Unknown,Transcriptomics,Genomics,Proteomics

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Roles of Cofactors and Chromatin Accessibility in Hox Protein Target Specificity

ABSTRACT: Regulation of specific target genes by transcription factors is central to gene network control in development. How target specificity is achieved in eukaryotic genomes is poorly understood, as exemplified by the Hox family, which show limited in vitro DNA-binding specificity but clear functional specificity in vivo. We generated genome-wide binding profiles for three Hox proteins, Ubx, Abd-A and Abd-B, in Drosophila Kc167 cells, revealing clear target specificity and a striking influence of chromatin accessibility. Ubx and Abd-A bind to similar target sites in accessible chromatin whereas Abd-B binds additional specific targets. Provision of the TALE class cofactors, Exd and Hth, alters the Ubx binding profile, enabling binding to additional targets in the genome. Both the Abd-B specific targets and the cofactor-dependent Ubx targets are in relatively DNase1 inaccessible chromatin, suggesting that competition with nucleosomes is a key factor determining Hox protein target specificity. This ChIP-Seq study performed on Kc167 cells involves two experiments and 6 ChIP samples. In Experiment 1, we generated genome-wide binding profiles for Ubx, Abd-A and Abd-B. An equal volume of input chromatin was retained from each of the Hox samples and combined to represent the input, which was purified alongside the ChIP samples. We performed two biological replicates for each sample. Sequencing was performed using the Illumina MiSeq platform. In Experiment 2, we generated genome-wide binding profiles for Ubx, mutant Ubx and Ubx in the presence of Hth. We performed two biological replicates for each sample except Ubx where we performed just one. Sequencing was performed using the Illumina HiSeq 2000 platform. For all samples, Experiment 1 input chromatin was used as the reference control to assay ChIP enrichment.

ORGANISM(S): Drosophila melanogaster

SUBMITTER: Robert White

PROVIDER: E-GEOD-69796 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Hox homeodomain transcription factors are key regulators of animal development. They specify the identity of segments along the anterior-posterior body axis in metazoans by controlling the expression of diverse downstream targets, including transcription factors and signaling pathway components. The Drosophila melanogaster Hox factor Ultrabithorax (Ubx) directs the development of thoracic and abdominal segments and appendages, and loss of Ubx function can lead for example to the transformation of third thoracic segment appendages (e.g. halters) into second thoracic segment appendages (e.g. wings), resulting in a characteristic four-wing phenotype. Here we present a Drosophila melanogaster strain with a V5-epitope tagged Ubx allele, which we employed to obtain a high quality genome-wide map of Ubx binding sites using ChIP-seq. We confirm the sensitivity of the V5 ChIP-seq by recovering 7/8 of well-studied Ubx-dependent cis-regulatory regions. Moreover, we show that Ubx binding is predictive of enhancer activity as suggested by comparison with a genome-scale resource of in vivo tested enhancer candidates. We observed densely clustered Ubx binding sites at 12 extended genomic loci that included ANTP-C, BX-C, Polycomb complex genes, and other regulators and the clustered binding sites were frequently active enhancers. Furthermore, Ubx binding was detected at known Polycomb response elements (PREs) and was associated with significant enrichments of Pc and Pho ChIP signals in contrast to binding sites of other developmental TFs. Together, our results show that Ubx targets developmental regulators via strongly clustered binding sites and allow us to hypothesize that regulation by Ubx might involve Polycomb group proteins to maintain specific regulatory states in cooperative or mutually exclusive fashion, an attractive model that combines two groups of proteins with prominent gene regulatory roles during animal development. Ubx was endogenously tagged with V5 epitope in Drosophila melanogaster (Ubx-V5). ChIP-seq was performed with chromatin from 0-16 hrs wild type and Ubx-V5 embryos. The samples were subjected to single-end sequencing in two replicates.

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Roles of Cofactors and Chromatin Accessibility in Hox Protein Target Specificity

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