numeric; the number of processors to use, one chromosome
is ran for each processor
ROI
character; either NULL or an object of class GRanges
consisting of genomic regions of interest for which DMRs are
identified
pmdGRanges
a GRanges object containing the genomic
coordinates of Partially Methylated Domains that will be masked
MCClass
character; the mC sequence context to be considered,
one of all, mCG, mCHG or mCHH
dmrSize
numeric; the number of consecutive mC to be
simulataneously considered; atleast 5
dmrBp
numeric; the max number of bp containing the dmrSize mC
binsize
numeric; the size of the bin used for smoothing the
methylation levels, useful for nonCG methylation in human
eprop
numeric; the max - min methylation level is determined
for each mC, or for each bin, and only mC (or bins) with
difference greater than eprop are considered
coverage
numeric; the minimum number of total reads at a given
cytosine genomic position
Pvalue
numeric; to select only those mC with significant p-value
SNPs
GRanges; if SNPs information is provided those cytosine
are removed from DMR computation
Details
Typically for nonCG methylation in human a dmrSize of 50, a
dmrBp of 50000 and a binsize of 1000 are used. For CpG methylation in
human and both CpG and nonCG methylation in plants the default
settings are usually fine. Partially Methylated Domains are usually
found in differentiated cells and can constitute up to one third of
the genome (Lister R et al, Nature 2009). Usually DMRs are not
selected within those regions especially when comparing differentiated
and pluripotent cells. Eprop is used to speed up the
analysis. According to the number of samples different test are used
to compare the methylation levels (percentage of methylated reads for
each mC). In case of two samples the non parametric wilcoxon test is
used. In case of more than two samples the kruskal wallis non
parametric testis used. Check consolidateDMRs to further
process and finalize the list of DMRs.
Value
A GRanges object of DMRs with the metadata slots for pValue,
MethDiff_Perc and log2Enrichment. When two samples are compared, MethDiff_Perc is the
diference between percentage methylation between the conditions compared. However, log2Enrichment
is the log2ratio between the mean for the samples.