Using Bioconductor To Analyse Beadarray Data
From Bridges Lab Protocols
- R, get from CRAN
- Bioconductor, get from Bioconductor
- Bioconductor packages. Install as needed:
- annotation data for the array (normally illuminaMousev2BeadID.db)
- To install bioconductor packages use:
- At a minimum you need the Probe Profile data (normally a txt file).
- For all R procedures first change directory to your working directory then next create a new script, and save all executed lines in that script file.
- Load the beadarray library, indictate dataFile (required), sampleSheet (normally a xls or csv file) and control set (Control Probe, normally a txt file)
data = "FinalReport_SampleProbe.txt" controls = "ControlProbe.txt" samplesheet = "Proj_54_12Aug09_WGGEX_SS_name.csv" BSData = readBeadSummaryData(dataFile = data, qcFile= controls, sampleSheet=samplesheet)
- You may need to alter either the ProbeID or ControlID to fit the illuminaprobe column from the sampleprobe or controlprobe datasets.
- This fits the data into the BSData dataframe. Phenotype data can be accessed by pData(BSData) and expression data can be accessed by exprs(BSData).
- Microarray data is typically quantile normalised and log2 transformed:
BSData.quantile = normaliseIllumina(BSData, method="quantile", transform="log2")
- To examine the effects of normalisation on the dataset use boxplots:
boxplot(as.data.frame(log2(exprs(BSData))),las=2,outline=FALSE, ylab="Intensity (Log2 Scale)") boxplot(as.data.frame(exprs(BSData.quantile)),las=2,outline=FALSE, ylab="Intensity (Log2 Scale)")
- Save these boxplots as postscript files.
- This analysis will generate a euclidean distance matrix then a cluster analysis of that matrix and will show the distribution between replicates. Ideally similar treatments will cluster together.
d = dist(t(exprs(BSData.quantile))) plot(hclust(d)
Differential Expression Analysis
- Normalised data can be analysed using the limma package for statistical differences
- First define groups for each treatment. If a samplesheet was provided correctly and had this information:
samples = pData(BSData)$Sample_Group
- Otherwise define these groups manually in the order that they were entered, check by looking at pData(BSData)
samples = c("Control", "Control", "Treatment1", "Treatment1, "Treatment2"...)
- Next the groups are used to set up a statistical design:
library(limma) samples = as.factor(samples) design = model.matrix(~0 + samples) colnames(design) = levels(samples) fit = lmFit(exprs(BSData.quantile), design)
- Now set up contrast matrices to define how you want the data analyses. For example you may want to compare some treatments to a control, as well as between some treaments. See the limma user guide for more information about specific analyses. When defining the contrast matrix use the sample group names as defined above.
cont.matrix = makeContrasts(Treatment1vsControl = Treatment1 - Control, Treatment2vsControl = Treatment2 - Control, Treatment1vsTreatment2 = Treatment1 - Treatment2, levels = design) fit.cont = contrasts.fit(fit, cont.matrix) ebFit = eBayes(fit.cont)
Generating a Venn Diagram for Differential Expression
- First define a cutoff criteria for inclusion. One option is to use the decideTests function:
results = decideTests(ebFit)
- The relevant options are for method and adjust.method
- default is "global", which allows for p-value comparasons
- adjust.method, this defines the false-discovery rate adjustment:
- default is "BH" for Benjami and Hochberg
- other options are "none", "fdr" (same as BH), "holm" and "BY"
- Now use that classification to generate the Venn Diagram. The following will include both up and downregulated genes and color the numbers accordingly:
vennDiagram(results, include="both", col=c("red","green")
Annotation of Expression Sets and Fitted Data
- To see all possible annotation criteria use:
- Normally you want to annotate with at least the gene symbol and gene name. Add other criteria as required
ids = rownames(exprs(BSData)) GeneName = mget(ids, illuminaMousev2BeadIDGENENAME, ifnotfound = NA) symbol = mget(ids, illuminaMousev2BeadIDSYMBOL, ifnotfound = NA) anno = cbind(GeneSymbol = as.character(symbol), GeneName = as.character(GeneName))
- To add this annotation to the data analysis file:
ebFit$genes = anno write.fit = (ebFit, file = "Filename.csv", adjust="BH")
- This example includes a false discovery rate ("BH") adjusted p.value.
- This function writes a tab-delimited text file containing for each gene (1) the average log-intensity, (2) the log-ratios, (3) moderated t-statistics, (4) t-statistic P-values, (5) F-statistic if available, (6) F-statistic P-values if available, (7) classification if available.
- To add this annotation data to the expression set:
data = exprs(BSData.quantile) data = cbind(anno,data) write.csv = (data, file = "Filename.csv")
- Remember that the expression set is Log2 adjusted, so to look at absolute expression levels use 2^value.