Programmed cell death (apoptosis) is a complex and tightly controlled process that is vital for the proper development of an organism as well as for maintaining its homeostasis.
ced-3 , a key player in the execution of programmed cell death in C. elegans , encodes a member of the caspase family of cysteine proteases. One particularly important area that has not been studied is the in vivo targets of the death caspases. In order to reveal downstream targets of CED-3, our lab developed a novel and sensitized genetic screen to isolate mutations that partially suppress or delay cell death caused by constitutively activated CED-3 death protease. In this screen, at least eight new genes (
cps-1,-2,-3,…,-8 ; C ED-3 p rotease s uppressors) have been identified. Here we report the characterization of the
cps-4 and
cps-5 genes which appear to function in interesting yet different ways to affect apoptosis. To study how
cps-4 and
cps-5 affect programmed cell death in nematodes, we performed time-course analyses of the appearance of embryonic cell corpses in
cps-4 and
cps-5 mutants. We found that both
cps-4 and
cps-5 mutants display a delay of cell death phenotype: the peak of cell corpses is shifted from the bean/comma embryonic stage (seen in wild type animals) to the 2-fold embryonic stage in
cps-4 and
cps-5 mutants. These phenotypes are similar but weaker than the delay-of-cell-death phenotype displayed by another cell death mutant,
ced-8 , in which the peak of cell corpses is found in late embryonic stage (late three-fold embryonic stage). We constructed double and triple mutants among
cps-4 ,
cps-5 ,
ced-8 and other cps genes and found that
cps-4 ,
cps-5 , and
ced-8 can significantly enhance one another's phenotype in delaying cell death. In addition,
cps-5 but not
cps-4 can also enhance the delay-of-cell-death phenotype of
cps-6 , which is involved in apoptotic DNA degradation and encodes an endonuclease (please see the abstract by Parrish et. al.). These results suggest that
cps-4 and
cps-6 may function in the same pathway while
cps-5 and
ced-8 may function in different pathways. Consistent with this hypothesis, we found that
cps-4 mutants contained significantly higher number of TUNEL-positive cells than that of wild-type animals, while the
cps-5 mutant has a similar number of TUNEL-positive cells as the wild-type animals. We mapped
cps-4 to linkage group I and
cps-5 to linkage group III and are in the process of fine mapping and cloning these two genes.