which aggregate at the cell center or redisperse uniformly throughout the cytoplasm. Pigment redistribution during aggregation involves transport to the minus ends of MTs. Pigment dispersion combines initial rapid movement to the MT plus ends and slow diffision-like movement along the AFs, which results in the homogeneous distribution of pigment in the cytoplasm. Therefore pigment transport requires coordination of the activities of multiple motors of different cytoskeletal specificity and polarity. Our recent work employed high resolution tracking of pigment granules to determine changes in the movement parameters of pigment granules along MTs and AFs during aggregation and dispersion. These movement parameters reflect the activities of the granule-bound molecular motors. The results of this analysis demonstrated that the switching between the two transport systems is controlled by the cytoplasmic levels of the second messenger cAMP, which determines the contribution of each transport system by selectively regulating the activities of individual MT- and AF-dependent motors.
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