Fig. 8

Models of alternative modes of B.al/rapaav cell death. a Suicide: B.al/rapaav initiates the suicide program and undergoes programmed cell death, resulting in a fully-refractile corpse, which is engulfed by the neighboring cell P12.pa. A suicide cell death would occur in engulfment mutants and in P12.pa-ablated animals but not in suicide-pathway mutants. Our data are inconsistent with this model, as the death does not occur in engulfment mutants. b Murder: B.al/rapaav is healthy until it is engulfed by P12.pa, after which it dies. This form of cell death would occur in suicide-pathway mutants but not in engulfment mutants or P12.pa-ablated animals (unless engulfed and killed by a different neighboring cell). Our data are inconsistent with this model, as the death does not occur in suicide mutants. c Induced suicide: B.al/rapaav is signaled by P12.pa to induce the suicide program. This form of cell death would not occur in suicide-pathway mutants or P12.pa-ablated animals but would occur in engulfment mutants (unless the death-inducing signal requires engulfment genes, which is not the case for B.al/rapaav, since the cell-death suicide genes are expressed in engulfment mutants). Our data are inconsistent with this model, as initiation of the B.al/rapaav death process is not dependent on the presence of P12.pa or the activities of the engulfment genes (the cell-death suicide genes are expressed in both cases, and death-related morphological changes can be seen in B.al/rapaav in engulfment mutants and in some animals in which P12.pa was ablated). d Assisted suicide: B.al/rapaav initiates the suicide program, which is ineffective at causing programmed cell death and results in a suicide-stalled cell. Once B.al/rapaav is engulfed, the death reaches completion. This form of cell death would not occur in suicide mutants, engulfment mutants, or P12.pa-ablated animals (unless engulfed by another cell). The suicide-stalled cell in an engulfment mutant might show signs of cell-death initiation. Our data are consistent with this model