Myosin-X induces filopodia by multiple elongation mechanism.
Filopodia are actin-rich finger-like cytoplasmic projections extending from the leading edge of cells. Unconventional myosin-X is involved in the protrusion of filopodia. However, the underlying mechanism of myosin-X-induced filopodia formation is obscure. Here, we studied the movements of myosin-X during filopodia protrusion using a total internal reflection microscope to clarify the mechanism of myosin-X-induced filopodia formation. Myosin-X was recruited to the discrete site at the leading edge where it assembles with exponential kinetics before the filopodia extension. The myosin-X-induced filopodia showed repeated extension-retraction cycles with each extension of 2.4 microm, which was critical to produce long filopodia. Myosin-X, lacking the FERM domain, could move to the tip as does the wild type. However, it was transported toward the cell body during filopodia retraction, did not undergo multiple extension-retraction cycles, and failed to produce long filopodia. During the filopodia protrusion, the single molecules of full-length myosin-X moved within filopodia. The majority of the fluorescence spots showed two-step photobleaching, suggesting that the moving myosin-X is a dimer. Deletion of the FERM domain did not change the movement at the single molecule level with the same velocity of approximately 600 nm/s as wild-type, suggesting that the myosin-X in filopodia moves without interaction with the attached membrane via the FERM domain. Based upon these results, we have proposed a model of myosin-X-induced filopodia protrusion.
Watanabe
Tomonobu M
TM
World Premier International Research Center Initiative, Immunology Frontier Research Center, Osaka University, Suita, Osaka 565-0871, Japan.
Tokuo
Hiroshi
H
Gonda
Kohsuke
K
Higuchi
Hideo
H
Ikebe
Mitsuo
M
D000818:Animals; D001692:Biological Transport; D019556:COS Cells; D002522:Chlorocebus aethiops; D003593:Cytoplasm / Q000378:metabolism; D007700:Kinetics; D008027:Light; D008856:Microscopy, Fluorescence / Q000379:methods; D008954:Models, Biological; D009218:Myosins / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D011554:Pseudopodia / Q000378:metabolism*; D013997:Time Factors
D009218:Myosins
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