The work will help
scientists better understand how genes are regulated, the study authors say.
'Our maps of looping revealed thousands of hidden switches that
scientists didn't know about before. In the case of genes that can cause cancer
or other diseases, knowing where these switches are is vital,' said study
author Miriam Huntley from Harvard University.
There are around two metres of DNA in each human cell, which is compacted
in a complex looping system to fit into the cell's nucleus. This brings together
regions of DNA that can interact with
each other, meaning the function of genes can be regulated, switching them 'on'
The research, led by Dr Erez Lieberman Aiden at the Baylor College of Medicine, used a technique called in situ Hi-C to create a 3D map of the structure of DNA. 'For over a century, scientists have known
that DNA forms loops inside of cells, and that knowing where the loops are is
incredibly important,' said Dr Suhas Rao, who worked on the study.
The research shows that there are around 10,000 loops in the human
genome, which is significantly lower than expected. 'The genome project
revealed far fewer genes than everyone was expecting; the fact that there are
so few loops is a similar surprise,' said Dr Aiden.
Many of the largest loops were found only on the second X chromosome in
women, indicating that loops play a major role in switching it off. 'The copy
of the X chromosome that is off in females contains gigantic loops that are up
to 30 times the size of anything we see in males,' said Huntley.
The work also highlighted differences and similarities in loop
structures between eight different cell types, including human cancer and mouse
cell lines. Many of the looping patterns
were conserved between cell lines, suggesting that many of these structures
have been maintained through evolution.