Fig. 4. Each Hox CP gene represses optix in its ventral, anterior ectodermal activity domain. Expression of optix (green) in (A) tsh^- HoxCP, (B) tsh^- Hox^- Scr⁺, (C) tsh^- Hox^- Antp⁺, (D) tsh^- Hox^- Ubx⁺, (E) tsh^- Hox^- abdA⁺, (F) tsh^- Hox^- AbdB⁺, (G) Dfd, (H) lab. (A) Elav staining (red) highlights the ventral side. (B-F) The distribution of Hox proteins is in red. Arrows delimit the boundaries between optix expression and Hox domains. Scr⁺ (B) has one patch less (Lab segment) compared with A; Antp⁺ (C) presents only two (Lab and T1), Ubx⁺ (D) four (Lab to T3), abdA⁺ (E) five (Lab to A1) and AbdB⁺ (F) has eight (Lab to A4) ectopic patches of optix. (G) Loss of Dfd induces an ectopic optix patch in the maxillary segment (white arrow); arrowheads indicate the two normal domains of optix in the gnathal segments. (H) optix distribution is normal in lab (compare Fig. 2B). All panels are ventral aspects.