Three distinct but related approaches have been used to quantitate programmed
cell death in C. elegans. The first and most direct approach takes advantage of the
highly reproducible anatomy of the worm, which allows the unambiguous
identification of each cell in the body. The absence of programmed cell death can
thus be scored indirectly by looking for the presence of extra ‘undead’ cells (cells that
should have died but instead survived). Undead cellscannot be distinguished from
normal cells by their appearance under the microscope, but may sometimes be
Figure 2. Morphology of apoptotic cells and genetic pathway of programmed cell death
(a) Morphology of programmed cell deaths occurring in the germ line (adapted from Gartner
et al., 2000). Various morphologic phases of apoptosis under DIC (differential interference
contrast) optics are depicted. Note, ‘a’ indicates a normal cell at 0 min, which becomes refractile
at 11 min (the nucleus is still discernible at this stage). At 12 min, the nuclear structure merges
with the surrounding cytoplasm, and this corpse-like structure persists until about 65 min and
disappears within less than 1 min. Corpse morphology during somatic development resembles
germ-cell corpse morphology (Gumienny et al., 1999). (b) Genetic pathway for programmed
cell death. The upper lane shows the status of cell-death signaling as a consequence of egl-1
activation. The lower panel indicates the status of signaling in surviving cells. Solid arrows and
solid T-bars indicate activation and repression, respectively. Dotted arrows and T-bars indicate
that activation and repression do not occur. Reprinted from Molecular Cell, Vol. 5, A. Gartner,
S. Milstein, S.Ahmed, J.Hodgkin and M.Hengartner. A conserved checkpoint pathway
meditates DNA damage-induced apoptosis and cell cycle arrest in C. elegans, pp. 435–443
(2000), with permission from Elsevier Science.
164 GENETICS OF APOPTOSIS