nf-core/rnafusion

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Introduction

This document describes the output produced by the pipeline. Most of the plots are taken from the MultiQC report, which summarises results at the end of the pipeline.

The directories listed below will be created in the results directory after the pipeline has finished. All paths are relative to the top-level results directory.

Pipeline overview

The pipeline is built using Nextflow and processes data using the following steps:

• Download and build references - Build references needed to run the rest of the pipeline
• STAR - Alignment for arriba, squid and STAR-fusion
• Cat - Concatenate fastq files per sample ID
• Arriba - Arriba fusion detection
• Pizzly - Pizzly fusion detection
• Squid - Squid fusion detection
• STAR-fusion - STAR-fusion fusion detection
• StringTie - StringTie assembly
• FusionCatcher - Fusion catcher fusion detection
• Samtools - SAM/BAM file manipulation
• Fusion-report - Summary of the findings of each tool and comparison to COSMIC, Mitelman, FusionGBD and FusionGDB2 databases
• FusionInspector - Supervised analysis of fusion predictions from fusion-report, recover and re-score evidence for such predictions
• Arriba visualisation - Arriba visualisation report for FusionInspector fusions
• Qualimap - Quality control of alignments
• Picard - Collect QC metrics
• FastQC - Raw read quality control
• MultiQC - Aggregate reports describing QC results from the whole pipeline
• Pipeline information - Report metrics generated during the workflow execution

Download and build references

Main pipeline workflow

If no argument is specified here, the tool was used with default parameters.

Directory structure

{outdir}
├── arriba
├── arriba_visualisation
├── cram_arriba
├── cram_starfusion
├── cram_squid
├── fastp
├── fastqc
├── fusioncatcher
├── fusioninspector
├── fusionreport
├── kallisto_quant
├── megafusion
├── multiqc
├── picard
├── pizzly
├── pipeline_info
├── pizzly
├── qualimap
├── samtools_sort_for_arriba
├── squid
├── star_for_arriba
├── star_for_starfusion
├── star_for_squid
├── starfusion
└── work
.nextflow.log

If no parameters are specified, the default is applied.

Arriba

Arriba is used for i) detect gene fusions and ii) create a PDF report for the fusions found (visualisation):

Detection

Visualisation

Cat

If multiple libraries or runs have been provided for the same sample in the input samplesheet (e.g. to increase sequencing depth) then these will be merged at the very beginning of the pipeline in order to have consistent sample naming throughout the pipeline. Please refer to the usage documentation to see how to specify these samples in the input samplesheet.

Fastp

If --trim_fastp is selected, fastp will filter low quality reads as well as bases at the 5’ and 3’ ends, trim adapters (automatically detected, but input with parameter --adapter_fasta is possible). 3’ trimming is also possible via parameter --trim_tail.

FastQC

FastQC gives general quality metrics about your sequenced reads. It provides information about the quality score distribution across your reads, per base sequence content (%A/T/G/C), adapter contamination and overrepresented sequences. For further reading and documentation see the FastQC help pages.

NB: The FastQC plots displayed in the MultiQC report shows untrimmed reads. They may contain adapter sequence and potentially regions with low quality.

FusionCatcher

FusionCatcher searches for novel/known somatic fusion genes translocations, and chimeras in RNA-seq data. Possibility to use parameter --fusioncatcher_limitSjdbInsertNsj to modify limitSjdbInsertNsj.

FusionInspector

FusionInspector performs a validation of fusion transcript predictions. Possibility to use --fusioninspector_limitSjdbInsertNsj to set limitSjdbInsertNsj to anything other than the default 1000000.

Fusion-report

Fusion-report is a tool for parsing outputs from fusion detection tools. The score is explained on the original fusion-report github page.

--fusionreport_filter can be used to filter the output of fusion-report to fusions identified by at least 2 different tools.

Kallisto

Quantifying abundances of transcripts from bulk and single-cell RNA-Seq data, or more generally of target sequences using high-throughput sequencing reads.

Megafusion

Megafusion converts RNA fusion files to SV VCF and collects statistics and metrics in a VCF file.

MultiQC

MultiQC is a visualization tool that generates a single HTML report summarising all samples in your project. Most of the pipeline QC results are visualised in the report and further statistics are available in the report data directory.

Results generated by MultiQC collate pipeline QC from supported tools e.g. FastQC. The pipeline has special steps which also allow the software versions to be reported in the MultiQC output for future traceability. For more information about how to use MultiQC reports, see http://multiqc.info.

Picard

Pizzly

Pizzly uses the following arguments:

-k 31 \
--align-score 2 \
--insert-size 400 \
--cache index.cache.txt

Qualimap

Samtools

Samtools view

Samtools view is used to convert the chimeric SAM output from STAR_FOR_SQUID to BAM

Samtools sort

Samtools sort is used to sort BAM files from STAR_FOR_STARFUSION (for arriba visualisation) and the chimeric BAM from STAR_FOR_SQUID

Samtools index

Samtools index is used to index BAM files from STAR_FOR_ARRIBA (for arriba visualisation) and STAR_FOR_STARFUSION (for QC)

Squid

Squid is run in two steps: i) fusion detection and ii) fusion annotation, but the output is in a shared squid directory

STAR

STAR is used to align to genome reference

STAR is run for 3 tools:

For arriba with the parameters:

--readFilesCommand zcat \
--outSAMtype BAM Unsorted \
--outSAMunmapped Within \
--outBAMcompression 0 \
--outFilterMultimapNmax 50 \
--peOverlapNbasesMin 10 \
--alignSplicedMateMapLminOverLmate 0.5 \
--alignSJstitchMismatchNmax 5 -1 5 5 \
--chimSegmentMin 10 \
--chimOutType WithinBAM HardClip \
--chimJunctionOverhangMin 10 \
--chimScoreDropMax 30 \
--chimScoreJunctionNonGTAG 0 \
--chimScoreSeparation 1 \
--chimSegmentReadGapMax 3 \
--chimMultimapNmax 50

For squid with the parameters:

--twopassMode Basic \
--chimOutType SeparateSAMold \
--chimSegmentMin 20 \
--chimJunctionOverhangMin 12 \
--alignSJDBoverhangMin 10 \
--outReadsUnmapped Fastx \
--outSAMstrandField intronMotif \
--outSAMtype BAM SortedByCoordinate \
--readFilesCommand zcat

For STAR-fusion with the parameters:

--twopassMode Basic \
--outReadsUnmapped None \
--readFilesCommand zcat \
--outSAMstrandField intronMotif \
--outSAMunmapped Within \
--chimSegmentMin 12 \
--chimJunctionOverhangMin 8 \
--chimOutJunctionFormat 1 \
--alignSJDBoverhangMin 10 \
--alignMatesGapMax 100000 \
--alignIntronMax 100000 \
--alignSJstitchMismatchNmax 5 -1 5 5 \
--chimMultimapScoreRange 3 \
--chimScoreJunctionNonGTAG -4 \
--chimMultimapNmax 20 \
--chimNonchimScoreDropMin 10 \
--peOverlapNbasesMin 12 \
--peOverlapMMp 0.1 \
--alignInsertionFlush Right \
--alignSplicedMateMapLminOverLmate 0 \
--alignSplicedMateMapLmin 30 \
--chimOutType Junctions \
--quantMode GeneCounts

STAR_FOR_STARFUSION uses ${params.ensembl}/Homo_sapiens.GRCh38.${params.ensembl_version}.chr.gtf whereas STAR_FOR_ARRIBA and STAR_FOR_SQUID use ${params.ensembl_ref}/Homo_sapiens.GRCh38.${params.ensembl_version}.gtf

The STAR index is generated with --sjdbOverhang ${params.read_length - 1}, params.read_length default is 100.

STAR-fusion

StringTie

Pipeline information

Nextflow provides excellent functionality for generating various reports relevant to the running and execution of the pipeline. This will allow you to troubleshoot errors with the running of the pipeline, and also provide you with other information such as launch commands, run times and resource usage.