developmental biology - university of minnesota...
TRANSCRIPT
Lateral Plate Mesoderm and Endoderm
July 30, 2008
Developmental Biology
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
Endoderm
Digestive system
Pharyngeal pouches
Liver, lung, etc.
Extraembryonic membranes
Heart
Blood vessel
Vasculogenesis
Angiogenesis
Blood cells
Cardiovascular development
Coelomic cavity formation
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 Endocardial primordia
Neural tube
Foregut
Pericardial cavity
Endocardial tube
Endocardium
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 day 28 newborn
RA
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
Constraints:
Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain 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
2. Evolutionary – e.g. aortic arches
Constraints:
Vertebrate model (e.g. human – 29 days)
Primitive fish
Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain constraints.
Human Aortic Arches
Mammals and birds convert 6 pairs of aortic arches into single aortic arch
Blood Vessel Formation
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
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
Every individual’s circulatory system is unique (genetic pattern?); however, each develops in a similar way because of certain constraints.
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
Angiogenesis
hemangioblasts Vasculogenesis
Splanchnic mesoderm
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:
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
~10 11 RBCs are replaced daily
Pluripotential hematopoietic stem cells (HSC) are capable of generating all blood and lymph cells
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
Endoderm
Digestive system
Pharyngeal pouches
Liver, lung, etc.
Extraembryonic membranes
Heart
Blood vessel
Vasculogenesis
Angiogenesis
Blood cells
Cardiovascular development
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
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
desiccation → amnion gas exchange → chorion waste disposal → allantois nutrition → yolk sac
Problem → Solution
Splanchnopleure
Somatopleure
desiccation → amnion gas exchange → chorion waste disposal → allantois nutrition → yolk sac
Problem → Solution
Somatopleure forms: Amnion Chorion
Splanchnopleure forms: Allantois Yolk sac
Chick / Placental Mammals
Allantois – forms portion of the umbilicus vascularizes umbilicus forms urachus – empties fetal bladder