Template for analysis with DESeq2

deseq2-analysis-template.R

## RNA-seq analysis with DESeq2
## Stephen Turner, @genetics_blog

# RNA-seq data from GSE52202
# http://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=gse52202. All patients with
# ALS, 4 with C9 expansion ("exp"), 4 controls without expansion ("ctl")

# Import & pre-process ----------------------------------------------------

# Import data from featureCounts
## Previously ran at command line something like this:
## featureCounts -a genes.gtf -o counts.txt -T 12 -t exon -g gene_id GSM*.sam
countdata <- read.table("counts.txt", header=TRUE, row.names=1)

# Remove first five columns (chr, start, end, strand, length)
countdata <- countdata[ ,6:ncol(countdata)]

# Remove .bam or .sam from filenames
colnames(countdata) <- gsub("\\.[sb]am$", "", colnames(countdata))

# Convert to matrix
countdata <- as.matrix(countdata)
head(countdata)

# Assign condition (first four are controls, second four contain the expansion)
(condition <- factor(c(rep("ctl", 4), rep("exp", 4))))

# Analysis with DESeq2 ----------------------------------------------------

library(DESeq2)

# Create a coldata frame and instantiate the DESeqDataSet. See ?DESeqDataSetFromMatrix
(coldata <- data.frame(row.names=colnames(countdata), condition))
dds <- DESeqDataSetFromMatrix(countData=countdata, colData=coldata, design=~condition)
dds

# Run the DESeq pipeline
dds <- DESeq(dds)

# Plot dispersions
png("qc-dispersions.png", 1000, 1000, pointsize=20)
plotDispEsts(dds, main="Dispersion plot")
dev.off()

# Regularized log transformation for clustering/heatmaps, etc
rld <- rlogTransformation(dds)
head(assay(rld))
hist(assay(rld))

# Colors for plots below
## Ugly:
## (mycols <- 1:length(unique(condition)))
## Use RColorBrewer, better
library(RColorBrewer)
(mycols <- brewer.pal(8, "Dark2")[1:length(unique(condition))])

# Sample distance heatmap
sampleDists <- as.matrix(dist(t(assay(rld))))
library(gplots)
png("qc-heatmap-samples.png", w=1000, h=1000, pointsize=20)
heatmap.2(as.matrix(sampleDists), key=F, trace="none",
          col=colorpanel(100, "black", "white"),
          ColSideColors=mycols[condition], RowSideColors=mycols[condition],
          margin=c(10, 10), main="Sample Distance Matrix")
dev.off()

# Principal components analysis
## Could do with built-in DESeq2 function:
## DESeq2::plotPCA(rld, intgroup="condition")
## I like mine better:
rld_pca <- function (rld, intgroup = "condition", ntop = 500, colors=NULL, legendpos="bottomleft", main="PCA Biplot", textcx=1, ...) {
  require(genefilter)
  require(calibrate)
  require(RColorBrewer)
  rv = rowVars(assay(rld))
  select = order(rv, decreasing = TRUE)[seq_len(min(ntop, length(rv)))]
  pca = prcomp(t(assay(rld)[select, ]))
  fac = factor(apply(as.data.frame(colData(rld)[, intgroup, drop = FALSE]), 1, paste, collapse = " : "))
  if (is.null(colors)) {
    if (nlevels(fac) >= 3) {
      colors = brewer.pal(nlevels(fac), "Paired")
    }   else {
      colors = c("black", "red")
    }
  }
  pc1var <- round(summary(pca)$importance[2,1]*100, digits=1)
  pc2var <- round(summary(pca)$importance[2,2]*100, digits=1)
  pc1lab <- paste0("PC1 (",as.character(pc1var),"%)")
  pc2lab <- paste0("PC1 (",as.character(pc2var),"%)")
  plot(PC2~PC1, data=as.data.frame(pca$x), bg=colors[fac], pch=21, xlab=pc1lab, ylab=pc2lab, main=main, ...)
  with(as.data.frame(pca$x), textxy(PC1, PC2, labs=rownames(as.data.frame(pca$x)), cex=textcx))
  legend(legendpos, legend=levels(fac), col=colors, pch=20)
  #     rldyplot(PC2 ~ PC1, groups = fac, data = as.data.frame(pca$rld),
  #            pch = 16, cerld = 2, aspect = "iso", col = colours, main = draw.key(key = list(rect = list(col = colours),
  #                                                                                         terldt = list(levels(fac)), rep = FALSE)))
}
png("qc-pca.png", 1000, 1000, pointsize=20)
rld_pca(rld, colors=mycols, intgroup="condition", xlim=c(-75, 35))
dev.off()


# Get differential expression results
res <- results(dds)
table(res$padj<0.05)
## Order by adjusted p-value
res <- res[order(res$padj), ]
## Merge with normalized count data
resdata <- merge(as.data.frame(res), as.data.frame(counts(dds, normalized=TRUE)), by="row.names", sort=FALSE)
names(resdata)[1] <- "Gene"
head(resdata)
## Write results
write.csv(resdata, file="diffexpr-results.csv")

## Examine plot of p-values
hist(res$pvalue, breaks=50, col="grey")

## Examine independent filtering
attr(res, "filterThreshold")
plot(attr(res,"filterNumRej"), type="b", xlab="quantiles of baseMean", ylab="number of rejections")

## MA plot
## Could do with built-in DESeq2 function:
## DESeq2::plotMA(dds, ylim=c(-1,1), cex=1)
## I like mine better:
maplot <- function (res, thresh=0.05, labelsig=TRUE, textcx=1, ...) {
  with(res, plot(baseMean, log2FoldChange, pch=20, cex=.5, log="x", ...))
  with(subset(res, padj<thresh), points(baseMean, log2FoldChange, col="red", pch=20, cex=1.5))
  if (labelsig) {
    require(calibrate)
    with(subset(res, padj<thresh), textxy(baseMean, log2FoldChange, labs=Gene, cex=textcx, col=2))
  }
}
png("diffexpr-maplot.png", 1500, 1000, pointsize=20)
maplot(resdata, main="MA Plot")
dev.off()

## Volcano plot with "significant" genes labeled
volcanoplot <- function (res, lfcthresh=2, sigthresh=0.05, main="Volcano Plot", legendpos="bottomright", labelsig=TRUE, textcx=1, ...) {
  with(res, plot(log2FoldChange, -log10(pvalue), pch=20, main=main, ...))
  with(subset(res, padj<sigthresh ), points(log2FoldChange, -log10(pvalue), pch=20, col="red", ...))
  with(subset(res, abs(log2FoldChange)>lfcthresh), points(log2FoldChange, -log10(pvalue), pch=20, col="orange", ...))
  with(subset(res, padj<sigthresh & abs(log2FoldChange)>lfcthresh), points(log2FoldChange, -log10(pvalue), pch=20, col="green", ...))
  if (labelsig) {
    require(calibrate)
    with(subset(res, padj<sigthresh & abs(log2FoldChange)>lfcthresh), textxy(log2FoldChange, -log10(pvalue), labs=Gene, cex=textcx, ...))
  }
  legend(legendpos, xjust=1, yjust=1, legend=c(paste("FDR<",sigthresh,sep=""), paste("|LogFC|>",lfcthresh,sep=""), "both"), pch=20, col=c("red","orange","green"))
}
png("diffexpr-volcanoplot.png", 1200, 1000, pointsize=20)
volcanoplot(resdata, lfcthresh=1, sigthresh=0.05, textcx=.8, xlim=c(-2.3, 2))
dev.off()

Super helpful. I am ran dds <- DESeqDataSetFromMatrix(countData= cc_all, colData=coldata, design= ~condition) just now and it returned : an error message saying NA values are not allowed in the count matrix. Should I use DESeqTransform or simply removed the NA values. Changing them to "0" is not recommended?

• For my project I am using ~mode_of_action. Also, I had to go back and fix my counts file with Multmerge and get rid of all my 0's before running DESeq since there is division (which will return NA's when there are 0's)

Hi,
Thanks for sharing this. I was wondering how I can regress out batch effect using DESeq analysis. Didn't find any argument which is specified for this.
Thanks