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A Schnurri/Mad/Medea complex attenuates the dorsal–twist gradient readout at vnd
Journal article   Open access   Peer reviewed

A Schnurri/Mad/Medea complex attenuates the dorsal–twist gradient readout at vnd

Justin Crocker and Albert Erives
Developmental biology, Vol.378(1), pp.64-72
06/01/2013
DOI: 10.1016/j.ydbio.2013.03.002
PMID: 23499655
url
https://doi.org/10.1016/j.ydbio.2013.03.002View
Published (Version of record) Open Access

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. ► A Schnurri:Mad:Medea silencer is conserved at the vnd neuroectodermal enhancer. ► SMM silencer element restricts expression of vnd in the dorsal embryonic ectoderm. ► SSE allows vnd NEE to have an early temporal (low threshold) response to dorsal. ► SSE can also attenuate NEEs that drive broad ectodermal expression.
 Enhancers Dorsal Dpp vnd Drosophila Morphogen gradients

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