Talk:Gastrointestinal Tract Development

Neural History

• 1857 Meissner was the first to describe a nerve plexus in the submucosa of the bowel wall.
• 1864 Auerbach described the myenteric plexus between the longitudinal and circular muscle layers.
• 1981 LeDouarin describes neural crest contribution to both plexuses.

+ Extrinsic parasympathetic cholinergic nerves (vagal and sacral) excite peristalsis and stimulate - Sympathetic noradrenergic nerves inhibit the transit of gut contents

Self Assessment Questions

1. What is a pharyngeal arch and pouch? List the muscle, arch cartilage and nerves of each arch. List the derivatives of each pharyngeal pouch.
2. Describe the main steps in the development of the tongue.
3. What are the derivatives of the fore-, mid- and hind-gut?
4. What is the buccopharyngeal membrane?
5. How does the thyroid gland develop?
6. Describe the normal development of the face and palate. List the major malformations of this region and their possible causes.
7. How is the liver developed?
8. What are the main processes involved in the elongation and rotation of the stomach and intestinal region?
9. Describe the development of the pancreas.
10. How does the myenteric plexus develop?
11. List the basic principles in the development of the peritoneum.
12. What are the functions of the liver and pancreas in the fetus? Does the gastro-intestinal tract function in the fetus?
13. What are the consequences of malrotation of the gut?

The serosal mesothelium is a major source of smooth muscle cells of the gut vasculature.

Wilm B, Ipenberg A, Hastie ND, Burch JB, Bader DM.

Most internal organs are situated in a coelomic cavity and are covered by a mesothelium. During heart development, epicardial cells (a mesothelium) move to and over the heart, undergo epithelial-mesenchymal transition (EMT), and subsequently differentiate into endothelial and vascular smooth muscle cells. This is thought to be a unique process in blood vessel formation. Still, structural and developmental similarities between the heart and gut led us to test the hypothesis that a conserved or related mechanism may regulate blood vessel development to the gut, which, similar to the heart, is housed in a coelomic cavity. By using a combination of molecular genetics, vital dye fate mapping, organ culture and immunohistochemistry, we demonstrate that the serosal mesothelium is the major source of vasculogenic cells in developing mouse gut. Our studies show that the gut is initially devoid of a mesothelium but that serosal mesothelial cells expressing the Wilm's tumor protein (Wt1) move to and over the gut. Subsequently, a subset of these cells undergoes EMT and migrates throughout the gut. Using Wt1-Cre genetic lineage marking of serosal cells and their progeny, we demonstrate that these cells differentiate to smooth muscle of all major blood vessels in the mesenteries and gut. Our data reveal a conserved mechanism in blood vessel formation to coelomic organs, and have major implications for our understanding of vertebrate organogenesis and vascular deficiencies of the gut.

PMID: 16284122

Pancreas cell fate.

http://www.ncbi.nlm.nih.gov/pubmed/19750517

"Diabetes is characterized by decreased function of insulin-producing beta cells and insufficient insulin output resulting from an absolute (Type 1) or relative (Type 2) inadequate functional beta cell mass. Both forms of the disease would greatly benefit from treatment strategies that could enhance beta cell regeneration and/or function. Successful and reliable methods of generating beta cells or whole islets from progenitor cells in vivo or in vitro could lead to restoration of beta cell mass in individuals with Type 1 diabetes and enhanced beta cell compensation in Type 2 patients. A thorough understanding of the normal developmental processes that occur during pancreatic organogenesis, for example, transcription factors, cell signaling molecules, and cell-cell interactions that regulate endocrine differentiation from the embryonic pancreatic epithelium, is required in order to successfully reach these goals. This review summarizes our current understanding of pancreas development, with particular emphasis on factors intrinsic or extrinsic to the pancreatic epithelium that are involved in regulating the development and differentiation of the various pancreatic cell types. We also discuss the recent progress in generating insulin-producing cells from progenitor sources."