Fig. 2. Fgf10-positive mesenchymal cells give rise to parabronchial smooth muscle cells. (A-D) Timecourse of ß-galactosidase expression in the accessory lobe between E11.5 and 12.5, showing the progressive extension of LacZ expression from distal mesenchyme (asterisk) toward the epithelium (arrow). Note the patchy expression of ß-galactosidase around the secondary bronchi at E12.5 (D). (E) A saggital vibratome section through an E12.5 Fgf10^LacZ/+ accessory lobe showing almost continuous flow of ß-galactosidase expression in the distal mesenchyme (asterisk) and around the distal and proximal epithelium (arrows). Note that not all the cells around the epithelium of the secondary bronchi are positive for ß-galactosidase (red arrows). (E') A transversal section in secondary bronchus located in the most proximal part of E13.5^LacZ/+ accessory lobe show that ß-galactosidase expression is found in the mesenchyme all around the epithelium. (F) Saggital section of E13.5 Fgf10^LacZ/+ accessory lobe showing a continuous layer of ß-galactosidase-positive cells around the secondary bronchus. (G) Co-localization by immunofluorescence of ß-galactosidase (in green; note the nuclear signal) and -SMA (in red). (H) Whole-mount immunohistochemistry with anti-cytokeratin (in red) and anti-SMA (in green) antibodies on E12.5 lung. Note the presence of -SMA expression around the bronchi (small white arrows) and the absence of -SMA expression in the ventral part of the trachea (white arrow). (I) High magnification of the accessory lobe shown in H, demonstrating the absence of -SMA expression in the most distal part of the lung. Scale bars: 210 µm in A,B; 240 µm in C; 270 µm in D; 120 µm in E,F; 450 µm in H; 200 µm in I.