neither to particular cell types nor to any particular cell lineage, the bulk of apoptotic
events affect neuronal cells and, to some extent, also hypodermal cells (Sulston and
Horvitz, 1977; Kimble and Hirsh, 1979; Sulston et al., 1983). The reproducibility
of cell death provides unique advantages for genetic analysis: cell death can be studied
on a single-cell level, and even mutations which cause only a very weak defect in
programmed cell death, or which affect only a small number of cell types can be
identified. Programmed cell death of somatic cells mostly occurs during embryonic
development (113/131 deaths), which takes place within approximately 14 h under
standard growth conditions. During embryogenesis, apoptosis occurs mostly between
220 and 440 min after fertilization (Sulston et al., 1983). Programmed cell death also
occurs, albeit to a lesser extent, during the transition through the four larval stages
(Sulston and Horvitz, 1977; Kimble and Hirsh, 1979; Sulston et al., 1983). Within
the somatic tissues of the adult worm, neither cell divisions nor programmed cell
deaths can be observed. However, recent studies suggest that apoptosis is very
prominent in adult hermaphrodites during female germ-cell development
(Gumienny et al., 1999).
3.
Identity and origin of cells undergoing programmed cell death
in the C. elegans germ lineOnly recently have the early observations, suggesting that programmed cell death can
occur in the C. elegans germ line, been followed up (Gumienny et al., 1999) (Figure 1).
Figure 1. Adult C. elegans hermaphrodite as observed under DIC optics.
An adult worm measures about 1 mm in length. Various organs are indicated.
162 GENETICS OF APOPTOSIS