Fig. 4. Tcf acts synergistically with SoxN. (A,B) Overexpressing the wild-type form of Tcf, using the arm-Gal4 driver, produces no effect on en expression (A) or on cuticle pattern (B), and most such embryos hatch into larvae (data shown in Table 1). (C,D) arm-Gal4 drives a lower level of expression than E22C-Gal4, producing milder effects of overexpressed SoxN. Under these conditions, en expression is only slightly narrowed (C) and cuticle pattern is mostly normal (D), with only occasional ectopic denticle formation (arrow) and little dorsal curvature. (E,F) When Tcf and SoxN are expressed together, using arm-Gal4 to drive a double-homozygous UAS stock, en expression is more severely narrowed (arrows, E), and ectopic denticles (arrows, F) appear with greater frequency and broader distribution across the ventral naked cuticle domain; cuticles are strongly curved due to defective dorsal patterning. The severity of the phenotype is comparable to expressing higher levels of UAS-SoxN alone with the stronger E22C-Gal4 driver (see Fig. 2F,H). Arrowheads in A, C and E indicate the posterior end of the ventral midline. Embryos are oriented with anterior to the left and dorsal side up.