Download 15. Lateral Plate Mesoderm and Endoderm

Developmental Biology
Lateral Plate Mesoderm and Endoderm July 30, 2008 Major Mesoderm Lineages
Lateral Plate Mesoderm
Lateral Plate Mesoderm/Coelom
Lateral Plate Mesoderm ­ Coelomic Cavities Lateral plate layers Somatic – associates with ectoderm ­ contributes to connective tissue of body wall & limbs Visceral – associates with endoderm Lateral plate derivatives surround coelomic cavities ­ pleural ­ pericardial ­ peritoneal
Coelomic Cavity Formation ­ mesentery – peritoneal membrane lining abdominal cavity ­ dorsal mesentery attaches gut to body wall ­ pericardial cavity closes off in ventral anterior coelom
Coelomic Cavity Formation ­ pleuropericardial folds displaced by growing lungs ­ pericardium forms as separate sac
Lateral Plate Mesoderm and Endoderm ­ Overview Coelomic cavity formation
Cardiovascular development Heart Blood vessel Vasculogenesis Angiogenesis Blood cells Endoderm Digestive system Pharyngeal pouches Liver, lung, etc. Extraembryonic membranes Heart Forming Cells Cardiogenic mesoderm ­ early through primitive streak ­ induced by endoderm signals – BMPs ­ inhibited by notochord – Noggin, chordin ­ inhibited by neural tube – Wnts ­ Wnts promote blood vessel formation (hemangiogenic mesoderm) ­ cells migrate towards midline
Cardiogenic Mesoderm Endocardium – forms endothelial lining; ­ cushion cells – form valves Atrial and ventricular myocytes – heart muscle
Formation of the Chick Heart Somatopleure Splanchnopleure Neural tube Foregut Endocardium
Endocardial tube Pericardial cavity Endocardial primordia Cardiac Looping / Chamber Formation Looping converts anterior­posterior polarity into right­left polarity Looping is dependent on L­R patterning proteins; e.g. Nodal After looping, differential expression in L and R chambers Human day 21 RA
day 28 newborn Blood Vessel Formation Blood vessels form independently from the heart ­ link with the heart soon after formation ­ heart primordia starts beating after first circulatory loop is established
Blood Vessel Formation Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain constraints. Constraints: 1. Physiological – embryos need to function as they develop: ­ food absorption from yolk or placenta ­ oxygen and waste exchange from chorionic or allantoic membranes
Blood Vessel Formation Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain constraints.
Constraints: 2. Evolutionary – e.g. aortic arches Vertebrate model (e.g. human – 29 days) Primitive fish Human Aortic Arches Mammals and birds convert 6 pairs of aortic arches into single aortic arch
Blood Vessel Formation Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain constraints.
Constraints: 1. Physiological – embryos need to function as they develop ­ food absorption from yolk or placenta ­ oxygen and waste exchange from chorionic or allantoic membranes 2. Evolutionary – e.g. aortic arches 3. Physical – laws of fluid movement and diffusion constrain the size and number of vessels ­ most effective fluid transport in large tubes ­ however, diffusion of nutrients and gases can take place only through small tube and at slow flow Blood Vessel Formation Vasculogenesis – first process: capillary network formed from lateral plate mesoderm Angiogenesis – second process: primary capillary networks are remodeled; veins and arteries made
Vasculogenesis and Angiogenesis Splanchnic mesoderm
Vasculogenesis hemangioblasts Angiogenesis Model for Blood Vessel Formation VEGF* gradient (green) from mesenchyme near blood islands induces endothelial cells to form arteries (red) ­ arteries induce veins (blue) *VEGF – vascular endothelial growth factor
Arterial and Venous Differentiation Angiogenesis How to make sure veins attach just to arteries, and vice versa? Artery precursor endothelial cells contain ephrin­B Vein precursors contain ephrin receptor Ephb4 tyrosine kinase
Blood Cell Development Stem cells: ~10 11 RBCs are replaced daily Pluripotential hematopoietic stem cells (HSC) are capable of generating all blood and lymph cells HSCs generate a series of intermediate stem cells with potencies restricted to certain lineages Embryonic hematopoiesis takes place in the blood islands; ­ mostly RBC production Definitive hematopoietic cells derived from splanchnic lateral mesoderm surrounding the aorta ­ later move to the fetal liver; later to the bone marrow
Blood Stem Cells
Lateral Plate Mesoderm and Endoderm ­ Overview Mesoderm lineages Cardiovascular development
Heart Blood vessel Vasculogenesis Angiogenesis Blood cells Endoderm Digestive system Pharyngeal pouches Liver, lung, etc. Extraembryonic membranes Endoderm Endoderm has two functions: 1. Instructions for the formation of notochord, heart, blood vessels, mesoderm 2. Construction of linings of the digestive tube (including liver, gall bladder, and pancreas), and respiratory tube ­ both the respiratory and digestive tubes are products of the primitive gut
Human Digestive System
Human Digestive System
Pharyngeal Pouches – Glandular Primorida
Pharyngeal Pouches
Regional Specification of the Gut ­ specified by regionally specific mesenchymal mesoderm ­ endoderm specified early; possibly before tube formation transcription factors
Liver, Pancreas, Gall Bladder
The Respiratory Tube Lungs are derived from the digestive tube ­ laryngeotracheal groove occurs in the center of the pharyngeal floor (between 4 th pharyngeal pouch pair)
Lung Maturation ­ Surfactant Lungs fully differentiate late in development; ­ alveolar (air sac) cells secrete a surfactant; allows cells to slide against one another ­ secreted late in gestation; ~ wk 34 (human)
Lung Maturation ­ Surfactant Lungs fully differentiate late in development; ­ alveolar (air sac) cells secrete a surfactant; allows cells to slide against one another ­ secreted late in gestation; ~ wk 34 (human) ­ birth may be triggered by maternal immune response to surfactant
Extraembryonic Membranes Reptiles, birds, and mammals are amniotes ­ eggs are adapted to develop on dry land ­ adaptations use combinations of ectoderm, endoderm, &mesoderm to solve specific problems of land eggs Somatopleure
Splanchnopleure Problem → Solution desiccation → amnion gas exchange → chorion waste disposal → allantois nutrition → yolk sac Somatopleure forms: Amnion Chorion Splanchnopleure forms: Allantois Yolk sac
Problem → Solution desiccation → amnion gas exchange → chorion waste disposal → allantois nutrition → yolk sac Chick / Placental Mammals Allantois – forms portion of the umbilicus ­ vascularizes umbilicus ­ forms urachus – empties fetal bladder