Drosophila brakeless interacts with atrophin and is required for tailless-mediated transcriptional repression in early embryos.
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ABSTRACT:
SUBMITTER: Haecker A
PROVIDER: S-EPMC1868043 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Developmental processes are robust, or canalised: dynamic patterns of gene expression across space and time are regulated reliably and precisely in the presence of genetic and environmental perturbations. It remains unclear whether canalisation relies on specific regulatory factors (such as heat-shock proteins), or whether it is based on more general redundancy and distributed robustness at the network level. The latter explanation implies that mutations in many regulatory factors should exhibit loss of canalisation. Here, we present a quantitative characterisation of segmentation gene expression patterns in mutants of the terminal gap gene tailless (tll) in Drosophila melanogaster. Our analysis provides new insights into the dynamic mechanisms underlying gap gene regulation, and reveals significantly increased variability of gene expression in the mutant compared to the wild-type background. We show that both position and timing of posterior segmentation gene expression domains vary strongly from embryo-to-embryo in tll mutants. This variability must be caused by a vulnerability in the regulatory system which is hidden or buffered in the wild-type, but becomes uncovered by the deletion of tll. Our analysis provides evidence that loss of canalisation in mutants could be more widespread than previously thought.
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Project description:The general consensus in the field is that limiting amounts of the transcription factor Dorsal establish dorsal boundaries of genes expressed along the dorsal-ventral (DV) axis of early Drosophila embryos, while repressors establish ventral boundaries. Yet recent studies have provided evidence that repressors act to specify the dorsal boundary of intermediate neuroblasts defective (ind), a gene expressed in a stripe along the DV axis in lateral regions of the embryo. Here we show that a short 12 base pair sequence ("the A-box") present twice within the ind CRM is both necessary and sufficient to support transcriptional repression in dorsal regions of embryos. To identify binding factors, we conducted affinity chromatography using the A-box element and found a number of DNA-binding proteins and chromatin-associated factors using mass spectroscopy. Only Grainyhead (Grh), a CP2 transcription factor with a unique DNA-binding domain, was found to bind the A-box sequence. Our results suggest that Grh acts as an activator to support expression of ind, which was surprising as we identified this factor using an element that mediates dorsally-localized repression. Grh and Dorsal both contribute to ind transcriptional activation. However, another recent study found that the repressor Capicua (Cic) also binds to the A-box sequence. While Cic was not identified 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 the ind dorsal boundary. Furthermore, our results also demonstrate that TGF-? signaling acts to refine ind CRM expression in an A-box independent manner in dorsal-most regions, suggesting that tiers of repression act in dorsal regions of the embryo.
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Project description:Tailless is a committed transcriptional repressor and principal regulator of the brain and eye development in Drosophila. Rpd3, the histone deacetylase, is an established repressor that interacts with co-repressors like Sin3a, Prospero, Brakeless and Atrophin. This study aims at deciphering the role of Rpd3 in embryonic segmentation and larval brain development in Drosophila. It delineates the mechanism of Tailless regulation by Rpd3, along with its interacting partners. There was a significant reduction in Tailless in Rpd3 heteroallelic mutant embryos, substantiating that Rpd3 is indispensable for the normal Tailless expression. The expression of the primary readout, Tailless was correlative to the expression of the neural cell adhesion molecule homologue, Fascilin2 (Fas2). Rpd3 also aids in the proper development of the mushroom body. Both Tailless and Fas2 expression are reported to be antagonistic to the epidermal growth factor receptor (EGFR) expression. The decrease in Tailless and Fas2 expression highlights that EGFR is upregulated in the larval mutants, hindering brain development. This study outlines the axis comprising Rpd3, dEGFR, Tailless and Fas2, which interact to fine-tune the early segmentation and larval brain development. Therefore, Rpd3 along with Tailless has immense significance in early embryogenesis and development of the larval brain.
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