Key concepts in early embryo development Flashcards
What is a stem cell? (2)
- Gives rise to more specialised cell types via differentiation
- Gives rise to more copies of itself (self-renewal)
What is a stem cell niche?
Environment which keeps the stem cells in a self-renewing state
What causes stem cells to differentiate?
Signals that are distinct from the signals in the niche which cause them to be self-renewing
What is the difference between progenitor cells and stem cells?
Progenitor cells’ capacity for self-renewal is limited whereas stem cells’ is more prolonged
What 3 cell lineages are established in the blastocyst before implantation?
- Trophectoderm
- Primitive endoderm
- Epiblast
What does the trophectoderm give rise to?
Placenta
What does the primitive endoderm give rise to?
Extraembryonic tissues and later develops into the yolk sac
What does the epiblast give rise to?
The embryo proper - becomes all of the cells in the foetus
What is a blastomere?
The cell type in the early embryo which is generated by cleavage of the zygote
What is a blastocyst? (2)
- The embryo at the time of implantation
- Contains primitive endoderm, trophectoderm and epiblast
What is potency?
The ability of a cell to differentiate into one or more cell types
What is totipotency?
The ability of a cell to differentiate into any embryonic or extraembryonic cell type
What is pluripotency?
The ability of a cell to differentiate into any embryonic cell type (but not extraembryonic)
What are the criteria for being a pluripotent cell? (2)
- Expression of pluripotency transcription factors
- Teratocarcinoma formation
Which transcription factors are markers for pluripotency? (3)
- Nanog
- Oct4
- Sox2
What is a teratocarcinoma assay? (2)
- Inject embryonic cells into a mouse above the kidney
- If they give rise to a teratocarcinoma they are pluripotent
What is a teratocarcinoma?
A type of tumour containing all embryonic cell types
What happens at gastrulation? (2)
- Differentiation of pluripotent cells to form 3 germ layers (ectoderm, mesoderm, endoderm)
- Establishment of the anterior-posterior axis
What are the 3 germ layers?
- Ectoderm
- Mesoderm
- Endoderm
What does the ectoderm give rise to?
Skin, peripheral and central nervous system etc.
What does the mesoderm give rise to?
Blood, heart, kidneys, muscle etc.
What does the endoderm give rise to?
Gut, liver, pancreas etc.
What is the primitive streak?
A groove that appears during gastrulation at the posterior end of the embryo which establishes the anterior-posterior axis
Which signals cause the formation of the primitive streak? (4)
- WNT
- FGF
- BMP
- Nodal
What is the epithelial-to-mesenchymal transition?
A process where cells lose their epithelial characteristics and become migratory
What is somatogenesis/axis elongation?
Formation of somites to build the trunk and body parts after gastrulation
What drives somatogenesis?
Neuromesodermal progenitors (NMPs)
What can neuromesodermal progenitors differentiate into? (2)
- Spinal cord neurons
- Paraxial mesoderm/somites (future skeletal muscle, bone, cartilage, vertebrae)
What is the potency of neuromesodermal progenitors?
Bipotent (2 cell fates)
Where is the niche of the neuromesodermal progenitors?
Posterior of the embryo, near the tail
Which signals are elevated in the NMP niche? (2)
- WNT
- FGF
Which transcription factors define NMPs? (2)
- T(Brachyury)
- Sox2
Which signal causes an NMP to become paraxial mesoderm?
Downregulation of Sox2 and upregulation of T
Which signal causes an NMP to become spinal cord neurons?
Upregulation of Sox2 and downregulation of T
What happens when there are defects in NMP differentiation? (2)
- Embryos lack the trunk
- Milder mutations can cause spina bifida (neural tube doesn’t close)
Where are neural stem cells located?
Central and peripheral nervous system
What is the potency of neural stem cells?
Bipotent
What can neural stem cells differentiate into? (2)
- Neurons
- Glia
Which signals mark the stem cell niche of neural stem cells? (2)
- EGF
- FGF
What can haematopoietic stem cells differentiate into?
All blood cell types
What is the potency of haematopoietic stem cells?
Multipotent
Where do haematopoietic stem cells arise in the foetus?
Aorta-Gonad-Mesonephros (AGM) region, later in the liver
Where is the haematopoietic stem cell niche in adults?
Bone marrow
How do you define haematopoietic stem cells? (2)
- Irradiate mice to remove the haematopoietic system
- If you transplant haematopoietic stem cells the system will be rescued
Which signals mark neural stem cell self-renewal? (2)
- Sox2
- RC2
What marker is expressed by glial cells?
GFAP
What marker is expressed by neurons?
TUJ1
