Jason Andrews

A pulsed-laser microbeam at 532 nm wavelength and a laser-induced optical trap at 1064 nm wavelength have been successively combined to dissect and manipulate chromosomes in live newt lung epithelial cells. These preliminary experimental results demonstrated that chromosome fragments dissected by laser microbeam surgery, regardless of their size, could be easily pulled or rotated by optical forces when positioned at the periphery of the mitotic spindle. In addition, chromosome arms which were not subjected to laser microsurgery also could be moved with the optical tweezers at the spindle periphery. In our previous study on rat kangaroo kidney cells, this degree of facility in manipulating chromosome movement was not possible, most likely due to the close proximity of the intermediate filament 'cage' to the spindle. It is concluded herein that optical scissors and tweezers can be used in combination to study the interaction of chromosomes with the mitotic spindle in cells where the peripheral regions of the spindle are unobstructed by intermediate filaments. This can be performed on newt cells, where the diameter of the cage can be substantially larger than the diameter of the 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-μm neodymium YAG 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.