GLI2 and Tracheomalacia: Similarly, Gli2−/−;Gli3+/− germline mouse mutants, with one copy of Gli3R but no Gli2A, displayed tracheomalacia, whereas Gli2+/−;Gli3−/− mice, which lack Gli3R, do not (Litingtung et al., 1998; Miller et al., 2004; Nasr et al., 2019; Park et al., 2010).