Poor dispersion fit in DESeq2
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Ben ▴ 10
@974411d6
Last seen 4 weeks ago
United Kingdom

I am attempting to run DESeq2, edgeR, and limma-voom to find DEGs between a condition sensitivity with factors 'lineage'. My samples are not really technical or biological replicates, but different cell lines in about 6 lineages.

My dispersion model doesn't seem to fit well to my data, but I wanted to check if it was acceptable, here is my code:

keep <- edgeR::filterByExpr(y = counts, group = sensitivity) # default filterByExpr settings
counts <- counts[keep, ]
dds <- DESeqDataSetFromMatrix(counts, metadata, design = ~ lineage + sensitivity)
dds <- DESeq(dds, fitType = fit_type, minReplicatesForReplace = Inf)
plotDispEsts(dds)

Here is my dispersion model fitted to my data using parametric fit type. parametric

And here is the model with the local fit type.

local

Any thoughts?

(crossposted from biostars)

limma DESeq2 RNASeq edgeR • 424 views
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I had some help over on biostars, suggesting my dispersions looked bimodal, which I agreed with, and offered the following reasoning:

One of your factors is "lineage". Is it possible that there are different cell types, and the genes with lower dispersion represent genes expressed in both cell types, and those with low dispersion represent those that are only expressed in one cell type?

I couldn't think of a quick way to determine which genes were differentially expressed between these, so I just individually ran a couple of lineages with the design ~ sensitivity.

It seems my data is still bimodal, any ideas what may be causing this poor fit?

Bowel:

bowel

Lung (ymin = 1e-03 as there as several outliers at 1e-08):

lung

CNS (ymin = 1e-04 as there as several outliers at 1e-08):

cns

He recommended I reach out to you for further help on this Michael Love, any help is really appreciated.

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@mikelove
Last seen 3 hours ago
United States

The fit (red line) doesn't matter because you have so many samples. Note there is almost no shrinkage.

Besides that you may be interested in figuring out why you have two groups of genes by dispersion.

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