Fig. 7. A framework for the morphogenesis of the maxillary segment in Drosophila. (A,C) Scanning electron micrographs of heads of stage 12 wild-type embryos. (B) Head of a stage 12 Dfd mutant embryo. The red arrow marks additional cells at the ventral side of the maxillary segment. (D) Head of a wg mutant embryo. The red arrow marks the size-reduced maxillary segment. (E,J) BrdU labeling of stage 12 wild-type and Dfd mutant embryos, respectively. Red arrows mark proliferating BrdU-positive cells at the ventral side of the maxillary segment. (F) Diagram of a stage 12 wild-type embryo. Mandibular (md), maxillary (mx) and labial (lb) segments are indicated; the box marks the area shown in G,H,I. (G,H,I) In stage 12 wild-type embryos, cells in the ventral part of the maxillary segment are round (G), whereas in Dfd mutant (H) and arm::hep^act. (I) embryos, cells are elongated (marked in red). (K-T) skl (K,P), wg (L,Q), Eip63E (M,R), prd (N,S) and CG5080 (O,T) RNA expression in wild-type and Dfd mutant embryos, respectively. The red arrows indicate the expression of the respective genes that differs in wild-type and Dfd mutant embryos.