Fig. 4. Deficiency of MS-derived cell types in tbx-35(tm1789) embryos. (A) Differential interference contrast (DIC) image showing the grinder (gr), indicative of MS-derived pharynx, in a wild-type threefold stage embryo. (B) A ceh-22::GFP reporter (pseudocolored yellow) shows the fully elongated pharynx with MS- and ABa-derived halves (Okkema and Fire, 1994). (C) Terminal glp-1(or178) embryo showing ceh-22 expression in only MS-derived pharynx. (D) Terminal tbx-35(tm1789) embryo arrested at 1.5-fold elongation, similar in appearance to med-1,2(-) embryos (Coroian et al., 2005). The grinder is absent, and internal cavities (arrows) are observed in 35% of such embryos, similar to the hypodermis-lined voids in skn-1(-) embryos (Bowerman et al., 1992). (E) ceh-22 expression in only ABa-derived pharynx in tbx-35(-). (F) Absence of pharynx in a glp-1(-); tbx-35(-) embryo. (G) Wild-type embryo at the 1.5-fold stage. (H) Expression of hlh-1::GFP in the embryo shown in G indicates muscle precursors (Chen et al., 1994). In wild type, an average of 46.8±1.4 cells (n=10) were scored as expressing at this stage. (I) In terminal pal-1(RNAi) embryos, muscles made by C and D are not made, resulting in a loss of posterior hlh-1 expression (arrows; compare arrows in H). Expression was seen in an average of 20±0.6 cells (n=33). (J) A 1.5-fold stage tbx-35(tm1789) embryo. (K) hlh-1::GFP expression in the embryo shown in J shows lack of signal in the anterior (arrowheads; compare H), while posterior expression persists (arrows) and a large cluster of hlh-1-expressing cells is seen near the center (^*). An average of 34.8±2.4 cells (n=10) was scored in these embryos. (L) Terminal tbx-35(-); pal-1(RNAi) embryos express hlh-1::GFP in only a small number of cells, with an average of 5.7±0.5 cells (n=40).