Proper development of embryonic foregut derivatives is essential for mammalian survival at birth. The rostral endodermal foregut tube divides into ventral respiratory (larynx and trachea) and dorsal alimentary (esophagus and stomach) components. Remarkably little is known about the underlying mechanisms, despite their pragmatic importance. For example, defects in foregut compartmentalization result in common birth defects involving abnormal communications between these systems, known clinically as tracheoesophageal fistulas (TEF) and laryngo-esophageal clefts. Sonic hedgehog (Shh) is essential for generation of distinct laryngeal/tracheal and esophageal tubes, as the Shh-null mouse foregut is uncompartmentalized. Our preliminary data indicate that later Shh expression in the developing trachea and esophagus is critical for the stratification of foregut epithelia and development of specialized foregut mesoderm. Our overall hypothesis is that shh signaling acts as a master regulator of foregut development, initially to control tissue remodeling essential for formation of esophagus, trachea and larynx from a common precursor, and subsequently to pattern the endodermal and mesodermal tissues of these nascent organs. We propose a series of tissue-specific and temporal genetic manipulations of Shh expression and reception in the mouse embryo, coupled with histological and molecular analyses, to investigate the roles of Shh signaling in foregut development.
Aim 1 determines the role of Shh signaling in normal separation of trachea from esophagus, the morphogenic process by which this occurs, and how the disruption of Shh signaling results in TEF.
Aim 2 in turn addresses the separation of larynx from esophagus, with special attention to the role of neural crest-derived laryngeal cartilages in this process.
Aim 3 elucidates the role of Shh in the different patterns of stratification and differentiation within the endoderm.
In Aim 4, we determine the spatiotemporal functions of Shh signaling in differentiation of specialized foregut mesoderm, including the tracheal cartilage rings, trachealis smooth muscle, and esophageal smooth muscle. Altogether, these studies will provide important insight into the roles of Shh signaling in normal development and congenital defects of the trachea, esophagus, and larynx.
Proper development of embryonic foregut derivatives is essential for mammalian survival at birth. The rostral endodermal foregut tube divides into ventral respiratory (larynx and trachea) and dorsal alimentary (esophagus and stomach) components. These must then develop into functional organs. Little is known about the underlying mechanisms, despite their pragmatic importance. This proposal is for a research project to dissect the roles of the Sonic hedgehog intercellular signaling pathway in mouse foregut development. We elucidate critical roles in the initial compartmentalization of the common foregut tube, and in the organ-specific differentiation of endoderm and mesoderm. Our results are of direct relevance to the mechanisms of human foregut birth defects and potentially to the pathogenesis of esophageal cancer.