Exam 3 - Embryonic Stem Cells

Question 1

What are the defining characteristics of a stem cell? What do those characteristics mean?

Answer 1

• self-renewing - capable of dividing and renewing themselves for a long period
• unspecialized - do not have any tissue-specific structures that allow them to perform specialized functions
• can give rise to specialized cells - differentiation causes a cell’s DNA to acquire changes that restrict DNA expression in the cell and can be passed on through cell division

Question 2

What is a totipotent stem cell? What are they capable of?

Answer 2

can develop into any cell in the body including the extraembryonic membranes
capable of producing an entire fertile adult organism

Question 3

What stage of embryonic development are totipotent stem cells acquired from?

Answer 3

blastomere (a 2-8 cell, day 1-3 embryo)

Question 4

What is a chimera?

Answer 4

a single organism composed of two or more genetically distinct cell lines that originated from different zygotes

Question 5

Suppose a chimeric red/blue embryo was developed into a blastocyst and then separated into the inner cell mass and the trophectoderm. What color cells would be in the inner cell mass, trophectoderm, fetus, and placenta?

Answer 5

red and blue in all the parts

Question 6

What are pluripotent stem cells? What are they capable of?

Answer 6

can develop into anything derived from the 3 germ layers (endoderm, mesoderm, and ectoderm) and the germ cells (eggs and sperm)
capable of forming the embryonic disc, amnion, yolk sac, but not the chorion (not the placenta)

Question 7

What stage of embryonic development are pluripotent stem cells acquired from?

Answer 7

inner cell mass of a day 5 embryo

Question 8

What tissues are derived from the endoderm, mesoderm, and ectoderm?

Answer 8

Endoderm - lining of respiratory tube (including lungs) and digestive tube (including liver, gall bladder & pancreas)
Mesoderm – skeleton, muscles, circulatory system, kidneys
Ectoderm – nervous system, outer layer of skin, hair, nails, tooth enamel

Question 9

If you inject the inner cell mass of a red embryo into the empty trophectoderm of a blue embryo, you create a red blue chimera. What colors will compose the inner cell mass, trophectoderm, fetus, and placenta?

Answer 9

ICM: red
trophectoderm: blue
fetus: red
placenta: blue

Question 10

If you inject cells from the inner cell mass of a red embryo into the trophectoderm of a blue embryo (which still contains its own ICM, you create a red blue chimera. What colors will compose the inner cell mass, trophectoderm, fetus, and placenta?

Answer 10

ICM: red and blue
trophectoderm: blue
fetus: red and blue
placenta: blue

Question 11

What are multipotent/progenitor stem cells? What are they capable of?

Answer 11

adult stem cells
can become specialized cells but generally only in the tissue or organ in which it resides
can give rise to several kinds of cells, tissues, or structures, within a related lineage

Question 12

If a genetic mutation occurred before Day 5, what cells would the mutation affect?

Answer 12

All cells, because those cells are totipotent

Question 13

What is the “original” way to make embryonic pluripotent stem cells? When was this done for the first time?

Answer 13

• create embryo
• remove inner cell mass from the blastocyst
• culture the cells

1998 - first human embryonic stem cell line created

Question 14

What are the tests to identify embryonic stem cells?

Answer 14

• grow and subculture for many months
• look for surface markers only found in undifferentiated cells
• examine the chromosomes, look for damage or changes in number
• determine if the cells can be grown after freezing, thawing, and re-plating
• demonstrate differentiation potential

Question 15

What protein is found only in undifferentiated cells?

Answer 15

Oct4 - only in pluripotent undifferentiated stem cells

Question 16

What are the methods of determining differentiation potential (name only)?

Answer 16

spontaneous differentiation, directed differentiation, teratoma formation, tetraploid complementation

Question 17

What is spontaneous differentiation? Describe its use as a way to test embryonic stem cells.

Answer 17

Cells eventually clump together to form 3 dimensional aggregates called embroid bodies

this is not an efficient way to produce cultures of a specific cell type

Question 18

What is directed differentiation? Describe its use as a way to test embryonic stem cells.

Answer 18

altering the surface of the cell culture dish (by changing chemical composition of the medium) or modifying the cells by inserting specific genes
embroid bodies can be guided down a particular pathway to become a certain type of cell

generates large numbers of a specific cell type

Question 19

What is PAX6?

Answer 19

a marker for neuroepithelial cells

Question 20

What is teratoma formation? Describe its use as a way to test embryonic stem cells.

Answer 20

can test the differentiation capacity of stem cells by injecting them into immuno-suppressed mice and inducing the formation of a teratoma in situ\

“gold standard” of pluripotency, demonstrates mixed cellular populations of all three embryonic germ layers

Question 21

What is tetraploid complementation? Describe its use as a way to test embryonic stem cells.

Answer 21

basic process: form a zygote, fuse the 2 2n cells to form a 4n cell that wont function, inject the stem cells into the now empty blastocyst, see if the embryo produces a fertile adult

most rigorous test of pluripotency, creates a chimera where the embryonic stem cells become the fetus and the extra-embryonic lineage becomes the placenta

Question 22

Describe the exact scheme of tetraploid complementation.

Answer 22

Get a fertilized zygote (2n)
Culture the zygote to the 2-cell stage (2 2n cells)
Use electrofusion to form a single 4n cell
4n cell mass stops functioning/dies/disappears but trophectoderm is fully functional
Inject the embryonic stem cells into the other embryo
ICM is derived from the ES cells, placenta is derived from the original “host” embryo
Surviving fetuses/adults are completely ES cell-derived and are fertile

Question 23

What is regenerative medicine?

Answer 23

branch of medicine that develops methods to regrow, repair, or replace damaged or diseased cells, organs, and tissues

includes generation and use of therapeutic stem cells, tissue engineering, and production of artificial organs

Question 24

What are some challenges of regenerative mediicne?

Answer 24

the stem cells must be made to…
- proliferate and generate enough tissue
- differentiate into desired cells
- be free of animal products
- survive in the recipient after the transplant
- integrate into the surrounding tissue after transplant
- function appropriately for the duration of a recipient’s life
- avoid harming the recipient in any way