On-off switch for key stem cell gene discovered

Scientists have uncovered an on-off switch for a key stem cell gene, a discovery that may propel advances in regenerative medicine.
University of Toronto researchers investigated stem cells in mice and showed that the activity of Sox2 gene which is critical for early development is regulated by a region elsewhere on the genome.
The discovery could mean a significant advance in the emerging field of human regenerative medicine, as the Sox2 gene is essential for maintaining embryonic stem cells that can develop into any cell type of a mature animal, researchers said.
"We studied how the Sox2 gene is turned on in mice, and found the region of the genome that is needed to turn the gene on in embryonic stem cells," said Professor Jennifer Mitchell of U of T's Department of Cell and Systems Biology.

"Like the gene itself, this region of the genome enables these stem cells to maintain their ability to become any type of cell, a property known as pluripotency. We named the region of the genome that we discovered the Sox2 control region, or SCR," said Mitchell.
It was previously thought that regions much closer to the Sox2 gene were the ones that turned it on in embryonic stem cells.

Mitchell and her colleagues eliminated this possibility when they deleted these nearby regions in the genome of mice and found there was no impact on the gene's ability to be turned on in embryonic stem cells.

"We then focused on the region we've since named the SCR as my work had shown that it can contact the Sox2 gene from its location 100,000 base pairs away," said study lead author Harry Zhou, a former graduate student in Mitchell's lab, now a student at U of T's Faculty of Medicine.
"To contact the gene, the DNA makes a loop that brings the SCR close to the gene itself only in embryonic stem cells. Once we had a good idea that this region could be acting on the Sox2 gene, we removed the region from the genome and monitored the effect on Sox2," Zhou said.

The researchers discovered that this region is required to both turn Sox2 on, and for the embryonic stem cells to maintain their characteristic appearance and ability to differentiate into all the cell types of the adult organism.
"Just as deletion of the Sox2 gene causes the very early embryo to die, it is likely that an abnormality in the regulatory region would also cause early embryonic death before any of the organs have even formed," said Mitchell.
"It is possible that the formation of the loop needed to make contact with the Sox2 gene is an important final step in the process by which researchers practicing regenerative medicine can generate pluripotent cells from adult cells," Mitchell added.

The findings are published in the journal Genes & Development.