Lec 6: Hematopoiesis

Question 1

What is a stem cell?

Answer 1

• early progenitor cell with the capacity to differentiate into mature cells
• potential to mature into a number of different cell types
• provides ‘raw material’ to repopulate cells that die (normal turnover), are killed, or are removed because of errors/injuries

Question 2

Describe the stem cell hierarchy

Answer 2

totipotent -> pluripotent -> multipotent

Question 3

Define totipotent.

Answer 3

the ability of stem cells to give rise to all embryonic and extra embryonic tissues

Question 4

Define pluripotent.

Answer 4

the ability to give rise to all embryonic tissues, but not extra embryonic tissues

Question 5

Define multipotent.

Answer 5

the ability to give rise to the diverse cell types of one or a few tissues

Question 6

All of the cells of the immune system derive from?

Answer 6

a common hematopoietic stem cell in the bone marrow

Question 7

How do HSC supply the entire repertoire of mature blood cells for the lifetime of an organism?

Answer 7

• self renewal capacity: maintains and expands stem cell pool
• multi-lineage differentiation potential: produces the diverse blood cell types of the mature hematopoietic system

Question 8

Describe how stem cells produce more stem cells are progenitor cells?

Answer 8

• on each division, gives rise to another stem cell and a progenitor cell
• the progenitor cell is committed to producing related cells
• the greater the level of differentiation, the greater the level of commitment to a particular lineage (more restricted) and lower capacity to self renew

Question 9

How can you differentiate between the various leukocyte populations?

Answer 9

• can do it at protein (surface or intracellular markers) or the gene (mRNA expression) level
• staining; label with antibodies/fluorochromes

Question 10

Describe how flow cytometry works.

Answer 10

• anti CD19 (red)
• anti CD3 (green)
• mix them all up; some are green, some are red, some are nothing
• go one by one through detector and cells are sorted based on fluorescence
• can tell what cell types you have and proportion of cell types

Question 11

How can you differentiate between the various leukocyte populations?

Answer 11

• can do it at protein (surface or intracellular markers) or the gene (mRNA expression) level
• staining; label with antibodies/fluorochromes

Question 12

Describe how flow cytometry works.

Answer 12

• anti CD19 (red)
• anti CD3 (green)
• mix them all up; some are green, some are red, some are nothing
• go one by one through detector and cells are sorted based on fluorescence
• can tell what cell types you have and proportion of cell types

Question 13

How can gene expression be used to answer questions about blood cells?

Answer 13

• is this cellular population expressing the genes we expect them to? (too much proliferation, mutated genes , high expression of inflammatory genes)
• does this tissue have high levels of a leukocyte specific gene?
• Can we identify why animal X responds well to a disease whereas another animal succumbs to the same challenge? (understand disease progression, genetics contribute to disease)

Question 14

Among Q-PCR, microarrays and microarrays, which can study the most genes at one time?

Answer 14

microarrays > macroarrays > Q PCR

Question 15

What is the hematopoietic microenvironment referred to as?

Answer 15

stem cell niche

Question 16

What is the role of the hematopoietic microenvironment?

Answer 16

• stem cells need a nurturing environment
• these and other cells provide soluble growth factors
• environment drive or simply selectively help mature a responsive cell following event
• bone marrow stem cell niche helps maintain stem cell properties, including self renewing capacity and ability to differentiate into multiple lineages
• critical component for sustaining dormant (quiescent) stem cells

Question 17

What are the 2 types of bone marrow and what is the difference?

Answer 17

• red marrow: actively generates blood cells

- yellow marrow: dormant; more fat cells

Question 18

Why is the quiescent state an essential mechanism to protect stem cells from stress and sustain long term hematopoiesis?

Answer 18

• want dormant stem cells because mutations can occur if continues to proliferate (maintains integrity of genetic coding), as well as saving energy and may need in future

Question 19

What does the bone marrow consist of?

Answer 19

• capillaries
• reticular fibres of connective tissue
• fibroblasts which secrete these fibres
• immature blood cells in all stages of maturation
• upon maturation these migrate through the endothelial cells that form the capillary walls into the blood stream

Question 20

Why is the quiescent state an essential mechanism to protect stem cells from stress and sustain long term hematopoiesis?

Answer 20

• want dormant stem cells because mutations can occur if continues to proliferate (maintains integrity of genetic coding), as well as saving energy and may need in future

Question 21

Stromal and other cells provide a nurturing environment through what 3 things?

Answer 21

• cell derived components (soluble growth factors, cell adhesion molecules, extracellular matrix molecules)
• systemic control factors (injury and neurohormones)
• physiological conditions (oxygen tension)

Question 22

What are some other hematopoietic organs?

Answer 22

• some in adult tissues (migrating stem cells or local de novo hematopoiesis in brain)
• depends on species (bony fish kidney and spleen)
• depends on development stage

Question 23

Stromal and other cells provide a nurturing environment through what 3 things?

Answer 23

• cell derived components (soluble growth factors, cell adhesion molecules, extracellular matrix molecules)
• systemic control factors (injury and neurohormones)
• physiological conditions (oxygen tension)

Question 24

What are some other hematopoietic organs?

Answer 24

• some in adult tissues (migrating stem cells or local de novo hematopoiesis in brain)
• depends on species (bony fish kidney and spleen)
• depends on development stage

Question 25

Define ontogeny.

Answer 25

the developmental life history of an organism

Question 26

Define primitive or embryonic hematopoiesis.

Answer 26

• occurs extra embryonically in the yolk sac, it is exceedingly rapid, and appears to ensure that sufficient oxygen is supplied to the developing embryo and that dying cells, resulting from rapid tissue turnover, are efficiently cleared out

Question 27

Define definitive hematopoiesis.

Answer 27

• sustains production of all blood cell lineages for the fetus as well as the adult.
• originates in the AGM region of the P-Sp where de novo formation of hematopoietic stem cells is believed to occur followed by their migration from the AGM to the liver, spleen and bone marrow where subsequent maturation takes place

Question 28

Describe overall regulation of hematopoiesis.

Answer 28

• proliferation, commitment ,differentiation, and survival events are coordinated through interactions with cells and extracellular matrix components through interactions with soluble factors (produced locally or arrive by blood) and through intrinsic mechanisms regulated by stochastic events
• integration of extracellular and intracellular stimuli culminates in overall response and expression of specific genes

Question 29

Where does this integration occur?

Answer 29

• all signal transduction pathways converge at the level of gene expression
• transcriptional factors are nodal point of hematopoietic control through integration of incoming signalling pathways and subsequent modulation of transcriptional machinery
• expression of genes dependent on interactions between transcription factors, coregulatory molecules and specific binding sequences in the DNA