Understanding Embryonic Stem Cells

‘Understanding Embryonic Stem Cells’ Name______

Howard Hughes Medical Institute 2006

Holiday Lectures on Science: Potent Biology: Stem Cells, Cloning and Regeneration

Douglas Melton, PhD Harvard

Part I

1. What is ‘differentiation’ and what is ‘growth’?

2. What was the theory of the ‘homunculus’ and human growth?

3. There are hundreds of different kinds of cells in your body. Name six:

4. What is ‘cleavage’ (in cells)

5. What is a blastocyst?

6. What is the difference between the cells in the inner cell mass (the ‘ICM’) and the outer cell mass?

The ICM becomes the ….

The outer cell mass becomes the ….

7. The ICM becomes disc-shaped and turns into three ‘germ layers’:

They are the ectoderm which makes the ______

The mesoderm which makes the ______,______and ______

And the endoderm which makes the ______, ______,______and ______.

8. Dr. Melton chooses the pancreas as his ‘sample organ’ to illustrate stem cells. What do you already know the pancreas does?

It also regulates the levels of sugar in your blood by releasing insulin or glucagon.

These are made in the pancreatic ______cells. This cell measures the

amount of sugar in your blood. Type I and II Diabetes occur when the pancreas does

not function properly.

9. You see on a slide the progression of changes that leads one cell to become a beta islet cell. How many stages of differentiation are there on this slide? ______

10. These changes occur as genes turn ______and ______.

11. Scientists can observe these changes on a DNA chip. Thirty thousand human genes are placed on a tiny chip. A sample of tRNA is taken from the nucleus of a cell under observation. These molecules represent genes that: (circle one)

ARE being expressed/ ARE NOT being expressed at the time of the sample

On the plastic game example, the green chips represent genes that are ‘turned on’ and the red chips are genes not being used at the time the sample was taken. In the slide entitled ‘Cell Types and Gene Expression’, why are there different combinations of red and green dots next to each of the three types of cell?

12. Cells make their decisions via internal and external signals. Internal signals

come from ______factors. External signals come from ______to

______interaction. These signals ‘tell’ the cell which genes to turn on or

off.

13. The signals are called ______factors because they make cells grow in Petri dishes.

Student question session….

Part II

1. Dr. Melton says that maintenance is actually just as important in cell differentiation as embryo to adult growth. He talks about ‘rates of turnover’ – what does that mean?

2. Stem cells are capable of:

3. A hematopoetic blood cell can turn into any type of blood cell the animal needs. True? False?

(skip ahead to chapter 35)

3. Fill in the captions and arrows from the slide:

‘Sources of Stem Cells’

Fertilization ______Fetus ______

______Cells Multipotent Cells

______

Stem Cells Stem Cells

4. Embryonic stem cells are called totipotent because they can form any kind of cell. What are their other characteristics?

What are the characteristics of adult stem cells, in comparison? These are called multipotent.

One source of embryonic stem cells is the cells from the ICM.

4. Why are these cells, when grown in Petri dishes, called ‘immortal’?

5. If left alone, do they begin to become different types of cells or do they just divide?

6. What is sonic hedgehog?

7. How does the chimeric mouse prove that ES (embryonic stem cells) injected into her as a blastocyst did survive and stay active as she developed and grew?

8. Were do human blastocysts come from for research?

9. What kind of cell is pulsing all by itself in a Petri dish full of ES cells in an experiment done by Harvard undergraduates every year?