AlleleSeq
From GersteinInfo
Contents |
General outline of pipeline
The basic goal of the pipeline is to take a large collection of reads generated from ChIP-seq or RNA-seq experiments associated with an individual and detect single nucleotide variants (SNVs) that correspond to significantly skewed number of reads. To do this, the pipeline starts with a preprocessing step, before the actual process.
(1) Pre-processing - diploid genome construction using vcf2diploid
In the Rozowsky et al. (2011) paper, the
pre-processing step separate (phase) the child's diploid genome into its parental
haplotypes based on the sequences of the parents.
(2) AlleleSeq pipeline - mapping and statistical testing using PIPELINE.mk package
a) Reads from ChIP-seq and RNA-seq experiments are aligned and mapped to both
haplotype genomes.
b) Then for each SNV position with mapped reads, we compare the allele
frequencies observed in the two parental haplotypes.
vcf2diploid
Essentially, it constructs a personal genome integrating the the variants from the parents and child to the reference genome.
Installation
1. Download the tool.
2. Type
$make
Usage
java -Xmx10000m -jar vcf2diploid.jar -id sample_id -chr file1.fa file2.fa ... [-vcf file1.vcf file2.vcf ...] > logfile.txt
OPTIONS: id - (required) the ID of individual whose genome is being constructed (e.g., NA12878). The tool recognizes by this ID in the VCF file
chr - (required) FASTA file(s) of reference sequence(s)
vcf - (required) VCF4.0 file(s) containing variants from parents and the individual
Xmx - max memory allocation for JAVA. In this example, 10GB was allocated. logfile.txt - stores the standard output produce from the run
Output
(a) Maternal and paternal FASTA files
These are the references used for the AlleleSeq pipeline.
(b) Map files
These are coordinate files that correspond to the variants on the parental genomes and
the reference genome. This is especially important when insertions and deletions
are included in the construction of the diploid genome, since the positions go out of sync in the personal and reference genomes.
(c) Chain files
Using the chain file, one can use the LiftOver tool to convert the annotation
coordinates from reference genome to personal haplotypes.
Please refer to the README of vcf2diploid for a more detailed description.
AlleleSeq Pipeline
Installation
AlleleSeq runs on LINUX/UNIX command line, and requires the following dependencies (at least the version stated or newer): (a) Python v2.5.1 (b) Bowtie v0.10.0.2 (Bowtie must be in your PATH)
For now, only Bowtie is supported. Some other aligners might be supported in future versions.
Input
(a) FASTA files for the paternal and maternal reference genomes.
(b) One or more collections of unmapped reads; zipped fastq formats "*.fastq.gz".
This is a typical file format for ChIP-seq and RNA-seq reads generated from Illumina.
All files matching "*.fastq.gz" will be combined into one dataset.
---NOTE: If you have something other than fastq.gz, e.g. BAM, you will need to add
a preliminary conversion step. For instance, bedtools or SAMtools can convert BAM
to fastq. Currently, AlleleSeq does not automatically convert them.
---SANITY CHECK: you can use the make target "check" to print out the set of
input fastq files. To do this, type "make check"; this should print the source files.
(c) SNV genotype file; tab-delimited file of a set of SNV locations for each of
the trio: father, mother and child. AlleleSeq expects this format, with the header:
chr pos ref Mat Pat Child Phase 1 114116078 A TT TT TA MUTANT 1 114117743 G CG GG GG HOMO 1 114120250 C AC AA CA PHASED 1 114120756 A CA CC AC PHASED
col1: chromosome
col2: chromosomal position
col3: reference allele
col4: maternal genotype
col5: paternal genotype
col6: child (subject) genotype, ordered: MatPat if phased
col7: phasing status describes the phasing in the trio.
Possible values are:
HETERO (all three heterozygous, no phasing possible)
HOMO (child is homozygous)
PHASED (child heterozygous and at least one parent homozygous)
MUTANT (child genotype is inconsistent with parents' genotype)
This can be generated by the user or converted from VCF file with a simple helper
PERL script provided together with the AlleleSeq package, vcf2snp.
vcf2snp -h for more information on running.
(d) CNV file; a set of normalized read depth values for all snp locations from a
separate genomic sequencing experiment. This reports the read depth at that snp
compared to overall coverage. This is used to filter out locations with very low
or high coverage, which would tend to indicate copy number variation. The file
should be in this format (with header):
chrm snppos rd 1 52066 0.902113 1 695745 0.909802 1 742429 0.976435
This can be generated from CNVnator (Abyzov et al. 2011).
(e) (optional) for ChIP-seq experiments, a set of "binding sites" for the
transcription factor of interest, showing regions in the genome where the
transcription factor binds. This will allow filtering of SNV locations to
just those within binding sites. If BINDINGSITES is set to a non-existing file,
no filtering will be done.
Typically, we used PeakSeq (Rozowsky J. et al. 2009) to determine binding regions.
The pipeline expects a BED file (tab-delimited file with no header in this format:
chr, start, end; only the first three columns will be read)
The format of chrom names must agree with the other files (usually chr#).
In PIPELINE.mk, set BNDS to this file. You can set it to an empty file, in which
case depth will be set to 1.0 and no filtering will be done.
