Fig. 1.

Experimental protocol for doxycycline treatment and lung sample collection. In order to induce precocious expression of FGF18, advanced as compared with endogenous peak, transgenic SP-C-rtTA- and (teto)₇-FGF18-mice were bred, and their progeny (gathering both single and double transgenic individuals, and rarely wild type individuals) was treated by the inducer doxycycline. Pregnant mice received first doxycycline in drinking water (0.5mg/ml) for the 2 last prenatal days. Doxycycline was removed from drinking water on the day of birth (designated postnatal day 0 or P0), and pups received then one daily subcutaneous injection of doxycycline aqueous solution 3 mg/ml (20 mg/kg bw) on P0, P1 and P2. Their lungs were collected on P3 and kept at −80°C until RNA extraction for gene-expression analyses, or on P4, P8 or P16 for lung fixation and morphological/morphometric analyses. Post-hoc genotyping of the pups was performed on DNA extracted from tail fragment.