1. The ftz upstream element drives late ftz stripes but is not required for regulation of Ftz target genes.
- Author
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Fischer, Matthew D., Graham, Patricia, and Pick, Leslie
- Subjects
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GENETIC regulation , *GENE expression , *TRANSGENE expression , *STRIPES , *GASTRULATION , *EMBRYOLOGY , *PROTEIN binding - Abstract
The regulation of gene expression in precise, rapidly changing spatial patterns is essential for embryonic development. Multiple enhancers have been identified for the evolving expression patterns of the cascade of Drosophila segmentation genes that establish the basic body plan of the fly. Classic reporter transgene experiments identified multiple cis -regulatory elements (CREs) that are sufficient to direct various aspects of the evolving expression pattern of the pair-rule gene fushi tarazu (ftz). These include enhancers that coordinately activate expression in all seven stripes and stripe-specific elements that activate expression in one or more ftz stripes. Of the two 7-stripe enhancers, analysis of reporter transgenes demonstrated that the upstream element (UPS) is autoregulatory, requiring direct binding of Ftz protein to direct striped expression. Here, we asked about the endogenous role of the UPS by precisely deleting this 7-stripe enhancer. In ftzΔUPS 7S homozygotes, ftz stripes appear in the same order as wildtype, and all but stripe 4 are expressed at wildtype levels by the end of the cellular blastoderm stage. This suggests that the zebra element and UPS harbor information to direct stripe 4 expression, although previous deletion analyses failed to identify a stripe-specific CRE within these two 7-stripe enhancers. However, the UPS is necessary for late ftz stripe expression, with all 7 stripes decaying earlier than wildtype in ftzΔUPS 7S homozygotes. Despite this premature loss of ftz expression, downstream target gene regulation proceeds as in wildtype, and segmentation is unperturbed in the overwhelming majority of animals. We propose that this late-acting enhancer provides a buffer against perturbations in gene expression but is not required for establishment of Ftz cell fates. Overall, our results demonstrate that multiple enhancers, each directing distinct aspects of an overall gene expression pattern, contribute to fine-tuning the complex patterns necessary for embryonic development. Multiple enhancers are required to generate the complex gene expression patterns during embryogenesis that establish the animal body plan. Fischer et al. show that the Ftz-dependent autoregulatory enhancer that directs expression in a typical seven-stripe pair-rule pattern is necessary only for maintenance of ftz stripes. This enhancer is unnecessary for wildtype expression of downstream target genes or segment formation, demonstrating that peak pair-rule expression at the blastoderm stage is the critical point at which expression is required to promote segmentation. [Display omitted] • The Ftz-dependent UPS was precisely deleted to determine its endogenous role. • Deletion homozygotes (ΔUPS 7S ) fail to maintain ftz expression after gastrulation. • Despite a decrease in ftz stripe 4 levels ΔUPS 7S homozygotes are viable and fertile. • Ftz cell fate -target gene expression and segmentation-is largely unperturbed. [ABSTRACT FROM AUTHOR]
- Published
- 2024
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