There isn’t a cell biologist out there who doesn’t fantasize about reaching her hands into a cell and physically manipulating whatever protein or structure that she obsesses over. While we can’t do that with our own hands, optical tweezers can…and the information we learn is invaluable. Today’s image is from a paper that uses optical tweezers to measure the forces within a mitotic spindle.
The mechanics within a mitotic spindle are complicated, and cannot be fully understood until all of the forces that exist within it are determined. A recent paper measures the forces of chromosome and spindle pole movements using optical tweezers to trap either kinetochores or spindle poles. Optical tweezers use refracted light to trap small objects within a cell, and are able to stop the movement of the object as the laser power of the trap approaches (or exceeds) the cell’s own force on the object. With this technology, Ferraro-Gideon and colleagues measured the forces in mitotic spindles in several samples—a flatworm, a crane fly, and a mammalian spindle. The force used to stop chromosome movement was closer to the theoretical values of chromosome force, much less than the force values calculated by experiments performed by Bruce Nicklas in the 1980s using needles to manipulate chromosome movement. In the DIC (left) and fluorescence images (right) above, a trap (square) is applied to kinetochores in mammalian cells. The trap did not damage the microtubules of the spindle (right image).
Ferraro-Gideon, J., Sheykhani, R., Zhu, Q., Duquette, M., Berns, M., & Forer, A. (2013). Measurements of forces produced by the mitotic spindle using optical tweezers Molecular Biology of the Cell, 24 (9), 1375-1386 DOI: 10.1091/mbc.E12-12-0901
Check out an extended report on these experiments, and others from this lab:
Sheykhani, R., Baker, N., Gomez-Godinez, V., Liaw, L., Shah, J., Berns, M., & Forer, A. (2013). The role of actin and myosin in PtK2 spindle length changes induced by laser microbeam irradiations across the spindle Cytoskeleton, 70 (5), 241-259 DOI: 10.1002/cm.21104