C1-HC4

Question 1

Primitive hematopoiesis:

Definitive hematopoiesis:

Answer 1

First hematopoiesis takes place in the fetal liver and BM.

Later in the development and after birth, it takes place in the BM and is called definitive hematopoiesis.

The process of hematopoietic starts very early during embryogenesis. Red areas are the primitive hematopoiesis. There is a strong connection between the start of the circulation in the early embryo and the formation of blood cells.

Question 2

How can we know that a certain cell is a stem cells?
2 techniques for in vitro assay:

1 technique for in vivo assay:

Answer 2

How can we know that a certain cell is a stem cells?
- In vitro assay: these techniques are not good anymore, because morphology can differ on different substrates. Some progenitors can divide and give progeny, but are not stem cells.
○ Cobble-stone area forming cell (CAFC): cell morphology has a specific appearance in the tissue culture dish. Then, use growth time to confirm it. The cells are visible after 5-7 weeks.
○ Long term culture-initiation cell (LTC-IC): is based on the ability to form a colony.
- In vivo assay: gives better information than in vitro.
○ Spleen colony forming unit (CFU-S): inject stem cell into mouse spleen to see if it starts to form outgrown areas of cells. You will need to discriminate the donor cells from the cells from the recipient. This can be done by using blood cell markers.

Question 3

A mature progenitor cell can/ cannot turn back to a stem cell (in general/ nature)?

Answer 3

A mature progenitor cell cannot turn back to a stem cell (in general/ nature). Thus, there is no plasticity. In the lab, this can be manipulated.

Question 4

Functional characteristics of HSCs:

Answer 4

Functional characteristics of HSCs:
		○ Self-renewal
		○ Differentiation
		○ Migration (into bone marrow & blood stream & other side of the body > important during injury to repopulate certain locations)
		○ Apoptosis (programmed cell death)

Question 5

Homing:

Answer 5

Homing: the cell is able to react on stimulation by migrating

Question 6

Cortical bone:

Trabecular bone:

Answer 6

Cortical bone is completely filled with matrix, which gives the bone its strength and stability.
Trabecular bone is very open and contains many blood vessels. It is a bit spongy; it can be bent and contains BM.

Question 7

Niche factors:

Answer 7

Niche factors have a strong influence on HSCs. Many factors secreted by cells present in the BM stimulate the state of HSC: quiescence, maintenance, migration, differentiation, and proliferation. Cell-bound factors keep the cell in a particular place for months.

Question 8

Osteoblasts and endothelial cells are part of the hematopoietic cell niche;
	- Osteoblasts...
		○ ?
		○ ?
		○ ?
	- Endothelial cells...
		○ ?.
		○ ?

Answer 8

Osteoblasts and endothelial cells are part of the hematopoietic cell niche;
- Osteoblasts…
○ express hematopoietic factors which influence the function of HSCs in the BM.
○ support hematopoietic progenitor cells (in vitro)
○ and a change in in osteoblast numbers may influence HSC numbers.
- Endothelial cells…
○ induce HSC differentiation. This is logical as ECs are closer to the blood vessel and after differentiation cells go into the blood.
○ support hematopoietic progenitor cells (in vitro).

Question 9

3 properties of CXCL12:

Answer 9

CXCL12:

- Important for the HSC niche.
- It is chemokine, which can make a gradient to which cells can respond. So they attract cells to a certain location.
- It is expressed by different cells in the BM and affects the niche factors.
- Experiment: knock-out of CXCL12. You can see where osteoblasts are formed.