CFTR and cystic fibrosis: Like ionocytes in mouse airways and human LAE [12, 13], the human SAE ionocytes highly expressed the transcription factors FOXI1 and ASCL3, V-ATPase-subunit genes (ATP6V1G3, ATP6V0B), and the Cl− ion channel CFTR, that when mutated, causes cystic fibrosis (CF).