FIGURE 7.

Stages of branching morphogenesis. Left panel shows a posterior view of the mouse lung (red) and the esophagus (blue) at E10. Images of embryonic and postnatal mouse lung from E14 to the alveolar period on postnatal day 14 are shown in A–D. Major stages of lung morphogenesis are shared in the human and mouse. In A–D, lung epithelial cells (thyroid transcription factor-1, TTF-1) are shown in green, endothelial cells in red (endomucin), and smooth muscle myofibroblasts in purple (α-smooth muscle actin, SMA). Lung morphogenesis proceeds from a solid branched organ to the open alveolar structures after birth. Major conducting airways are formed by branching morphogenesis from the embryonic to canalicular period of fetal development. Sacculation and alveolarization are completed in the perinatal and postnatal period, creating the gas exchange region. Insets show higher magnifications. (Left image courtesy of Dr. Aaron Zorn, used with permission.)