Help:WikiPathways Webservice/Gene set enrichment in R

From WikiPathways

---

Revision as of 13:38, 23 January 2009

The R script below runs the Parametric Analysis of Gene Set Enrichment (PAGE) algorithm on GEO dataset GSE7023, using human WikiPathways pathway as gene sets. See the manual of the PGSEA libraray for more details on the gene set enrichment calculation.

# Load the required libraries
library(SSOAP)		#To use WikiPathways web service
library(GEOquery)	#To download GEO experiments
library(GSEABase)	#Gene Set data structures
library(PGSEA)		#Parametric Gene Set Enrichment
library(limma)		#Used for mining the GSEA results

# Create a SOAPServer instance for the web service
srv = SOAPServer("http://www.wikipathways.org/wpi/webservice/webservice.php");

# Get a list of all pathways from WikiPathways
reply = .SOAP(
	srv, "listPathways", 
	action=I("listPathways"), handlers=NULL
)
# Parse the xml document
doc = xmlParse(reply$content, asText=TRUE)

# Extract the pathway info
pathwayNodes = xmlElementsByTagName(xmlRoot(doc), "pathways", TRUE)
pathways = lapply(pathwayNodes, function(n) {
	children = xmlChildren(n, addNames= TRUE)
	if(xmlValue(children$species) == "Homo sapiens") {
		p = list()
		p[["id"]] = xmlValue(children$id)
		p[["name"]] = xmlValue(children$name)
		p[["species"]] = xmlValue(children$species)
		p[["url"]] = xmlValue(children$url)
		return(p)
	} else {
		return() # Skip non-human pathways
	}
})

# Remove NULL entries (non-human pathways)
pathways = pathways[!sapply(pathways, is.null)]

# A function that downloads a GeneSet for a pathway
createGS = function(p) {
	print(p[["id"]])
	# Download the gene list (translated to Entrez ids)
	reply = .SOAP(srv, "getXrefList", pwId = p[["id"]], code="L", 
						action=I("getXrefList"), handlers=NULL)
	doc = xmlParse(reply$content, asText=TRUE)
	# Find the xref nodes with an xpath query
	resultNodes = xmlElementsByTagName(xmlRoot(doc), "xrefs", TRUE)
	# Extract the gene ids
	geneIds = sapply(resultNodes, xmlValue)
	if(length(geneIds) > 0) { # Skip empty lists
		# Create a GeneSet object
		geneSet = GeneSet(geneIds, geneIdType=EntrezIdentifier(), 
			setName=paste(p[["id"]], " (", p[["name"]], ")", sep="")
		)
		return(geneSet)
	}
}
geneSets = lapply(pathways, createGS) #Apply the createGS function on all pathways
geneSets = geneSets[!sapply(geneSets, is.null)] #Remove empty sets
geneSetCollection = GeneSetCollection(geneSets)

# Save the downloaded gene sets, so we can use them for later calculations
save(geneSetCollection, file="/home/thomas/code/webservice-examples/Hs_genesets.Rd")

# Get an expression set from GEO
gse = getGEO("GSE7023", GSEMatrix = TRUE)
eset = gse[[1]]

# Reformat the phenotype labels
subtype = gsub("subtype: ", "", phenoData(eset)$characteristics_ch1)
subtype = gsub("\\.", "_", subtype)

# Run the PGSEA calculation (reference sample is 'NO')
pg = PGSEA(eset, geneSetCollection, ref = which(subtype == "NO"), p.value=0.005)

# Plot the result matrix
smcPlot(
	pg, factor(subtype), scale=c(-15,15), show.grid = TRUE, margins = c(1, 1, 4, 10), 		col = .rwb, r.cex = 0.35
)

# Find the pathways most different between P1 and P2B
pgNF <- PGSEA(eset, geneSetCollection, ref = which(subtype == "NO"), p.value = NA)
design <- model.matrix(~-1 + factor(subtype))
colnames(design) <- names(table(subtype))
fit <- lmFit(pgNF, design)
contrast.matrix <- makeContrasts(P2B - P1, levels = design)
fit <- contrasts.fit(fit, contrast.matrix)
fit <- eBayes(fit)

# Plot the top 25
smcPlot(pg[as.numeric(rownames(topTable(fit, n = 30, resort.by = "logFC"))),], factor(subtype, levels = c("P1", "P2B")), col = .rwb, scale = c(-15, 15), margins = c(1, 1, 4, 10), show.grid = TRUE, r.cex = 0.75)