Fig. 1. Dronc and Drice are essential for apoptosis in S2 cells. (A,B) DIC images of control S2 cells (A) and S2 cells treated with actinomycin D for 6 hours (B). Apoptotic cells undergoing membrane blebbing, a characteristic of apoptosis, are circled in (B). (C) Quantification of the apoptotic index of control S2 cells (column 1) and S2 cells incubated with actinomycin D for 6 hours (column 2). Results are the mean of three independent experiments and error bars indicate standard errors. (D) Time course of caspase activity towards peptide substrates in lysates from S2 cells treated with actinomycin D, which induces a robust increase in DEVDase and YEVDase activity. (E) Real-time PCR quantification of dcp-1 (columns 1 and 2) and decay (columns 3 and 4) transcript levels in control S2 cells (columns 1 and 3) compared with cells incubated for 72 hours with the respective dsRNA (columns 2 and 4). Dcp-1 dsRNA has no effect on dcp-1 transcript levels whereas Decay dsRNA reduces decay transcript levels by 72%. Results are the mean of three independent measurements and error bars indicate standard errors. (F) DEVDase activity of lysates from actinomycin-D-treated (6 hours) control S2 cells and S2 cells incubated with dsRNA targeting the indicated caspases. DEVDase activity is expressed as a fold-change compared with lysates from the corresponding cell population not treated with actinomycin D. Results are the mean of three independent experiments and error bars indicate standard errors. ^*P<0.01, values that differ significantly from untreated cells. (G) YEVDase activity of lysates from actinomycin-D-treated control S2 cells and S2 cells incubated with dsRNA targeting the indicated caspases. YEVDase activity is expressed as a fold-change compared with lysates from the corresponding cell population not treated with actinomycin D. ^*P<0.01, values that differ significantly from untreated cells. Results are the mean of three independent experiments and error bars indicate standard errors. RNAi of Dronc or Drice significantly reduces DEVDase and YEVDase activity compared with control S2 cells. (H) Apoptotic indices of actinomycin-D-treated control S2 cells and S2 cells incubated with dsRNA targeting the indicated caspases. Dronc and Drice dsRNA block the onset of actinomycin-D-mediated apoptosis. Results are the mean of three independent experiments and error bars indicate standard errors. ^*P<0.01, values that differ significantly from untreated cells.