Building functional internal organs from a naïve endodermal sheet

Abstract

The organs perform physiological functions with mature tissues composed of variously specialized cell types. Full maturation and proper population balances of these cell types are necessary to generate functional organs and a healthy body. Most of the internal organs are derived from the definitive endoderm (DE), which is a naïve epithelial sheet formed at an early embryonic stage, E7.5, in the mouse. Especially, the anterior pocket of the DE is the foregut known as the origin of functional epithelial cells of many vital internal organs, including the thyroid, thymus, lung, liver and pancreas. I start this review with describing the foregut formation process in the DE and spatial arrangement of the internal organs within this area. Then, I highlight developmental and physiological mechanisms that specify, pattern, and regulate morphogenesis of the lung. Recent advances have begun to define molecular mechanisms that control many of the important processes required for lung organogenesis; however, many questions remain. I, furthermore, focus on airway epithelial development, which generates the bronchial branching structure and many different functional cells. Finally, I discuss a fundamental strategy for regulating the population and localization of various cell types during organogenesis.