Question about Diffbind counts
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slrpatty • 0
@3f073f21
Last seen 14 months ago
United States

I am trying to compare two different conditions (with 2 replicates each) using Diffbind. For my Diffbind output, I'm getting 0 counts for one of the conditions and high counts for the other condition. This doesn't seem to match my normalized browser tracks. There's clearly a peak around the chromosome position, but Diffbind is calculating it as 0 counts. There's definitely still a change in peak intensity between the two conditions, but it doesn't seem like it's reduced to 0. I was wondering if I'm doing something wrong or if I'm not understanding how the counts are calculated?

DiffBind • 1.1k views
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Could you show us the script you are using for the DiffBind analysis?

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samples <- read.csv("UDDF.csv")

tamoxifen <- dba(sampleSheet="UDDF.csv")

tamoxifen.counted <- dba.count(tamoxifen, summits=250, bUseSummarizeOverlaps=F, score=DBA_SCORE_NORMALIZED)
counts <- dba.peakset(tamoxifen.counted, bRetrieve=T)
TEST <- as.data.frame(counts)

#the counts from the normalization is making some genomic regions 0 when they don't appear to be 0
#the counts do not match my browser tracks which are also normalized based on read depth

dba.plotPCA(tamoxifen.counted, attributes=DBA_TISSUE, label=DBA_ID)

tamoxifen.contrast <- dba.contrast(tamoxifen.counted, contrast=c("Condition","UD","DF"), minMembers=2)

tamoxifen.analysed <- dba.analyze(tamoxifen.contrast, method=DBA_ALL_METHODS, bBlacklist=F, bGreylist=F)

dba.plotVenn(tamoxifen.analysed,contrast=1,method=DBA_ALL_METHODS)
dba.show(tamoxifen.analysed, bContrasts=T)

report_deseq <- dba.report(tamoxifen.analysed, method=DBA_DESEQ2, contrast=1, th=1, bCounts=T)
report_edger <- dba.report(tamoxifen.analysed, method=DBA_EDGER, contrast=1, th=1, bCounts=T)

report.deseq_2 <- as.data.frame(report_deseq)
report.edger_2 <- as.data.frame(report_edger)

#also getting 0 counts after running deseq or edger
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I notice you are using bUseSummarizeOverlaps=FALSE. Do you have a particular reason for doing so? Do you get the same behavior when you use the default bUseSummarizeOverlaps=TRUE?

Also, can you try running it with summits=0 and see if you still are getting zero counts?

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Hi Rory. I discovered that the culprit were my input files. I had another question though. When using summits=250, some of my peaks aren't 500 bp. Although most of them are 500 bp, some of them are an odd width. Is there a reason for that? Thanks!

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Yes, this is possible.

In the first step, the summits are computed for all merged peaks in the consensus peakset. Next, the peaks are re-centered around this summit, so will all be of width summits*2+1. If any of these newly re-centered peaks overlap, they will be merged, and hence will be wider than summits*2+1 bp.

It is possible to force recaluation of the summits, re-centering and merging, until all of the peaks have the same width:

tam <- dba(sampleSheet="tamoxifen.csv")
summitsize <- 1000
tam1 <- dba.count(tam, summits=summitsize)
centered <- dba.peakset(tam1, bRetrieve=TRUE)
while(!all(width(centered)==(summitsize*2+1))) {
  cat("RECENTER",length(centered),"\n")
  tam1 <- dba.count(tam, peaks=centered, summits=summitsize)
  centered <- dba.peakset(tam1, bRetrieve=TRUE)
  cat("RECENTERED",length(centered),"\n")
}

with output:

Computing summits...
Re-centering peaks...
RECENTER 2503 
Computing summits...
Re-centering peaks...
RECENTERED 2499 
RECENTER 2499 
Computing summits...
Re-centering peaks...
RECENTERED 2499
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Thank you!

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-redundant entry removed-

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-redundant entry removed-

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