27 | February | 2020 | Roberts Lab

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