Lots of things can be solved by this mechanism.” “We will know how chromosomes condense, how they segregate, how genes talk to enhancers. If it exists, it will solve lots of problems,” says Leonid Mirny, a professor of physics in MIT’s Institute for Medical Engineering and Sciences, who led the research. “Nobody has ever directly observed this mechanism of loop extrusion. The MIT team suggests that two proteins thought to function primarily as “staples” that hold DNA together, cohesin and condensin, can also actively manipulate DNA. This mechanism, outlined in three recent papers published in Cell Reports, eLife, and Biophysical Journal, suggests that chromosome organization relies on proteins that act as molecular motors that pull strands of DNA into progressively larger loops. Moreover, the researchers demonstrate that a similar model explains how chromosomes are organized when cells are not dividing, and they hypothesize that loop extrusion by molecular motors splits chromosomes into separate domains, helping to control which genes are expressed in a given cell.
CHROMOSOMES CONDENSE SERIES
In computer simulations, the researchers demonstrate that certain molecular “machines” can transform chromosomes from a loosely tangled rope into a series of tiny loops that condense each chromosome and allow it to extricate itself from the others. When cells divide, they must first condense these chromosomes - each of which when fully extended is a thousand times longer than the cell’s nucleus and physically indistinguishable from the others - into compact structures that can be easily separated and packaged into their offspring.Īn MIT-led team has now developed a model that explains how cells handle this difficult task. Human cells contain 23 pairs of chromosomes that form a loosely organized cluster in the cell nucleus.
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