Using the Integrative Genomics Viewer (IGV)

In this tutorial, we're going to view the aligned reads and variants that we called in the past two lessons in the Integrated Genomics Viewer from the Broad Center. You'll need the output from Introduction to mapping (bowtie, BWA) and Introduction to variant calling (SAMtools).

Getting situated

You can start this tutorial two ways

1. If you have an introduction_to_mapping directory from doing the previous tutorials, then you can use it for this tutorial.

cd $SCRATCH/intro_to_mapping

If you do not have the results, you can copy some "canned" ones that we provide using these commands. Remove any existing intro_to_mapping directory in your $SCRATCH space before running these commands, if you have one.

cds
cp -r /corral-repl/utexas/BioITeam/ngs_course/intro_to_mapping/data intro_to_mapping
cd intro_to_mapping
cp -r /corral-repl/utexas/BioITeam/ngs_course/intro_to_mapping/samtools_* .
cp -r /corral-repl/utexas/BioITeam/ngs_course/intro_to_mapping/comparison .

Prepare a GFF feature file for the reference sequence

IGV likes its reference genome files in GFF (Gene Feature Format). Unfortunately, our old friend bp_seqconvert.pl doesn't do GFF. Fortunately, it's cousin bp_genbank2gff3.pl does.

module load bioperl
cp /corral-repl/utexas/BioITeam/ngs_course/scripts/bp_genbank2gff3.pl .
./bp_genbank2gff3.pl NC_012967.1.gbk

Where's the output?

NC_012967.1.gbk.gff

Take a look at the original Genbank file and the new GFF3 file and try to get a handle on what is going on in this conversion.

(NB: I had to "fix" bp_genbank2gff3.pl to work on our GenBank file, by removing a line in the Perl script that caused an error. If someone knows of an easier way to get a GFF file from a file downloaded from Genbank, please share!)

Side-note on displaying BLAST results as GFF files in IGV or other browsers

Another useful trick with either IGV or UCSC: displaying your own BLAST results: BioPerl allows for super-easy conversion from blast output to a gff file; IGV and the UCSC browser both understand GFF files. The short script bl2gff.pl does the conversion.

Let's use the blast result we had from the earlier test for the JAG1 gene to show you how. You'll need to provide the input file - it's the ".oNNNNNN" output file from your blast job.

Displaying BLAST results in IGV or UCSC

grep '^gi' blast_jag1.o586038 > jag1_blast.out
module load perl
module load bioperl
/corral-repl/utexas/BioITeam/bin/bl2gff.pl jag1_blast.out > jag1_blast.out.gff

The resulting jag1_blast.out.gff can be moved to your local machine and opened in IGV. Load the human reference first though!

Copy files to your desktop

IGV is an interactive graphical viewer program. You can't run it on TACC, so we need to get the relevant files back to your desktop machine.

They include:

Indexed reference FASTA files
GFF reference sequence feature files
Sorted and indexed mapped read BAM files
VCF result files
... and possibly many other types of files.

We're going to copy all of these into a new directory called IGV to make it easier to just transfer the ones that we want.

mkdir IGV
cp NC_012967.1.gbk.gff IGV
cp samtools_bowtie/NC_012967.1.fasta IGV
cp samtools_bowtie/NC_012967.1.fasta.fai IGV
cp samtools_bowtie/SRR030257.sorted.bam IGV/bowtie.sorted.bam
cp samtools_bowtie/SRR030257.sorted.bam.bai IGV/bowtie.sorted.bam.bai
cp samtools_bwa/SRR030257.sorted.bam IGV/bwa.sorted.bam
cp samtools_bwa/SRR030257.sorted.bam.bai IGV/bwa.sorted.bam.bai
cp comparison/* IGV

Now, copy this entire IGV directory back to your local Desktop machine.

Remember how? Try it on your own first, before peeking...

In the terminal connected to Lonestar, figure out the complete path to the IGV directory.

pwd

Open a new terminal window on your Desktop. Fill in the parts in brackets <> in this command:

scp -r <username>@lonestar.tacc.utexas.edu:</full/path/to/IGV/> .

Launching IGV

There are two ways, in you're web browser or by downloading the binaries locally and running IGV from your machine.

In Browser

Navigate a web browser to this page:http://www.broadinstitute.org/software/igv/download

Go ahead and click on the "Launch with 2 GB" option. This will download a "Java Web Start" file that you can launch by locating it on your Desktop and double-clicking.

Locally

wget http://www.broadinstitute.org/igv/projects/downloads/IGV_2.1.14.zip
unzip IGV_2.1.14.zip
cd IGV_2.1.14
java -Xmx4g -jar igv.jar

Load genome into IGV

From the main window of IGV, click on File -> Import Genome and you should be presented with the following window.

Enter the ID and Name of the Genome you are working with and select the path to your *.fasta file (the index, *.fai file needs to be in the same directory), then select the path to your *.gff file for the Gene File.

Load mapped reads into IGV

From the main window of IGV, click on File -> Load File. Choose bowtie.sorted.bam

After importing your reference genome and loading an alignment file, your screen should look similar to the following:

And you are now free to investigate different areas and their alignments in the genome.

Load variant calls into IGV

We're really interested in places in the genome where we think there are mutations. You can load the VCF file to check out those spots, but first you need to (guess what?) index it.

You can do this from within IGV:

Choose File -> Run igvtools....
Choose "index" from the commands drop-down menu.
Select your *.vcf file (Ex: bowtie.vcf) for "Input File"
Click the "run" button.

It will look like nothing has happened, but you can now close the "Run" window and choose File -> Load File. If you navigate to your IGV directory, you will now see a brand new bowtie.vcf.idx file. You can now load the file bowtie.vcf, and it will show up as a new track near the top of your window.

Tip: You can index BAM and FASTA files the same way inside of IGV if you haven't already created indexes for them.

Navigating in IGV

There are a lot of things you can do in IGV. Here are a few:

Jump to the next point of interest. Click on a track name on the left side of the window (Ex: bowtie.vcf), to select it. You can then use control-f and control-b to jump forward and backward within that list of features. Try this on the variant calls track.
Jump right to a gene. Type its name into the search box. Try "topA".
Navigate more quickly. The page-up page-down, home, end.
Load multiple VCF and BAM alignments at once. Try this to compare a few different regions between the bowtie and BWA results.
Change the appearance of genes. Right click on the gene track and try "expanded". Experiment with the other options.
Change the appearance of reads. Right click on a BAM track and choose "show all bases" and "expanded". Experiment with the other options.

See the IGV Manual for more tips and how to load other kinds of data.

Exercises

Check out the rbsA gene region? What's going on here?
What is going on in the pykF gene region? You might see red read pairs. What does that mean?
Go to coordinate 2,698,092. Compare the bowtie and BWA alignments. Can you explain what's going on here?
Go to coordinate 475,263. ompare the bowtie and BWA alignments. What's the story here?

Advanced exercise: human data scavenger hunt

Data from the CEU trio from the 1000 Genomes Project can be found directly from the Broad's server for IGV.

Find the dbSNP accession number for the SNP apparent in the two 1000 genomes project trios in the intron between exons 8 and 9 of the GABBR1 gene.

Steps:

Download and install the Integrative Genome Viewer from the Broad Institute.
Select "Human hg18" as the reference genome
Get some data: File -> “Load from Server…” -> 1000 genomes -> CEU and YRI trios
Find the gene and the right exons
Zoom in until you find the SNP
Load and look at the SNP track: File -> Load from server -> Annotations -> Variants -> dbSNP

This is whole genome coverage data; later we'll look at exome data.

Answer

rs29220