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Fig. 7. Ser is sequentially regulated by the Ap, N and Wg pathways during
larval development. (A) Alignment of the Ser minimal wing enhancer
regions in D. melanogaster (mel; 794 bp) and D.
pseudoobscura (pse; 810 bp). Both enhancers are located within 1 kb
downstream of the Ser 3'UTR. Locations of Ap (green), Su(H)
(bold type) and dTCF (red) binding sites are indicated, which are defined
based on the in vitro DNA-protein binding data in this study. Non-canonical
sites are italicized. Conserved nucleotides of the two species are denoted in
blue. (B) Sequential regulation of Ser by the Ap, N and Wg pathways
represents an integration point for proper wing development. The selector
protein Ap directly activates Ser expression in the dorsal
compartment during early third instar, which induces N activation at the DV
border in mid third instar. The N pathway then regulates Ser
expression by a positive-feedback loop along the DV boundary. Finally, as a
result of Wg signaling, at the end of the third instar, Ser is
expressed in two stripes flanking the DV boundary.
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