Key concepts in early embryo development

Question 1

What is a stem cell? (2)

Answer 1

• Gives rise to more specialised cell types via differentiation
• Gives rise to more copies of itself (self-renewal)

Question 2

What is a stem cell niche?

Answer 2

Environment which keeps the stem cells in a self-renewing state

Question 3

What causes stem cells to differentiate?

Answer 3

Signals that are distinct from the signals in the niche which cause them to be self-renewing

Question 4

What is the difference between progenitor cells and stem cells?

Answer 4

Progenitor cells’ capacity for self-renewal is limited whereas stem cells’ is more prolonged

Question 5

What 3 cell lineages are established in the blastocyst before implantation?

Answer 5

• Trophectoderm
• Primitive endoderm
• Epiblast

Question 6

What does the trophectoderm give rise to?

Answer 6

Placenta

Question 7

What does the primitive endoderm give rise to?

Answer 7

Extraembryonic tissues and later develops into the yolk sac

Question 8

What does the epiblast give rise to?

Answer 8

The embryo proper - becomes all of the cells in the foetus

Question 9

What is a blastomere?

Answer 9

The cell type in the early embryo which is generated by cleavage of the zygote

Question 10

What is a blastocyst? (2)

Answer 10

• The embryo at the time of implantation
• Contains primitive endoderm, trophectoderm and epiblast

Question 10

What is potency?

Answer 10

The ability of a cell to differentiate into one or more cell types

Question 11

What is totipotency?

Answer 11

The ability of a cell to differentiate into any embryonic or extraembryonic cell type

Question 12

What is pluripotency?

Answer 12

The ability of a cell to differentiate into any embryonic cell type (but not extraembryonic)

Question 13

What are the criteria for being a pluripotent cell? (2)

Answer 13

• Expression of pluripotency transcription factors
• Teratocarcinoma formation

Question 14

Which transcription factors are markers for pluripotency? (3)

Answer 14

• Nanog
• Oct4
• Sox2

Question 15

What is a teratocarcinoma assay? (2)

Answer 15

• Inject embryonic cells into a mouse above the kidney
• If they give rise to a teratocarcinoma they are pluripotent

Question 16

What is a teratocarcinoma?

Answer 16

A type of tumour containing all embryonic cell types

Question 17

What happens at gastrulation? (2)

Answer 17

• Differentiation of pluripotent cells to form 3 germ layers (ectoderm, mesoderm, endoderm)
• Establishment of the anterior-posterior axis

Question 18

What are the 3 germ layers?

Answer 18

• Ectoderm
• Mesoderm
• Endoderm

Question 19

What does the ectoderm give rise to?

Answer 19

Skin, peripheral and central nervous system etc.

Question 20

What does the mesoderm give rise to?

Answer 20

Blood, heart, kidneys, muscle etc.

Question 21

What does the endoderm give rise to?

Answer 21

Gut, liver, pancreas etc.

Question 22

What is the primitive streak?

Answer 22

A groove that appears during gastrulation at the posterior end of the embryo which establishes the anterior-posterior axis

Question 23

Which signals cause the formation of the primitive streak? (4)

Answer 23

• WNT
• FGF
• BMP
• Nodal

Question 24

What is the epithelial-to-mesenchymal transition?

Answer 24

A process where cells lose their epithelial characteristics and become migratory

Question 25

What is somatogenesis/axis elongation?

Answer 25

Formation of somites to build the trunk and body parts after gastrulation

Question 26

What drives somatogenesis?

Answer 26

Neuromesodermal progenitors (NMPs)

Question 27

What can neuromesodermal progenitors differentiate into? (2)

Answer 27

- Spinal cord neurons - Paraxial mesoderm/somites (future skeletal muscle, bone, cartilage, vertebrae)

Question 28

What is the potency of neuromesodermal progenitors?

Answer 28

Bipotent (2 cell fates)

Question 29

Where is the niche of the neuromesodermal progenitors?

Answer 29

Posterior of the embryo, near the tail

Question 30

Which signals are elevated in the NMP niche? (2)

Answer 30

- WNT - FGF

Question 31

Which transcription factors define NMPs? (2)

Answer 31

- T(Brachyury) - Sox2

Question 32

Which signal causes an NMP to become paraxial mesoderm?

Answer 32

Downregulation of Sox2 and upregulation of T

Question 33

Which signal causes an NMP to become spinal cord neurons?

Answer 33

Upregulation of Sox2 and downregulation of T

Question 34

What happens when there are defects in NMP differentiation? (2)

Answer 34

- Embryos lack the trunk - Milder mutations can cause spina bifida (neural tube doesn't close)

Question 35

Where are neural stem cells located?

Answer 35

Central and peripheral nervous system

Question 36

What is the potency of neural stem cells?

Answer 36

Bipotent

Question 37

What can neural stem cells differentiate into? (2)

Answer 37

- Neurons - Glia

Question 38

Which signals mark the stem cell niche of neural stem cells? (2)

Answer 38

- EGF - FGF

Question 39

What can haematopoietic stem cells differentiate into?

Answer 39

All blood cell types

Question 40

What is the potency of haematopoietic stem cells?

Answer 40

Multipotent

Question 41

Where do haematopoietic stem cells arise in the foetus?

Answer 41

Aorta-Gonad-Mesonephros (AGM) region, later in the liver

Question 42

Where is the haematopoietic stem cell niche in adults?

Answer 42

Bone marrow

Question 43

How do you define haematopoietic stem cells? (2)

Answer 43

- Irradiate mice to remove the haematopoietic system - If you transplant haematopoietic stem cells the system will be rescued

Question 44

Which signals mark neural stem cell self-renewal? (2)

Answer 44

- Sox2 - RC2

Question 45

What marker is expressed by glial cells?

Answer 45

GFAP

Question 46

What marker is expressed by neurons?

Answer 46

TUJ1