To confirm the selectivity of lamin cleavage by caspase-6, we made use of mouse embryonic fibroblast (MEF) cells generated from wild-type and caspase-62/2 (C6wt and C6ko) mice [27] . These cells only differ in their expression of caspase-6 ( Fig. 2A) , making them an ideal system to study the specificity of caspase-6 substrates. Apoptosis was induced by the addition of 50 nM staurosporine to the culture medium, and the activation of caspase-6 was monitored over time by assessing the cleavage of endogenous lamin A via Western blotting (Fig. 2B ) or with the Ac-VEID-AFC peptide substrate (Fig. 2F ). The antibody used to detect full length lamin A at 70 kDa cross-reacts with the closely related lamin C protein (60 kDa, [28] ), and the N-terminal fragments of both cleaved lamin A and C are detected at the same size of 28 kDa (Fig. 2B+E) . Furthermore, using a cell line that does not express caspase-3 but expresses caspase-6 ( Fig. 2C ), we found that the lamin proteins are still processed after the induction of apoptosis with camptothecin ( Fig. 2D ), confirming the requirement of caspase-6 but not caspase-3 for this process.