Development week 3&4

Question 1

What is gastrulation?

Answer 1

Gastrulation is the process of formation of three cell layers:

1. Endoderm
2. Ectoderm
3. Mesoderm

Question 2

What are the three layers that are formed? What organs do the three layer will develop into? Which structure they develop from? How are they structured?

Answer 2

The three layers that are formed during gastrulation are endo-, ecto- and mesoderm.

1. The endoderm will develop into digestive and respiratory tract
2. The ectoderm will form the neural tube during development, which will develop into the brain and the spinal chord
3. The mesoderm will develop into muscles, body walls and vertebrae

The endoderm and mesoderm are formed by epiblasts cells.

Question 3

What types of mesoderm there are?

Answer 3

The mesoderm is divided into:
1, Intramembryonic mesoderm
2. Extraembryonic mesoderm

In general, the distance of the mesoderm from the midline, determine the type of mesoderm that it will develop into:

1. Axial (Notochord)
2. Head mesoderm
3. Paraxial
4. Intermediate
5. Lateral plate

The notochord serves as a source of midline signals that pattern surrounding tissues and as a major skeletal element of the developing embryo. It is formed by the invagination of the primitive streak towards the cranial region.

The paraxial mesoderm will develop into the axial skeleton. It will form somites, embryonic transitional organs, which are then going to differentiate into dermatome, myotome and sclerotome.

Question 4

What types of ectoderm there are?

Answer 4

The ectoderm is the cell layer that will give rise to the neural tube, which will develop into the brain and the spinal cord.
The ectoderm is mainly formed by epiblasts, which will form the neural plate and the epidermis (peripheral surface ectoderm).

Question 5

What is neurulation? How does this process occur? What will it develop into? How the nervous system is regulated? How will the tube close? What can cause failure in it?

Answer 5

Neurulation is the process of formation of the nervous system:

1. The neural plate thickens on the dorsal surface of the embryo
2. The neural tissue rolls and forms neural tube (CNS)
3. the rim forms the neural crest (PNS)
4. The notochord plays an important role in the induction of the neural plate

Neurulation is an highly regulated process: there are 6 main key factors that regulate it:
1. Shh
2. FGF8
3. Wnt
4. BMP4
5. Chordin
6. Noggin
FGF and Shh are upregulated by the paraxial mesoderm, which stimulate chordin and noggin, causing the inhibition of BMP4 activity. Shh and FGF will induce the formation of the forebrain and midbrain.
BMP4 is a very important factor, because without its regulation, all tissues would become neural plate.
- BMP4 transforms epiblasts into epidermis
- Wnt and FGF are necessary for the formation of hindbrain and spinal chord