Overview
Alternative splicing is a fundamental mechanism by which a single gene can produce multiple mRNA isoforms, greatly expanding the coding capacity of the genome. Nearly 95% of human multi-exon genes undergo alternative splicing, generating distinct protein products that can have different, even opposing, functions. The choice of which exons are included or excluded is tightly regulated and tissue-specific. Alternative splicing analysis aims to identify and quantify these isoform-level differences across conditions, developmental stages, or disease states, revealing an additional layer of gene regulation beyond simple expression changes.
Methods
Detection of alternative splicing events from RNA-seq data requires specialized computational approaches. Isoform quantification tools (such as Salmon, Kallisto, or RSEM) estimate the abundance of each known transcript isoform. Event-based tools (rMATS, MAJIQ, or SUPPA2) classify splicing events into categories: cassette exon skipping, mutually exclusive exons, alternative 5’ or 3’ splice sites, and intron retention. These tools use count matrices of reads mapping to splice junctions versus exons and test for significant differences using paired statistical models. De novo splice detection (by StringTie or Cufflinks) assembles transcripts without annotation to discover novel isoforms. Visualizing splicing differences with sashimi plots (from MISO or IGV) helps interpret complex patterns.
Applications
Alternative splicing dysregulation is a hallmark of many diseases. In cancer, splicing factors are frequently mutated, producing tumor-specific isoforms that drive proliferation and metastasis. Neurological disorders such as spinal muscular atrophy and frontotemporal dementia result directly from splicing defects. Understanding splicing patterns aids interpretation of RNA structure and types and builds on concepts from transcription and RNA processing. Splicing analysis also intersects with gene regulation and epigenetics, as chromatin state influences cotranscriptional splice site selection, and splicing feedback can regulate transcription elongation.
