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  • ErikFas
    Member
    • Jun 2014
    • 86

    Help with baySeq and limma for RNA-seq DE-analysis

    I'm currently trying to learn how to use the other DE-analysis pipelines that I don't already use (DESeq2), and I have started with limma and baySeq. I'm having some problems, though...

    First, baySeq. I'm reading the vignette from Bioconductor, and while I can get some results using the example data, I can't do that with my own data. This is a small piece of my counts table:

    Code:
                    hct_a hct_b hct_c rko_a rko_b rko_c
    ENSG00000XXXXXX  3376  3469  3917  2704  1713  1847
    ENSG0000XXXXXXX     0     0     0     0     0     0
    ENSG00000XXXXXX  5299  4700  4974  3212  2503  3340
    ENSG00000XXXXXX   892  1130  1386   262   360   362
    ENSG0000XXXXXXX  1453   568  1610  1482   514   908
    ENSG0000XXXXXXX     0     0     0     0     0     0
    ... (20,000 ish genes)
    Following the procedure in the vignette, my code looks like this:

    Code:
    replicates = c(rep("hct", 3), rep("rko", 3))
    groups = list(NDE=c(rep(1, 6)), DE=c(rep(1, 3), rep(2, 3)))
    CD = new("countData", data = merged, replicates = replicates, groups = groups)
    libsizes(CD) = getLibsizes(CD)
    plotMA.CD(CD, samplesA="hct", samplesB="rko", col=c(rep("red", 100), rep("black", 900)))
    ... and that's as far as I come. The resulting plot looks really weird, not a MA-plot at all: I only have six points! Obviously this has something to do with my data or the way I handle it, and I assume that the six points has something to do with the 3 + 3 replicates. I did try the rest of the vignette standard procedure as well, but the Volcano plot looks equally weird and the lowest FDR.DE I get is around 85%, so whatever is wrong must be wrong even before that. Can anybody see what I've screwed up?

    Secondly, limma: this has gone much better, and I have a finished script that works just fine. The only question I have is about the counts table to use, and pertains to this line in the vignette: "The limma-voom method assumes that rows with zero or very low counts have been removed." Does that mean that I remove genes where ALL the samples have 0 count, or do I remove genes that have ANY samples with 0 count? (related to this: is this needed for baySeq, or do I use the counts table as-is?)
  • dpryan
    Devon Ryan
    • Jul 2011
    • 3478

    #2
    Regarding limma/voom, just remove rows where rowSums() is really low. They don't all have to be 0, but if they're all really low then the mean-dispersion relationship isn't always fit very well (and then you get funky results).

    I have no idea about baySeq, I've never used it.

    Comment

    • ErikFas
      Member
      • Jun 2014
      • 86

      #3
      Thanks for your reply! Exactly what do you mean by "really low"? I've seen various cutoffs in various papers, from 10 to 16 to 20 counts, but I'm not sure if those were for individual sample counts or for the row sums.

      Comment

      • dpryan
        Devon Ryan
        • Jul 2011
        • 3478

        #4
        You'll have to have a look at the diagnostic plots. It's usually pretty apparent if the fit is really off at the low end.

        Comment

        • ErikFas
          Member
          • Jun 2014
          • 86

          #5
          Okay, thanks!

          Anybody with baySeq experience that have any ideas as to why I can't get it to work?

          Comment

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