Our newly developed ELISA method, however, could not be directly applied to neuronal cultures, since lamin A is not expressed in embryonic mouse brain [31] . Neurons in early stages of development up until postnatal day 5 express lamins of the B1 and B2 subtypes, which differ from the lamin A and C sequence at the caspase cleavage site (VEVD in B-type lamins and VEID in lamins A and C (Fig. 4A) [24, 31] ). Furthermore, the cleavage of lamins B1 and B2 at this site is not specific for caspase-6, as has been shown in a caspase-6-deficient cell line [24] . In agreement with these findings, we observed cleavage of lamin B1 in primary cortical neurons derived from both C6wt and C6ko mice at embryonic day 16.5 ( Fig. 4B) , while lamins A and C were not detected (data not shown). To overcome this obstacle, we decided to spike C6wt and C6ko neuronal lysates with purified lamin A protein, and after incubation at 37uC to allow for its cleavage by endogenous caspase-6 activity, we subjected the samples to our ELISA assay. We detect a significant increase in cleavage of lamin A protein when the incubation was performed in the presence of extracts derived from camptothecin-stressed C6wt neurons, whereas no increase in cleaved lamin A signal was observed in the presence of camptothecin-stressed C6ko neuronal extracts (Fig. 4C) . The ELISA method is therefore also suitable to detect caspase-6 activity in samples that do not contain endogenous lamin A or C protein.