bio-isoform-switching

name	bio-isoform-switching
description	Analyzes isoform switching events and functional consequences using IsoformSwitchAnalyzeR. Predicts protein domain changes, NMD sensitivity, ORF alterations, and coding potential shifts between conditions. Use when investigating how splicing changes affect protein function.
tool_type	r
primary_tool	IsoformSwitchAnalyzeR

Isoform Switching Analysis

Identify isoform switches and predict their functional consequences on protein structure and function.

IsoformSwitchAnalyzeR Workflow

library(IsoformSwitchAnalyzeR)

# Import transcript quantification from Salmon
salmonQuant <- importIsoformExpression(
    parentDir = 'salmon_quant/',
    addIsofomIdAsColumn = TRUE
)

# Create switch analysis object
switchAnalyzeRlist <- importRdata(
    isoformCountMatrix = salmonQuant$counts,
    isoformRepExpression = salmonQuant$abundance,
    designMatrix = data.frame(
        sampleID = colnames(salmonQuant$counts),
        condition = c('control', 'control', 'control', 'treatment', 'treatment', 'treatment')
    ),
    isoformExonAnnoation = 'annotation.gtf',
    isoformNtFasta = 'transcripts.fa'
)

# Filter lowly expressed isoforms
switchAnalyzeRlist <- preFilter(
    switchAnalyzeRlist,
    geneExpressionCutoff = 1,  # Minimum TPM
    isoformExpressionCutoff = 0,
    removeSingleIsoformGenes = TRUE
)

# Test for isoform switches
switchAnalyzeRlist <- isoformSwitchTestDEXSeq(
    switchAnalyzeRlist,
    reduceToSwitchingGenes = TRUE
)

Functional Annotation

# Extract sequences for external analysis
switchAnalyzeRlist <- extractSequence(
    switchAnalyzeRlist,
    pathToOutput = 'sequences/',
    writeToFile = TRUE
)

# Run external tools and import results:
# - CPC2 for coding potential
# - Pfam for protein domains
# - SignalP for signal peptides
# - IUPred2 for intrinsic disorder

# After running external tools, import results
switchAnalyzeRlist <- analyzeCPC2(
    switchAnalyzeRlist,
    pathToCPC2resultFile = 'cpc2_results.txt',
    removeNoncodinORFs = TRUE
)

switchAnalyzeRlist <- analyzePFAM(
    switchAnalyzeRlist,
    pathToPFAMresultFile = 'pfam_results.txt'
)

switchAnalyzeRlist <- analyzeSignalP(
    switchAnalyzeRlist,
    pathToSignalPresultFile = 'signalp_results.txt'
)

switchAnalyzeRlist <- analyzeIUPred2A(
    switchAnalyzeRlist,
    pathToIUPred2AresultFile = 'iupred2_results.txt'
)

Consequence Analysis

# Analyze functional consequences of switches
switchAnalyzeRlist <- analyzeSwitchConsequences(
    switchAnalyzeRlist,
    consequencesToAnalyze = c(
        'intron_retention',
        'coding_potential',
        'ORF_seq_similarity',
        'NMD_status',
        'domains_identified',
        'signal_peptide_identified'
    ),
    dIFcutoff = 0.1,  # Minimum isoform fraction change
    showProgress = TRUE
)

# Extract significant switches
significantSwitches <- extractSwitchSummary(
    switchAnalyzeRlist,
    filterForConsequences = TRUE
)

print(significantSwitches)

Visualization

# Plot individual gene switches
switchPlot(
    switchAnalyzeRlist,
    gene = 'GENE_OF_INTEREST',
    condition1 = 'control',
    condition2 = 'treatment'
)

# Summary of consequence types
extractConsequenceSummary(
    switchAnalyzeRlist,
    consequencesToAnalyze = 'all',
    plotGenes = FALSE
)

# Enrichment of consequences
extractConsequenceEnrichment(
    switchAnalyzeRlist,
    consequencesToAnalyze = 'all'
)

Significance Thresholds

Parameter	Default	Description
Switch q-value	< 0.05	Significance of isoform switch
dIF (delta isoform fraction)	> 0.1	Minimum usage change
Consequence q-value	< 0.05	Significance of consequence

Consequence Types

Consequence	Impact
NMD sensitive	Transcript targeted for degradation
Domain loss/gain	Altered protein function
ORF disruption	Truncated/altered protein
Signal peptide loss	Changed localization
Coding potential loss	Switch to non-coding

Related Skills

• differential-splicing - Identify differential events first
• splicing-quantification - PSI-level analysis
• pathway-analysis/go-enrichment - Pathway enrichment of switching genes