Stem Cells

Question 1

What is asymmetric and symmetric division?

How is this determined? What is the mechanism behind it?

Answer 1

Asymmetric is meant to keep a baseline ratio between differentiated and undifferentiated cells. It is where one stem cell divides and one becomes a differentiated cell and the other is a stem cell.

Symmetric division is where a stem cell divides and becomes two stem cells, this is when you need a lot of stem cells (development or injury).

So there is an asymmetrical distribution of factors that promote stemness to one cell and not the other. One cell is exposed to the niche (microenvironment) and the other is displaced from the niche so the default is to differentiate.

Question 2

What is the cell intrinsic regulation of stem cell self renewal and what is the extrinsic regulation?

Answer 2

Intrinsic: Sox2-Oct4-Nanog suppress expression of differentiation promoting genes.

DNA binding protein Ronin suppresses transcription of differentiation inducing genes GATA4 and GATA6.

Extrinsic regulation, LIF, BMP work through STAT3 and SMAD-Id to block MAPK pathway.

Question 3

What is the stem cell niche and how is it responsive?

Answer 3

The niche is the microenvironment the stem cells find themselves in. It is cell to cell interaction, cell to substrate interactions, cell to cytokine interactions, growth factors

When a tissue is injured, a lot of things rush in changing the microenvironment. This can lead to proliferation of the stem cells and differentiation.

Question 4

Describe the intestinal crypt niche

Answer 4

The crypt base columnar cells are the stem cell population. They will give rise to TA (transient amplifying cells) that can differentiate into all the cell types needed in the villi and to Paneth cells.

TA move up the villi and Paneth cells remain in close proximity to the stem cells.

There is a 1:1 ratio of Paneth to stem cell and without it the stem cells can’t divide.

Question 5

What are four kinds of stem cells and their function (possibly examples

Answer 5

1. Adult stem cells: an undifferentiated cell found in differentiated tissue that can self renew and differentiate into all the cell types of the tissue (like intestinal crypt)
   
   • primarily to repair tissue in which they are found in. In bone marrow there are two populations of adult stem cells (hematopoietic stem cells - all the blood cells) and (stromal stem cells- bone, fat, connective tissue)
2. Induced pluripotent cell: make pluripotent stem cell from a non pluripotent cell (differentiated cell and force the expression of specific genes.
3. Embryonic stem cells: undifferentiated stem cells taken from the up to 8 cell stage preimplantation embryo which is totipotent
4. Cancer stem cells: the stem cells that drive tumorigenesis.

Question 6

Difference between totipotent, pluripotent, multipotent, oligopotent, and unipotent

Answer 6

1. Totipotent: Stem cells from a preimplantation embryo that can give rise to all the embryonic cells and extra embryonic cells.
2. Pluripotent: derivatives of totipotent cells that can differentiate into any of the three germ layers and cells in ICM are first totipotent but then pluripotent.
3. Multipotent: stem cells differentiate into a number of cells that are closely related (hematopoetic stem cells)
4. Oligopotent: stem cells can only differentiate into a few cells (lymphoid or myeloid)
5. Unipotent: the stem cell an only become one kind of cell but has the ability of self renewal which makes them different from non-stem.

Question 7

How are stem cells cultured in vitro?

2 ways

Answer 7

You place them on a layer of fibroblast feeder cells which are dead and so they give a source of growth factors and attachment but no signals for differentiation.

2. Better to use LIF, which will inhibit differentiaton by activating the JAK/Stat3 pathway and block MAPK pathway of differentiation.

Question 8

Stem cells are exceedingly rare (1 - 10,000 and 1/100,000)

Answer 8

You use a multi-parameter flow which identifies using a specific five antigen combination that if is matched, is that of a human stem cell.

Fluorescence activated cell sorting.

Question 9

What are three ways adult and embryonic stem cells are stimulated to differentiate.

Answer 9

1. Change the chemicals the cells are exposed to, which is mostly hit or miss. Try this factor, try that one.
2. Alter the surface of the cell culture. If the substrate is soft like a brain, a neuron forms. If it is plastic, a bone forms.
3. Modify the genes.

Question 10

What are four ways a differentiated cell stays differentiated/

Answer 10

1. The transcription factor that is activated in the cell is a transcription factor for its own gene (postive feedback)
2. Synthesize DNA modifying proteins that will keep specific genes accessible
3. If differentiation is dependent on a signal-receptor interaction, the cell will continue to make both the signal and the receptor.
4. Cells can interact with neighboring cells to maintain each other’s differentiation.

Question 11

What is the old cancer cell theory and how is it different from the new one.

How does the new theory explain why cancers are resistant to UV and chemo?

Example is glioblastoma and Temozolomide chemotherapy.

Answer 11

True: cancer is due to unregulated growth through expression of genes that promote proliferation, silencing of growth inhibiting genes and cell death.

Old: all tumor cells can form new tumor cells and are all equally tumorigenic.

New: there are specific cells (cancer stem cells) that have self renewal (can divide and maintain the undifferentiated state) and multipotency. A problem in regulation of stem cell renewal leads to unregulated growth. These stem cells are what leads to tumor formation so cancer is a stem cell disorder.

This distinct subpopulation is likely the cause for metastasis and relapses.

Stem cells divide slowly, giving them plenty of time to repair any damage from radio or chemotherapy which will only kill off the differentiated cells and allow the stem cells to make more tumors.

Stem cells also intrinsically have multiple drug resistance so tend to be chemoresistant.