Exam 4 CHAPTER 22: STEM CELLS

Question 1

Zygote

Answer 1

The fertilized egg
Has 2 sets of chromosomes = diploid (2n)

Question 2

Stem cell

Answer 2

Cells that have the potential to continuously replicate and have not yet differentiated
Have the ability to differentiate into one or more specific cell types

Question 3

Differentiation

Answer 3

Cells that change into specialized cell types
(Skin cells, neurons, muscles cells, etc.)
Progressively become more limited in their developmental potential
May not be capable of changing into other cell types

Question 4

What is plasticity? What cells have this?

Answer 4

The ability to differentiate into different cell types
Stem cells have plasticities but differentiated cells usually do not

Question 5

Totipotent stem cells

Answer 5

Can generate all cell types in the body
The fertilized egg or zygote
Embryonic cells to the 8-cell stage are all totipotent stem cells

Question 6

Stem cells

Answer 6

Undifferentiated cells that can produce daughter cells that can be either
a stem cell (self-renewal) or a cell that commits to differentiation

Question 7

Pluripotent stem cell

Answer 7

Can generate all germ layers (Endoderm, mesoderm, ectoderm)
Cannot generate extra embryonic tissues
(Placenta, etc.)
Therefore, they are the next step from totipotent
Embryonic cells at 16-cell stage are pluripotent,not totipotent

Question 8

Multipotent cells

Answer 8

Can differentiate into some cell types, but not all

Question 9

Pluripotent cells derived from the ______ of the blastocyst can generate all germ layers

Answer 9

inner cell mass

Question 10

What are the germ layers?

Answer 10

Endoderm= become the digestive tract
Mesoderm= connective tissues, bone, cartilage, etc.
Ectoderm= skin, hair, brain, spinal cord, etc.

Question 11

Adult animal contain stem cells in: (9 answers). But these are limited in what they can usually differentiate into
They are mostly multipotent or unipotent

Answer 11

Blood (bone marrow)
Intestine
Skin
Ovaries
Testes
Muscle
Liver
Even the nervous system contains stem cells

Question 12

Embryonic stem cell production in the lab

Answer 12

Cleavage stage embryos are grown from in vitro fertilization
To the blastocyst stage
The inner cell mass is isolated from extra embryonic tissues
Inner cell mass is plated onto a layer of fibroblast “feeder” cells
(Help nourish the ES cells, provide growth factors and irradiated to be unable to divide)
ES cells are isolated and dissociated into single cells
Single cells are replated onto new fibroblast “feeder cells”
ES cells form colonies
ES cells colonies

Question 13

What are the stem cell transcription factors expressed by pluripotent cells?

Answer 13

Oct4 and Nanog

Question 14

What are the stem cell transcription factors expressed by pluripotent cells and multipotent cells?

Answer 14

Sox2

Question 15

What do stem cell transcription factors do?

Answer 15

These transcription factors bind to promoters of thousands of genes
Activate genes for proliferation and pluripotency
Repress genes that induce cell differentiation
Also induce production of these transcription factors

Question 16

Animal stem cells can cure disease/damage

Answer 16

Use animal stem cells and differentiate them into other cell types, then inject them into animals in the right places
Animal differentiated cells have been used to cure animal diseases and to repair damage(Muscle damage, Heart damage, etc)

Question 17

Finding in 2006 by Takahashi and Yamaka at Kyoto University, Japan

Answer 17

Reprogrammed differentiated human fibroblasts to become pluripotent stem cells
Defined the induced pluripotent stem cells (iPS cells)
These were similar to human embryonic stem cells
Required direct reprogramming of the cells

Question 18

Methodology of human facial dermal fibroblasts

Answer 18

Packaged 4 human transcription factor genes into human retrovirus (lentivirus)
Oct3/4, Sox2, Klf4 and c-Myc
Oct3/4 and Sox2 for stemness
C-Myc drives cell proliferation
Klf4 modifies chromatin structure to allow activation of genes
Infected fibroblasts
Retrovirus integrates the genes into the cell DNA
After 6 days, collect cells and culture on a feeder cell layers
Add primate ES cell culture medium + basic fibroblast growth factor
30 days afterward, characterized the cell

Question 19

Distinction between a stem cell and differentiated cells

Answer 19

Stem cells usually maintain telomerase activity
Enzyme which adds nucleotides to the telomere ends of the chromosome
Prevents chromosome shortening due to DNA replication
Differentiated cells don’t have telomerase but can continue to do DNA replication

Question 20

Are there alternatives to using retrovirus?

Answer 20

Need the 4 transcription factors
Oct4
Klf4
Sox2
c-Myc
Can just provide the mRNA or the protein
Yes but requires multiple injections over time
There are even chemicals that can stimulate the expression and activation of transcription factors

Question 21

Two possible strategies for using person’s own iPS

Answer 21

Use iPS to make human neurons in culture then test drugs on the neurons
OR
Use iPS and repair the problem then inject these functional neurons into the patient

Question 22

Pros of IPS

Answer 22

Many uses:
IPS cells possible use for therapy
(Stroke, muscular degeneration, osteoarthritis, neurodegenerative disease (Parkinson’s and Alzheimers), diabetes)
Differentiate iPS cells into whatever you want
(Use for testing drugs or use for research on specific cell types)
Person’s own cells so no immune rejection

Question 23

Cons of IPS

Answer 23

Presence of retroviral integration
(Could lead to mutations and tumors)
iPS cells themselves could induce cancer
By unregulated proliferation
Viral proteins could induce immune response
Efficiency is low ~1 per 5000 cells
iPS are not identical to hES cells
Need further studies

Question 24

Stem cells divide to give all types of intestinal epithelial cells (3 kinds of cells)

Answer 24

Paneth cell (immune cell)
Another stem cell
Transient amplifying cell

Question 25

What does the transient amplifying cell become?

Answer 25

Rapidly divides becomes the differentiating cell, differentiates itno epithelial cell types (Absorptive enterocyte, mucus secreting goblet cells and enteroendocrine cells)

Question 26

How do we identify these hematopoietic stem cells?

Answer 26

Flow cytometry for surface markers
But there is no one marker for stem cells
CD150, Sca-1, C-kit on human HSC
Other adult stem cell types
Specific combination of integrins and other receptor