Loss of Nfib in mesenchyme affects type I and type II epithelial cell differentiation. E18.5 lung sections from Nfibflox/flox and Nfibflox/flox, D1-Cre embryos were stained for AQP5 (A, B), pro-SPC (C, D) and CC10 (E, F). AQP5, pro-SPC and Foxj1 transcript expression was also reduced in Nfibflox/flox, D1-Cre lungs, as shown by RT-QPCR (I). In contrast, immunostaining and RT-QPCR revealed CC 10 (Scgb1a1) protein and transcript levels were similar in Nfibflox/flox and Nfibflox/flox, D1-Cre lungs. Along with reduced Sftpc expression, Sftpa1, Sftpb and Sftpd expression was significantly reduced in Nfibflox/flox, D1-Cre lungs (H). *P<0.05; Scale bars, 50 µm.