Fig. 2.

Ectopically patterned En uses exd to repress wg in vivo. All embryos carry a UAS-en transgene. (A) Wild-type embryo stained for En. (B) Embryo carrying a prd-Gal4 driver transgene, in addition to UAS-en. Notice the anteriorly expanded alternate En stripes, which overlap alternate wg and slp stripes (Fig. 3). (C-J) Embryos were derived from either exd^+/+ females (C,D) or from females with exd mutant germlines (E-J), and received either a wild-type exd allele (E,F) or no exd allele (G-J; exd is on the X chromosome) from their father. Thus exd[mat⁺ zyg⁺] refers to either a homozygous or hemizygous wild-type exd genotype; exd[mat^- zyg^-/+] refers to heterozygous females that lack a maternal contribution; and exd[mat^- zyg^-] refers to hemizygous mutants that also lack a maternal contribution. These embryos were double-stained for wg RNA by in situ hybridization and either for Exd (C-H), indicating whether they do or do not have a wild-type exd allele, or for a balancer marker (I,J; hb-lacZ, in brown, indicating absence of the prd-Gal4 driver transgene; lacZ-negative indicates the presence of the driver). Notice that, in exd wild-type embryos, wg is completely repressed by the ectopic En expression within alternate (even-numbered) stripes induced by prd-Gal4, whereas, in heterozygous exd embryos (which lack a maternal exd contribution), this repression is reduced. This effect was greater in embryos lacking all exd function (H,J). J is inferred to be exd mutant because of the weak and incomplete odd-numbered wg stripes that characterize them, as seen in H; H is inferred to contain prd-Gal4 because of the repression of even-numbered wg stripes in the abdomen, as seen in J. Notice the lack of repression of even-numbered stripes (particularly stripes 0, 2 and 4) in H and J, and, to a lesser extent, in F. Staining for En showed no difference in either the pattern or extent of ectopic expression between the wild-type and exd mutant populations (not shown).