Alveologenesis occurs during postnatal development in humans and mice and this process allows for the growth of gas exchange surface area of the lung. One of the key events during this phase is the establishment of the elastin-based matrix in the distal airway. Hox5 genes (Hoxa5, Hoxb5, Hoxc5) are exclusively expressed in the lung mesenchyme during embryogenesis and severe phenotypes result from constitutive loss-of-function of all three genes. Our lab is trying to understand how Hox5 genes regulate lung fibroblasts and distal lung extracellular matrix formation during lung development, maintenance and regeneration.