Fig. 8. Competition between CES-1 and HLH-2/HLH-3 for binding to the egl-1 promoter specifies the cell-death fate of the NSM sister cells. In wild-type animals, the level of CES-1 in the NSM sister cells might not be sufficient to compete with HLH-2/HLH-3 for binding to Region B, resulting in the activation of egl-1 transcription and NSM sister cell death. In ces-1(gf) or ces-2(lf) animals, elevated levels of CES-1 in the NSM sister cells might successfully compete with HLH-2/HLH-3 for binding to Region B, resulting in egl-1 repression and NSM sister cell survival.