# ![nf-core/chipseq](docs/images/nfcore-chipseq_logo.png)

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## Introduction
**nfcore/chipseq** is a bioinformatics analysis pipeline used for Chromatin ImmunopreciPitation sequencing (ChIP-seq) data.

The pipeline is built using [Nextflow](https://www.nextflow.io), a workflow tool to run tasks across multiple compute infrastructures in a very portable manner. It comes with docker containers making installation trivial and results highly reproducible.

### Pipeline summary

1. Raw read QC ([`FastQC`](https://www.bioinformatics.babraham.ac.uk/projects/fastqc/))
2. Adapter trimming ([`Trim Galore!`](https://www.bioinformatics.babraham.ac.uk/projects/trim_galore/))
3. Alignment ([`BWA`](https://sourceforge.net/projects/bio-bwa/files/))
4. Mark duplicates ([`picard`](https://broadinstitute.github.io/picard/))
5. Merge alignments from multiple libraries of the same sample ([`picard`](https://broadinstitute.github.io/picard/))
    1. Re-mark duplicates ([`picard`](https://broadinstitute.github.io/picard/))
    2. Filtering to remove:
        * reads mapping to blacklisted regions ([`SAMtools`](https://sourceforge.net/projects/samtools/files/samtools/), [`BEDTools`](https://github.com/arq5x/bedtools2/))
        * reads that are marked as duplicates ([`SAMtools`](https://sourceforge.net/projects/samtools/files/samtools/))
        * reads that arent marked as primary alignments ([`SAMtools`](https://sourceforge.net/projects/samtools/files/samtools/))
        * reads that are unmapped ([`SAMtools`](https://sourceforge.net/projects/samtools/files/samtools/))
        * reads that map to multiple locations ([`SAMtools`](https://sourceforge.net/projects/samtools/files/samtools/))
        * reads containing > 4 mismatches ([`BAMTools`](https://github.com/pezmaster31/bamtools))
        * reads that have an insert size > 2kb ([`BAMTools`](https://github.com/pezmaster31/bamtools); *paired-end only*)
        * reads that map to different chromosomes ([`Pysam`](http://pysam.readthedocs.io/en/latest/installation.html); *paired-end only*)
        * reads that arent in FR orientation ([`Pysam`](http://pysam.readthedocs.io/en/latest/installation.html); *paired-end only*)
        * reads where only one read of the pair fails the above criteria ([`Pysam`](http://pysam.readthedocs.io/en/latest/installation.html); *paired-end only*)
    3. Alignment-level QC and estimation of library complexity ([`picard`](https://broadinstitute.github.io/picard/), [`Preseq`](http://smithlabresearch.org/software/preseq/))
    4. Create normalised bigWig files scaled to 1 million mapped reads ([`BEDTools`](https://github.com/arq5x/bedtools2/), [`bedGraphToBigWig`](http://hgdownload.soe.ucsc.edu/admin/exe/))
    5. Generate gene-body meta-profile from bigWig files ([`deepTools`](https://deeptools.readthedocs.io/en/develop/content/tools/plotProfile.html))
    6. Calculate genome-wide IP enrichment relative to control ([`deepTools`](https://deeptools.readthedocs.io/en/develop/content/tools/plotFingerprint.html))
    7. Calculate strand cross-correlation peak and ChIP-seq quality measures including NSC and RSC ([`phantompeakqualtools`](https://github.com/kundajelab/phantompeakqualtools))
    8. Call broad/narrow peaks ([`MACS2`](https://github.com/taoliu/MACS))
    9. Annotate peaks relative to gene features ([`HOMER`](http://homer.ucsd.edu/homer/download.html))
    10. Create consensus peakset across all samples and create tabular file to aid in the filtering of the data ([`BEDTools`](https://github.com/arq5x/bedtools2/))
    11. Count reads in consensus peaks ([`featureCounts`](http://bioinf.wehi.edu.au/featureCounts/))
    12. Differential binding analysis, PCA and clustering ([`R`](https://www.r-project.org/), [`DESeq2`](https://bioconductor.org/packages/release/bioc/html/DESeq2.html))
6. Create IGV session file containing bigWig tracks, peaks and differential sites for data visualisation ([`IGV`](https://software.broadinstitute.org/software/igv/)).
7. Present QC for raw read, alignment, peak-calling and differential binding results ([`MultiQC`](http://multiqc.info/), [`R`](https://www.r-project.org/))

### Documentation
The nf-core/chipseq pipeline comes with documentation about the pipeline, found in the `docs/` directory:

1. [Installation](https://nf-co.re/usage/installation)
2. Pipeline configuration
    * [Local installation](https://nf-co.re/usage/local_installation)
    * [Adding your own system config](https://nf-co.re/usage/adding_own_config)
    * [Reference genomes](https://nf-co.re/usage/reference_genomes)
3. [Running the pipeline](docs/usage.md)
4. [Output and how to interpret the results](docs/output.md)
5. [Troubleshooting](https://nf-co.re/usage/troubleshooting)

## Credits
These scripts were orginally written by Chuan Wang ([@chuan-wang](https://github.com/chuan-wang)) and Phil Ewels ([@ewels](https://github.com/ewels)) for use at the [National Genomics Infrastructure](https://portal.scilifelab.se/genomics/) at [SciLifeLab](http://www.scilifelab.se/) in Stockholm, Sweden. It has since been re-implemented by Harshil Patel ([@drpatelh](https://github.com/drpatelh)) from [The Bioinformatics & Biostatistics Group](https://www.crick.ac.uk/research/science-technology-platforms/bioinformatics-and-biostatistics/) at [The Francis Crick Institute](https://www.crick.ac.uk/), London.

Many thanks to others who have helped out along the way too, including (but not limited to): [@apeltzer](https://github.com/apeltzer), [@bc2zb](https://github.com/bc2zb), [@drejom](https://github.com/drejom), [@KevinMenden](https://github.com/KevinMenden), [@pditommaso](https://github.com/pditommaso).

## Citation

<!-- If you use nf-core/chipseq for your analysis, please cite it using the following doi: [10.5281/zenodo.XXXXXXX](https://doi.org/10.5281/zenodo.XXXXXXX) -->

You can cite the `nf-core` pre-print as follows:  
Ewels PA, Peltzer A, Fillinger S, Alneberg JA, Patel H, Wilm A, Garcia MU, Di Tommaso P, Nahnsen S. **nf-core: Community curated bioinformatics pipelines**. *bioRxiv*. 2019. p. 610741. [doi: 10.1101/610741](https://www.biorxiv.org/content/10.1101/610741v1).
