Acinus (apoptotic chromatin condensation inducer in the nucleus) is a caspase substrate that has been implicated in nuclear changes during apoptosis. Chromatin condensation and DNA fragmentation are both nuclear morphological features associated with apoptosis. Acinus is expressed in different isoforms (L, S, S') most likely generated by alternative splicing. During apoptosis Acinus is cleaved by caspase-3 to generate a 23 kDa fragment that was reported to induce chromatin condensation. Acinus has been identified to be a component of the spliceosome complex, ASAP, suggesting a role in pre-mRNA processing. Down regulation of Acinus by RNA interference inhibits cell growth (5). This study also found that loss of Acinus inhibits DNA fragmentation but not chromatin condensation during apoptosis.