Photonic and Magnetic Force Micro-piston: An integrated force/microfluidic device for investigating expansion and compression stress in chromatin/chromosomes and their roles in chromosome function.

Abstract

Dynamic changes in the state of chromosomes (changes in the level of chromatin compaction) take place in the confined environment of the nucleus throughout the cell cycle. These changes have been hypothesized to determine both the mechanical properties and, as a direct consequence of such effects, the function of chromosomes (Kleckner et al., 2004). To test this hypothesis, we have developed devices that can use either photon pressure or magnetic force to push beads in microfluidic channels, creating compression chambers in which the response of a confined biological specimen can be investigated as a function of force as well as changes in buffer, extract or biochemical composition. Photon pressure is generated by a weakly focused laser beam emanating from a fiber optic mounted directly on to our microfluidic chip, thus eliminating the need for the fixed optics associated with typical laser trapping systems. As a result, heating and the associated risk to a biological specimen is greatly reduced. Magnetic force is generated by a thin foil electromagnet system capable of producing high field and field gradients that, when used in conjuction with a 4.5 micron magnetic bead, can produce hundreds of picoNewtons of compression force on a biological specimen. These devices will be used to address three immediate questions of interest: (i) What is the magnitude of the force generated by chromatin expansion? (ii) When two chromatin masses are present, to what extent do they intermingle? and (iii) When expansion is constrained by confinement, does the resulting compression stress alter the structure and/or properties of chromatin?