isoformSwitchTestDRIMSeq {IsoformSwitchAnalyzeR} | R Documentation

## Statistical Test for identifying Isoform Switching via DRIMSeq.

### 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

    isoformSwitchTestDRIMSeq(
        switchAnalyzeRlist,
        alpha = 0.05,
        dIFcutoff = 0.1,
        testIntegration = 'isoform_only',
        reduceToSwitchingGenes = TRUE,
        reduceFurtherToGenesWithConsequencePotential = TRUE,
        onlySigIsoforms = FALSE,
        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).

`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:

- `'isoform_only'` : Only the FDR adjusted P-values of the isoform level test are used. This is the default since we believe that if an isoform is significant and the effect size is large then the overall effect on the gene should be considered even if the overall gene analysis is not significant.

- `'gene_only'` : Only the FDR adjusted P-values of the gene level test are used. Isoform level data are not used.

- `'intersect'` : The FDR adjusted P-values of the isoform level test are used for cases where the gene level FDR adjusted P-values is smaller than or equal to the smallest FDR adjusted P-values of all associated isoform.

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:

- `1`: Two columns, `isoform_switch_q_value` and `gene_switch_q_value` in the `isoformFeatures` entry have been filled out summarizing the result of the above described test as affected by the `testIntegration` argument.

- `2`: A `data.frame` containing the details of the analysis have been added (called 'isoformSwitchAnalysis').

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

- `iso_ref` : A unique reference to a specific isoform in a specific comparison of conditions. Enables easy handles to integrate data from all the parts of a `switchAnalyzeRlist`.

- `gene_ref` : A unique reference to a specific gene in a specific comparison of conditions. Enables easy handles to integrate data from all the parts of a `switchAnalyzeRlist`.

- `isoform_id`: The name of the isoform analyzed. Matches the 'isoform_id' entry in the 'isoformFeatures' entry of the switchAnalyzeRlist

- `gene_lr`: likelihood ratio statistics based on the DM model.

- `gene_df`: Degrees of freedom

- `gene_p_value`: Gene level P-values.

- `gene_q_value`: Gene level False Discovery Rte (FDR) corrected P-values (q-values).

- `iso_lr`: likelihood ratio statistics based on the BB model.

- `iso_df`: Degrees of freedom

- `iso_p_value`: Isoform level P-values.

- `iso_q_value`: Isoform level False Discovery Rte (FDR) corrected P-values (q-values).

### Author(s)

Kristoffer Vitting-Seerup

### References

- Vitting-Seerup et al. The Landscape of Isoform Switches in Human Cancers. Mol. Cancer Res. (2017).

- Nowicka, M., & Robinson, M. D. (2016). DRIMSeq: a Dirichlet-multinomial framework for multivariate count outcomes in genomics. F1000Research, 5(0), 1356. https://doi.org/10.12688/f1000research.8900.2

### See Also

`preFilter`
`isoformSwitchTestDEXSeq`
`extractSwitchSummary`
`extractTopSwitches`
`dmPrecision`
`dmFit`
`dmTest`

### Examples

    ### 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)

[Package IsoformSwitchAnalyzeR version 1.8.0 Index]