Fig. 3. Expression of tbx-35 is specific for the early MS lineage. (A,B) A reporter tbx-35::GFP transcriptional fusion shows GFP fluorescence in the two daughters of MS (MSa and MSp) and their descendants for several divisions. (C) Depletion of mex-1 by RNAi results in ectopic expression (arrows) of tbx-35 in AB descendants, consistent with a transformation of the AB granddaughters to MS (Mello et al., 1992). (D) Expression of tbx-35::GFP (arrows) in early C descendants, consistent with a C to MS transformation in pie-1(RNAi) embryos (Mello et al., 1992). (E) Depletion of the divergent ß-catenin wrm-1 by RNAi results in an E to MS transformation (Rocheleau et al., 1997), and concomitant expression of tbx-35::GFP in both the E and MS lineages. (F) Although MS adopts an E-like fate in pop-1(-) embryos (Lin et al., 1995), expression of tbx-35::GFP occurred in the early MS lineage of all mutant embryos examined (n>30). (G) tbx-35 mRNA accumulates in MS as detected by in situ hybridization. Seventy-eight percent of embryos at this stage (n=50) showed MS expression and 22% of embryos did not stain. (H) Ectopic tbx-35 mRNA in a mex-1(RNAi) embryo. Seventy percent of embryos at this stage (n=54) showed ectopic expression, 9% showed normal MS-specific expression and 20% did not stain. (I) Ectopic activation of tbx-35 in E in a lit-1(t1512) embryo grown at 25°C (Kaletta et al., 1997). Sixty-five percent of embryos (n=55) showed expression in MS and E, 22% showed MS-specific expression and 13% did not stain. (J) Normal expression of tbx-35 mRNA in a pop-1(RNAi) embryo. Seventy-eight percent of embryos (n=65) showed staining in MS, while 22% did not stain. For these and subsequent embryo images, anterior is towards the left, and dorsal is upwards, and the eggshell (seen by Nomarski optics) is shown with a broken blue line. Scale bar: 10 µm.