A Massachusetts General Hospital (MGH) research team has identified the essential role of a structural protein in the silencing of the inactive X chromosome, a process that prevents both copies of the same gene from being expressed in female mammals, which carry two copies of the X chromosome. In their report published online in the journal Cell, the investigators describe finding that the SMCHD1 protein is required for the inactive X chromosome to be processed in a way that blocks the expression of its genes.