Fig. 4. Alteration of embryonic expression of Dll, hdc and esg in the absence of btd and Sp1function. (A) Wild-type Dll expression. The antennal (ant), maxillary (mx) and labial (la) head segments contain Dll activity, as well as the three thoracic (T1, T2, T3) primordia. (B) btd^XG81 embryo. The expression in the antennal segment is lost and there is a marked reduction of Dll activity in the three thoracic primordia (arrows). (C) Df(1)C52 embryo showing complete loss of btd activity in the thoracic primordia. The expression in the maxillary and labial segments is not altered. (D) Ubx-Gal4/UAS-btd embryo exhibiting ectopic Dll expression in the abdominal segments, which do not normally contain Dll activity. Note the expression in the amnioserosa cells (arrow). (E) Ventral view of a wild-type embryo showing hdc expression restricted to the anterior region of the ventral cord and the thoracic discs primordia (arrows). (F) Df(1)C52 embryo with loss of hdc activity in the thoracic primordia. (G) Ventral view of ptc-Gal4/UAS-btd embryo showing high levels of hdc activity (compare with E). (H) Wild-type expression of esg in the thoracic discs primordia. Wing (w) and haltere (h) clusters are indicated. The three arrows point to the three leg primordia. (I) esg expression in a Df(1)C52 embryo. Expression in the wing and haltere primordia remain but no activity is seen in the region corresponding to the leg primordia.

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