Imaging Myosin-X at the Single-Molecule Level Reveals a Novel Form of Motility in Filopodia

• Published in: Current biology Vol. 19; no. 11; p. 967
• Main Authors: Kerber, Michael L., Jacobs, Damon T., Campagnola, Luke, Dunn, Brian D., Yin, Taofei, Sousa, Aurea D., Quintero, Omar A., Cheney, Richard E.
• Format: Journal Article
• Language: English
• Published: 23.04.2009
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2009.03.067

Although many proteins, receptors, and viruses are transported rearward along filopodia by retrograde actin flow[ 1 - 3 ], it is less clear how molecules move forward in filopodia. Myosin-X (Myo10) is an actin-based motor hypothesized to use its motor activity to move forward along actin filaments to the tips of filopodia[ 4 ]. Here we use a sensitive total internal reflection fluorescence (TIRF) microscopy system to directly visualize the movements of GFP-Myo10. This reveals a novel form of motility at or near the single-molecule level in living cells wherein extremely faint particles of Myo10 move in a rapid and directed fashion towards the filopodial tip. These fast forward movements occur at ∼600 nm/s over distances of up to ∼10 μm and require Myo10 motor activity and actin filaments. As expected for imaging at the single-molecule level, the faint particles of GFP-Myo10 are diffraction-limited, have an intensity range similar to single GFP molecules, and exhibit stepwise bleaching. Faint particles of GFP-Myo5a can also move towards the filopodial tip, but at a slower characteristic velocity of ∼250 nm/s. Similar movements were not detected with GFP-Myo1a, indicating that not all myosins are capable of intrafilopodial motility. These data indicate the existence of a novel system of long-range transport based on the rapid movement of myosin molecules along filopodial actin filaments.