The third copy of chromosome 21 that causes Down’s syndrome has been silenced in a cell culture model of the disorder, a Nature paper reports this week. The research marks a step towards ‘whole chromosome therapy’ for disorders such as Down’s, and should aid research into the basic biology underlying these disorders.
Jeanne Lawrence and colleagues used an enzyme to introduce an RNA gene, called XIST, into cultured stem cells derived from Down’s syndrome patients. XIST RNA coated the extra third copy of chromosome 21, silencing the genes on it. By comparing cells with and without the extra chromosome silenced, the team noted that XIST helps correct the unusual patterns of cell growth and differentiation seen in Down’s syndrome-derived cells. The strategy can be used to help define the cellular and molecular changes underpinning the condition.
The work was inspired by a naturally occurring event – during development XIST switches off one of the two X chromosomes present in female embryos, ensuring daughters avoid a double dose of X chromosome genes. As such, the research also provides a model with which to study normal chromosome silencing.