Hello! I want to look at the differentially expressed genes between two groups (Healthy vs Infected) in single-cell data. However, I want to control for days post symptoms. How would I go about doing that? In bulk RNAseq I would usually set the design as ~group, group:time, however using MAST using this vignette (https://satijalab.org/seurat/v3.0/de_vignette.html) I don't see that option.
Would it be okay for me to set Healthy as day 7 and run this analysis - regressing time out?
Example data structure: Pt1: Heatlhy Pt2: Healthy Pt3: Infected, 3 days post symptoms Pt4: Infected, 7 days post symptoms Pt5: Infection, 0 days post symptoms
Following up on this, I would recommend the following chapter of the OSCA book: Marker gene detection with blocking factors.
For turning a Seurat object into an SCE object, see the Satija Lab's description
What I found crucial is to filter for a minimum fraction of cells per clusters that express the gene (so have counts > 0) in at least one of the two groups one compares. That saves you from spurious DE results based on a few outlier cells both on the pseudobulk and the single-cell level. I personally use 0.1 (so 10%) by default, for markers that one might want to use for FACS analysis maybe even a higher fraction like 0.2 might make sense.