Fig. 3. Symmetric stripes of sim and m8 are induced in embryos lacking Dorsal gradients. Embryos were collected from Tollrm9/Tollrm10 (A-C) or gd–/gd– females (D-I). The former mutants contain low, uniform levels of Dorsal in all nuclei. The latter embryos completely lack nuclear Dorsal protein. Different stripe2-NotchIC transgenes were introduced into the mutant backgrounds, and stained with either a digoxigenin-labeled sim (A-F) or m8 probe (G-I). (A-C) Tollrm9/Tollrm10 embryos. (A) sim expression is restricted to the termini of mutant embryos that lack a stripe2-NotchIC transgene. (B) A strong stripe of sim staining is induced by a strongly expressed stripe2-NotchIC transgene. (C) A faint sim stripe is induced by the weakly expressed stripe2-NotchIC transgene. These mutant embryos lack snail expression (Fig. 4E), which might explain why the ectopic sim stripes are symmetrically expressed in dorsal and ventral regions. (D-F) gd–/gd– embryos. (D) sim expression is essentially absent in mutant embryos lacking a stripe2-NotchIC transgene. A weak sim stripe (see arrowhead) is induced by the strongly expressed stripe2-NotchIC transgene (E), whereas the weakly expressed transgene fails to induce sim expression (F). (G-I) gd–/gd– embryos. There is general, weak expression of the m8 gene throughout mutant embryos (G). This staining might be due to the derepression of the staining pattern that is normally restricted to the dorsal ectoderm. Both the strong (H) and weak (I) stripe2-NotchIC transgenes induce stripes of m8 expression.
