This week’s video tip shows you a new way to look at the multiWig track data at the UCSC Genome Browser. A new option has recently been released (see 06 May 2014), a “stacked” view, and it’s a handy way to look at the data with a new strategy. But I’ll admit it took me a little while of working with it to understand the details. So in this tip I hope you’ll see what the new visualization offers.
I won’t go into the background on the many types of annotation tracks available–if you need to be introduced to the idea of the basic track views, start out with our introduction tutorial that touches on the different types of graphical representations. Custom tracks are touched on in the advanced tutorial. For guidance specifically how to create the different track types, see the UCSC documentation. The type of track I’m illustrating in the video today, a MultiWig track, has its own section over there too. Basically, if you are completely new to this, the “wiggle” style is a way to show a histogram display across a region. MultiWig lets you overlay several of these histograms in one space. In the example I’ll show here, the results of looking at 7 different cell lines are shown for some histone mark signals (Layered H3K27Ac track).
When I saw the announcement, I thought this was a good way to show all of the data simultaneously. When we do basic workshops, we don’t always have time to go into the details of this view, although we do explore it in the ENCODE material, because the track I’m using is one of the ENCODE data sets. I’ll use the same track in the same region as the announcement, which is shown here:
But when I first looked at this, I wasn’t sure if the peak–focus on the pink peak that represents the NHLF cell line–was meant to cover the whole area underneath or not. What I was trying to figure out is essentially this (a graphical representation of my thought process follows):
By trying out the various styles I was pretty sure I had the idea of what was really being shown, but I confirmed that with one of the track developers. The value is only the pink band segment, not the whole area below it. And Matthew also noted to me that they are sorting the tracks in reverse alphabetical order (so NHLF is the highest in the stack). That was an aspect I hadn’t realized yet. They are not sorting based on the values at that spot. This makes sense, of course, but it wasn’t obvious to me at first.
I like this option very much–but I figured if I had to do some noodling on what it actually meant others might have the same questions.
In the video I’ll show you how this segment looks with the different “Overlay method” settings on that track page. I’ll be looking at the SOD1 area, like the announcement example. I tweaked a couple of the other settings from the defaults so it would be easier to see on the video (see arrowheads for my changes). But I hope this conveys the options you have now to look at this type of track data effectively.
So here is the video with the SOD1 5′ region in the center, using the 4 different choices of overlay method, illustrating the histone mark data in the 7 cell lines. I’m not going into the details of the data here, but I’ll point you to a reference associated with this work for more on how it’s done–see the Bernstein lab paper below. I wanted to just demonstrate this new type of viewing options that will be available on wiggle tracks. Some tracks will have too much data for one type or another, or will be clearer with one or another style. But now you have an additional way to consider it.
UCSC Genome Browser: genome.ucsc.edu
UCSC Intro tutorial: http://openhelix.com/ucscintro
UCSC Advanced tutorial: http://openhelix.com/ucscadv
These tutorials are freely available because UCSC sponsors us to do training and outreach on the UCSC Genome Browser.
Kent W.J., Zweig A.S., Barber G., Hinrichs A.S. & Karolchik D. (2010). BigWig and BigBed: enabling browsing of large distributed datasets., Bioinformatics (Oxford, England), PMID: 20639541
Karolchik D., Barber G.P., Casper J., Clawson H., Cline M.S., Diekhans M., Dreszer T.R., Fujita P.A., Guruvadoo L. & Haeussler M. & (2013). The UCSC Genome Browser database: 2014 update., Nucleic acids research, PMID: 24270787
Ram O., Goren A., Amit I., Shoresh N., Yosef N., Ernst J., Kellis M., Gymrek M., Issner R. & Coyne M. & al. Combinatorial patterning of chromatin regulators uncovered by genome-wide location analysis in human cells., Cell, PMID: 22196736
The ENCODE Project Consortium, Bernstein B.E., Birney E., Dunham I., Green E.D., Gunter C. & Snyder M. et al. (2012). An integrated encyclopedia of DNA elements in the human genome., Nature, 489 PMID: 22955616
Also see the Nature special issue on ENCODE data, especially the chromatin accessibility and histone modification subset (section 02): http://www.nature.com/encode/