Figure 2. Abnormalities in the cell-death process in
dpl-1(
n3380) and
mcd-1(
n4005) animals. (A) P9.aap in a
dpl-1(
n3380); nIs106 animal was condensed 2 hr 10 min after its generation. By 4 hr 10 min after its generation, P9.aap had recovered and appeared morphologically normal; 36 hr later, P9.aap expressed Plin-11gfp. P9.aap is indicated by an arrow. Anterior, left. Posterior, right. Dorsal, top. Ventral, bottom. In the 4-hr 10-min image anterior is right and posterior is left. (B) P11.aap in an
mcd-1(
n4005); nIs106 animal condensed 3 hr 22 min after its generation. This cell had first displayed attributes of a dying cell 1 hr 35 min after its generation. Three hours 27 min after generation P11.aap recovered, and P11.aaap had normal nuclear morphology. Three hours 42 min after generation, P11.aap condensed, and P11.aaap was condensed as well. Three hours 47 min after generation, P11.aap recovered. P11.aap was observed until 5 hr 25 min after generation without any further obvious attempts at death. Thirty-six hours later, no GFP fluorescence was detected in the P11 region, indicating that this cell either failed to express
lin-11 or ultimately died. P11.aap is indicated by a black arrow and P11.aaap is indicated by a red arrow. Anterior, left. Posterior, right. Dorsal, bottom. Ventral, top. (C) Model for the effects of
dpl-1 and
mcd-1 on cell killing. Top, in a cell specified to die in wild-type animals, the CED-3 caspase is activated and the MCD-1 Zn finger, DPL-1 DP, LIN-35 Rb, EFL-1 E2F, LIN-37 Mip40, and LIN-52 dLin52 proteins mediate transcriptional regulation of unknown targets to allow cell death to occur. Middle, in the absence of the CED-3 caspase, cells fail to display the morphological alterations characteristic of cell death. Bottom, in the absence of
mcd-1 or
dpl-1, CED-3 is still activated and initiates the cell-death process. The execution of cell death occasionally fails, and cells can survive and differentiate. (D) Multiple activities function independently and additively to promote cell death. The MCD-1 Zn finger, DPL-1 DP, LIN-35 Rb, EFL-1 E2F, LIN-37 Mip40, and LIN-52 dLin52 proteins define a transcriptional regulatory activity that promotes cell death. This activity functions in an additive manner with the cell-killing activity of the CED-9 Bcl-2 and CED-8 XK proteins, as well as with the genes that control the process of engulfment to promote cell death. Multiple other activities could exist and act in a similar additive manner to control cell-death execution.