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.
The CED-3::GFP translational reporter was expressed mostly in embryos and the adult germline. In embryos, we often found an enrichment of GFP signal within the apoptotic corpses compared with the surrounding cells. In the germline, CED-3::GFP was expressed primarily in the oocyte region, with very weak to no expression in the mitotic and early meiotic zones.
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.
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.