TMPRSS2 and infection: In this study, we cloned the ACE2 gene of tree shrews, carried out bioinformatics analysis, detected the expression of ACE2, TMPRSS2 and TMPRSS4 in various tissues of tree shrews to assess the risk of tree shrew infections with SARS-CoV-2, and established ACE2-, TMPRSS2- and TMPRSS4-related disease models in tree shrews.