Lung morphogenesis revisited: old facts, current ideas

Classical studies using epithelial-mesenchymal recombinants have identified basic rules of how tissue interactions regulate patterning of developing branching structures such as the lung. Nevertheless, only recently, molecular mediators of these interactions have been identified. Formation of bronchi or pre-alveolar structures seems to depend on the activity of distinct gene networks along the proximal-distal axis of the respiratory tract. Recent studies reveal that these networks and the mechanisms that they regulate can be conserved among species and comprise a variety of soluble and transcription factors also found in other developing organs. Here, current data and ideas about how these factors act regulating lung development will be reviewed.