We isolated pEECs from the uteri of these mice and infected them with ecotropic MuLE lentiviruses expressing GFP to label infected cells, After 48 hours only a few Pax8-tdTomato-expressing cells were GFP-positive but the majority of GFP-expressing cells were Pax8-tdTomato-negative (Fig 2C, top half), demonstrating that infection of epithelial cells by MuLE viruses is rare. This evidence concerns the gene PAX8 and infection.