Regulation of Bidirectional Microtubule-Dependent Organelle Transport in Xenopus Laevis Melanophores

114 p.Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2005.The regulated transport of cellular components is of paramount importance to a number of processes in the eukaryotic cell including mitosis, protein sorting, and axis-determination. Therefore, understanding the regulatory mechanisms that govern this transport can provide important insights into cellular functions, and can aid in the identification and treatment of diseased states of the cell. An excellent model system in which to study regulated transport is Xenopus laevis melanophores, which contain pigment-filled organelles termed melanosomes that can be aggregated to the perinuclear region or dispersed throughout the cytoplasm by the motor proteins kinesin-2, cytoplasmic dynein, and myosin V. While the motor proteins responsible for melanosome transport have been identified, the regulatory mechanisms that control melanosome transport are less known. The following dissertation seeks to shed light on the mechanisms that regulate microtubule-based melanosome transport by identifying receptor proteins for microtubule motors as well as signaling cascades that regulate microtubule-based melanosome movement. Biochemical assays and in vivo analysis of melanosome transport were utilized to determine that dynactin, a large multi-subunit protein complex, acts as a receptor for both kinesin-2 and dynein on the melanosome surface, and may serve to coordinate the activity of these motors during regulated transport. Further exploration into the mechanisms that regulate melanosome transport reveals that bidirectional melanosome transport is under tight control of the ERK signaling cascade. This dissertation demonstrates that MEK and ERK exist in a functional signaling complex on melanosomes, and are transiently activated at the onset of aggregation. This activation correlates with an increase of melanosome transport, and is required for proper melanosome aggregation to occur. In addition, ERK signaling acts downstream from the classical melanosome transport regulatory pathway involving PKA. The results of these studies characterize the contribution of two novel components of bidirectional, microtubule-based melanosome transport, and support a model of coordination between microtubule motors of opposite polarity.U of I OnlyRestricted to the U of I community idenfinitely during batch ingest of legacy ETD