Fig. 11. Role of Ubx or Abd-A in repression by En. (A) Coexpression of En and Abd-A (ochre) repress ci expression at the anterior of the germ band (as well as in the abdomen) of a hth mutant embryo. This includes T2 and also head segments (not shown). Remember that expression of En alone in a hth mutant does not lead to repression there (Fig. 10A). (B) Ectopic expression of Abd-A alone in a wild-type embryo (or in a hth mutant; not shown) has no effect on ci expression. Normal repression in the domain of en expression is seen but no ectopic repression is seen in the paired domain (marked with an anti-Abd-A antibody in ochre). (C) Coexpression of En and Antp does not lead to ci repression in T2 of a hth mutant. Expression of ci is the same as if En alone were expressed (as in Fig. 10A). In this picture, expression of Antp (ochre) is partially masked by the signal coming from ci transcripts (blue). (D) As expected, paired-Gal4 driven Antp alone has no effect on ci expression whether in a wild type or a hth mutant (not shown). (E-F) Co-expression of Ubx allows VP16En to activate wg expression in T2 of a hth mutant embryo (E), whereas VP16En is unable to activate there on its own (F; also shown in Fig. 9D). (G) Distribution of ci transcripts (blue) and En protein (ochre) in a Ubx, abd-A double mutant [Df(3R)Ubx¹⁰⁹] overexpressing En with paired-Gal4. In such embryos, repression of ci occurs throughout the domain of ectopic En expression. There is no overlap between En (ochre) and ci (blue). Thus, removal of Ubx and Abd-A does not prevent En from repressing in the abdomen (compare to Fig. 1B). (H) Expression of ci (blue) and En (ochre) in a Ubx, abd-A, hth^64-1 triple mutant. Here, no repression of ci expression is seen despite the strong ectopic expression of En (see panel I). Thus in the absence of Ubx, Abd-A and Hth, the repressive activity of En is abolished. (I) Embryos of the same genotype as in H stained for En alone. This panel shows that the paired-Gal4 driver is not affected in the triple mutant.