egl-1 appears to be specifically expressed in cells destined to die during embryogenesis, including the NSM sister cells. The NSM sister cells normally die during a stage called the 1.5-fold stage of embryogenesis. At this stage of development it is difficult to identify cells on the basis of their position within the embryo. The authors therefore analysed the expression of Pegl-1his24-gfp in the background of the
ced-3 lf mutation
n717.
ced-3(
n717) blocks programmed cell death, including the death of the NSM sister cells. They found that the activity of EGL-1 is regulated at the transcriptional level in the NSMs and NSM sister cells and, hence, that the cell-death fate of these cells is specified by egl- 1 expression.