Lecture 11: Ectoderm and Mesoderm Development Flashcards by Rachel Chin

What are the three major derivatives of ectoderm?

Surface ectoderm - forms skin

Neural crest - forms periphery of NS

Neural plate/neural tube - forms CNS

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What are the three major derivatives of ectoderm?

What does surface ectoderm form?

skin

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What does neural crest form?

periphery of NS

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What does the neural plate form?

the central nervous system

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How is specification accomplished in the ectoderm?

Regulating levels of BMP

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The epidermis has ______ levels of BMP while the neural plate was _____ levels of BMP

High levels = epidermis

Low levels = neural plate

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Ectoderm development - Neurulation

What does it consist of?

Primary and secondary neurulation

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Ectoderm development - Neurulation

Towards the front end

Rostral

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Ectoderm development - Neurulation

Towards the tail end

Caudal

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Nervous System Development

Neural tube differentiation into various region of the brain and spinal cord occurs ______

simultaneously

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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

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Nervous System Development

Early development of vertebrate brains is ______

similar

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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

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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

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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

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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

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What are the 5 secondary vesicles? Where do they form?

They form at the caudal region (posterior)

Telencephalon
Diencephalon
Mesencephalon
Metencephalon
Myelencephalon

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Adult brain structures are derived from _____.

secondary vesicles

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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

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The A-P patterning of the hindbrain and spinal cord is controlled by what?

Hox gene complexes

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What is another name for the hindbrain?

rhombencephalon

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True or False: Polarity is also established along the DV axis of the neural tube.

True

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Early neural tube is made up of ________

progenitor neuroepithelial cells divided into discrete domains

depends on which TF are present

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As progenitor domains differentiate further, they eventually give rise to what?

specific neuronal cell types

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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?

1. Specification at the border of the neural plate 2. Localization at the neural fold apex 3. Delamination at the point of neural tube closure 4. 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