MACS2 is a widely used peak caller for identifying enriched genomic regions in ChIP-seq data.
Peak calling is the process of detecting genomic regions where ChIP-seq reads are enriched relative to background. MACS2 models the distribution of aligned reads and identifies regions with statistically significant enrichment. It is commonly used for transcription factor binding and histone modification analysis.
MACS2 compares ChIP signal to an expected background. When an input control is provided, the control helps estimate local background bias. MACS2 then reports regions that show enrichment beyond what would be expected from background noise.
MACS2 can be used for narrow peak calling and broad peak calling. Narrow mode is commonly used for transcription factors and sharp binding events. Broad mode is more appropriate for histone marks that cover wider regions, such as H3K27me3 or H3K36me3.
Peak files usually contain genomic coordinates and statistical scores. A peak does not automatically prove functional regulation. It indicates enrichment that may represent binding, chromatin marking, or a related biological signal depending on the experiment.
Common mistakes include using the wrong genome build, using narrow peak settings for broad histone marks, ignoring input control, using overly loose thresholds, or interpreting peaks without checking QC and signal tracks.
Treat MACS2 output as one part of the evidence. Combine peak calls with read quality, mapping quality, replicate consistency, known marker behavior, and biological context.
This guide is provided for research and educational purposes. Always validate important biological conclusions with appropriate experimental design, quality control, and independent interpretation.