Figure 1.

Expression of vein in the ventral ectoderm is induced by DER through Pointed P1. (A) In wild-type embryos at stage 9, vein is expressed in three to four cell rows on each side of the ventral midline. (B) By stage 11, expression of vein is confined to one cell row. (C) In rho^Δ38 mutant embryos, expression of vein in the ventral ectoderm is eliminated at stage 10/11, whereas all other aspects of vein expression are normal. (D) Induction of rho expression by Kr–Gal4 gives rise to ectopic expression of vein in the same domain. (E) Induction of secreted Spitz expression by en–Gal4 gives rise to ectopic expression of vein in a stage 11 embryo. (F) Expression of vein in the ventral ectoderm is eliminated in a pointed^Δ88 stage 11 mutant embryo. (G) Induction of Pointed P1 expression by Kr–Gal4 gives rise to ectopic vein expression in the same domain. (H) Induction of activated Yan expression by Kr–Gal4 eliminates vein expression in the same domain. Arrowheads mark the ventral midline; arrows show anterior border of Kr domain in the T1/T2 segment boundary.