Fig. 1. Immunohistochemical analysis of KLF5 in the developing mouse lung. (A) At E12.5, during the early pseudoglandular stage of development, KLF5 was detected in nuclei of epithelial cells in the proximal bronchial tubules (arrow). Staining was generally more intense along medial aspects of the tubules. ES, esophagus. Arrowhead indicates peripheral epithelial cells. (B) At E15.5, KLF5 was detected at highest levels in bronchiolar tubules (arrow); however, staining of subsets of cells lining the peripheral lung buds (arrowhead) was also noted. (C) At E18.5, KLF5 was present in both peripheral (arrowhead) and proximal (arrow) airways. (D) In mature lung, KLF5 was detected in nuclei of subsets of epithelial cells in both conducting airways (arrow) and alveolar regions (arrowhead). Insets are higher magnifications of the corresponding figures. (E-G) Dual immunolabeling for KLF5 (green nuclei) and (E) proSPC (red cytoplasm), (F) CCSP (red cytoplasm), and (G) FOXJ1 (red nuclei) was performed on E18.5 lung sections. KLF5 staining was observed in proSPC-positive (large arrow) and -negative (small arrow) cells (E), in CCSP-positive cells (large arrow, F), and in FOXJ1-negative cells (small arrow, G). Yellow signal is due to the autofluoresence of red blood cells, detectable in both channels. Scale bars: 100 µm.