Finally, we assessed the expression of these genes in central nervous system (CNS) tissues despite their uniformly low expression and lack of detection in brain samples from GTEx and HPA, respectively (data not shown). scRNAseq data suggests similarly low expression across CNS populations, including various regions of the mouse brain and the human retina (Figure 2—figure supplement 17). From the Tabula Muris study, Ace2 is detected in a small number of pericytes (22 of 146) and an even lower fraction of endothelial cells (Figure 2—figure supplement 17B). Dpp4 is also expressed here in ~20% of endothelial cells (Figure 2—figure supplement 17B), which may warrant follow-up but importantly is not reflected in endothelial cells of the cerebral cortex by IHC (Figure 2—figure supplement 18). In all brain-derived cell populations from the Mouse Cell Atlas (Figure 2—figure supplement 17C–D) and human retina-derived populations (Figure 2—figure supplement 17E–F), these genes were uniformly not detected at significant levels.