Scientists believe they have solved one of life’s great mysteries – how chromosomes come into an X shape.
Chromosomes are long DNA molecules that contain the genetic material of an organism. These structures were discovered in the late 1800s after the invention of the optical microscope.
They are X-shaped, but the reason behind this has been a mystery. They are known to form shape during cell division, but the researchers wondered how this happened.
Scientists led by Professor Daniel Panne from the University of Leicester and Dr Benjamin Rowland from the Netherlands Cancer Institute believe the answer lies in a protein called shugoshin, which ‘locks’ chromosomes into an X shape.
When a cell divides, it copies its DNA and divides it equally between the two new cells. The DNA in each cell is about two meters long, so it must be compressed into a compact package to fit.
Cells leave two copies in between until they divide. Under a microscope, such a package looks like an X. Just before cell division, the X is released in the middle, and each arm of the X enters a separate cell.
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Dr Rowland said: “A chromosome actually consists of two identical long strands of DNA that are initially joined along their entire length.
“Many ring-shaped cohesin molecules hold the two threads together. When the cell is about to divide, the cohesin ring opens and the arms of the DNA separate.”
The researchers found that the protein, also known as SGO1, locks onto cohesin rings, giving chromosomes an X shape.
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When cells begin to divide, the “molecular scissors” cut the loops, separating the DNA.
Professor Panne said: “Finally understanding at the molecular and atomic level how the hallmark X-shaped chromosomes are created during cell division is exciting.
“Not only has this interested generations of scientists, but it’s also important for our understanding of how this process can go awry in disease.”
The study was published in the journal Nature Structural and Molecular Biology.