Ylg

yellow ac se l'sc ase

pTG ANWP '

FIGURE 4.7 Transcription control of regulatory genes in the regional specification of the 3rd instar Drosophila wing disc. (A) Modular enhancers of the achaete-scute gene complex (AS-C). (A I) Map of the locus; (A2) the proneural clusters controlled by each of the enhancers in the imaginal wing disc; and (A3) the location of the sensory structures to which they give rise in the adult wing and the dorsal surface of the adjoining thorax (heminotum). The enhancers, the proneural clusters, and the sensory organs are color coded. The achaete (ac) and scute (sc) genes encode bHLH transcription factors required for sensory organ development and are expressed in patches of cells within which the sensory organ precursor cell is subsequently specified (see following section of this chapter). The black box represents an enhancer required for expression in the sensory organ precursor (SOP) cells. The colored enhancer elements in (AI) promote expression of both ac and sc. Above the line representing the AS-C DNA, transcription units for the genes of the cluster are shown as arrows: the proneural genes, ac, sc, lethal of scute (I'sc) and aserise (ase) solid; other genes, open. Distances are given in kb. In A2 and A3, sensory organ domains for which the enhancers are not indicated in this diagram are shown in gray. The positions

(Continues)

FIGURE 4.7 (Continued)

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