DEseq2 coefficient
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JKim • 0
@4035f8c1
Last seen 2 days ago
United States

Hello,

I apologize if this question was answered many times before. I'm a little bit confused by DEseq2 coefficient. I have two factors, genotype (WT, KO) and batch (B1, B2, B3) variables and would like to see gene expression between WO and KO while accounting for batch effect. I came across a similar post and I'm just not sure if pulling coefficient by results(dds, contrast=c("genotype","KO","WT")) would be genotype effect within Batch B1 (reference level) or overall difference between genotype. i.e. sample 1~6 (WT) vs sample 7 ~ 12 (KO).


library(DESeq2)
library(tidyverse)

dds <- makeExampleDESeqDataSet(n = 1000, m = 12, betaSD = 2)
dds$genotype <- factor(rep(c("WT", "KO"), each = 6))
dds$genotype <- relevel(dds$genotype, "WT")
dds$batch <- factor(rep(c("B1", "B2", "B3"), 4))
dds$batch <- relevel(dds$batch, "B1")

colnames(dds) <- paste0("sample", 1:ncol(dds))

design(dds) <- ~1 + batch + genotype
dds <- DESeq(dds)
resultsNames(dds)
mod_mat <- model.matrix(design(dds), colData(dds))

results(dds, contrast=c("genotype","KO","WT"))
> mod_mat
         (Intercept) batchB2 batchB3 genotypeKO
sample1            1       0       0          0
sample2            1       1       0          0
sample3            1       0       1          0
sample4            1       0       0          0
sample5            1       1       0          0
sample6            1       0       1          0
sample7            1       0       0          1
sample8            1       1       0          1
sample9            1       0       1          1
sample10           1       0       0          1
sample11           1       1       0          1
sample12           1       0       1          1
DESeq2 coefficient • 351 views
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Entering edit mode
@mikelove
Last seen 9 hours ago
United States

With standard coding in R, and no interaction term, it's across all batches.

If you add an interaction, the interpretation changes though to just the reference level of any controlling covariate. This can be visualized with ExploreModelMatrix, a package by some Bioconductor developers for helping users understand designs.

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Thanks a lot, Dr. Love.

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The key point to remember about designs with interaction terms is that, unlike for a design ~genotype + condition, where the condition effect represents the overall effect controlling for differences due to genotype, by adding genotype:condition, the main condition effect only represents the effect of condition for the reference level of genotype (I, or whichever level was defined by the user as the reference level). The interaction terms genotypeII.conditionB and genotypeIII.conditionB give the difference between the condition effect for a given genotype and the condition effect for the reference genotype. From deseq2 - vignettes, interaction

I'm sorry. I should've paid more attention to the vignettes.

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