SEK-1 MAPKK is required for linker cell death. (A) Linker cell survival in sek-1(ag1) mutants expressing the indicated promoter::cDNA constructs. Numbers, percentages. Error bars, SEM. n≥70. (B) Expression of the 2.5 kb pqn-41::GFP reporter in late L4 (wild-type) or young adult (lin-29, sek-1) animals. n≥50. (C) EM of linker cell in fig. S9A. Arrow, swollen ER. Scale bar, 2 μm. (D) Late L4 male expressing a sek-1 promoter::GFP reporter. Scale bar, 5 μm.