Fig. 1. Mlc1v-nLacZ-24^+/– expression recapitulates Fgf10 expression. (A) Fgf10 expression by whole-mount in-situ hybridization in E10.5 wild-type control lungs. Note the expression in the right distal lung mesenchyme (black arrows), the thyroid and the developing stomach. (B) X-gal-stained E10.5 Mlc1v-nLacZ-24^+/– lungs recapitulate the Fgf10 expression pattern at this stage in the distal lung mesenchyme (black arrow) and the thyroid. (C) Fgf10 expression by whole-mount in-situ hybridization in E11.5 wild-type control lungs. Note the expression in the left distal lung mesenchyme (white dotted box). (D) X-gal staining of E11.5 Mlc1v-nLacZ-24^+/– lungs recapitulates the Fgf10 expression pattern at this stage, except in the left lobe (white dotted box). (E) Fgf10 expression by whole-mount in-situ hybridization in E12.5 wild-type control lungs. Note the expression in the distal lung mesenchyme (black arrows). The area in the dotted box is magnified in (F). (G) LacZ expression at RNA level in Mlc1v-nLacZ-24^+/– lungs. (H) LacZ is expressed at the tip of the accessory lobe recapitulating the Fgf10 pattern (dotted box in G). Notice the absence of Fgf10 expression close to the epithelium (small double white arrow) (I) ß-galactosidase activity shown by X-gal staining is found in the distal mesenchyme (white arrow) and at the level of the bronchi of Mlc1v-nLacZ-24^+/– lungs (small white arrows). Note that X-gal staining is now present in the mesenchyme of the left lobe. Note also that ß-galactosidase-positive cells are not detected in the primary bronchi (black arrows). (J) High magnification of the accessory lobe (dotted box in I). (K) Fgf10 expression at RNA level by whole-mount in-situ hybridization in E14.5 wild-type control lungs. Note the expression in the mesenchyme at the periphery of the lobes. (L) X-gal staining of E14.5 Mlc1v-nLacZ-24^+/– lungs showing LacZ expression at the periphery of the lobes similar to the Fgf10 expression pattern. Note ß-gal expression at the level of the bronchi (black arrow). (M) High magnification of the surface of the cranial lobe shown in L. (N-Q) Control E11.5 Mlc1v-nLacZ-24^+/– lung grown in absence of cyclopamine. (O) After 28 hours in culture new branches are formed. Note that the distal epithelium is not dilated (arrow). (P) X-gal staining of the cultured lung shown in O. ß-gal expression is found in the distal mesenchyme. (Q) Vibratome section through the left lobe shown by the arrow in P. Note the low level of ß-gal expression. (R-U) E11.5 Mlc1v-nLacZ-24^+/– lung grown in presence of 5 µmol/l of cyclopamine. (S) After 28 hours of culture the lung exhibits dilated end buds (arrow). (T) X-gal staining of the cultured lung shown in S. Note the increase in ß-gal expression throughout the lung in comparison with the lung grown in the absence of cyclopamine shown in P. (U) Vibratome section through the left lobe of the lung shown by the arrow in T. Note the marked increase in LacZ expression compared with the untreated lung (Q). Scale bar: 110 µm in A,B; 180 µm in C,D; 210 µm in E,G,I; 105 µm in F,H,J; 435 µm in K,L; 80 µm in M; 175 µm in J; 250 µm in N,O; 300 µm in O,S; 190 µm in P,T; 50 µm in Q,U. acc, accessory lobe; br, bronchus; cont, control; cran, cranial lobe; st, stomach; th, thyroid; tr, trachea.