Mesoderm and dorsalization

What type of mesoderm does the notochord consist of?

Axial mesoderm

After the axial mesoderm, what is the next innermost layer of mesoderm?

Paraxial mesoderm

What is the 3rd innermost layer of mesoderm?

Intermediate mesoderm

WHat is the outermost layer of mesoderm?

Lateral plate mesoderm

What two layers does the lateral plate mesoderm consist of?

Splanchnic (ventral) and somatic (dorsal)

What is the prochordal plate?

A thickened region of the hypoblast, indicating which will be the anterior end of the embryo

Define delamination

Seperation into constituent layers

Mesoderm cells ingressing through the node form what type of mesoderm?

Axial mesoderm

Mesoderm cells ingressing through the primitive streak form which type(s) of mesoderm?

Paraxial, intermediate and lateral plate

In humans, what is most of the notochord replaced by?

Axial skeleton (vertebrae and ribs)

In humans, where is a small amount of the notochord retained?

The nucleus pulposus of the intervertebral disks

What model is used to explain somite formation?

Clock and wavefront model

A gradient of which two signalling molecules is involved in the clock and wavefront model?

FGF and WNT

What does FGF stand for?

Fibroblast growth factor

Expression of which gene is involved in the clock and wavefront model?

Hes1

What is an isoform?

A protein variant

Are the first somites formed at the anterior or posterior end?

Anterior (head) end

In the clock and wavefront model, is there a higher concentration of signalling factors at the anterior or posterior end?

Posterior

By which process do somitocoel cells at the centre of each somite become sclerotome?

Epithelial to mesenchymal transition (EMT)

Somite cells closest to the notochord form a migratory population called the sclerotome. What do the remaining cells become?

Dermomyotome, from which they may become dermatome (which forms connective tissue in the skin) and myotome (which forms muscles)

What fate is induced in somite cells by SHH only?

Sclerotome

What fate is induced in somite cells by WNT only?

Dermatome

What fate is induced in somite cells by SHH and WNT?

Epaxial myotome

What fate is induced in somite cells by SHH and BMP?

Hypaxial myotome

From where is SHH secreted?

Notochord and floor plate

From where is WNT secreted?

Roof plate and epidermis

From where is BMP secreted?

Ventral / lateral portion

What does somatopleuric (associated with epidermis) lateral plate mesoderm form in the adult?

Limb bones, connective tissue of limbs and body wall

What does splanchnopleuric (associated with endoderm) lateral plate mesoderm form in the adult?

Connective tissue and smooth muscle layers of gut/ heart/ circulatory system

Which cavities are formed by the coelom inside the embryo?

Pericardial, pleural and peritoneal (surrounding heart, lungs, and viscera respectively)

What does intermediate mesoderm form in the adult?

The kidneys and parts of the male and female reproductive system

What does the signalling protein nodal initiate formation of?

The primitive streak

Which three morphogens does nodal induce?

Chordin, noggin and follistatin

Which morphogen do chordin, noggin and follistatin bind to and inhibit?

BMP

Cells closest to the node have the most [dorsal or ventral?] fates. Why?

Dorsal, because they are receiving the lowest concentration of BMP.

What is the Kartagener triad?

Infertility, frequent respitory infections, situs inversus

Movement of cilia on cells in the node causes different gene expression along which axis?

Left-right

In Nieuwkoop’s experiment, what happened when prospective epidermis is cultured on its own?

Forms only epidermis

In Nieuwkoop’s experiment, what happened when endoderm is cultured on its own?

Forms only endoderm

In Nieuwkoop’s experiment, what happened when prospective epidermis and endoderm are cultured together?

There is formation of mesoderm, showing that mesoderm is formed by the prospective epidermis but relies on a signal from the endoderm.

How many pairs of somites are produced in a human embryo?

42-44

How many pairs of somites persist in human embryogenesis?

37-38 because the most caudal somites (those of the tail) are destroyed

How many pairs of cervical somites are initially formed in a human embryo?

8 pairs (contributing to 7 cervical vertebrae)

The ventral medial wall of each somite breaks down to form a loose mesenchymal population. What name is given to this population of cells?

Sclerotome

Which myotomes form the skeletal muscle of the tongue?

Occipital myotomes

Which signalling molecule induces the sclerotome region of somites?

SHH