Use of a laser-induced optical force trap to study chromosome movement on the mitotic spindle

A laser-induced optical force trap was used to alter the movement of chromosomes in mitotic cells in vitro. The trap was produced by using a 1.06-microns neodymium YAG (yttrium/aluminum garnet) laser focused through a phase-contrast microscope. The trap was applied to one side of centrophilic chromosomes off the mitotic spindle and to late-moving chromosomes on the mitotic spindle. In both situations, chromosome movement was initiated in the direction opposite to that of the applied force. When the force was applied, chromosomes moved at velocities 10-20 times normal. These studies verify and extend the feasibility of using this new technique to study factors that influence organelle motility.