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Old 04-04-2014, 07:51 AM   #1
Location: Germany

Join Date: Dec 2013
Posts: 16
Default DESeq2 - understanding multi-factor DE analysis

Hello again dear SeqAnswers,

I have another question regarding RNA-seq data processing, this time with DESeq. I had count tables from my experiment generated successfully by DEXSeq counting script. Since I wanted to use DESeq2 this time, without having to re-count all the samples, I used geneCountTable function on my ExonCountSet in R to "compress" all exon bins into genes.

1) I hope this is correct approach to obtaining gene count tables for DESeq ?

Now the main question, my study is about gender differences in response to some knock-out. So I have 4 sample groups:

Wild-type male
Wild-type female
Knock-out male
Knock-out female

I generated all the necessary tables following the DESeq2 vignette:

sex strain
WTM_1.counts male WT
WTM_2.counts male WT
WTM_3.counts male WT
WTF_1.counts female WT
WTF_2.counts female WT
WTF_3.counts female WT
KOM_1.counts male KO
KOM_2.counts male KO
KOM_3.counts male KO
KOF_1.counts female KO
KOF_2.counts female KO
KOF_3.counts female KO

2) What is then a proper approach to see differences between gene expression of KO samples that would take into consideration the natural variance between genders in wild-type (like sex-specific genes) ?

I know I can manipulate the GLM with the formula, but to be honest I am unsure if I understand the entire meaning behind it.

Currently, just for fun, I used formula (design = ~ sex + strain). Now what I got back are 3 tables with fold-changes - Intercept, male vs female, KO vs WT.

3) What is intercept exactly ? Are values in tables male vs. female and KO vs. WT simply pair-wise comparisons, like ones I would get by using formulas: design = ~ sex and design = ~ strain separately ?

I know this might take a longer answer so I will patiently wait for somebody's time. I will be extremely thankful for any insight, I am a beginner in RNA-seq , hence those questions might seem trivial for some.

All the best!
kajot is offline   Reply With Quote