Worm Breeder's Gazette 14(1): 95 (October 1, 1995)
Department of Molecular Biology and Biochemistry, Rutgers University, New Brunswick, NJ 08855
The mechanisms of cell killing in programmed cell death (ced-3- and ced-4-mediated) and degenerative cell death (for example, mec-4(d)-mediated death of the touch receptor neurons) are genetically and morphologically distinct. However, we have found that one of the final stages of programmed and degenerative death pathways--the removal of corpses--occurs, at least in part, by a common process. The completion of a study of the ultrastructural changes occurring during the time course of mec- 4(d)-induced death (see wm95 p188) lead us to wonder how degenerative cell death corpses were eliminated and whether any known "undertaker" genes, such as the engulfment ced genes, were involved. ced genes needed for efficient removal of PCD corpses appear to act in two parallel pathways (one includes ced-1, ced-6, and ced-7; the other ced-2, ced-5, and ced-10; see Ellis et al. 1991 Genetics 129:79). Since the persistence of mec-4(d)-induced touch cell corpses had not been examined under conditions in which both pathways operative in programmed cell death corpse removal were inactivated, we constructed the triple mutant ced-7(n1892); ced-5(n1812); mec-4(u231). Strikingly, degenerative death corpses persist this strain. For example, in one comparison of L3 stage animals, we found that 71% of ced-7; ced-5; mec- 4(d) animals still had vacuolar degeneration in the tail whereas only 2% of ced(+); mec-4(d) animals exhibited vacuoles in the tail at this stage. Thus, ced-5, ced-7, or both appear necessary for efficient removal of touch cell corpses. To investigate which individual ced genes were involved and to ask if one or both corpse removal paths were involved, we looked at persistence of degenerative cell death corpses in individual ced; mec-4(u231) double mutants. The following data were recorded: Strain L2 L3 mec-4(u231) 17% 2% ced-1(e1735); mec-4(u231) 38% 9% ced-6(n2095); mec-4(u231) 54% 14% ced-7(n1892); mec-4(u231) 48% 16% ced-2(e1752); mec-4(u231) 52% 34% ced-5(n1812); mec-4(u231) 65% 56% ced-10(n1993); mec-4(u231) 45% 22% ced-7(n1892); ced-5(n1812); mec-4(u231) 87% 71% Thus, preliminary data suggest that 1) all engulfment ced genes contribute somewhat to the removal of degenerative corpses, 2) genes ced-2, ced-5, and ced-10 play the most important role. The latter finding is interesting because ced-2, ced-5, and ced-10 have been found to be required for lin-24(sd)- and lin-33(sd)-induced "degenerative" Pn.p deaths (S. Kim and R. Horvitz, see also wm91 p188).