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obs.), and other studies have recognized a later role forgrhin supportingftzexpression[48]. both contribute toindtranscriptional activation. However, another recent study found that the repressor Capicua (Cic) also binds to the A-box sequence. While Cic was not recognized through our A-box affinity chromatography, utilization of the same site, the A-box, by both factors Grh (activator) and Cic (repressor) may also support a switch-like response that helps to sharpen theinddorsal boundary. Furthermore, our results also demonstrate that TGF- signaling acts to refineindCRM expression in an A-box impartial manner in dorsal-most regions, suggesting that tiers of repression take action in dorsal regions of the FRP embryo. == Introduction == During development the embryo is usually patterned by the localized expression of genes to discrete parts of the embryo. Such tight spatial regulation of gene expression is necessary to set the boundaries that distinguish different cell types required for proper development. One mechanism to impart spatial information is usually to regulate gene expression through transcription factors that are spatially localized. Alternately, localized activation of signaling pathways in particular domains can also influence the boundaries of gene expression. InDrosophila melanogaster, the dorsal-ventral (DV) axis of the pre-gastrula embryo is usually patterned by a nuclear gradient of the NF-B 1A-116 homologous transcription factor Dorsal[1]. High levels of nuclear Dorsal are present in ventral regions of theDrosophilaembryo and nuclear levels decrease progressively toward more dorsal regions. Due in part to these differing nuclear Dorsal levels, different 1A-116 domains of gene expression are established along the DV axis to specify different cell types[2]. In the ventral most regions of the embryo, high concentrations of nuclear Dorsal drive expression of genes such astwistandsnail (sna)to specify the presumptive mesoderm. In ventral lateral regions of the embryo, intermediate levels of Dorsal activate genes such asrhomboid (rho)andventral neuroblast defective(vnd) and low levels of Dorsal support expression of genes such asshort gastrulation (sog)in broad lateral domains of the embryo (that encompass both ventral-lateral and dorsal-lateral 1A-116 regions) to specify distinct domains within the presumptive neurogenic ectoderm[3],[4],[5]. Lastly, as Dorsal can also function as a repressor, the expression of some genes such aszerknllt(zen) are limited to dorsal regions of the embryo, leading cells in this domain name to adopt 1A-116 amnioserosa and non-neurogenic dorsal ectoderm cell fates[2],[6],[7]. Even though Dorsal provides positional information through its dorsal-ventrally modulated nuclear gradient, combinatorial interactions of transcription factors are very influential towards DV patterning. Specifically, Dorsal regulates gene expression together with other transcription factors, such as the bHLH factor Twist and the early ubiquitous activator Zelda[8],[9],[10]. More and more evidence suggests that signaling pathways also help to define gene expression patterns in the early embryo. For example, the expression domains of several Dorsal target genes cannot be explained by changing Dorsal levels (and/or the localization of any other previously characterized transcription factors). Additionally, it is well comprehended that signaling molecules provide positional information to help define the very specific expression domain encompassed by the genesingle-minded (sim).simis expressed as a stripe of a single cell width present in ventrolateral regions of the embryo, within cells located between the presumptive mesoderm and neurogenic ectoderm boundary.simexpression is supported by combinatorial interactions of Dorsal and Twist transcription factors and also through Notch-dependent signaling[11]. Along similar lines, the geneintermediate neuroblast defective (ind)is usually 1A-116 expressed in dorsal-lateral regions of the embryo in a stripe of 57 cells in width, which is narrower than the broad domain name encompassed bysog. Genetic studies support the view that refinedindexpression is usually supported by.