A discrete region of the D4Z4 is sufficient to initiate epigenetic silencing

The DUX4 transcription factor is briefly expressed in the early embryo and is epigenetically repressed in somatic tissues. Loss of epigenetic repression can result in the aberrant expression of DUX4 in skeletal muscle and can cause facioscapulohumeral dystrophy (FSHD). Multiple factors have been identified as necessary to maintain epigenetic silencing of DUX4 in skeletal muscle, but whether specific sequences at the DUX4 locus are sufficient for epigenetic silencing has been unknown. We cloned fragments of the D4Z4 macrosatellite repeat, the DNA region that encompasses the DUX4 retrogene, adjacent to a reporter driven by a constitutive promoter and identified a single fragment sufficient to epigenetically repress reporter gene expression. Previously identified suppressors of DUX4 expression-SETDB1, ATF7IP, SIN3A/B, and LRIF1-were necessary for silencing activity and p38 inhibitors enhanced suppression. These findings identify a key regulatory sequence for D4Z4 epigenetic repression and establish a model system for mechanistic and discovery studies.