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. Author manuscript; available in PMC: 2016 Jan 24.
Published in final edited form as: Wiley Interdiscip Rev Dev Biol. 2014 May 29;3(5):301–330. doi: 10.1002/wdev.138

FIGURE 10.

FIGURE 10

A model for Dorsal-mediated control of the snail (sna) transcription unit in the mesoderm and in the dorsal ectoderm/neurectoderm. At top is shown the position of the sna transcription unit in relation to the positions of the primary and shadow enhancer regions.205 In regions of lower nuclear Dorsal concentrations (dorsal ectoderm/neurectoderm), there is no Dorsal binding to either enhancer, and RNA Pol II is paused at the start site.209,212 In the ventral cells with high levels of nuclear Dorsal (mesoderm), Dorsal is bound to both enhancers. The binding of Dorsal induces the previously paused RNA Pol II to initiate sna transcription.