geneXtendeR

geneXtendeR optimizes functional annotation of chromatin immunoprecipitation sequencing (ChIP-seq) peaks by iteratively extending gene boundaries to link peaks, including histone modification peaks, to nearby genes and cis-regulatory elements such as enhancers and promoters.

Key Features:

• Variable-Length Gene Body Annotation: Annotates ChIP-seq peaks to the first-closest, second-closest, and up to the nth-closest gene to capture multiple potential gene associations.
• Iterative Extension Analysis: Iteratively extends gene boundaries upstream and downstream to incorporate cis-regulatory elements (CREs) such as enhancers and promoters when assessing peak–gene associations.
• Ranking and Comparison: Ranks peak-to-gene associations based on biologically relevant events and compares overlap fidelity across a user-defined range of extensions.
• Robustness Against Variability: Accommodates differentially enriched peaks with large variance in length distribution and total count to mitigate variability from different peak caller algorithms and improve association accuracy in regions with closely spaced genes.

Scientific Applications:

• Functional Genomics: Improves assignment of regulatory elements to genes in functional genomics studies using ChIP-seq data.
• Regulatory Element Identification: Facilitates identification of enhancers and promoters linked to genes by capturing distal cis-regulatory associations.
• Epigenetics: Enhances interpretation of histone modification patterns and other epigenetic modifications across different tissues.
• Experimental Follow-up: Provides gene–peak associations suitable for designing primers for quantitative PCR (qPCR) validation.

Methodology:

Computationally, geneXtendeR iteratively adjusts upstream and downstream gene boundaries, ranks and compares peak-to-gene overlap fidelity across user-defined extension ranges, and was tested on 547 human transcription factor ChIP-seq ENCODE datasets and 198 human histone modification ChIP-seq ENCODE datasets.