IsoformSwitchTestDRIMSeq: Statistical Test for identifying Isoform Switching via...

Description Usage Arguments Details Value Author(s) References See Also Examples

Description

This function is an interface to an analysis with the DRIMSeq package analyzing all isoforms (isoform resolution) and conditions stored in the switchAnalyzeRlist object.

Usage

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isoformSwitchTestDRIMSeq(
    switchAnalyzeRlist,
    alpha = 0.05,
    dIFcutoff = 0.1,
    testIntegration = 'isoform_only',
    reduceToSwitchingGenes = TRUE,
    reduceFurtherToGenesWithConsequencePotential = TRUE,
    onlySigIsoforms = FALSE,
    keepIsoformInAllConditions = TRUE,
    dmFilterArgs=list(
        min_feature_expr = 4,
        min_samps_feature_expr = min(
            switchAnalyzeRlist$conditions$nrReplicates
        )
    ),
    dmPrecisionArgs = list(),
    dmFitArgs = list(),
    dmTestArgs = list(),
    showProgress = TRUE,
    quiet = FALSE
)

Arguments

switchAnalyzeRlist

A switchAnalyzeRlist object.

alpha

The cutoff which the FDR correct p-values must be smaller than for calling significant switches. Default is 0.05.

dIFcutoff

The cutoff which the changes in (absolute) isoform usage must be larger than before an isoform is considered switching. This cutoff can remove cases where isoforms with (very) low dIF values are deemed significant and thereby included in the downstream analysis. This cutoff is analogous to having a cutoff on log2 fold change in a normal differential expression analysis of genes to ensure the genes have a certain effect size. Default is 0.1 (10%).

testIntegration

A string indicating how to interpret the DRIMSeq test for differential isoform usage (see also details). Since DRIMSeq both test at gene and isoform level there are multiple options. Must be one the following:

  • 'isoform_only' : Only considers the test at isoform level resolution (and ignores the gene level test). This analysis have isoform resolution (meaning exactly which isoforms are switching is known). Default

  • 'gene_only' : Only considers the test at gene level resolution (and ignores the isoform level test). This analysis have gene resolution (meaning exactly which isoforms are switching is NOT known - but the power is higher compared to isoform level analysis (probably more genes identified)).

  • 'intersect' : Only considers the cases where BOTH the gene and the isoforms are significant. This analysis have isoform resolution (meaning exactly which isoforms are switching is known) and is the conservative version of 'isoform_only' since it is also required that the gene level test for the parent gene is significant. See details.

reduceToSwitchingGenes

A logic indicating whether the switchAnalyzeRlist should be reduced to the genes which contains at least one isoform significantly differential used (as indicated by the alpha and dIFcutoff parameters) - works on dIF values corrected for confounding effects if overwriteIFvalues=TRUE. Enabling this will make the downstream analysis a lot faster since fewer genes needs to be analyzed. Default is TRUE.

reduceFurtherToGenesWithConsequencePotential

A logic indicating whether the switchAnalyzeRlist should be reduced to the genes which have the potential to find isoform switches with predicted consequences. This argument is a more strict version of reduceToSwitchingGenes as it not only requires that at least one isoform is significantly differential used (as indicated by the alpha and dIFcutoff parameters) but also that there is an isoform with the opposite effect size (e.g. used less if the first isoform is used more). The minimum effect size of the opposing isoform usage is also controlled by dIFcutoff. The existence of such an opposing isoform means a switch pair can be formed. It is these pairs that can be analyzed for functional consequences further downstream in the IsoformSwitchAnalyzeR workflow. Enabling this will make the downstream analysis a even faster (than just using reduceToSwitchingGenes) since fewer genes needs to be analyzed. Requires that reduceToSwitchingGenes=TRUE to have any effect. Default is TRUE.

onlySigIsoforms

A logic indicating whether both isoforms the pairs considered if reduceFurtherToGenesWithConsequencePotential=TRUE should be significantly differential used (as indicated by the alpha and dIFcutoff parameters). Default is FALSE (aka only one of the isoforms in a pair should be significantly differential used).

keepIsoformInAllConditions

A logic indicating whether the an isoform should be kept in all comparisons even if it is only deemed significant (as defined by the alpha and dIFcutoff parameters) in one comparison. This will not affect downstream runtimes only make the switchAnalyzeRlist use slightly more memmory (scaling with the number of conditions compared). Default is TRUE.

dmFilterArgs

Offers a way to pass additional arguments to the DRIMSeq::dmFilter() function enabling filtering based on replicate data. Must be supplied as a named list. Default is 4 counts in at least as many libraries as there are replicates in the smallest condition

dmPrecisionArgs

Offers a way to pass additional arguments to the DRIMSeq::dmPrecision() function. Must be supplied as a named list. Please remember some parameters are shared between multiple of the dm*() functions so if you change a parameter for one function you might also need to change it for the other functions.

dmFitArgs

Offers a way to pass additional arguments to the DRIMSeq::dmFit() function underlying the test. Must be supplied as a named list. Please remember some parameters are shared between multiple of the dm*() functions so if you change a parameter for one function you might also need to change it for the other functions.

dmTestArgs

Offers a way to pass additional arguments to the DRIMSeq::dmTest() function underlying the test. Must be supplied as a named list. Please remember some parameters are shared between multiple of the dm*() functions so if you change a parameter for one function you might also need to change it for the other functions.

showProgress

A logic indicating whether to make a progress bar (if TRUE) or not (if FALSE). Defaults is FALSE.

quiet

A logic indicating whether to avoid printing progress messages (incl. progress bar). Default is FALSE

Details

This wrapper for DRIMSeq utilizes all data to construct one linear model (one fit) on all the data (including the potential extra covariates/batch effects indicated in the designMatrix entry of the supplied switchAnalyzeRlist). From this unified model all the pairwise test are performed (aka each unique combination of condition_1 and condition_2 columns of the isoformFeatures entry of the supplied switchAnalyzeRlist are tested individually). This is only suitable if a certain overlap between conditions are expected which means if you are analyzing very different conditions it is probably better to remove particular comparisons or make two separate analysis (e.g.. Brain vs Brain cancer vs liver vs liver cancer should probably be analyzed as two separate switchAnalyzeRlists whereas WT vs KD1 vs KD2 should be one switchAnalyzeRlists).

The result of the testIntegration (see arguments and below) is only applied to the isoformFeatures entry of the switchAnalyzeRlist. The full DRIMSeq analysis is unmodified and added to the isoformSwitchAnalysis entry of the switchAnalyzeRlist.

The testIntegration integration works as follows:

A 'union' option is not supported due to the loss of False Discovery Rate that would lead to.

To use the dmPrecisionArgs, dmFitArgs, dmTestArgs arguments a named list should simply be supplied - so if you want to modify the 'prec_subset' argument in the dmPrecision() function you should supply dmPrecisionArgs=list(prec_subset=x) where x is the value you want to pass to the 'prec_subset' argument.

Please note that: 1) DRIMSeq approach depends on the filtering on the data since if to many lowly expressed transcripts are included the gene precision cannot be calculated. Therefore if you think to few genes have been tested you can try to make a more strict filtering with the preFilter() function. 2) DRIMSeq can be a bit slow for large comparisons (testing of many isoforms) and 0.5-1 hour per comparison is not unusual.

Value

A switchAnalyzeRlist where the following have been modified:

The data.frame added have one row per isoform per comparison of condition and contains the following columns:

Author(s)

Kristoffer Vitting-Seerup

References

See Also

preFilter
isoformSwitchTestDEXSeq
extractSwitchSummary
extractTopSwitches
dmPrecision
dmFit
dmTest

Examples

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### Please note
# 1) The way of importing files in the following example with
#       "system.file('pathToFile', package="IsoformSwitchAnalyzeR") is
#       specialized way of accessing the example data in the IsoformSwitchAnalyzeR package
#       and not something you need to do - just supply the string e.g.
#       "myAnnotation/isoformsQuantified.gtf" to the functions
# 2) importRdata directly supports import of a GTF file - just supply the
#       path (e.g. "myAnnotation/isoformsQuantified.gtf") to the isoformExonAnnoation argument

### Import quantifications
salmonQuant <- importIsoformExpression(system.file("extdata/", package="IsoformSwitchAnalyzeR"))

### Make design matrix
myDesign <- data.frame(
    sampleID = colnames(salmonQuant$abundance)[-1],
    condition = gsub('_.*', '', colnames(salmonQuant$abundance)[-1])
)

### Create switchAnalyzeRlist
aSwitchList <- importRdata(
    isoformCountMatrix   = salmonQuant$counts,
    isoformRepExpression = salmonQuant$abundance,
    designMatrix         = myDesign,
    isoformExonAnnoation = system.file("extdata/example.gtf.gz", package="IsoformSwitchAnalyzeR")
)

### Filter with very strict cutoffs to enable short runtime
aSwitchListAnalyzed <- preFilter(
    switchAnalyzeRlist = aSwitchList,
    isoformExpressionCutoff = 10,
    IFcutoff = 0.3,
    geneExpressionCutoff = 50
)
aSwitchListAnalyzed <- subsetSwitchAnalyzeRlist(
    aSwitchListAnalyzed,
    aSwitchListAnalyzed$isoformFeatures$condition_1 == 'hESC'
)

### Test isoform swtiches
aSwitchListAnalyzed <- isoformSwitchTestDRIMSeq(aSwitchListAnalyzed)

# extract summary of number of switching features
extractSwitchSummary(aSwitchListAnalyzed)

kvittingseerup/IsoformSwitchAnalyzeR documentation built on May 12, 2021, 12:25 p.m.