Lecture 21. Organogenesis Flashcards
What is neurulation ?
A special type of organogenesis, where it sets cells aside and forms the entire nervous system
Where does the nervous system arise from ?
The ectoderm
Where does the somites and the heart arise from ?
The mesoderm
Where does the lungs arise from ?
The endoderm
What is organogenesis ?
The interaction of cells within and across the germ layers to form organ systems
What is organogenesis characterised by ?
Local interactions superimposed on the information laid down with the basic body plan, to allow definition and development of an organ
What does organogenesis involve ?
The interaction and rearrangement of cells to produce tissues and organs
How does neurulation begin ?
As cells from the dorsal mesoderm form the notochord
What causes the ectoderm to form the neural plate ?
Signalling molecules secreted by the notochord and other tissues
What processes cause the formation of the neural plate ?
Induction using sonic the hedgehog
What happens as the neural folds and fuse ?
The adjacent surface ectoderm fuses to enclose the neural tube which becomes the brain and spinal cord
What happens after the neural tube forms ?
Neural crest cells migrate away from the dorsal aspect of the tube to peripheral locations where they give rise to the peripheral nervous system
What are neural crests cells formed by ?
Interactions between surface and neural ectoderm
How do neural crest cells form the peripheral nervous system ?
They migrate away from the dorsal midline as the neural folds fuse
What is the peripheral nervous system made up of ?
- The sensory system and motor system
2. Autonomic nervous system
What is neurulation ?
Signalling from the notochord, using Shh which also influences the type of neuron that differentiates along the dorso-ventral axis
What is neurogenesis ?
The formation of the central nervous system
What is the choice of forming a neuron or glial cell specified by ?
Delta notch signalling pathway
What does the activation of delta notch pathway equal ?
Differentiation of neuron
What does the hox code act as ?
Operated to provide positional information along the anterior posterior axis of the central nervous system
What are somites ?
Mesoderms cells that form into blocks on either side of the neural tube
What type of structures are somites ?
Transitionary structures that later form muscle blocks of the body and limbs and the vertebrate of the back bone
Where does regionalisation of the mesoderm germ layer occur ?
From the center midline:
- Notochord
- Somites
- Intermediate mesoderm - kidney, gonads
- Lateral plate mesoderm
What does the lateral plate mesoderm split into ?
Splits into two divided by a coelom cavity
What is the coelom ?
Cavity into which mesodermal organs can grow
What is the dorsal lateral plate layer ?
Somatic mesoderm (that underlies the ectoderm and with the ectoderm forms the somatopleure)
What is the ventral lateral plate layer ?
Splanchic mesoderm (That overlies the endoderm and with the endoderm forms the splanchnopleure
What must the flat chick and mammalian embryo do to enclose the gut and form the tube within a tube structure ?
Must fold ventrally
How is the lateral plate mesoderm split in two ?
Somatic becomes outer body and splanchic
What is an example of organogenesis in the mesoderm ?
The developing heart and circulatory system
What is the formation of the heart tube an example of ?
A process called mesenchyme to epithelial transition
What is mesenchyme ?
A type of tissue organisation typified by loosely connected cells often derived from mesoderm
What is an epithelium ?
A type of tissue organisation where cells adhere tightly together to form a sheet which can be single or multilayered
How are epithelia separated from underlying tissue ?
By basal lamine of extracellular matrix
What can epithelia be induced to form ?
Within the mesenchyme to give rise to tubes or tubules, sheets
What do heart tubes form from ?
Lateral plate mesoderm
What does the mesoderm that surrounds the heart tube form ?
The myocardium
What is the myocardium responsible for ?
Heart contraction
How does the heart form in mammals ?
- Linear tube
- Looping then occurs
- Septation to divide ventricles and formation of valves
What are the signaling molecules implicated in heart development ?
- BMPs
2. Wnts and noth
What does BMP signalling control the expression of ?
Nkx2,5
What is Nkx2.5
A transcriptional regulator needed for differentiation of cardiac muscle
What is the first working units in the developing embryo ?
The circulatory system
What develops concurrently with heart development ?
The circulatory network
How are circulatory loops formed ?
Blood vessels form independently from the heart and link up with the heart
What does a dual circulatory system connect ?
With the extra embryonic structure during development and another with the lungs after birth
What are the steps of the circulatory system building ?
- Mesenchymal to epithelial transition
2. Extensive branching morphogenesis
What do angioblasts assemble into ?
Main vessels
What is angiogenesis ?
Elaboration of the vascular system by vessel branching and extension
What is haematopoiesis ?
Blood cell formation
Where do blood cells first form ?
In blood islands within the lateral plate mesoderm at the yolk sac
Why are the formation of blood islands in the yolk sac are important ?
Blood cells formed here bring the first nutrients through the circulatory system
What are the two phases of blood production ?
- The embyronic phase
2. Definitive phase
What is the importance of the embryonic phase of blood development ?
It quickly supplies the embryo with blood so that circulation can be initiated
What is the definitive phase of blood production ?
More cell types being produced
Where does the blood production switch from at day 11 in the mouse ?
The yolk sac to the aorta-gonad mesonephros
What do definitive blood cells do ?
They are distinguishable from embryonic cells and populate the liver
What is the function of the liver ?
The major site of blood formation until birth
What do cells from the liver populate ?
The bone marrow
What does the bone marrow become ?
The site of blood cell production throughout life
What are pluripotent stem cells called ?
Haematopoetic stem cells
Where do haematopoetic stem cells reside and give rise to ?
They reside in the bone marrow and give rise to all different blood cell types
What do blood cells derive from ?
Mulitpotent haemopoietic stem cells
What do the multipotent haematopoietic stem cells give rise to ?
Two distinct multipotent progenitor cells called GATA+TF and Flt3
What does the cardiovascular system have ?
- A muscular pump - heart
- A set of interconnecting vessels - vasculature
- A circulatory fluid - blood
What is an example of an endodermal organ ?
Lung
What does the endoderm produce ?
The digestive tract and the respiratory tract
What do the lungs arise from ?
Budding outgrowths from the respiratory track
What is a general characteristic of endodermal organs ?
Inductive interactions between epithelial endoderms and surrounding mesenchyme
What is the predominate feature of lung formation ?
Branching
What is branching about by ?
The interaction between FGF and Shh signaling
Where is Fgf-10 expressed in and what can it induce?
- Chest mesenchyme
2. Branching in culture
Where is Shh expressed and what is its function ?
- Epithelium
2. Limits outgrowth and encourages branching
