NarrowPeaks (version 1.12.0)

NarrowPeaks-package: Shape-based Analysis of Variation in ChIP-Seq using Functional PCA

Description

The package applies a functional version of principal component analysis (FPCA) to: (1) Process data in wiggle track format (WIG) commonly produced by ChIP-Seq peak callers by applying FPCA over a set of read-enriched regions (ChIP-Seq peaks). This is done in order to shorten the genomic locations accounting for a given proportion of variation among the enrichment-score profiles. The function 'narrowpeaks' allows splitting and trimming binding sites in close proximity to each other, narrowing down the length of the putative transcription factor binding sites while preserving the information present in the variability of the dataset and capturing major sources of variation. (2) Analyse differential variation between multiple ChIP-Seq samples with replicates. The function 'narrowpeaksDiff' quantifies differences between the shapes, and uses Hotelling's T2 tests on the functional principal component scores to identify significant differences across conditions.

Details

Package:

NarrowPeaks

Type:

Package

Version:

1.11.4

Date:

2015-02-01

License:

Artistic-2.0

LazyLoad:

yes

References

Madrigal P, Krajewski P (in preparation) Shape-based Dimensionality Reduction Analyses by Functional PCA Reveal Associations between First and Higher Order Components in Next-Generation Sequencing Coverage Profiles.

Examples

owd <- setwd(tempdir())

##For this example we will use a subset of the AP1 ChIP-Seq data (Kaufmann et
##al., 2010)
##The data is obtained after analysis using the CSAR package available in 
##Bioconductor 
data("NarrowPeaks-dataset")
writeLines(wigfile_test, con="wigfile.wig")

##Write binary files with the WIG signal values for each chromosome 
##independently and obtain regions of read-enrichment with score values greater
##than 't', allowing a gap of 'g'. Data correspond to enriched regions found up
##to 105Kb in the Arabidopsis thaliana genome
wigScores <- wig2CSARScore(wigfilename="wigfile.wig", nbchr = 1, 
chrle=c(30427671))
gc(reset=TRUE) 
library(CSAR)
candidates <- sigWin(experiment=wigScores$infoscores, t=1.0, g=30)

##Narrow down ChIPSeq enriched regions by functional PCA
shortpeaks <- narrowpeaks(inputReg=candidates, 
scoresInfo=wigScores$infoscores, lmin=0, nbf=150, rpenalty=0, 
nderiv=0, npcomp=2, pv=80, pmaxscor=3.0, ms=0)

###Export GRanges object with the peaks to annotation tracks in various 
##formats. E.g.:
library(GenomicRanges)
names(elementMetadata(shortpeaks$broadPeaks))[3] <- "score"
names(elementMetadata(shortpeaks$narrowPeaks))[2] <- "score"
library(rtracklayer)
export.bedGraph(object=candidates, con="CSAR.bed")
export.bedGraph(object=shortpeaks$broadPeaks, con="broadPeaks.bed")
export.bedGraph(object=shortpeaks$narrowPeaks, con="narrowpeaks.bed")

setwd(owd)