TopHat

TopHat aligns RNA-Seq reads from mRNA sequencing to a reference genome and discovers exon-exon splice junctions to identify known and novel splice variants.

Key Features:

• Alignment without known splice sites: Performs alignment without depending on pre-existing splice junction annotations, enabling ab initio discovery of novel splice variants.
• Efficient read mapping (Bowtie): Built upon the ultrafast short-read mapper Bowtie and capable of mapping nearly 2.2 million reads per CPU hour for large RNA-Seq datasets.
• Discovery of novel splice junctions: Recovers over 72% of junctions identified by annotation-based approaches in mammalian RNA-Seq experiments and reported nearly 20,000 previously unreported splice junctions.
• Short fragment handling: Maps short sequence fragments generated from mRNA sequencing to support transcript-level analyses.
• Ab initio splice site discovery challenges: Implements ab initio splice junction discovery while highlighting algorithmic challenges in accurately predicting novel junctions in complex genomic contexts.

Scientific Applications:

• Gene expression and transcriptomics: Characterizes gene expression and transcript structure in genomics and transcriptomics studies.
• Alternative splicing analysis: Identifies alternative splicing events and novel splice variants for studies of gene regulation in health and disease.
• Annotation-independent junction discovery: Enables annotation-independent discovery of splice junctions in mammalian RNA-Seq experiments.

Methodology:

Uses Bowtie for ultrafast short-read mapping and aligns RNA-Seq reads to a reference genome to identify exon-exon splice junctions without relying on known splice site annotations.