Lecture 13 - The Germ Layers

Question 1

Do the epithelial cells or the mesonchymal cells have tighter tight junctions?

Answer 1

Epithelial cells a lot tighter than mesenchymal

Question 2

What is the role of the primitive streak?

Answer 2

Gives the embryo bilateral symmetry.

Question 3

How does the primitive streak form?

Answer 3

Ingression

Question 4

What is an EMT cell?

Answer 4

A mesoderm precurser

Question 5

Epithelial-mesenchyme transition

Answer 5

Look at page 11 for good diagram.

Question 6

What does EMT and MET stand for?

Answer 6

EMT = epithelial-mesenchyme transition (e.g. epithelium to mesoderm)
MET = mesenchymal-epithelial transition (e.g. mesoderm to endoderm)

Question 7

What do soluble proteins do?

Answer 7

Transmit growth and differentiation signals! from one developing cell type to another

Question 8

What are 4 different types of soluble proteins?

Answer 8

1. Transforming growth factor (TGF)
2. Wnts
3. Hedgehog proteins
4. Fibroblast growth factors!

Question 9

What does the endoderm produce?

Answer 9

Water, acid & food proof because of tight junctions. e.g. whole of GI tract, glands, thymus, gallbladder, liver, pancreas, thyroid, genital/urinary system etc.

Question 10

What does the ectoderm produce?

Answer 10

Skin, nervous system, adrenal medulla, pituitary and pineal epithelium

Question 11

What does the mesoderm produce?

Answer 11

Bone, cartilage, tendons, ligaments, heart, skeletal muscle, blood cells, kidney, reproductive tissues, lymphatic vessels etc.

Question 12

What 2 molecules are essential for gastrulation? What is the name of the transporter for this molecule?

Answer 12

1. Glucose - Transporter = Slc2a3 (glucose transporter 3) –> embryos lacking this transporter fail to complete gastrulation.
2. Copper - Transporter = Ctr1 (Slc31a1) –> embryos lacking this transporter fail to complete gastrulation.
   * ** cannot go through ingression process and therefore no formation of mesoderm

Question 13

What are teratomas?

Answer 13

• Tumor made up of several different types of tissue, such as hair, muscle, or bone. They contain cells from all three germ layers.

Question 14

What is the neural crest?

Answer 14

• Transient population appearing after gastrulation
• Cells migrate out from the neuroepithelium after the neural folds have fused
• Thought of as the ‘4th germ layer’

Question 15

What cell type are derived from the neural crest?

Answer 15

Peripheral nervous system, endocrine cells of adrenal medulla etc.

Question 16

What are the 3 genetic conditions arising from defects in the neural crest?

Answer 16

1. Piebaldism
2. Hirchsprung’s disease
3. Waardenburg syndrome

Question 17

What is piebaldism?

Answer 17

Melanocytes fail to migrate completely to the ventral midline leaving part of the body unpigmented e.g. big stripe of grey hair
- Come from mutations in SCF

Question 18

What is Hirchsprung’s disease?

Answer 18

Patients suffer from severe gastrointestinal problems -constipation, pain, abdominal distention - problem with enteric NS. Can’t move food along the way. peristalsis is driving by the nervous system.
- Comes from mutations in Ret

Question 19

What is Waardenburg syndrome?

Answer 19

Defects in multiple cell types derived from the neural crest.
Can cause: deafness, iris hypopigmentation, white patches of skin and hair, altered face shape.