Stem Cells Flashcards
Stem cells do not…
…age
Stem cells can differentiate into…
…different tissues in our body
Stem cells were first identified in…
…plants
What are the important features of stem cells?
1) Unspecialised
2) Can differentiate (can transform into different cell types)
3) Self-renewal (i.e. regenerate / lifelong)
Stem cells have very little…
… phenotypic features. Look like a blob.
Normal cells age and die. Stem cells are…
…replicatively immortal and can divide continually. They do not age and they do not die.
Stem cells have an unlimited capacity to…
…self-renew and produce ‘differentiated’ cells of various types
The ‘progenitor cells’, midway down have limited capacity to…
…self-renew and differentiate
Terminally differentiated cells do not…
…self-renew and do not differentiate
Terminally differentiated cells are no longer …
…stem cells.
Totipotent stem cells are the …
…‘ULTIMATE’ stem cell
Totipotent stem cells have the ability to…
…differentiate into ALL body cell, including cells that make the placenta
Pluripotent stem cells can
differentiate into…
… the 3 ‘germ’ layers of the human body
Multipotent stem cells can…
…differentiate into limited cell types
Blastula stage =
cell differentiation of tissue.
Once a stem cell differentiates the first time into a type of cell, it can still…
…further differentiate, but the diversity its differentiation is limited. This is known as lineage committed.
The 3 germ layers of pluripotent stem cells:
…Ectodermal, Mesodermal
and Endodermal
What will the ectoderm form?
- Epidermal layer of skin
What will the neural ectoderm (midline) form?
- Will form the nervous system
The grey crescent is the site where…
…major cell movement will begin.
What will the mesoderm form?
muscle, bone, kidneys, blood, gonads, and connective tissues.
What will the endoderm form?
Endoderm will form the lining of the gut, the liver, and the lungs.
A good example of multipotent stem cells are…
…Haematopoietic stem cells (HSC)
Where are Haematopoietic stem cells (HSC) found?
within bones marrow
HSC’s can…
…self renew and are lifelong
What are HSC’s ?
Haematopoietic stem cells
Common myeloid progenitors
(CMP) are …
‘omnipotent’ i.e. can differentiate
into all myeloid blood cells
What is CMP?
Common myeloid progenitor
Embryonic Stem Cells are…
…pluripotent stem cells that have the capacity to differentiate into the 3 germ layers
Embryonic stem cells form the…
…embryo which ultimately grows /
differentiates into all of the cell types, tissues and organs that make a
complete human being (or animal…)
Embryonic Stem Cells can be isolated at …
…1 week following in vitro fertilisation (IVF) and cultured in a tissue culture laboratory
Cloning involves…
…the generation of embryonic stem cells from a mature cell
Describe the process of cloning.
Nucleus from mature cell is inserted into a fertilised egg, which has had it’s nucleus removed. The biochemistry of the egg genetically reprogrammes the mature DNA, activating embryonic genes
What are ACS?
Adult Stem Cells
The intestinal stem cell niche
lies at…
… the bottom of the crypt – the stem cells self-renew and repair the gut
haematopoietic stem cells are central to…
… blood cell renewal
Adult stem cells are also known as…
… ‘somatic stem cells’ or ‘tissue stem cells’
Adult stem cells are…
multipotent
Where are Adult stem cells found?
throughout body tissues in stem cell niches
Adult stem cells are central to…
…normal growth and repair throughout life through
the progeny they produce.
stem cells have really important properties which are…
- They are unspecialised i.e., can differentiate
- They are immortal and can self-renew
The human karyotype contains…
23 homologous pairs of chromosomes (46 in total)
If stem cells contain the same set of 46 chromosomes as terminally
differentiated cells, why isn’t differentiated tissue also immortal?
Answer – because of the Hayflick Limit
Whats the Hayflick Limit?
the limit of the number of times a cell can divide. Terminally differentiated cells have divided the maximum number of times and now can no longer divide any further.
As the cell divide over time…
…telomeres shorten until cell division stops (senescence)
Telomeres decrease in size at…
…each divide.
But stem cells replicate for self-renewal i.e., divide, so what about their telomers?
Answer – because stem cell express the gene hTERT which codes for the telomerase enzyme.
Function of telomerase?
Telomerase builds back the telomers, which are TTAGGG base pair repeats
Telomerase saves the cell from…
…the hayflick limit and prevents apoptosis.
- Therefore, stem cells avoid apoptosis
(programmed cell death).
If stem cells contain the same 46 chromosomes (genes) as terminally
differentiated cells, why do stem cells remain undifferentiated?
Answer – chromatin is organised differently in stem cells
DNA in the nucleus exists in a…
…complex with Histone proteins
DNA wraps around a…
…histone protein core.
DNA is negatively charged because of…
…the phosphate group (which is negatively charged)
Histone proteins and DNA are…
…biochemically modified
Amino acid tails can be …
…modified
Biochemical modification
alters…
… the wrap tightness
Loose wrap =
Euchromatin
Tight wrap =
Heterochromatin
Phosphate (PO4-) contains…
…oxygen
Because phosphate contains oxygen, it creates…
…negative dipoles
Methyl groups (CH4) have no…
…oxygen
Because Methyl groups have no oxygen, they are…
…hydrophobic
Add methyl to DNA & Histone
tails creates…
‘sticky’ patches, leading to heterochromatin
Acetate creates…
…euchromatin
Methyl creates…
…heterochromatin
Add Acetate (C2H3O2-) to
histones creates…
… negatively charged histones, which repel negatively charged DNA leading
to euchromatin
Embryonic stem cells express a gene known as…
…DNMT3L
Whats does DNMT3L code for?
codes for one of the DNA methyltransferase chromatin remodelling enzyme
What does expression of the gene DNMT3L result in?
The result is euchromatin in
regions of the genome that allow
the expression of stem cell specific
genes (e.g. hTERT), whereas genes
required for tissue specific
differentiation are closed off
Stem cells must divide to…
…self-renew
Whats hTERT?
telomerase which builds up telomeres.
The hTERT and DNMT3L genes keep the stem cells in an…
…immortal and undifferentiated state due to the activity of telomerase and the stem-cell specific euchromatin regions.
Stem cells express high level of the…
…MYC gene.
Function of MYC gene?
promotes cell cycle i.e., cell division
hTERT keeps stem cells …
…immortal
DNMT3L creates…
…stem cell specific euchromatin
MYC promotes…
…stem cell division
Epigenetics is the study of…
…stable phenotypic changes that do not involve alterations in the DNA sequence
Histone protein 3 (H3) appears
to be really important in…
…maintaining the stem cell state
‘stemness’
Whats H3?
Histone protein 3
Methyl groups (CH4) are added to…
…lysine residues (K) on the tails of H3
up to […] methyl groups can be added at any one time
(hypermethylation)
up to three methyl groups can be added at any one time
(hypermethylation)
H3K4me3 is seen in…
…genes which are active i.e. switches gene transcription on
H3K27me3 inactivates…
…gene transcription
H3K4me3 is observed in the…
… promotor region of several thousand
lineage specific genes in stem cells – yet these genes are not expressed
H3K27me3…
…blocks these genes from being produced
This bivalent modification of H3 poises…
…the stem cell for differentiation
Describe nuclear
transplantation technique
Nucleus from a mammary gland cell
transferred to an enucleated oocyte
in the metaphase-II state
MYC promotes…
…cell division
Function of Oct4?
promotes the expression of self-renewal genes
Function of Sox2?
promotes the expression of self-renewal genes
Function of Klf4?
mediates cell division, survival
and self-renewal
Like MYC, Sox3 and Oct4 - Klf4 is a…
…transcription factor
How do transcription factors work?
TFs bind to specific sequences
of DNA (consensus sequence),
upstream of a gene and
promote gene transcription
The oocyte has MYC, Sox3, Oct4 and Klf4 proteins, which…
…genetically reprogramme the nucleus, including building back telomeres
The stem cell niche is the…
… microenvironment where stem cells reside
All adult stem cells (pluripotent) exist in…
…niche in cell to cell contact
with other cells
Purpose of stem cells existing in niches?
this provides the signals that the
stem cell needs to maintain function
What does CXCL12 bind to?
CXCR4 receptor on HSC plasma membrane
Where are Hematopoietic
stem cells (HSCs) located?
in the perivascular region of sinusoids and arterioles in close proximity to
mesenchymal stem cells (MSC)
and endothelial cells (EC)
Purpose of mesenchymal
stem cells (MSC) and endothelial
cells (EC)?
regulate HSC maintenance and
differentiation.
What does binding of CXCL12 to CXCR4 receptor promote?
quiescence and retention of the HSC to the bone marrow → this signal tells the HSC to stay put
Function of VCAM1?
protects the HSC in the bone marrow from innate immune cell destruction
HSCs also express the …
c-Kit receptor.
c-Kit receptor binds to…
…a soluble signal known as stem cell factor (SCF)
When the c-Kit receptor on the HSC
binds SCF…
… a set of intracellular signal transduction events takes place, result in in the activation of key transcription factors e.g., MYC
Whats the Spina bifida?
a neural tube defect (NTD) whereby the spinal cord fails to develop properly in the womb.
What are the consequences of Spina bifida?
This can have profound consequences, including paralysis.
Stem cell patches have been
used to…
…regenerate numerous tissues e.g., heart.
How do stem cell patches work?
- Autologous multi /
pluripotent stem cells are
printed onto a biocompatible
material and introduced - The stem cells differentiate
into new tissue
In HSC Transplantation, a HLA matched donor is given…
…cytokine to stimulate the HSCs including G-CSF (granulocyte colony stimulating factor)
In HSC Transplantation, what happens when the donor is given cytokines?
the bone marrow goes into overdrive, causing HSC’s to leave the niche and enter the blood stream.
In HSC Transplantation, donor HSCs are…
…harvested and purified by a process known as apheresis and are then given to the recipient.
How do the donor HSCs know where to go?
HSC respond to the signals from:
1) CXCL12
2) VCAM1
Other sources of HSC include …
…umbilical cord blood
Cord blood is separated into…
…red and white blood cells via
density centrifugation
HSCs from umbilical cord blood express…
… the cell marker CD34 on their surface
