RMS question in MEDIPS
Entering edit mode
enrique.yeh ▴ 10
Last seen 3.7 years ago

Hello everyone,

I'm trying to use the tool MEDIPS to find the RMS value of each genes.

There are 6 samples (GD16003-GD16008), 2 of them are hyper-methylated (GD16005 & GD16008) and comfirmed in RPKM value, but these two samples are not having the highest value in RMS value.

Does anyone knows why the hyper-methylated samples not having the highest RMS value? 

Mean value are listed below.

CpG   rpkm rms
CpG GD16003 0.676719 0.2192527
CpG GD16004 0.526604 0.202631
CpG GD16005 1.492834 0.1860266
CpG GD16006 0.328434 0.1620868
CpG GD16007 0.395263 0.233723
CpG GD16008 1.40204 0.1974412
Gene   rpkm rms
Gene GD16003 0.949448 0.4457013
Gene GD16004 0.958066 0.4601055
Gene GD16005 1.179833 0.4229319
Gene GD16006 0.887107 0.4300184
Gene GD16007 0.803318 0.4130587
Gene GD16008 1.131659 0.428664

And here's the Rscript,

prcBamFile <- "GD16007.bam"
ROI <- read.delim("ROI_gene.txt")
Input <- MEDIPS.createSet(file=prcBamFile, BSgenome=BSgenome, extend=extend, shift=shift, uniq=uniq, window_size=ws)
CS = MEDIPS.couplingVector(pattern="CG", refObj=Input)
mr.edgeR <- MEDIPS.meth(MSet1 = Input, CSet = CS, p.adj="bonferroni", diff.method="edgeR", CNV=FALSE, MeDIP=TRUE, minRowSum=10, diffnorm="tmm")
mr.edgeR.roi <- MEDIPS.selectROIs(results=mr.edgeR, rois=ROI, columns=NULL, summarize="avg")
write.table(mr.edgeR.roi, file="GD16007_result_roiGene.tmp", quote=FALSE, sep="\t", row.names=FALSE, col.names=TRUE)


RMS RPKM MEDIPS • 569 views
Entering edit mode
Lukas Chavez ▴ 570
Last seen 3.7 years ago

Hi enrique.yeh,

thanks for sharing these results! I agree that rms values of the hyper-methylated samples should reflect the elevated signals you see by the rpkm values. Instead of looking at the mean values only, I am wondering how the genome wide distribution/ histogram of rms values compare between the samples? If they are similar across the samples including the hyper-methytlated samples, then its really only due to the way MEDIPS shifts the data range of rms values (which are basically nothing else than the observed/ expected ratio) into the interval [0,1]. While MEDIPS will make the rpkm values of genomic regions with different CpG densities more comparable within a sample (--> relative methylation values), transformation into absolute methylation values (such as 20% or 80% methylation) is conceptually weak. Therefore, we have developed a much better R/Bioconductor tool qsea (http://bioconductor.org/packages/release/bioc/html/qsea.html), which does a much better job. It would be great, if you can apply qsea to your data and let us know, if it works on your data!

Please note, MEDIPS performs differential coverage analysis based on count data (by emplying edgeR) and does not depend on rms values.

All the best,



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