ALI cultures derived from cystic fibrosis ferret tracheal airway basal cells demonstrated a lack of CFTR-mediated currents (Extended Data Fig. 7l) and a significant increase in pulmonary ionocytes as assessed by the expression of transcription factors FOXI1 and ASCL3 (Extended Data Fig. 7m,n). This evidence concerns the gene FOXI1 and cystic fibrosis.