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RNA-Seq-Flow

RNA-Seq Flow is the script written in python snakemake format which starts from the raw fastq files and ends all the way to give you gene and Isoform level count using RSEM, to Increase the mapping effeciency, it does 2nd pass STAR Allignment by indexing the genome again using the merged SJ.0UT.tab files from the 1st pass. for the quality control it does Fastqc as well as does trimming though Trim-Galore.

workflow

Required Tools

  • FastQC (A quality control tool for high throughput sequence data)

  • Trim-galore (Automates quality control and adapter trimming of fastq files)

  • STAR (Spliced aware ultrafast transcript alligner to reference genome)

  • Picard (Cammand line set tool to manipulate high-throughput sequencing data)

  • RNA-SeQC (Qualiy Control metrices of RNA-Seq data)

  • RSEM (Accurate quantification of gene and isoform expression levels from RNA-Seq data)

Setting up conda environment for tools and their dependencies

  • Install anaconda or load it if it's already on your server

  • conda create --name rnaseq-env

  • source activate rnaseq-env

  • conda install -c bioconda star

  • conda install -c bioconda fastqc

  • conda install -c bioconda rsem

Use STAR to index the genome for 1st pass allignment, the 2nd pass allignemnt uses the new index from merged SJ.out.tab files from the script

 STAR  --runMode genomeGenerate --runThreadN 24 --genomeDir ./ --genomeFastaFiles hg38_noALT_noHLA_noDecoy_ERCC.fa  --sjdbGTFfile  gencode.v30.annotation.ERCC.gtf 

To Generate the combined fastqc report of all the samples (.txt)"

 python3 fastqc-summary -s $INDIR > "QC_Report.txt"

The ERCC GTF file was download from broadInstitute and Gene- and transcript-level attributes were added to the ERCC GTF with the following Python code taken from GTexTopMed github page

with open('ERCC92.gtf') as exon_gtf, open('ERCC92.genes.patched.gtf', 'w') as gene_gtf:
for line in exon_gtf:
    f = line.strip().split('\t')
    f[0] = f[0].replace('-','_')  # required for RNA-SeQC/GATK (no '-' in contig name)

    attr = f[8]
    if attr[-1]==';':
        attr = attr[:-1]
    attr = dict([i.split(' ') for i in attr.replace('"','').split('; ')])
    # add gene_name, gene_type
    attr['gene_name'] = attr['gene_id']
    attr['gene_type'] = 'ercc_control'
    attr['gene_status'] = 'KNOWN'
    attr['level'] = 2
    for k in ['id', 'type', 'name', 'status']:
        attr['transcript_'+k] = attr['gene_'+k]

    attr_str = []
    for k in ['gene_id', 'transcript_id', 'gene_type', 'gene_status', 'gene_name',
        'transcript_type', 'transcript_status', 'transcript_name']:
        attr_str.append('{0:s} "{1:s}";'.format(k, attr[k]))
    attr_str.append('{0:s} {1:d};'.format('level', attr['level']))
    f[8] = ' '.join(attr_str)

    # write gene, transcript, exon
    gene_gtf.write('\t'.join(f[:2]+['gene']+f[3:])+'\n')
    gene_gtf.write('\t'.join(f[:2]+['transcript']+f[3:])+'\n')
    f[8] = ' '.join(attr_str[:2])
    gene_gtf.write('\t'.join(f[:2]+['exon']+f[3:])+'\n')

To quantify the gene expression levels and compatibility with RNA-SeQC, the gencode GTF needs to be collapsed using the GTex script collapse_annotation.py

python3 collapse_annotation.py gencode.v30.annotation.ERCC.gtf gencode.v30.GRCh38.genes.gtf
cat gencode.v30.GRCh38.genes.gtf ERCC92.genes.patched.gtf \
    > gencode.v30.ERCC.genes.gtf 

To Run the pipeline on cluster using this command 'modify cluster.json parameters according to your cluster configuration

snakemake -j 999 --configfile config.yaml --use-conda --nolock --cluster-config cluster.json --cluster "sbatch -A {cluster.account} -p {cluster.partition}  -N {cluster.N} -n {cluster.n}  -t {cluster.time} --mem {cluster.mem}"

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RNA-Seq Analysis pipeline using Snakemake workflow

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