Question: DESeq2 analysis design - different individuals for all samples
0
11 months ago by
Maithê Barros10 wrote:

Hello,

I have to perform the differential gene expression analysis for 6 RNA-seq samples using DESeq2.

My colData looks like this:

      sample   tissue    horse
sample_60.bam  ex_vivo      1
sample_65.bam  ex_vivo      2
sample_75.bam  ex_vivo      3
sample_80.bam  in_vivo      4
sample_81.bam  in_vivo      5
sample_82.bam  in_vivo      6  

I have biopsies collected from live animals (in_vivo) and collected from animals slaughtered at an abattoir (ex_vivo), and I want to investigate the differences in gene expression between these two "tissue" groups.

However, there are 6 distinct individuals and I wanted to perform the analysis controlling for individuals. But the matrix is not full rank (when I tried design ~ tissue + horse). But there is no way of adding that extra ".n" to the colData to run a matrix.model because the individuals only appear once (horses 1 to 6).

I ran the analysis as:

library(GenomicAlignments)
bam_exp4 <-c("sample_60.bam", "sample_65.bam", "sample_75.bam", "sample_80.bam", "sample_81.bam", "sample_82.bam")

library(Rsamtools)
bamfiles <- BamFileList(bam_exp4)

library(GenomicFeatures)
txdb_exp4 <- makeTxDbFromGFF("Equus_caballus.EquCab2.89.gtf", format="gtf")
ebg_exp4 <- exonsBy(txdb_exp4, by="gene")
mode="Union",
singleEnd=FALSE,
ignore.strand=TRUE,
fragments=TRUE )

colData(se_exp4) <- DataFrame(sampleTableExp4)

library(DESeq2)
dds_exp4 <- DESeqDataSet(se_exp4, design = ~ tissue)
dds_exp4 <- DESeq(dds_exp4)
res_exp4 <- results(dds_exp4, contrast=c("tissue", "ex_vivo", "in_vivo"))

However, I am not sure that using the ~ tissue design is the correct thing to do.

Many thanks.

modified 11 months ago • written 11 months ago by Maithê Barros10
Answer: DESeq2 analysis design - different individuals for all samples
0
11 months ago by
Michael Love25k
United States
Michael Love25k wrote:

Can you explain what you mean by “controlling for individual”? Is there any pairing or repetition of individuals?

There is no pairing or repetition, just 2 groups with 3 different individuals in each group.

I read a bunch of stuff about DESeq2 and I understood that when comparing two groups with different individuals, I would need to control for expected differences between individuals. That is the reason why I thought I had to use the ~ tissue + horse design.

You would just use ~tissue here. The different individuals are biological replicates here.