Necrosis is not a chaotic uncontrolled reaction to cellular trauma, but a finely controlled cell death program. We have developed a model for analysis of genetic control of necrosis. In our model, nicotinamide induced necrosis of the uterine-vulval
uv1 cells in
pnc-1 animals is robustly rescued by overactivation of EGF signaling. LET-23, an EGF receptor, has many functions in C. elegans development, and two signaling pathway are known to mediate LET-23 signaling effects; one that signals through LET-60/ Ras and a second through ITR-1. LET-60 signaling downstream of LET-23 is necessary but not sufficient for rescue of necrosis and ITR-1 is neither necessary nor sufficient. These results suggest that an as yet unidentified pathway downstream of LET-23 mediates rescue in concert with the LET-60 pathway. We carried out a targeted RNAi screen and have discovered two genes,
pmt-1 and
cdk-2, that are required for
let-23gf rescue of
uv1 necrosis. PMT-1 is a phosphoethanolamine methyltransferase that catalyses the first step of the conversion of ethanolamine to phosphocholine, followed by conversion to phosphatidylcholine. To confirm the relevance of this pathway we knocked down
pmt-2, downstream of
pmt-1, and supplemented
pmt-1 and
pmt-2 RNAi animals with choline, an alternative substrate for phosphocholine synthesis.
pmt-2 RNAi phenocopied
pmt-1 RNAi and choline supplementation restored rescue . However, choline supplementation in a
pnc-1 background did not rescue
uv1 necrosis, which confirms that phosphocholine synthesis via the PMT pathway is required but not sufficient for rescue. We hypothesised that the PMT pathway is required for
let-23gf uv1 rescue to maintain LET-23 cell membrane localization and activity. To test this we investigated the effect of
pmt-1 and
pmt-2 RNAi on two
let-23gf phenotypes; excess vulval induction and excess
uv1 cell specification. We found that neither
pmt-1 nor
pmt-2 RNAi affected either of these phenotypes, which suggests an alternative hypothesis; that phosphocholine itself is required for a LET-23 survival signal. This was supported by the failure of
cept-1 or Y49A3A.1 RNAi, both genes required for phosphatidylcholine synthesis, to affect rescue.