Analysis of the ftz upstream element: germ layer-specific enhancers are independently autoregulated.

Abstract

The Drosophila fushi tarazu (ftz) upstream element is an enhancer-like element that is required for the correct expression of fez in developing embryos and that directs transcription from a minimal promoter in a ftz-like seven-striped pattern. Using a deletion analysis, we have identified several independent c/s-regulatory elements in the upstream element. A distal enhancer directs fusion gene expression in seven stripes primarily in the mesoderm. A more complex proximal enhancer contains a mesodermally active element and a second element with which it interacts to generate seven stripes in the ectoderm. Striped expression directed by each enhancer is ftz-dependent, and each contains binding sites for purified ftz homeo domain. We suggest that ftz protein acts in combination with germ layer-restricted transcription factors directly and positively to regulate the transcription of its own gene. The development of a complex organism from a fertilized egg requires the differential expression of genetic information in a temporally and spatially restricted fashion. This differential expression is frequently regulated at the level of transcription initiation (for reviews, see Maniatis et al. 1987;Mitchell and Tjian 1989). In such cases, cis-acting DNA sequences mediate interactions between trans-acting protein factors and RNA polymerase II or the "general transcription machinery" to activate transcription. Promoter elements, located close to the transcription start site, are required for efficient initiation and positioning of the start site, whereas upstream regulatory elements or enhancers act to increase the rate of transcription from a given promoter. Enhancers are characterized by their abilities to (1) stimulate transcription over large and varying distances, (2) act in an orientation-independent fashion, and (3) stimulate transcription of heterologous promoters (Serfling et al. 1985). For both viral and cellular genes, discrete cisacting regulatory elements have been identified that direct transcription in a cell type-restricted fashion. Although some cell type-specific enhancers have been studied in detail (Atchison 1988), only a small number have been examined in their native cellular environments in transgenic animals (Posakony et al. 1985;Garabedian et al. 1986;Hammer et al. 1987; Pinkert et al. 1987; Johnson et al. 1989;Logan et al. 1989). Much of what we know about enhancer function comes from studies of viral model systems. Analysis of the wellcharacterized viral SV40 enhancers suggests that the basic building blocks of enhancers are short "enhansons" that correspond to the binding sites for transacting factors (Ondek et al. 1988}. Different enhancer motifs may be active in different cell types, suggesting that the availability of cell type-specific transcription factors may control the specificity of enhancer activation {Schirm et al. 1987). Given the complexity of promoter and enhancer elements, it is possible to construct a scenario in which transcriptional specificity is determined by the combinatoria...

Long-range enhancer–promoter interactions in the Scr-Antp interval of the Drosophila Antennapedia complex

“…2A). Two of the clusters correspond to previously identified cis-regulatory DNAs, the AE1 enhancer, and the ftz zebra element, which initiates ftz expression in early embryos (12)(13)(14). A third cluster was also identified that maps just downstream of the ftz transcription unit (cluster 3, see Fig.…”

DNA binding specificity of two homeodomain proteins in vitro and in Drosophila embryos.

“…In embryos, strong and relatively uniform cross-linking by eve and ftz proteins was seen on many kilobase pairs of these two targets in vivo (3). In contrast, earlier in vitro studies reported that ftz protein binds only to a 2-kb upstream autoregulatory region of theftz promoter (8,9), and that eve protein binds only to three short regions of the eve promoter (6, 7). Significantly, at 150 mM NaCl, we observed binding of eve, ftz, and Dfd proteins to other regions of these promoters as well, and, in most cases, only 2-to 3-fold differences in binding are seen between many fragments across a promoter (Fig.…”

How to make stripes: deciphering the transition from non-periodic to periodic patterns inDrosophilasegmentation

“…Antp gene, which is strongly expressed in parasegment 4 (Hiromi and Gehring, 1987;Pick et al, 1990). The ftz_(-7) element, which falls outside the originally dissected region, drove expression of stripes 3 and 6/7.…”