17 May 2016

finding new intron-exon junctions using the public Encode RNASeq data

I've been asked to look for some new / suspected / previously uncharacterized intron-exon junctions in public RNASeq data.
I've used the BAMs under http://hgdownload.cse.ucsc.edu/goldenPath/hg19/encodeDCC/wgEncodeCaltechRnaSeq/.

The following command is used to build the list of BAMs:

curl -s  "http://hgdownload.cse.ucsc.edu/goldenPath/hg19/encodeDCC/wgEncodeCaltechRnaSeq/" |\
tr ' <>"' "\n" | grep -F .bam | grep -v bai | sort | uniq | sed 's/.bam$//' | sed 's/$/ \\/' 

wgEncodeCaltechRnaSeqGm12878R1x75dAlignsRep1V2 \
wgEncodeCaltechRnaSeqGm12878R1x75dAlignsRep2V2 \
wgEncodeCaltechRnaSeqGm12878R1x75dSplicesRep1V2 \
wgEncodeCaltechRnaSeqGm12878R1x75dSplicesRep2V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il200AlignsRep1V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il200AlignsRep2V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il200SplicesRep1V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il200SplicesRep2V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il400AlignsRep2V2 \
wgEncodeCaltechRnaSeqGm12878R2x75Il400SplicesRep2V2 \

This list is inserted as a list named SAMPLES a Makefile.

For each BAM, we use samtools to retrieve the reads in the region(s)) of interest. The reads are then filtered with samjs (https://github.com/lindenb/jvarkit/wiki/SamJS) to only keep the reads carrying an intron-exon junction at the desired location(s). Basically, the javascript-based filter loops over the CIGAR string of the read, computes the genomic interval skipped when the cigar operator is a deletion or a skipped region/intron. The read is printed if it describes the new intron-exon junction.

All in one:

That's it,


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