title: A Schnurri/Mad/Medea complex attenuates the dorsal-twist gradient readout at vnd.
abstract: Morphogen gradients are used in developing embryos, where they subdivide a field of cells into territories characterized by distinct cell fate potentials. Such systems require both a spatially-graded distribution of the morphogen, and an ability to encode different responses at different target genes. However, the potential for different temporal responses is also present because morphogen gradients typically provide temporal cues, which may be a potential source of conflict. Thus, a low threshold response adapted for an early temporal onset may be inappropriate when the desired spatial response is a spatially-limited, high-threshold expression pattern. Here, we identify such a case with the Drosophila vnd locus, which is a target of the dorsal (dl) nuclear concentration gradient that patterns the dorsal/ventral (D/V) axis of the embryo. The vnd gene plays a critical role in the "ventral dominance" hierarchy of vnd, ind, and msh, which individually specify distinct D/V neural columnar fates in increasingly dorsal ectodermal compartments. The role of vnd in this regulatory hierarchy requires early temporal expression, which is characteristic of low-threshold responses, but its specification of ventral neurogenic ectoderm demands a relatively high-threshold response to dl. We show that the Neurogenic Ectoderm Enhancer (NEE) at vnd takes additional input from the complementary Dpp gradient via a conserved Schnurri/Mad/Medea silencer element (SSE) unlike NEEs at brk, sog, rho, and vn. These results show how requirements for conflicting temporal and spatial responses to the same gradient can be solved by additional inputs from complementary gradients.
authors.affiliation: Janelia Farm Research Campus, Howard Hughes Medical Institute, 19700 Helix Drive, Ashburn, VA 20147, USA.
authors.forename: Justin
authors.initials: J
authors.lastname: Crocker
authors.forename: Albert
authors.initials: A
authors.lastname: Erives
mesh_terms: D000818:Animals; D001483:Base Sequence; D019295:Computational Biology / Q000379:methods; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D004331:Drosophila melanogaster / Q000196:embryology*; D004475:Ectoderm; D004742:Enhancer Elements, Genetic; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D020868:Gene Silencing; D018398:Homeodomain Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D051901:Smad4 Protein / Q000235:genetics / Q000502:physiology*; D013997:Time Factors; D014018:Tissue Distribution; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; D018398:Homeodomain Proteins; C112506:MAD protein, Drosophila; C112504:Med protein, Drosophila; D051901:Smad4 Protein; D014157:Transcription Factors; C064196:dpp protein, Drosophila; C094066:shn protein, Drosophila; C094797:vnd protein, Drosophila