Fig. 8.

Cartoon representation of module exclusion by looping. (A), Map of the locus of the gatae gene with three active cis-regulatory modules; B, an upstream region which drives expression ubiquitously; the intron module 10, which drives expression in the endomesoderm during blastula; the intron module 24, which drives expression in endoderm at gastrula and pluteus stages. The basal promoter is denoted Bp. (B), In the endomesoderm of the blastula (green box), module 10 associates with Bp to drive expression when it is occupied by its endomesoderm transcription factors; in the rest of the embryo (pink box), modules B and 24 are associated by looping and the gatae gene is not transcribed. (C), In the midgut and hindgut of the gastrula (green box), module 24 associates with the Bp, when it is occupied with the gut factors for which it contains sites, to drive specific expression. The rest of the embryo (pink box) follows a similar scheme as in (B).