GSNAP

GSNAP aligns short reads from next-generation sequencing to reference genomes or transcriptomes to detect splicing events, complex variants, SNP-tolerant mappings, and methylation-related signals.

Key Features:

• Read support: Supports alignment of single-end and paired-end reads, handling sequences as short as 14 nucleotides and of arbitrarily long lengths.
• Splice detection: Detects complex splicing events, including interchromosomal splicing, using probabilistic models or a database of known splice sites.
• SNP-tolerant alignment: Accommodates all possible combinations of major and minor alleles to reveal alternate genomic mappings.
• Bisulfite alignment: Aligns bisulfite-treated DNA reads to enable analysis of methylation states.
• Search strategy: Employs a successively constrained search that merges and filters position lists from a genomic index to enhance detection of complex variants and splicing.
• Complex variant detection: Efficiently identifies variants with multiple mismatches and indels, including cases with four or more mismatches, insertions of 1–9 nucleotides, and deletions up to 30 nucleotides.
• Performance: Maintains competitive speeds relative to other aligners, particularly for reads of 70 nucleotides or longer.

Scientific Applications:

• RNA-seq splicing analysis: Detection and characterization of complex and interchromosomal splicing in transcriptomic data.
• Variant discovery: Identification of complex variants with multiple mismatches and indels from short-read data.
• Allele-aware mapping: Analysis of alternate genomic mappings arising from SNPs in transcriptomic studies.
• Methylation analysis: Alignment of bisulfite-treated reads to infer changes in DNA methylation states.

Methodology:

GSNAP performs a successively constrained search that merges and filters position lists from a genomic index, detects splicing using probabilistic models or a database of known splice sites, implements SNP-tolerant alignment by accommodating all combinations of major and minor alleles, and supports alignment of bisulfite-treated DNA reads.