Fig. 4. rib functions downstream of, or in parallel to, WG signaling and is independent of sal. All views are lateral. Early stage 12 wild-type (A) and rib¹ (B) embryos hybridized with an antisense sal RNA probe show sal accumulation in dorsal tracheal cells (arrow). Wild-type (C) and rib¹ mutant (D) embryos carrying the sal-TSE-lacZ reporter construct stained with anti-ß-gal, which detects expression in the dorsal tracheal cells (arrow), and with anti-CRB to visualize the trachea. Slightly lower levels of sal-ß-gal are detected in rib mutants. Anti-CRB staining of a rib¹ embryo carrying both UAS-sal and btl-Gal4 transgenes (F) reveals that DT migration (arrow) is not rescued with increased sal expression compared with rib¹ alone (E). The DT (arrow) in rib¹ mutants fails to migrate (G), whereas the DB (arrowhead), LT, and GB fail to form in tkv^A12 mutants (H). Embryos doubly mutant for rib¹ and tkv^A12 (I,J) form only the TC (arrow in I) and VB (arrow in J).