Exam 4 CHAPTER 22: STEM CELLS Flashcards
Zygote
The fertilized egg
Has 2 sets of chromosomes = diploid (2n)
Stem cell
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
Differentiation
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
What is plasticity? What cells have this?
The ability to differentiate into different cell types
Stem cells have plasticities but differentiated cells usually do not
Totipotent stem cells
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
Stem cells
Undifferentiated cells that can produce daughter cells that can be either
a stem cell (self-renewal) or a cell that commits to differentiation
Pluripotent stem cell
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
Multipotent cells
Can differentiate into some cell types, but not all
Pluripotent cells derived from the ______ of the blastocyst can generate all germ layers
inner cell mass
What are the germ layers?
Endoderm= become the digestive tract
Mesoderm= connective tissues, bone, cartilage, etc.
Ectoderm= skin, hair, brain, spinal cord, etc.
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
Blood (bone marrow)
Intestine
Skin
Ovaries
Testes
Muscle
Liver
Even the nervous system contains stem cells
Embryonic stem cell production in the lab
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
What are the stem cell transcription factors expressed by pluripotent cells?
Oct4 and Nanog
What are the stem cell transcription factors expressed by pluripotent cells and multipotent cells?
Sox2
What do stem cell transcription factors do?
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
Animal stem cells can cure disease/damage
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)
Finding in 2006 by Takahashi and Yamaka at Kyoto University, Japan
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
Methodology of human facial dermal fibroblasts
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
Distinction between a stem cell and differentiated cells
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
Are there alternatives to using retrovirus?
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
Two possible strategies for using person’s own iPS
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
Pros of IPS
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
Cons of IPS
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
Stem cells divide to give all types of intestinal epithelial cells (3 kinds of cells)
Paneth cell (immune cell)
Another stem cell
Transient amplifying cell
What does the transient amplifying cell become?
Rapidly divides becomes the differentiating cell, differentiates itno epithelial cell types (Absorptive enterocyte, mucus secreting goblet cells and enteroendocrine cells)
How do we identify these hematopoietic stem cells?
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
