title: POLYPHEMUS: R package for comparative analysis of RNA polymerase II ChIP-seq profiles by non-linear normalization.
abstract: Chromatin immunoprecipitation coupled with massive parallel sequencing (ChIP-seq) is increasingly used to map protein-chromatin interactions at global scale. The comparison of ChIP-seq profiles for RNA polymerase II (PolII) established in different biological contexts, such as specific developmental stages or specific time-points during cell differentiation, provides not only information about the presence/accumulation of PolII at transcription start sites (TSSs) but also about functional features of transcription, including PolII stalling, pausing and transcript elongation. However, annotation and normalization tools for comparative studies of multiple samples are currently missing. Here, we describe the R-package POLYPHEMUS, which integrates TSS annotation with PolII enrichment over TSSs and coding regions, and normalizes signal intensity profiles. Thereby POLYPHEMUS facilitates to extract information about global PolII action to reveal changes in the functional state of genes. We validated POLYPHEMUS using a kinetic study on retinoic acid-induced differentiation and a publicly available data set from a comparative PolII ChIP-seq profiling in Caenorhabditis elegans. We demonstrate that POLYPHEMUS corrects the data sets by normalizing for technical variation between samples and reveal the potential of the algorithm in comparing multiple data sets to infer features of transcription regulation from dynamic PolII binding profiles.
authors.affiliation: Department of Cancer Biology, Institut de Génétique et de Biologie Moléculaire et Cellulaire/CNRS/INSERM/Université de Strasbourg, BP 10142, 67404 Illkirch Cedex, France. marco@igbmc.fr
authors.forename: Marco A
authors.initials: MA
authors.lastname: Mendoza-Parra
authors.forename: Martial
authors.initials: M
authors.lastname: Sankar
authors.forename: Mannu
authors.initials: M
authors.lastname: Walia
authors.forename: Hinrich
authors.initials: H
authors.lastname: Gronemeyer
mesh_terms: D000465:Algorithms; D000818:Animals; D001665:Binding Sites; D017173:Caenorhabditis elegans / Q000196:embryology / Q000235:genetics / Q000254:growth & development; D002454:Cell Differentiation; D002843:Chromatin / Q000235:genetics; D047369:Chromatin Immunoprecipitation; D003627:Data Interpretation, Statistical; D059014:High-Throughput Nucleotide Sequencing; D012319:RNA Polymerase II / Q000378:metabolism*; D017422:Sequence Analysis, DNA; D012984:Software; D024363:Transcription Initiation Site
chemical_list: D002843:Chromatin; D012319:RNA Polymerase II