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Install with (under BioC 2.14):
source("http://bioconductor.org/workflows.R")
workflowInstall("arrays")
  

Using Bioconductor with Microarray Analysis

Bioconductor has advanced facilities for analysis of microarray platforms including Affymetrix, Illumina, Nimblegen, Agilent, and other one- and two-color technologies.

Bioconductor includes extensive support for analysis of expression arrays, and well-developed support for exon, copy number, SNP, methylation, and other assays.

Major workflows in Bioconductor include pre-processing, quality assessment, differential expression, clustering and classification, gene set enrichment analysis, and genetical genomics.

Bioconductor offers extensive interfaces to community resources, including GEO, ArrayExpress, Biomart, genome browsers, GO, KEGG, and diverse annotation sources.

Sample Workflow

The following code illustrates a typical R / Bioconductor session. It uses RMA from the affy package to pre-process Affymetrix arrays, and the limma package for assessing differential expression.

## Load packages
library(affy)   # Affymetrix pre-processing
library(limma)  # two-color pre-processing; differential
                  # expression

## import "phenotype" data, describing the experimental design
phenoData <- 
    read.AnnotatedDataFrame(system.file("extdata", "pdata.txt",
    package="arrays"))

## RMA normalization
celfiles <- system.file("extdata", package="arrays")
eset <- justRMA(phenoData=phenoData,
    celfile.path=celfiles)

## Warning: replacing previous import by 'utils::head' when loading 'hgfocuscdf'
## Warning: replacing previous import by 'utils::tail' when loading 'hgfocuscdf'

## 

## differential expression
combn <- factor(paste(pData(phenoData)[,1],
    pData(phenoData)[,2], sep = "_"))
design <- model.matrix(~combn) # describe model to be fit

fit <- lmFit(eset, design)  # fit each probeset to model
efit <- eBayes(fit)        # empirical Bayes adjustment
topTable(efit, coef=2)      # table of differentially expressed probesets

##              logFC AveExpr      t   P.Value adj.P.Val     B
## 204582_s_at  3.468  10.151  39.03 1.970e-14 1.732e-10 19.86
## 211548_s_at -2.326   7.179 -22.73 1.541e-11 6.776e-08 15.89
## 216598_s_at  1.936   7.693  21.74 2.659e-11 7.793e-08 15.48
## 211110_s_at  3.158   7.909  21.19 3.625e-11 7.969e-08 15.25
## 206001_at   -1.591  12.403 -18.64 1.715e-10 3.017e-07 14.02
## 202409_at    3.274   6.705  17.73 3.157e-10 4.626e-07 13.52
## 221019_s_at  2.252   7.104  16.35 8.353e-10 1.049e-06 12.69
## 204688_at    1.813   7.125  14.75 2.834e-09 3.115e-06 11.62
## 205489_at    1.241   7.552  13.62 7.265e-09 7.098e-06 10.77
## 209288_s_at -1.226   7.604 -13.33 9.401e-09 7.785e-06 10.53

A top table resulting from a more complete analysis, described in Chapter 7 of Bioconductor Case Studies, is shown below. The table enumerates Affymetrix probes, the log-fold difference between two experimental groups, the average expression across all samples, the t-statistic describing differential expression, the unadjusted and adjusted (controlling for false discovery rate, in this case) significance of the difference, and log-odds ratio. These results can be used in further analysis and annotation.

      ID logFC AveExpr    t  P.Value adj.P.Val     B
636_g_at  1.10    9.20 9.03 4.88e-14  1.23e-10 21.29
39730_at  1.15    9.00 8.59 3.88e-13  4.89e-10 19.34
 1635_at  1.20    7.90 7.34 1.23e-10  1.03e-07 13.91
 1674_at  1.43    5.00 7.05 4.55e-10  2.87e-07 12.67
40504_at  1.18    4.24 6.66 2.57e-09  1.30e-06 11.03
40202_at  1.78    8.62 6.39 8.62e-09  3.63e-06  9.89
37015_at  1.03    4.33 6.24 1.66e-08  6.00e-06  9.27
32434_at  1.68    4.47 5.97 5.38e-08  1.70e-05  8.16
37027_at  1.35    8.44 5.81 1.10e-07  3.08e-05  7.49
37403_at  1.12    5.09 5.48 4.27e-07  1.08e-04  6.21

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Installation and Use

Follow installation instructions to start using these packages. You can install affy and limma as follows:

source("http://bioconductor.org/biocLite.R")
biocLite(c("affy", "limma"))

To install additional packages, such as the annotations associated with the Affymetrix Human Genome U95A 2.0, use

source("http://bioconductor.org/biocLite.R")
biocLite("hgu95av2.db")

Package installation is required only once per R installation. View a /packagesfull list of available packages.

To use the affy and limma packages, evaluate the commands

library("affy")
library("limma")

These commands are required once in each R session.

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Exploring Package Content

Packages have extensive help pages, and include vignettes highlighting common use cases. The help pages and vignettes are available from within R. After loading a package, use syntax like

help(package="limma")
?topTable

to obtain an overview of help on the limma package, and the topTable function, and

browseVignettes(package="limma")

to view vignettes (providing a more comprehensive introduction to package functionality) in the limma package. Use

help.start()

to open a web page containing comprehensive help resources.

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Pre-Processing Resources

The following provide a brief overview of packages useful for pre-processing. More comprehensive workflows can be found in documentation (available from package descriptions) and in Bioconductor Books and monographs.

Affymetrix 3'-biased Arrays

affy, gcrma, affyPLM

xps

Affymetrix Exon ST Arrays

oligo

exonmap

xps

Affymetrix Gene ST Arrays

oligo

xps

Affymetrix SNP Arrays

oligo

Affymetrix Tiling Arrays

oligo

Nimblegen Arrays

oligo

Illumina Expression Microarrays

lumi

beadarray

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sessionInfo()

## R version 3.1.0 (2014-04-10)
## Platform: x86_64-unknown-linux-gnu (64-bit)
## 
## locale:
##  [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C              
##  [3] LC_TIME=en_US.UTF-8        LC_COLLATE=en_US.UTF-8    
##  [5] LC_MONETARY=en_US.UTF-8    LC_MESSAGES=en_US.UTF-8   
##  [7] LC_PAPER=en_US.UTF-8       LC_NAME=C                 
##  [9] LC_ADDRESS=C               LC_TELEPHONE=C            
## [11] LC_MEASUREMENT=en_US.UTF-8 LC_IDENTIFICATION=C       
## 
## attached base packages:
## [1] parallel  stats     graphics  grDevices utils     datasets  methods  
## [8] base     
## 
## other attached packages:
## [1] hgfocuscdf_2.14.0   affy_1.42.3         Biobase_2.24.0     
## [4] BiocGenerics_0.10.0 limma_3.20.8        knitr_1.6          
## 
## loaded via a namespace (and not attached):
##  [1] affyio_1.32.0         AnnotationDbi_1.26.0  BiocInstaller_1.14.2 
##  [4] DBI_0.2-7             evaluate_0.5.5        formatR_0.10         
##  [7] GenomeInfoDb_1.0.2    IRanges_1.22.9        preprocessCore_1.26.1
## [10] RSQLite_0.11.4        stats4_3.1.0          stringr_0.6.2        
## [13] tools_3.1.0           zlibbioc_1.10.0

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Fred Hutchinson Cancer Research Center