Figure 7. svb Controls Denticle Pigmentation through the Regulation of y Transcription.

(A) Cuticle preparations (A3–A4 segments) showing the effect of Ptc-Gal4–driven ectopic expression of svb. Ectopic cuticular extensions (arrowheads) are as densely pigmented as normal denticles, as demonstrated by bright-field observation (right).

(B) Summary of the cuticular pigmentation pathway, showing genes that are putatively implicated in the transformation of tyrosine to pigmented compounds. Of the ten genes thought to be involved in pigment production we tested, only four (red) are expressed in the embryonic epidermis at the time of cuticle formation.

(C) In situ hybridization showing the expression of y mRNA in the epidermis in late embryos. In wild type, y mRNA accumulates in three stripes per segment. Due to deep morphological folds at this stage, it is hard to define accurately the number of cell rows that express y in each segment. y transcription is controlled by svb, since staining is strongly decreased in svb mutant and an ectopic stripe of y mRNA (arrowheads) results from svb ectopic expression in wg cells.