Expression of canonical WNT/β-CATENIN signaling transcription factors in the developing human lung. ( A- D) Expression of canonical WNT signaling transcription factor TCF4 was detected in both the distal epithelium and the lung mesenchyme of human embryos at 7 W, 12 W, 17 W and 21 W (W: week of gestation). ( E- H) LEF1 staining of in situ hybridization showed a strong reactivity in the distal epithelium of the lung at 7 W, 12 W, 17 W and 21 W in human embryos. ( I- L) Sections with SOSTDC1 staining showed particular expression patterns in the distal lung epithelium of the embryos at 7 W, 12 W, 17 W and 21 W (W: week of gestation). ( M- P) Negative control for in situ hybridization in the developing human lung. Scale bars = 100 μm in A- P.