Dominant negative Cul1 impairs E2F inactivation in S phase. Third instar discs were labelled for BrdU to detect S phase cells (green) and for E2F (red). (A-C) Wild-type wing disc. (D-F) mCul1-overexpressing wing disc. No overlap is seen in wild-type whereas there is overlap (arrowheads in F) in some cells that overexpress mCul1. Scale bar is 5 μm.