Fluorescence microscopy revealed that a TRIM-21::mCherry or TRIM-21::GFP fusion reporter co-localized to the surface of cell corpses with CED-1::GFP and mCherry::CED-6 reporters in C. elegans.
GFP-tagged CED-9 is expressed broadly in pre-elongation embryos in a cytoplasmic lattice-like pattern, as has been reported for the CED-9 protein. CED-9::GFP is enriched in the gonadal region where germ cell apoptosis is observed.
CED-7 was widely expressed in embryos and was localized to the plasma membrane. In larvae and adults, CED-7 expression appeared restricted to specific cells. Specifically, CED-7 was detected in the amphid sheath cells, the pharyngeal-intestinal valve, and the phasmid sheath cells. CED-7 expression was also detected in both germline precursors and germline, except sperm in larvae and adults, respectively.
CED-3::GFP (representing both proCED-3::GFP and active CED-3::GFP) was observed in the NSM neuroblast (NSMnb) before its division into the NSMsc and NSM. During NSMnb division, CED-3::GFP was equally segregated into the NSMsc and NSM so that the concentrations of CED-3::GFP in the two daughter cells after the completion of cytokinesis were almost identical (t = 0 min). However, starting 10 min post cytokinesis, CED-3::GFP concentration gradually increased in the NSMsc. This increase reached a maximum 21min post cytokinesis, by which time the NSMsc had adopted the morphology typical of a cell corpse (t = 21 min). Conversely, starting 10min post cytokinesis, CED-3::GFP concentration gradually decreased in the NSM. As a result, at 21 min post cytokinesis, the concentration of CED-3::GFP in the NSMsc was more than twofold higher than that in the NSM.
Fixed embryos stained with antiCED-9 revealed that CED-9 was present in all cells during C. elegans embryogenesis, beginning as early as the two-cell stage. CED-9 levels peaked at approximately the 200 cell stage and slowly diminished, becoming undetectable around the time of hatching. CED-9 protein was not observed in larvae or adults.