Figure 7.

Insv is required for Fab-7 function in vivo. (A) Adult abdominal cuticle preparations of a wild-type (Wt) male. The fifth and sixth tergites are pigmented, the A6 sternite is recognizable by the absence of bristles and a specific form. Trichomes are visible in the dark field and cover all the surface of the A5 tergite, and only a thin stripe along the anterior and ventral edges of the A6 tergite. (B and D) Homozygous males with a sensitized genetic background of Fab-7: HS1 + HS2 (B) and Fab-7^GAGA1–5 (D) (see the text). (C) In the absence of the endogenous Insv, HS1 + HS2 males show a strong gain-of-function (GOF) transformation of A6 to A7, as revealed by the marked reduction of the A6 tergite and the absence of the sternite. (E): insv^23B; Fab-7^GAGA1–5 homozygous males have a mixed GOF and loss-of-function (LOF) phenotype. A6 is partially transformed into A7 (GOF transformation), but at the same time the residual A6 cuticle has morphological features characteristic of A5 (trichomes visible in the dark field) (LOF transformation). (F) Rescue of the mutant insv^23B; Fab-7^GAGA1–5 phenotype with a genomic rescue construct insv^+3.67. The genomic Insv fragment restores the boundary function of Fab-7^GAGA1–5. The A6 tergite is only marginally smaller than in Wt, and the trichomes are usually limited to small patches. The numbers 4, 5, and 6 indicate A5, A6, and A7 abdominal segments, respectively. Arrows in (D) show extra bristles on the A6 sternite.