Hi everyone, I am analyzing super-enhancers (SEs) from H3K27ac CUT&Tag data and have observed some confusing results. I would greatly appreciate any advice on my workflow and result interpretation. I have three biological replicates per condition. My original pipeline was: call peaks individually for each replicate with MACS2, merge peak files using bedtools merge, and pool all replicate BAM files for downstream ROSE SE calling.
I noticed several unusual features in my SE results, and I'm unsure whether these are normal or technical artifacts:
1. SE regions appear relatively broad: average ~30 kb and a maximum of ~180 kb.
2. Over 40% of SEs annotate to promoter regions (<1 kb from TSS).
I suspect that these unexpected patterns may result from my simple replicate merging strategy, which might retain noisy, non-reproducible peaks and artificially expand SE intervals. I have two key questions:
- Are these metrics (broad SE regions, high promoter occupancy) acceptable for standard SE profiles, or are they likely preprocessing artifacts?
- What is the proper, robust strategy to integrate three replicates for ROSE? Should I use a consensus peak set (2/3 replicates overlap) instead of simple merging to filter noise and avoid over-broad SE calls? Thanks in advance for any suggestions or shared experience!
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Sorry for the late response, your strategy makes sense for calling peaks between replicates.
Perhaps if you see a lot of peaks specific to only 1 sample, you can select only the peaks found in at least 2 samples.
How did you call your peaks with MACS2, H3K27ac is expected to be quite sharp, so if you called on broad peaks and then aggregate between replicates, you might end up with quite large regions.
Have you tried modifying the STITCHING_DISTANCE in ROSE ? From GitHub
Investigate these 3 cues and hopefully you will end up with less broad SE regions.