Lecture 11: Ectoderm and Mesoderm Development Flashcards
What are the three major derivatives of ectoderm?
Surface ectoderm - forms skin
Neural crest - forms periphery of NS
Neural plate/neural tube - forms CNS
What are the three major derivatives of ectoderm?
What does surface ectoderm form?
skin
What does neural crest form?
periphery of NS
What does the neural plate form?
the central nervous system
How is specification accomplished in the ectoderm?
Regulating levels of BMP
The epidermis has ______ levels of BMP while the neural plate was _____ levels of BMP
High levels = epidermis
Low levels = neural plate
Ectoderm development - Neurulation
What does it consist of?
Primary and secondary neurulation
Ectoderm development - Neurulation
Towards the front end
Rostral
Ectoderm development - Neurulation
Towards the tail end
Caudal
Nervous System Development
Neural tube differentiation into various region of the brain and spinal cord occurs ______
simultaneously
Nervous System Development
Neural tube differentiation into various region of the brain and spinal cord occurs simultaneously.
What are the levels that occur at the same time?
Cellular level - neuroepithelial stem cells differentiate into numerous types of NEURONS and GLIA
Tissue level - cell populations within neural tube arrange themselves into diff functional regions
Gross anatomical level - neural tube and its lumen bulge and constrict to form brain and spinal cord vesicles
Nervous System Development
Early development of vertebrate brains is ______
similar
Nervous System Development
Early development of vertebrate brains is similar.
What happens?
Neural folds start closing at the dorsal-most region
This forms the neural tube
NS Development - A-P Axis
In the anterior region (rostral), what happens to the neural tube?
It begins to differentiate into distinctive brain regions
Forebrain, midbrain, hindbrain
In nervous system development and forming of the A-P axis, what the neural tube begins to differentiate into distinctive brain regions.
Where does this occur?
What are they and what are they all called?
At the anterior (rostral) region
Forebrain
Midbrain
Hindbrain
PRIMARY VESICLES
NS Development - A-P Axis
In the posterior region (caudal), what happens to the neural tube by the time this end closes?
Five SECONDARY VESICLES form
What are the 5 secondary vesicles? Where do they form?
They form at the caudal region (posterior)
Telencephalon Diencephalon Mesencephalon Metencephalon Myelencephalon
Adult brain structures are derived from _____.
secondary vesicles
Adult brain structures are derived from secondary vesicles.
Patterning results in the formation of ______
territories
cells within a territory express unique combinations of TFs
specific patterns of differentiation
The A-P patterning of the hindbrain and spinal cord is controlled by what?
Hox gene complexes
What is another name for the hindbrain?
rhombencephalon
True or False: Polarity is also established along the DV axis of the neural tube.
True
Early neural tube is made up of ________
progenitor neuroepithelial cells divided into discrete domains
depends on which TF are present
As progenitor domains differentiate further, they eventually give rise to what?
specific neuronal cell types
Morphogenetic signals from the notochord induce ________
and overlying epidermis induces _______
Morphogenetic signals from the notochord induce ventral pattern and overlying epidermis induces dorsal patterns
Nervous System Development of D-V Axis
Specification initiated by gradient of which two major paracrine factors?
Sonic hedgehog (Shh) from the notochord
TGF-beta from dorsal ectoderm
Overlap of _____ and _____ specifies motor neurons
Overlap of Pax6 and Nkx6.1 specifies motor neurons
Experiment: Place a second notochord next to the neural tube. What happens?
Development of second set of floor plate and motor neurons.
Overall, several signalling gradients determine the differentiation of cells along the AP and DV axis.
Opposing gradients of Retinoic Acid (RA) and Fgf/Wnt (among other signals determine the fate of bipotential
neuromesodermal progenitor (NMP) cells
The neurons are organized into different regions that arise from the three same basic zones.
What are these zones?
Ventricular zone
Intermediate zone
Marginal zone
The neurons are organized into different regions that arise from the three same basic zones.
What are the ventricular zone?
Layer next to the lumen of the neural tube.
It forms ependyma (epithelial lining of brain and spinal cord cavities)
What is the epithelial lining of brain and spinal cord cavities called?
ependyma
The neurons are organized into different regions that arise from the three same basic zones.
What is the intermediate zone?
aka mantle
cells differentiate into both neuronal and glial cells –> forms grey matter
What si the intermediate zone also known as?
The mantle
The neurons are organized into different regions that arise from the three same basic zones.
What is the marginal zone?
Neuronal cell-poor regions but enriched in axons
—> forms white matter
What forms white matter?
The marginal zone - regions that are poor in neuronal cells but rich in axons
What forms grey matter?
The intermediate zone - where cells differentiate into neuronal and glial cells
Why is the neural crest sometimes called the “fourth germ layer”?
It gives rise to many cell types
What are the 4 major steps of neural crest development?
- Specification at the border of the neural plate
- Localization at the neural fold apex
- Delamination at the point of neural tube closure
- Migration
Neural cell crest delamination and migration is dependent on:
Gradients of signalling molecules
Cytoskeletal remodelling
Differential expression of cell adhesion molecules
Positive and negative interactions between signalling molecules
Neural cell crest differentiation/commitment will depend on the factors that are present at a given time and location
Name the four kinds of cells.
These cells are committed and act as their respective progenitor cells
C = Cartilage/bones
G = Glia
N = Neurons
M = Melanocytes
What are the types of neural crest?
Cranial (Cephalic) Neural Crest
Cardiac Neural Crest
Trunk Neural Crest
Vagal and Sacral Neural Crest
What are the types of neural crest?
What does the Trunk Neural Crest form?
Cranial (Cephalic) Neural Crest
Cardiac Neural Crest
Trunk Neural Crest
Vagal and Sacral Neural Crest
Trunk Neural Crest
- Dorsal root ganglia
- Adrenal medulla
- Nerve clusters surrounding the aorta
- Melanocytes
What does the Cranial (Cephalic) Neural Crest form?
cranial nerves
bone
cartilage
connective face tissue
What does the Cardiac Neural Crest form?
septum that separates the pulmonary circulation from aorta
What does the Vagal and Sacral Neural Crest form?
parasympathetic NS of the gut and digestive system
Cranial neural crest cells migrate to produce
Various migratory pathways into the pharyngeal arches (p1-4) form a number of structures
cranio-facial structures
i.e.
cranial nerves
bone
cartilage
connective face tissue
Mesoderm Development
What are the four major derivatives of mesoderm?
Intermediate mesoderm - forms kidneys, gonads
Chordamesoderm - forms notochord
Paraxial mesoderm - forms head, somites
Lateral plate mesoderm - circulatory system, body cavity, limb bones, etc
What does the head and somites form from?
Paraxial mesoderm
What does the chordamesoderm form?
notochord
What do kidneys and gonads form from?
intermediate mesoderm
What does the lateral plate mesoderm form?
circulatory system, body cavity, limb bones etc.
What is the developmental process of forming somites from paraxial mesoderm called?
somitogenesis
Somitogenesis
Initial patterning is called ______ is via Hox genes (thought to work via chromatin remodeling)
presomitic mesoderm
Somitogenesis
Forms ____ to ____
Forms rostral (head) –> caudal (tail)
All skeletal muscles develop from somites (craniofacial muscles are an exception)
Form in all vertebrates but numbers vary between species
All skeletal muscles develop from somites.
What is the exception?
Craniofacial muscles
Somite formation requires
_________
Once the somite is formed, it is surrounded by the ________ cells.
mesenchyme-to-epithelial transition (MET)
What is the dorsolateral portion of the somites called?
What does it contain?
Dermomyotome
contains progenitor cells for skeletal muscle and dermis
What are the various ‘zones’ contain progenitor cells for a number of structures called?
What is its function?
Sclerotome
maintains segmental arrangement
The fate of somite cells depends on the signals received from
adjacent tissues
i.e. notochord induces sclerotome
Somite formation results from _______ along the embryonic axis resulting in cyclic gene expression.
Involves formation of gradients of a number of factors (e.g. FGF8, WNT3A which then induce other transcription factors)
What is this model called?
molecular oscillations (clock)
Clock and Wavefront Model
What is the developmental process of forming muscles called?
Myogenesis
What are the three major phases of myogenesis?
Commitment - muscle precurssor cells (myoblasts) become restricted to the myogenic pathway
Differentiation - transcription of skeletal muscle and fiber-specific genes
Maturation - final changes to form muscles fibres
Neural tube and notochord promote determination of myotome cells through
paracrine factors
i.e. Wnt, Shh which then induce the activation of muscle specific transcription factors such as MyoD, Myf5
Once growth factors are used up, myoblasts (mononucleated) exit the cell cycle, align together and fuse to form
myotube – multinucleated single large cell
Myoblast recognition and alignment occurs only with other myoblasts (e.g. chick and rat myoblasts fuse in vitro not species specific)
Fusion mediated by meltrins (metalloproteinases – proteases that require metal ions to function)
induces activation of myogenin – muscle specific regulatory factor that is necessary for differentiation
Myotubes mature and organize to form contracting muscle fibers
Myostatin (belongs to TGF-β family) negatively regulates muscle development —> loss-of-function mutation results in muscle hypertrophy (larger fibers) and hyperplasia (more fibers)
Myostatin inhibitors (e.g. Myo-X) are (ab)used in body-building
Loss of function of myostatin results in muscle hypertrophy (larger fibers) and hyperplasia (more fibers)
What is used in growth and generation of muscles in adults?
A population of stem cells/progenitor cells resides along the adult muscle fibers
there are called satellite cells
What is the first functional organ in the developing embryo?
Hint: It is critical to the circulatory system
The heart!
Heart development starts with the formation of _______ and _______
primary and secondary heart fields (aka cardiogenic mesoderm)
Heart development starts with
- formation of primary and secondary heart fields (aka cardiogenic mesoderm) at the cardiac crescent stage
- followed by formation of heart tube that then loops and partitions to form different chambers
Heart Cell Differentiation
Heart cell types differentiate from lateral plate mesoderm to form
multipotent cardiovascular progenitor cells
which further differentiate into specific cell types based on signals and receptors
