CellManipulator Optical Tweezers Reveal Tspan7’s Role in Membrane Tethers
Researchers from Tsinghua University China recently used CellManipulator Optical Tweezers integrated to a confocal microscope to study the membrane tether stabilization, especially at retraction fibers. What are membrane tethers? Membrane tethers are finger-like extensions from the cell membrane. They play an important role in many cell processes, such as motility, tissue morphogenesis, immune function, and cancer metastasis. How about retraction fibers? Retraction fibers are sub-cellular structures resembling elongated protrusions that maintain attachment to the substrate during cellular migration. Furthermore, they serve as force transmitters and intercellular communication probes. In doing their function, membrane tethers experience constant and dynamic mechanical stress. The cytoskeleton dynamics interacting with the tether is the primary source of the stress. Apart from the cytoskeleton, they discovered the high dose of Tspan7 positively correlates to the length and number of retraction fibers emanating from cells. Furthermore, the protein preferred to localize on fibers (tubular membrane) instead of cell body (planar membrane). It seems the Tspan7 is sensitive to high-curvature membranes.
Optical Tweezers Test Tspan7’s Preference for High-Curvature Membranes
To test this, researchers generated Giant Plasma Membrane Vesicles (GPMVs) from Tspan7-GFP expressing cells. They also used CellManipulator Optical Tweezers to extrude a membrane tether from a vesicle. Indeed, Tspan7-GFP was more localized on the extruded membrane compared to the vesicle. It suggests an intrinsic preference for a high curvature membrane. Interpreting the results from live cell imaging, in vitro reconstitution, and in situ cryo-EM, the researchers suggested that Tspan7 forms a transmembrane skeleton. The authors imply "This structure, akin to the cytoskeleton, serves not only as a structural support but may also other roles".
