The lungs are divided, both structurally and functionally, into two distinct components, the
proximal airways, which conduct air, and the peripheral airways, which mediate gas
exchange. The mechanisms that control the specification of these two structures during lung
development are currently unknown. Here we show that β-catenin signaling is required for
the formation of the distal, but not the proximal, airways. When the gene for β-catenin was
conditionally excised in epithelial cells of the developing mouse lung prior to embryonic day …