Several variables were not significant determinants of gut or lung Ace2 expression: genetic background (C57BL/6 versus Swiss-Webster mice); Ret (gene critical to enteric nervous system development); Apc (tumor suppressor commonly mutated in colorectal cancer; Fig 2D); gender; age (comparing 9-16-week-old SPF wild-type mice); or a high-fat diet (p>0.05, one-way ANOVA tests performed for each sample tissue type for each variable; specific comparisons denoted in S1 Table). This evidence concerns the gene RET and neoplasm.