Abstract
Originally described in crane-fly spermatocytes, tethers physically link and transmit force between the ends of separating chromosomes. Optical tweezers and laser scissors were used to sever the tether between chromosomes, create chromosome fragments attached to the tether which move toward the opposite pole, and to trap the tethered fragments. Laser microsurgery in the intracellular space between separating telomeres reduced chromosome strain in half of tested chromosome pairs. When the telomere-containing region was severed from the rest of the chromosome body, the resultant fragment either traveled towards the proper pole (poleward), towards the sister pole (cross-polar), or movement ceased. Fragment travel towards the sister pole varied in distance and always ceased following a cut between telomeres, indicating the tether is responsible for transferring a cross-polar force to the fragment. Optical trapping of cross-polar traveling fragments places an upper boundary on the tethering force of ~1.5 pN.
Highlights
During mitosis various biochemical and mechanical cues guide the controlled segregation of chromosomes
Optical tweezers and laser scissors were used to sever the tether between chromosomes, create chromosome fragments attached to the tether which move toward the opposite pole, and to trap the tethered fragments
When the telomere-containing region was severed from the rest of the chromosome body, the resultant fragment either traveled towards the proper pole, towards the sister pole, or movement ceased
Summary
During mitosis various biochemical and mechanical cues guide the controlled segregation of chromosomes. During the anaphase stage of mitosis sister chromatids are divided and the chromosomes transported to the poles of the cell by a Brownian ratchet mediated kinetochore force and microtubule depolymerization [8,9,10] While useful parameters such as tension, strain, and elastic modulus can be studied using biosensors, and ex vivo experimentation [3,11,12,13,14,15], the underlying physical forces which move chromosomes in anaphase (motility force) are not well known. LaFountain et al found that two of four sister chromatids in crane-fly spermatocytes were linked by a physical tether connecting their telomere regions such that a ‘cross-polar’ force elongated segregating chromosomes and moved severed chromosome fragments through the cell [24]. Optically trapping the chromosome fragments offers a limited but non-intrusive method of measuring forces acting on the chromosome
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