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Fig. 1. Simultaneous repression and activation from a compact regulatory element. (A) Knirps repression of adjacent Dorsal and Twist activators. Dorsal and Twist proteins, normally active in a broad (22-24 nuclei) ventral swathe of the blastoderm embryo, fail to activate a linked Hsp70 lacZ transgene in regions containing Knirps (kni) protein (arrow). (B) Giant repression of Dorsal and Twist. Repression is seen in anterior and posterior regions where the Giant (gt) repressor is expressed (arrows). (C,D) Gal4 activators, expressed in a narrower (18-20 nuclei) ventral swathe, are not inhibited by Knirps and Giant. (E) A composite element containing Dorsal, Twist and Gal4 activators exhibits repression of Dorsal and Twist by Knirps, while the narrower Gal4-driven expression pattern is unaffected. (F) A composite element with Dorsal, Twist and Gal4 activators, and Giant repressor, exhibits a similar complex expression pattern (arrows). (G) A similar pattern of selective repression of the Dorsal and Twist activators within the composite element used in F is seen when the activator Gal4 is driven throughout the embryo under the control of the nanos promoter (NGT40, Bloomington Stock no. 4442). In the central regions of the embryo more intense staining is visible, indicative of additive or synergistic gene activation by Dorsal, Twist and Gal4. In the regions of the embryo where the repressor Giant is expressed (arrows), the intensity of lacZ staining is the same as in the dorsal regions of the embryo where activation is driven by Gal4 alone. The difference in lacZ staining intensity between cells containing or lacking Giant or Knirps is due to a difference in intensity in each cell, not the number of cells stained. Patterns of gene expression were visualized in 2-4 hour embryos by in situ hybridization with digU-labeled antisense lacZ probes. Embryos are oriented anterior to left; ventrolateral views (A-E,G) and ventral view (F) are shown.





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