H2AX and colorectal carcinoma: We recently carried out a genome-wide small interfering RNA (siRNA) screen in HCT116 colorectal carcinoma-derived cells to identify previously uncharacterized regulators of genome stability, using phosphorylation of the histone variant H2AX on Ser139 (γH2AX) as a marker of increased DNA damage (Staples et al., 2012, Staples et al., 2014).