Fig. 3. Ectopic PAL-1 activates HLH-1 and the body wall muscle-like developmental program. The left panels (A) show a wild-type embryo with the body wall muscle cells at 3 hours post-fertilization highlighted by hlh-1::gfp expression (top); descendants of the C and D lineage are visible at this time. A comma stage embryo stained for MHC A (middle) shows the left side focal plane of body wall muscle quadrants; a corresponding diagram is shown below [adapted from Sulston et al. (Sulston et al., 1983)]. The center column of panels (B) show the response of muscle markers to heat shock-induced PAL-1 activity. Strong activation of hlh-1::gfp occurs within 3 hours of treatment in many cells (top). After overnight incubation, most cells in the embryo are MHC A positive (middle) when compared with the DAPI image of the same embryo (bottom). The right set of panels (C) show that the depletion of POP-1 activity by RNAi enhances the myogenic activity of ectopic PAL-1 (compare to B). Embryo staging and staining in C are the same as those in B, and images in these panels are representative of most focal planes of the embryo.