Epigenetics reading group feedback!
Although the whole gang wasn’t present Mac and Steven gave me some great feedback on the C. virginica edits I started on! Here are some of the highlights:
Minor improvements
- Clearly defining what I consider a DML, since a locus doesn’t have to be one base pair
- Rephrasing GO-MWU input creation methods
- Not using signed p-values for GO-MWU. Mac made a good point that understanding how up- or downregulated genes influence enrichment patterns makes more sense for transcription than seeing how hyper- and hypomethylated DML influence enrichment. We don’t know what methylation is doing in a gene, and using signed p-values doesn’t shed any light on that function. Additionally, hypermethylation could lead to increased or decreased gene activity. If that gene is responsible for repressing another gene function, assigning a positive or negative value based solely on methylation status doesn’t take into account gene function.
- Removing DMG analysis since the actual function of methylation in these genes is unknown (no paired transcription data) and it didn’t add anything to the paper.
- I moved the percent methylation across genome feature figure to Figure 1 instead of keeping it with Figure 2.
- Changed Figure 8 so it was colored by gene group, not biological process
- Mac suggested I convert the multiple barplots in Figure 5 (panels c-f) to stacked barplots. I created a new versions of this plot after doing some standard dataframe manipulation.
Calculating “genome methylation”
In the paper, I state that 22% of the C. virginica genome was methylated. Mac and Steven were hesitant to make this claim since it wasn’t clear how I got this number, and I couldn’t find it in the methods anywhere. When I looked at the 3,181,904 methylated CpGs (> 50% methylated) versus the 14,458,703 total CpGs in the C. virginca gneome, I got 22%. This doesn’t saying that 22% of the genome is methylated. Instead, 22% of CpGs were found to be methylated. I clarified this statement in the abstract, results, and discussion.
Methylation islands
I removed the methylation island bar in Figure 2, since the methylated CpGs and methylation islands are correlated. Mac described methylation islands as a smoothing function, so it’s not really interesting to see where they are located with respect to the other genome features beyond just knowing what’s genic and intergenic. I also removed Figure 2b (individual feature locations in methylation islands). After calculating median and ranges for methylation island length and number of mCpGs, I tried creating a histogram of island lengths in this R Markdown file. When I created a preliminary plot, it was clear that I would need a gapped axis! I previously created a barplot with a gapped axis, so I thought I could recycle code. I kept getting the following error when I tried plotting my data:
Error in rect(xtics[littleones] - halfwidth, botgap, xtics[littleones] + : cannot mix zero-length and non-zero-length coordinates In the meantime, I looked at the histogram bins and how many islands were in each bin. I wrote up a quick description for the results section.
Things to improve in the discussion
- Look at list of genes with DML and see if any of them have been reported in ocean acidification and gene expression studies
- Add ocean acidification context to final two discussion paragraphs, along with caveat about experimental design confounding responses to ocean acidification with potential differences in gamete maturation
Going forward
- Address remaining comments about discussion text
- Update manuscript text
- Update response to reviewers
- Consolidate any co-author feedback
- Submit comment responses and reviesed manuscript
- Post revised paper on bioRXiv
- Update paper repository with new code and figures
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