Molecular regulation of lung development

There is increasing evidence suggesting that formation of the tracheobronch ial tree and alveoli results from heterogeneity of the epithelial-mesenchym al interactions along the developing respiratory tract. Recent genetic data support this idea and show that this heterogeneity is likely the result of activation of distinct networks of signaling molecules along the proximal- distal axis. Among these signals, fibroblast growth factors, retinoids, Son ic hedgehog, and transforming growth factors appear to play prominent roles . We discuss how these and other pattern regulators may be involved in init iation, branching, and differentiation of the respiratory system.