Caspase activation and DNA fragmentation induced by camptothecin is reduced in Apaf1^-/- and Hq/Apaf1^-/- neurons. Cortical neurons cultured from wild-type (wt), Hq, Apaf1^-/-, and Hq/Apaf1^-/- littermates were treated with camptothecin (10 μm). A, Caspase activity was measured by DEVD-AFC (N-acetyl-Asp-Glu-Val-Asp-(7-amino-4-trifluoromethyl-coumarin)) cleavage (n = 3). B, Immunocytochemistry of active caspase 3 and nuclear staining by Hoechst at 24 h. C, Quantification of TUNEL staining (n = 3). D, TUNEL staining and nuclear staining by Hoechst at 24 h. Scale bar, 50 μm.