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Hello everyone!
I'm just starting my MSc and I'm new to bioinformatics! I'm currently
stucked in a DE analysis of Arabidopsis thaliana sRNA seq comparing a
wild type (control group) vs several different mutants (geneA, geneB,
geneC, doubleGeneAC, tripleGenesXYZ) with two biological replicates
for each group (12 columns in the counts table); for what I've been
looking, there aren't many examples of what to do in such cases and I
would like to have some feedback regarding if I'm doing something
wrong in the analysis!
Basically what I do in edgeR is give the design the groups as factors
(releveling the Wt as the control):
[1] Ath_genA Ath_genA Ath_genB Ath_genB Ath_genC
Ath_genC Ath_genAC Ath_genAC Ath_genXYZ Ath_genXYZ Ath_wt Ath_wt
Levels: Ath_wt Ath_genA Ath_genB Ath_genC Ath_genAC Ath_genXYZ
> design <- model.matrix(~0+groups)
then, make the contrasts
> contrasts <- makeContrasts(
AvsWT = Ath_genA-Ath_wt,
BvsWt = Ath_genB-Ath_wt,
CvsWT = Ath_genC-Ath_wt,
ACvsWT = Ath_genAC-Ath_wt,
XYZvsWT = Ath_genXYZ-Ath_wt,
ACvsA = Ath_genAC-Ath_genA,
ACvsC = Ath_genAC-Ath_genC,
AandCvsAC = (Ath_genA+Ath_genC)/2-Ath_genAC,
levels=design)
The rest is basically what I've read in the edgeR vignette:
> d <- DGEList(counts = TableCountsFilter, genes= InfoFilter ,group =
groups)
> d <- calcNormFactors(d, method = "TMM")
> d <- estimateGLMCommonDisp(d,design, verbose=T)
> d <- estimateGLMTrendedDisp(d,design)
> d <- estimateGLMTagwiseDisp(d,design)
> fit <- glmFit(d, design)
Then, I would perform a likelihood ratio test for each contrast
> glmLRT(fit, contrast=contrasts[,for_each_Contrast])
to finally get the top DE miRNAs using topTags for a given contrast.
For what I know, mutations in genA and genB produce similar phenotypes
and some Northern blots confirm that miR156 is upregulated in those
mutations compared to WT, while miR172 is downregulated compared to
WT, yet in my results the logFC of miR156 is close to 0.5 for genA and
-0.1 for genB.
Am I doing something wrong with the analysis?
I came across the function geneas() in limma which accounts for
multiple groups testing against a single control but no homologue
function for edgeR, could this be causing the conflict I'm seeing in
the DEanalysis vs Northern blots?
I sincerely appreciate your help!
J. Rodriguez-Medina
-- output of sessionInfo():
> sessionInfo()
R version 3.0.2 (2013-09-25)
Platform: x86_64-pc-linux-gnu (64-bit)
locale:
[1] LC_CTYPE=en_US.UTF-8 LC_NUMERIC=C
LC_TIME=en_US.UTF-8
[4] LC_COLLATE=en_US.UTF-8 LC_MONETARY=en_US.UTF-8
LC_MESSAGES=en_US.UTF-8
[7] LC_PAPER=en_US.UTF-8 LC_NAME=C
LC_ADDRESS=C
[10] LC_TELEPHONE=C LC_MEASUREMENT=en_US.UTF-8
LC_IDENTIFICATION=C
attached base packages:
[1] splines grDevices datasets utils parallel stats
graphics methods base
other attached packages:
[1] edgeR_3.2.4 limma_3.16.8 Biobase_2.20.1
BiocGenerics_0.6.0
loaded via a namespace (and not attached):
[1] tools_3.0.2
--
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