|Ph.D Student||Goltzman Sivan|
|Subject||Morphogenesis and Differentiation of the Ventral Gut|
|Department||Department of Medicine||Supervisor||Professor Thomas Schultheiss|
In amniote embryos, the prospective gut starts out as a flat sheet of endodermal cells, which subsequently folds into a tube. The first stage in the morphogenetic formation of the gut tube is the appearance of the anterior intestinal portal (AIP) on the ventral side of the embryo. Subsequently, anterior and lateral regions of the endoderm fold medially-ventrally and move posteriorly in a wave-like movement. The two folding sides meet in the ventral gut midline and merge to form a closed gut tube. Fate mapping studies have found that the ventral gut is comprised of cells from two sources: lateral endoderm that folds medially, and anterior AIP endoderm that migrates posteriorly.
The ventral gut midline is the location of several gut-derived organs, including the thyroid, lungs, liver, ventral pancreas, and common bile duct. These organs develop in the ventral midline at particular locations along the anterior-posterior axis. These organs develop through a complex morphogenetic process that is not well understood. This process involves the folding of lateral endodermal and mesodermal regions towards the midline and the integration of the organ primordia from the two lateral sides into a unified organ which is connected to the gut. The goal of this thesis research was to understand the morphogenesis of the ventral midline structures of the gut tube and its associated gut-derived organs. In addition, I aimed to understand whether cells in the ventral gut midline play a role in directing the morphogenesis or the differentiation of the ventral gut-derived organs, or of the morphogenesis of the gut tube itself.
Using a fluorescent dye fate mapping approach, I traced the formation of the ventral gut midline from the flat embryo stage. I found that the Prechordal Plate (PrCP), a population of cells, that migrates from the dorsal to ventral side of the forming gut tube, always comprised, at least in part, the ventral gut midline since the PrCP is known to play an organizer role in other embryonic regions, this raised the question of whether the gut midline cells play a role in directing the development of gutderived organs. Microsurgical approaches to remove the gut midline cells prevented closure of the gut tube, but did not prevent initial differentiation of the gut-derived organs, which remained on the lateral side of the flat embryo. This result revealed a crucial role for the gut midline cells in gut morphogenesis but not in the initial stages of differentiation of the organs.
In additional experiments I used fluorescent dye and electroporation-based approaches to trace movements of endodermal cells during closure of the gut tube. These studied provided new insights into the complex movements of endodermal cells towards the AIP and within the closed gut tube. These data, together previously published studies, were used to build a revised model of the morphogenesis of the gut tube and the incorporation of the precursors of the gut-derived organs into the ventral wall of the foregut.