l-giremi 0.1.8

a software for analysis of RNA editing sites from long-read RNA-seq data

L-GIREMI

L-GIREMI (Long-read Genome-independent Identification of RNA Editing by Mutual Information) is a software for analysis of RNA editing sites from long-read RNA-seq data which adopts similar logic with the GIREMI software (Zhang and Xiao, 2015).

Requirement

The L-GIREMI software was developed with python3 on Linux, which demands several python packages.

• python3.5+: with sys, argparse, re, functools, collections, multiprocessing.
• scikit-learn: 0.20+
• scipy: 1.5+
• numpy: 1.10+
• pandas: 1.0+
• pysam: 0.16+

And the analysis with L-GIREMI also needs additional software:

• samtools
• bcftools
• bgzip
• tabix
• minimap2

Installation

It's advised to install the software into a virtual environment.

Create virtual environment:

conda create -n l_giremi
conda activate l_giremi

Or:

virtualenv l_giremi
source bin/activate

From github

Download from github:

git clone https://github.com/gxiaolab/L-GIREMI
cd L-GIREMI

Install the package:

python setup.py install

From pip

pip install l-giremi

Reference data

Be aware to use reference files with same assembly version and the same chromosome name pattern in all the process.

Genome fasta file

The L-GIREMI requires a genome fasta file as input. For human genome, the fasta file can be obtained from UCSC or NCBI. The fasta file should include sequences from all the chromosomes.

SNP vcf file

The L-GIREMI will use SNP vcf file to get putative heterozygous SNPs. dbSNP vcf are a possible reference. And it's even better to use sample specific SNP vcf files. The vcf files should be converted into bcf format, sorted, and indexed.

The following is a example to convert the dbSNP chromosomes into UCSC chromosomes.

wget "https://ftp.ncbi.nih.gov/snp/latest_release/VCF/GCF_000001405.38.gz"

wget "https://ftp.ncbi.nih.gov/snp/latest_release/VCF/GCF_000001405.38.gz.md5"

md5sum -c GCF_000001405.38.gz.md5

wget "https://ftp.ncbi.nlm.nih.gov/genomes/all/GCA/000/001/405/GCA_000001405.28_GRCh38.p13/GCA_000001405.28_GRCh38.p13_assembly_report.txt"

egrep -v "^#" GCA_000001405.28_GRCh38.p13_assembly_report.txt | cut -f 7,10 | tr "\t" " " > GRCh38-to-hg38.map

bcftools annotate --rename-chrs GRCh38-to-hg38.map GCF_000001405.38.gz -Ob -o dbsnp.38.hg38.bcf

bcftools index dbsnp.38.hg38.bcf

Gene annotation gtf

A gene annotation gtf is required for the L-GIREMI, which can be obtained from gencode. The gtf file should be sorted, zipped, and indexed.

The following are codes for gtf file preparation:

(grep ^"#" gencode.v37.annotation.gtf; \
    grep -v ^"#" gencode.v37.annotation.gtf | \
    sort -k1,1 -k4,4n) | \
    bgzip > gencode.v37.annotation.sorted.gtf.gz

tabix -p gff gencode.v37.annotation.sorted.gtf.gz

Simple repeat region table

The simple repeat region table is used by L-GIREMI to filter sites. It can be obtained from UCSC table browser. The table format should be: chromosome, start, end. No header needed for the file.

Usage

usage: l-giremi [-h] -b BAM_FILE [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX] [-t THREAD] --genome_fasta GENOME_FASTA
                  --snp_bcf SNP_BCF --repeat_txt REPEAT_TXT --annotation_gtf ANNOTATION_GTF
                  [--mapq_threshold MAPQ_THRESHOLD] [--min_allele_count MIN_ALLELE_COUNT]
                  [--gene_padding GENE_PADDING] [--exon_padding EXON_PADDING] [--min_rc_cov MIN_RC_COV]
                  [--homopoly_length HOMOPOLY_LENGTH] [--min_AB MIN_AB] [--min_AC MIN_AC]
                  [--min_het_snp_ratio MIN_HET_SNP_RATIO] [--max_het_snp_ratio MAX_HET_SNP_RATIO]
                  [--mi_min_common_read MI_MIN_COMMON_READ] [--mi_min_read MI_MIN_READ] [--mip_threshold MIP_THRESHOLD]

L-GIREMI (Long-read Genome-independent Identification of RNA Editing by Mutual Information)

optional arguments:
  -h, --help            show this help message and exit
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, sorted and indexed
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  -t THREAD, --thread THREAD
                        cores to be used
  --genome_fasta GENOME_FASTA
                        path of genome fasta file
  --snp_bcf SNP_BCF     path of dbSNP bcf file
  --repeat_txt REPEAT_TXT
                        path of txt file of simple repeats [chromosom, start, end] (0 based)
  --annotation_gtf ANNOTATION_GTF
                        gtf (gz and tabix indexed) file of genome annotation (gencode)
  --mapq_threshold MAPQ_THRESHOLD
                        Min MAPQ to be considered in bam file (default: 20)
  --min_allele_count MIN_ALLELE_COUNT
                        Min allele read count (default: 2)
  --drop_non_spliced_read DROP_NON_SPLICED_READ
                        Drop non spliced reads (default: True)
  --min_dist_from_splice MIN_DIST_FROM_SPLICE
                        Drop sites within the distance from splice junctions (default: 4)
  --gene_padding GENE_PADDING
                        expand the range when searching gene gtf (default: 500)
  --exon_padding EXON_PADDING
                        expand the range when searching exon gtf (default: 10)
  --min_rc_cov MIN_RC_COV
                        min coverage of read cluster to be considered (default: 2)
  --homopoly_length HOMOPOLY_LENGTH
                        left and right sequence length to be searched for the homopoly around sites (default: 5)
  --min_AB MIN_AB       Min mismatch ratio to be considered (default: 0.1)
  --min_AC MIN_AC       Min mismatch read count to be considered (default: 3)
  --min_het_snp_ratio MIN_HET_SNP_RATIO
                        Min ratio to be considered as heterogenous SNPs (default: 0.35)
  --max_het_snp_ratio MAX_HET_SNP_RATIO
                        Max ratio to be considered as heterogenous SNPs (default: 0.65)
  --mi_min_common_read MI_MIN_COMMON_READ
                        Min common read for site pairs to calculate MI (default: 6)
  --mi_min_read MI_MIN_READ
                        Min read for a variant of a site in a site pair to calculate MI (default: 1)
  --mip_threshold MIP_THRESHOLD
                        MI p value threshold to be used to separate RNA editing sites (default: 0.05)

Analysis process

Running L-GIREMI requires some annotation files:

• reference FASTA file: for example hg38 fasta.
• SNP VCF file: dbSNP VCF file (the chromosome names should be agreed with the reference FASTA file), or known SNP VCF file for teh sample.
• genome annotation GTF file: with exon annotation and gene annotation, for example GENCODE gtf file.

Firstly, map the long-read RNA-seq fastq file using minimap2 with cs tag information provided, which is required by l-giremi.py.

minimap2 -t 8 -ax splice -uf \
         --secondary=no -N 5 --cs \
         -o SAM_FILE GENOME_FILE FASTQ_FILE

Then, remove unmapped and non-unique mapped reads from SAM file, and sort SAM into an indexed BAM file.

samtools view -O BAM -F 2052 -h $SAM_FILE | \
    samtools sort -O BAM -@ 7 -o $BAM_FILE -

samtools index $BAM_FILE

Next, run l-giremi.

l-giremi \
    -t 8 \
    --bam_file $BAM_FILE \
    --output_prefix $OUTPREFIX \
    --genome_fasta $GENOME_FILE \
    --snp_bcf $SNP_FILE \
    --repeat_txt $REPEAT_FILE \
    --annotation_gtf $GTF_FILE \
    --chromosomes chr1 chr2 chr3 chr4 \
    chr5 chr6 chr7 chr8 chr9 chr10 chr11 chr12 \
    chr13 chr14 chr15 chr16 chr17 chr18 chr19 \
    chr20 chr21 chr22 chrX chrY

Output

l-giremi generates several result files.

• corrected read strand files: the files are saved my chromosome, and are stored as $OUTPREFIX.$CHROMOSOME.strand. columns:
  1. read_name: the read name.
  2. seq_strand: original read mapping strand.
  3. read_strand: corrected read strand.
• site position files: stored as $OUTPREFIX.site. columns:
  1. chromosome: chromosome name.
  2. pos: position on the chromosome, 0-based.
  3. ref: sequence of reference genome, strandless.
  4. snp: SNP mark, 0 for not found overlapping with input SNP annotations, 1 for overlapping with input SNP annotations.
• mutual information files: stored as $OUTPREFIX.mi. columns:
  1. type: het_snp, for mismatch sites that overlapping with SNP annotations and with mismatch ratio satisfying the parameters. mimatch for other types.
  2. chromosome: chromosome name.
  3. pos: position on the chromosome, 0-based.
  4. strand: strand of the mismatch sites.
  5. change_type: the mismatch type, [ref]>[alt].
  6. mi: site mutual information.
  7. n: n sites pairs for the calculation of site mutual information.
  8. pairs: the names of the paired sites.
  9. jakarta: Jakarta index for each site pairs.
  10. mis: mutual information for each site pairs.
  11. mi_cov: mutual information read coverage.
  12. mip: emperical p value of the MI
• mismatch score file: stored as $OUTPREFIX.score. columns:
  1. type: het_snp, for mismatch sites that overlapping with SNP annotations and with mismatch ratio satisfying the parameters. mimatch for other types.
  2. chromosome: chromosome name.
  3. pos: position on the chromosome, 0-based.
  4. strand: strand of the mismatch sites.
  5. change_type: the mismatch type, [ref]>[alt].
  6. read_count: the read count for the mismatch.
  7. depth: the total read count for the site.
  8. ratio: the mismatch ratio.
  9. up_seq: a 5' nucleotide ahead of the mismatch sites.
  10. down_seq: a 3' nucleotide after the mismatch sites.
  11. score: RNA editing score by the GLM model.

Useful scripts

There are also some useful scripts for download anslysis provided with the main l-giremi script.

get_aei

get_aei.py is used for the calculation of Alu Editing Index (AEI) from long-read RNA-seq data (Roth et al., 2019). Calculation of AEI neads the read strand files (output of l-giremi.py), the genome fasta file, a txt file with Alu locations, and the SNP BCF reference.

usage: get_aei [-h] -b BAM_FILE --strand_file STRAND_FILE [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX]
                  --genome_fasta GENOME_FASTA --snp_bcf SNP_BCF --alu_txt ALU_TXT [-t THREAD]

Calculate AEI from bam file, both in read level and Alu level

optional arguments:
  -h, --help            show this help message and exit
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, with cs tags, sorted and indexed
  --strand_file STRAND_FILE
                        corrrect strand file for reads, generated by the L-GIREMI
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  --genome_fasta GENOME_FASTA
                        path of genome fasta file
  --snp_bcf SNP_BCF     path of dbSNP bcf file
  --alu_txt ALU_TXT     path of bed file of simple repeats [chromosom, start, end, name] (0 based)
  -t THREAD, --thread THREAD
                        cores to be used

get_read_site

get_read_site output a table that has the read name, genomic position, and the nucleotide of the position on the read. Running the script requires a file that provides the genomic position of sites that are interested.

usage: get_read_site [-h] -s SITE_FILE -b BAM_FILE [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX]
                        [--mapq_threshold MAPQ_THRESHOLD] [-t THREAD]

Get read and site information from bam file

optional arguments:
  -h, --help            show this help message and exit
  -s SITE_FILE, --site_file SITE_FILE
                        input site file: [chromosome, pos], without header, separated by tab
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, with cs tags, sorted and indexed
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  --mapq_threshold MAPQ_THRESHOLD
                        Min MAPQ to be considered in bam file (default: 20)
  -t THREAD, --thread THREAD
                        cores to be used

get_read_mismatch

get_read_mismatch is similar to get_read_site.py, except that it only output the read name and the mismatched sites, without matched sites. get_read_mismatch.py also requires a file that provides the genomic position of sites that are interested.

usage: get_read_mismatch [-h] -s SITE_FILE -b BAM_FILE [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX]
                            [--mapq_threshold MAPQ_THRESHOLD] [-t THREAD]

Get read and mismatch site information from bam file

optional arguments:
  -h, --help            show this help message and exit
  -s SITE_FILE, --site_file SITE_FILE
                        input site file: [chromosome, pos], without header, separated by tab
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, with cs tags, sorted and indexed
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  --mapq_threshold MAPQ_THRESHOLD
                        Min MAPQ to be considered in bam file (default: 20)
  -t THREAD, --thread THREAD
                        cores to be used

get_read_splice

get_read_splice outputs read names and the splicing sites detected by minimap2 in the reads.

usage: get_read_splice [-h] -b BAM_FILE [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX]
                          [--mapq_threshold MAPQ_THRESHOLD] [-t THREAD]

Get read and splice sites from bam file

optional arguments:
  -h, --help            show this help message and exit
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, with cs tags, sorted and indexed
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  --mapq_threshold MAPQ_THRESHOLD
                        Min MAPQ to be considered in bam file (default: 20)
  -t THREAD, --thread THREAD
                        cores to be used

correct_splice_site

Since the raw splicing sites detected in the long-read RNA-seq data have many errors, the splicing sites should be corrected (Wyman and Mortazavi, 2019). correct_splice_site adopted similar correction strategies with TranscriptClean. The correction needs a GTF annotation file.

usage: correct_splice_site [-h] -s SPLICE_FILE --annotation_gtf ANNOTATION_GTF
                              [-c [CHROMOSOMES ...]] [-o OUTPUT_PREFIX] [--window WINDOW]

Correct splice sites by gtf file

optional arguments:
  -h, --help            show this help message and exit
  -s SPLICE_FILE, --splice_file SPLICE_FILE
                        input splice file [read_name, chromosome, pos, type] with column names
  --annotation_gtf ANNOTATION_GTF
                        gtf (gz and tabix indexed) file of genome annotation (gencode)
  -c [CHROMOSOMES ...], --chromosomes [CHROMOSOMES ...]
                        chromosomes to be analyzed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  --window WINDOW       window to be considered as the same splice site (default: 10)

calculate_site_splice_mi

calculate_site_splice_mi can calculate the mutual information for mismatched sites (RNA editing sites or SNPs) and splicing sites.

usage: calculate_site_splice_mi [-h] [-m READ_SITE] [-s READ_SPLICE] [-o OUTPUT_PREFIX]

calculate the mutual information of mismatch site and splice site pairs

optional arguments:
  -h, --help            show this help message and exit
  -m READ_SITE, --read_site READ_SITE
                        read-site file: [read_name, chromosome, pos, seq]
  -s READ_SPLICE, --read_splice READ_SPLICE
                        corrected read-splice file: [read_name, chromosome, pos, type, corrected_pos,
                        annotation]
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file

split_bam_by_site

split_bam_by_site can fetch reads that cover one genomic location and save the reads into separated SAM files by the location, which can be used in IGV ploting.

usage: split_bam_by_site [-h] -b BAM_FILE [-o OUTPUT_PREFIX] [-c CHROMOSOME] [-p POS]

Save reads that cover one position into separated SAM files by the genomic location

optional arguments:
  -h, --help            show this help message and exit
  -b BAM_FILE, --bam_file BAM_FILE
                        input bam file, with cs tags, sorted and indexed
  -o OUTPUT_PREFIX, --output_prefix OUTPUT_PREFIX
                        prefix of output file
  -c CHROMOSOME, --chromosome CHROMOSOME
  -p POS, --pos POS

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