Intracellular transport is ubiquitous in animal cells and has fundamental importance for diverse biological phenomena, such as secretion, neuronal signaling, organization of endomembranes, and mitosis. The driving force for intracellular transport is provided by molecular motors bound to the surface of cargo organelles and moving along microtubules (MTs) and actin filaments (AFs). Switching between these two types of transport must be precisely regulated for the delivery of organelles to specific regions of the cytoplasm. However, the mechanisms of such regulation remain a mystery. Here, we propose to answer the question about the regulation of switching between MTs and AFs using Xenopus melanophores as an experimental system. These cells rapidly redistribute in the cytoplasm thousands of membrane-bounded pigment granules, which aggregate in the cell center or disperse throughout the cytoplasm by means of pigment granule-bound molecular motors that use both MT and AF tracks. Switching of pigment granules between MTs and AFs is controlled by the levels of the second messenger cAMP. Background data by the principal investigator suggest that switching between the two types of tracks is based on a continuous tug-of-war between transport systems. The outcome of the tug-of-war is decided by the relative activities of MT-based and AF-based molecular motors simultaneously bound to the same pigment granule. Preliminary data also indicate that besides molecular motors, organelle transport and its switching between MT and AF tracks involves additional proteins that regulate docking of organelles to the destination track. This proposal will use molecular, cellular, and biochemical approaches to test the hypothesis that aggregation and dispersion signals regulate organelle docking and activities of granule-bound molecular motors through interconnected mechanisms that generate distinct kinetics of transferring pigment granules between MTs and AFs during aggregation and dispersion. To examine these regulatory mechanisms, docking molecules will be identified, and the regulation of their binding to transport tracks and pigment granules will be elucidated. The role of phosphorylation of subunits of molecular motors in regulation of their activities will be also determined.

Public Health Relevance

The goal of this proposal is an understanding of how membrane organelles switch between the two types of cytoskeletal transport tracks, microtubules and actin filaments. Such switching is a critical part of the intracellular transport process, which is essential for normal cell function. Defects in intracellular transport are responsible for many human diseases and our understanding of the molecular basis of these defects is paving the way to future effective therapeutics of diseases such as cancer, diabetes/Wolcott- rallison syndrome, and neurodegenerative disorders including Alzheimer and Huntington diseases.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM062290-11
Application #
8306112
Study Section
Nuclear and Cytoplasmic Structure/Function and Dynamics Study Section (NCSD)
Program Officer
Gindhart, Joseph G
Project Start
2001-06-01
Project End
2015-06-30
Budget Start
2012-07-01
Budget End
2013-06-30
Support Year
11
Fiscal Year
2012
Total Cost
$318,227
Indirect Cost
$111,586
Name
University of Connecticut
Department
Anatomy/Cell Biology
Type
Schools of Medicine
DUNS #
022254226
City
Farmington
State
CT
Country
United States
Zip Code
06030
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