Mice, Inbred CFTRCystic Fibrosis Transmembrane Conductance RegulatorMice, Inbred C57BLChloridesMice, TransgenicAnimals, NewbornMice, KnockoutChloride ChannelsEpithelial CellsMutationAgingCells, CulturedMice, Inbred StrainsRNA, MessengerCell LineRespiratory MucosaCell DifferentiationGene Expression Regulation