The bxd PRE from Bithorax Complex of Drosophila melanogaster Has Weak Insulator Activity

The autonomous functioning of regulatory domains in the Bithorax complex (BX-C) of Drosophila melanogaster is maintained by boundaries (insulators) that prevent inappropriate enhancer-promoter interactions. Polycomb response elements (PREs) maintain epigenetic memory within regulatory domains and are often located near insulators, enhancing their blocking activity. The bxd PRE is a well-characterized silencer that regulates the bxd/pbx domain of the Ubx gene in the first abdominal segment. We used a boundary replacement strategy to assess the insulator activity of the bxd PRE. Substituting the bxd PRE for the Fab-7 boundary, which separates the Abd-B regulatory domains in the BX-C, revealed that the bxd PRE has weak insulator activity.