Stem Cells and Diseases of the Blood

Question 1

What what germ layer do blood cells arise?

Answer 1

• The early mesoderm

Question 2

How is mesoderm patterned in a anterior to vegetal pattern?

Answer 2

• NODAL factors in the vegetal pole induce mesoderm
• The fate of each cell depends on the time and specific local morphogen concentrations
• Nodal (TGFB) act on type 1 and type 2 receptors and then via Smad receptors regulate activin/nodal genes
• Is it the specific gradient of nodals such as cyclops and squint and nodal inhibitors such as lefty (competes with nodal for receptor binding) that induce the mesoderm differentiation

Question 3

How is meoderm patterned in a ventral to dorsal pattern?

Answer 3

• High concentration of BMP on ventral side of embryp

- High concentration of chordin on dosal side of embryo

Question 4

Where to haematopoietic stem cells originate from?

Answer 4

• From hemangioblast which arises from mid-streak in the embryo
• HSCs bud from the dorsal aorta

Question 5

How does are HSCs generated from the endothelium?

Answer 5

• Endothelial to hematopoietic transition
  1. Atrial endothelium begins expressing endothelial factors e.g. klf2a
  2. It becomes hemogenic endothelium and produced putative EHT reprogramming factors e.g. GATA2B and draculin
  3. The HSCs then form which express late blood factors e.g. Klfd and Gata1

Question 6

What is a pioneering transcription factor?

Answer 6

• A transiction factor that binds to a section of chromatin in a silent state and enables other factors to access it (making it in a competent state)

Question 7

What features are needed for efficient cell reprogramming?

Answer 7

1. A combination of TFs from different classes
2. Some TFs to have pioneering activity alone/together
3. Some TFs to be proliferation drivers
4. Switching off of competing programs
5. The correct niche or growth factor combination
6. Also potentially a receptive epigenetic environment

Question 8

What are the developmental origins of HSCs?

Answer 8

1. Primitive haematopoiesis:
   - Bipotential mesoderm progenitor gives rise to endothelium and some primitive blood lineages
2. Definitive haematopoiesis:
   - The hemogenic endothelium of the AGM gives rise to HSCs then then populate the fetal liver and then bone marrow
   - Zeb2 important for this migration

Question 9

What are the 4 factors required for human induced pluripotent stem cells?

Answer 9

1. Oct4
2. Klf4
3. Sox2
4. c-Myc

Question 10

What are some uses of iPS technology?

Answer 10

1. Used to study human disease in vitro (and potential treatment)
2. Generate transplantable HSCs from regeneration or disease modelling- in vitro derived HSCs have similar progeny
3. Means of generating AML disease model (generated from blood cells of patients with the disease)
   - gives rise to transplantable disease in mice
   - uses Sendai viral reprogramming
   - presents opportunity to assess CRISPR/Cas9 technology