The Evolution and Development of the Gut Dr Mike Wride School of Natural Sciences Zoology Department email: wridem@tcd.ie
The gut? Gut Function and Regulation (Dr. Alan Tuffery) Absorption of nutrients (the digestive system) Structure of the gut: Anatomy Embryological Origin Development Comparative anatomy/development
Topics to be covered in today s lecture Early Development - gastrulation (a reminder) Endoderm Gut development and genetics Gut nervous innervation: Hirschsprung s disease Gut evolution
Gut anatomy Wikipedia: http://en.wikibooks.org/wiki/ Anatomy_and_Physiology_of_Animals/The_Gut_and_Digestion
Gut ultrastructure: Small intestine Villi
Useful texts for gut structure, physiology and development Developmental Biology 8th Ed. Scott S Gilbert. Sinauer. Chapter 15 pages 493-499. Vertebrates, Comparative Anatomy, Function and Evolution. Kenneth V. Kardong. McGraw Hill 4th International Ed. Chapter 13, pages 496-535 Animal Physiology. Hill, Wyse, Anderson. 2nd Ed. Chapter 5, pages 111-142
Gastrulation: a reminder Gastrulation begins between days 14 and 16 of human development and at about E6.5 in the mouse Gastrulation results in formation of the 3 germ layers: mesoderm (e.g. muscle, bone, kidneys), endoderm (e.g. gut) and ectoderm (e.g. nervous system/epidermis)
Gastrulation cont... Figure 11.34. Gilbert Chapter 11, page 354 Endoderm forms gut is derived from endoderm
Endoderm 1: Induces several mesodermal tissues (notochord, heart, blood vessels, germ layer) II: Constructs linings of 2 tubes of vertebrate body plan: Digestive tube and respiratory tube i.e. both derived from primitive gut Buds from digestive tube form: liver, gallbladder, pancreas Region of digestive tube anterior to respiratory tube: called the pharynx
Formation of the Human Digestive System at (A) 16 days (B) 18 days
Formation of the Human Digestive System at (C) 22 days (D) 28 days
Development of the Pharynx
The digestive tube and its derivatives Regional specification of the gut endoderm and its derivatives Involves reciprocal interactions between endoderm and mesoderm does this ring a bell?
Regional specification of gut Digestive tube meets different kinds of mesenchyme (splanchnic lateral plate mesoderm) at different levels (rostral-caudal; head-tail) Digestive tube differentiates into different kinds of structures: oesophagus, stomach, small intestine, large intestine and colon There is an emerging consensus on the steps leading to regional specification of gut tube
The role of Barx1 in gut development Kim BM, Buchner G, Miletich I, Sharpe PT, Shivdasani RA. The stomach mesenchymal transcription factor Barx1 specifies gastric epithelial identity through inhibition of transient Wnt signaling. Dev Cell. 2005 Apr;8(4):611-22. -/- Barx1 knockout mouse
BMP signaling influences development of muscle types Theodosiou NA, Tabin CJ. Sox9 and Nkx2.5 determine the pyloric sphincter epithelium under the control of BMP signaling. Dev Biol. 2005 Mar 15;279(2):481-90.
Liver pancreas and gall bladder
Nervous innervation of the gut - Hirschsprung s disease Enteric nervous system (ENS): provides intrinsic innervation of the gastrointestinal tract Controls essential functions such as motility, secretion and blood flow Comprises a vast number of neurons and glial cells organized into complex networks of interconnected ganglia distributed throughout the entire length of the gut wall Hirschsprung s disease (congenital aganglionic megacolon): 1in 5000 babies - enlargement of colon caused by bowel obstruction resulting from an aganglionic section of bowel (the normal enteric nerves are absent)
Arrangement of the ENS Farlie et al Birth Defects Research (Part C) 72:173 189 (2004)
The Neural Crest Enteric neurons and glia - derived from neural crest cells (undergo extensive migration, proliferation, differentiation and survival to form a functional ENS).
Migration paths of neural crest cells to colonize the gut Farlie et al (2004)
Farlie et al (2004) Holschneider and Puri (2008)
Comparative Gut Anatomy/Evolution Symbiosis with heterotrophic microbes - provide metabolic capabilities that the animal lacks Include anaerobic bacteria, protists, yeasts, fungi carrying out fermentation Development of specialised enlarged/ dilated gut chambers during evolution
Foregut fermenters: ruminant mammals 1. fermentation - of non digestible compounds 2. Synthesis of B vitamins and essential amino acids 3. Recycling of waste nitrogen (urea) to make proteins
Hindgut fermenters Similar to foregut fermenters in terms of fermentation but vitamin synthesis and nitrogen recycling do not occur to the same extent
Variations in the stomach and intestines of lower vertebrates and birds
Variations in the stomach and intestines of mammals
Stomachs of Various Vertebrates
Summary of Today s Lecture Early Development - gastrulation (a reminder) Endoderm Gut development and genetics gut nervous innervation: Hirschsprung s disease Gut evolution