Fig. 8. The activity of the hh signaling pathway is required for the transcriptional activation of svp. Stage 13 embryos double stained with an anti-Engrailed (En, brown) antibody to position the segmental boundaries and either a DIG-labeled svp riboprobe (blue, A,C,E,G-J) or anti-Tin (blue, B,D,F). Anterior is to the left and dorsal is up. (A,B) Whole embryos; (C-J) enlargements showing the central abdominal region of the embryo. (A-D) Wild-type embryos. svp is expressed in seven pairs of cardioblasts per hemi-embryo in the segments A1-A7 (arrow), in the chordotonal organs (white arrowhead) and in the oenocytes (open arrowhead). Tin is expressed in four cardioblasts (arrow) per hemi-embryo in the segments T3 to A7 and in a subset of pericardiac cells (arrowhead). Tin and svp are expressed in different subsets of cardioblasts (see Fig. 2P). (E,F) In hh^9K, expression of svp is abolished in svp cardioblasts (arrowhead) as well as in the chordotonal organs. More cells express Tin (arrowhead), including cardioblasts that express svp in the wild type. (G) The expression of Ci^rep driven by twist-GAL4/24B represses svp expression in the cardioblasts (arrowhead), although not completely (compare with E). (H) Expression of Hh in ectodermal En-expressing cells rescues the expression of svp (arrowhead). (I) Expression of a GPI membrane-bound form of Hh does not rescue svp expression (arrowhead). (J) Hh expression is maintained in the En-expressing cells in an otherwise wg mutant background. The function of wg is not required for the expression of svp (arrowhead).

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