In the gonad of adult C. elegans hermaphrodites about 50% of all germ cells are eliminated by programmed cell death (referred to as 'physiological germ cell death'). In contrast to the developmental death of somatic cells, physiological germ cell death is not determined by lineage and might be induced by cell-autonomous as well as cell non-autonomous factors. The genes
ced-9,
ced-4 and
ced-3 (ced, cell death abnormal), which define the central machinery involved in developmental cell death, also act in the germ line:
ced-3 and
ced-4 loss of function (lf) mutations block physiological germ cell death: in contrast,
ced-9 (lf) mutations lead to the massive death of germ cells. However, the factors that act upstream of the central cell death pathway to regulate its activation appear to differ in soma and germ line. For example, loss-of-function mutations in the cell-death activator gene
egl-1 (egl, egg-laying defective), which acts upstream of
ced-9, block developmental cell death but not physiological germ cell death. To identify genes that are required for physiological germ cell death, we performed a clonal F2 screen in a
ced-6 (
n2095) background, in which the engulfment of apoptotic germ cells is partially blocked and in which persistent germ cells corpses consequently accumulate. To visualize and quantify the number of persistent germ cell corpses, the reporter Plim-7CED-1::GFP (lim, lim domain family) was used, which drives the expression of a CED-1::GFP fusion protein in the sheath cells, the cells that engulf apoptotic germ cells. We screened about 8,600 haploid genomes for mutations that cause a reduced number of persistent germ cell corpses, and isolated the mutation
bc202.
bc202 blocks most physiological germ cell death in the hermaphrodite gonad: 48 h after the L4 stage homozygous
bc202;
ced-6(
n2095) animals have 4.4+/-2.3 corpses compared to 46.9+/-3.3 corpses found in
ced-6(
n2095) animals. Furthermore, treatment with DNA damage inducing agents does not lead to an increase in the number of persistent germ cell corpses in
bc202;
ced-6(
n2095) animals, suggesting that
bc202 also blocks non-physiological germ cell death. Epistasis analysis suggests that
bc202 acts downstream of or in parallel to
ced-9 to kill germ cells. The gene defined by
bc202 maps to a 0.5 m.u. interval on LG I. We are currently trying to clone the gene using transformation rescue and RNAi experiments.