Lecture 15 - Stem Cell Basics Flashcards
What is the epiblast?
Stage of embryonic development that gives rise to the germ layers (ectoderm, mesoderm, endoderm).
Begins around the time of implantation into the uterus
How do cell differentiation and determination occur?
Epigenetic changes (alterations to chromatin)
Determination
Occurs before overt differentiation.
Not morphologically obvious
Differentiation
Result of changes in gene expression
Commitment to a cell lineage
Cell changes morphologically so that it can carry out particular function
Transdifferentiation
A cell committed to one lineage switches pathways to another lineage.
Examples of transdifferentiation
Intestinal metaplasia of the oesophagus.
Squamous metaplasia of the intestinal tract.
Can transdifferentiation be induced?
Yes. In cell culture, ectopic expression of master regulator transcription factors
Example of transdifferentiation between two closely-related cell types
Pancreatic-lineage cells can transdifferentiate into hepatocytes
Intestinal metaplasia
Damage to the oesophageal epithelium through acid reflux leads to conversion of normal squamous epithelium into intestinal epithelium.
Danger of intestinal metaplasia of the oesophagus
Is a precursor to oesophageal adenocarcinoma
Stem cell that can give rise to several types of mature cell
Multipotent
Stem cell that can give rise to any mature cell
Pluripotent
Stem cell that can give rise to a new individual, given appropriate support
Totipotent
Types of adult tissue
1)
2)
3)
1) Continuously renewing
2) Conditionally renewing
3) Non renewing
Example of continuously renewing adult tissues
Bone marrow, skin, gut
Examples of conditionally renewing adult tissues
Liver, kidneys (to a lesser extent)
Example of a non renewing adult tissue
Cardiac muscle
How often is the lining of the GIT replaced?
Once every four days
Number of cells lost each day form each person
~20 billion
What is a stem cell?
Primitive, undifferentiated cell that can give rise to more specialised cell types or renew itself.
Features of stem cells 1) 2) 3) 4) 5) 6)
1) Capable of self-renewal and differentiation
2) May give rise to transit amplifying cells (compartment-committed cells with a limited division capacity)
3) Often lack specialised organelles, have a high nucleus:cytoplasm ratio
4) Express telomerase (long-lived)
5) Slowly-dividing
6) Few in number
How do stem cells normally sit in the body?
Restricted to specific niches
Adult-tissue stem cell features
1)
2)
1) Tightly regulated function by powerful transcription factors
2) In an altered environment, tight transcriptional regulation might be relaxed, leading to plasticity.
Ways to identify stages of differentiation 1) 2) 3) 4)
1) Transcription factors
2) Surface molecules (EG: CD)
3) Cytostructural molecules (EG: intermediate filaments)
4) Specific functional gene products
Regions of the brain that are stem-cell niches
1)
2)
1) Subventricular
2) Hippocampal
Where do neurons from the subventricular zone end up?
In the olfactory epithelium
What might hippocampal neurogenesis have a role in?
Memory
Number of cell types in the gut that constantly form from stem cells
Four (goblet, paneth, enteroendocrine, enterocyte)
Where in the gut do stem cells sit?
Crypts
Paneth cell role
Gut innate immunity.
Produce defensins and lysosome
Signalling pathways that regulate crypt stem cell differentiation
Wnt
Notch
Where in the hair follicle do stem cells sit?
The bulge
Signalling pathways involved in hair follicle stem cell regulation
BMP
Wnt
How do stem cells in body niches often behave?
Quiescent stem cells that are not dividing are a tissue reserve that is activated upon damage.
Quiescent stem cells give rise to active or progenitor stem cells which are responsible for homeostasis under normal circumstances
Type of stem cells in the liver
Facultative stem cells (can conditionally renew)
Where are liver stem cells found?
Bipotential stem cells found in the biliary tree
How can the liver regenerate?
Either by hepatocyte proliferation or from bipotential stem cells in the biliary tree
How can the liver’s regenerative ability be impaired?
Cirrhosis, viral infection can lead to scarring,
Factors added to fibroblasts to make them become pluripotent stem cells
Yamanaka factors
Three sources of stem cells
1) Embryonic
2) iPS
3) Somatic cell nuclear transfer
Properties of pluripotent stem cells
1)
2)
3)
1) Grow indefinitely in vitro
2) Capable of colonising all tissues after injection into a blastocyst (chimaeric animal)
3) Maintain normal genetic makeup
At which stage do stem cells switch from being totipotent to pluripotent?
At around the 4-8 cell stage
Signalling systems that control animal development 1) 2) 3) 4) 5) 6) 7)
1) Wnt
2) Hedgehog
3) Notch
4) TGFb
5) Tyr kin
6) Nuclear rec
7) Jak/Stat
Yamanaka factors to induce pluripotency 1) 2) 3) 4)
1) Oct-4
2) Sox2
3) Klf4
4) C-myc
How are Yamanaka factors introduced to cells?
Viral transfection
Possible application of iPS in biomedical research 1) 2) 3) 4)
1) Basic studies of human development and disorders
2) Functional genomics of human cells
3) Discovery of novel factors controlling tissue regeneration and repair
4) In vitro models for drug discovery, toxicology
Particular use for iPS in studying human development
Human brain development is very different to that of other animals
iPS can be used to model human cortical development, model developmental diseases such as autism, schizophrenia, epilepsy
