A key part of cell division is the separation of the chromosomes. If this is not done correctly, the daughter cells will not have the correct number of chromosomes, leading to disease and death. A team of scientists from the Fred Hutchinson Cancer Research Center and from the University of Washington has isolated the machinery involved in chromosome separation and found that the process relies on tension.
During the separation process, chromosomes are attached to microtubules by protein structures called ‘kinetochores’. The microtubules pull the chromosomes apart to opposite ends of the cell. Eventually, the cell will divide between the two sets of chromosomes, resulting in two new cells.
Image of the mitotic spindle in a human cell showing microtubules in green, chromosomes (DNA) in blue, and kinetochores in pink.
The scientists were able to purify the kinetochore proteins and study their function. It seems that the main job of the kinetochore is to maintain proper tension in the microtubules lines. If the chromosomes are aligned correctly, the tension will be high, and the kinetochore will stablize the attachment to the microtubules as they pull on the chromosomes. If, on the other hand, the chromosomes are not properly aligned, the slackness in the lines causes the kinetochores to release or readjust the microtubules. The process can then be restarted.
Caption: If microtubules don't line up correctly on either side of a chromosome pair, the tension is weak and the attachment is released and fixed. A proper alignment secures the attachment through mechanical tension, and helps assure the chromosomes will separate accurately during cell division.
Credit: Charles Asbury lab