Lecture 15 - Stem Cells: Basic Concepts Flashcards
Develpoment from blastocyst involves a series of fate choices, what does the epiblast give rise to?
The 3 germ layers:
Endoderm
mesoderm
ectoderm
Determination and differentiation results not from changes in genes, but…
changes in gene expression (exception being immune system and gametes)
What makes this change in gene expression?
alterations in chromatin structure and transcription factor expression
Often quite permanent and heritable through many cell divisions
Determination occurs prior to overt…
differentiation - heritable change in a cell’s developmental potential -operationally defined
cells don’t LOOK like the cells they will become, but have made the decision to do so
What is differentiation?
results of the change in gene expression
cells acquires correct shape polarity, orientation with respect to neighbour, appropriate organelles and proteins which enable it to carry out metabolic signalling, transport or contractile signalling, transport or contractile functions required in a partilcular tissue3
What is transdifferentiation?
cell normally committed to one lineage is switched to a different lineage pathway
Many known examples from disease states - intetinal metaplasis of the esophagus
May be induced experimentally by ectopic expression of master regulator transcription factors
Describe Intestinal metaplasia, and how it is caused?
What can it lead to?
Damage to esophageal epithelium through acid reflux from the stomach leads to conversion of squamous epithelium into intestine
The condition is a precurosor to esophageal adenocarcinoma
Define a multipotent cell
cell that can give rise to several types of mature cells - not that many, limited.
Define a pluripotent cell
Cell that can give rise to ALL types of adult tissue cells plus extraembryonic tissue: cells which support embryonic development
Define a totipotent cell
cell that can give rise to a new individual given appropriate maternal support - Restricted to the blastomeres; the early cells of the embryo
What are the different types of adult tissue, with respect to renewal?
continuously renewing - bone marrow, skin, gut
Conditionally renewing - liver, kidney
Non renewing - cardiac muscle
We lose __ billion cells per day
20 billion
The lining of the intestineis replaced every 4 days
every 4 weeks a completely new epidermis is generated
some tissues turn over slowly, e.g?
hepatocytes live for 300 days, cardiomyocytes 0.5% annually
One blood stem cell gives rise to…
red cells, white cells and platelets
Stem cells may give rise to transit amplifying cell compartment, what is this?
group of commited cells with limited division capacity
Stem cells are often lacking in ____ _____
specialised organelles, and show high nucleus/cytoplasm ration
What makes stem cells live long?
express telomerase - helps with keeping DNA intact
Stems cells live in anatomically specific zones called
niches
Proper tissue organisation and response to demands of growth or repair require that there be restrictions on…
developmental potential of adult stem cells
limits are strictly imposed by powerful molecular constraints on gene expression and are heritable during many rounds of cell division (epigenetics)
What is needed to from a cell to prove it is a stem cell?
ability to repopulate a issue and give rise to differentiated progeny as well as more stem cells
identified in transplantation assays with marked cells
There are a range of cell surface markers, specifially expressed at certain stages in the lineage - what is the use of this?
Useful in diagnosis - expressed on corresponding malignancies that are ‘hung up’ at specific stages in the lineage
Recent findings show that tissues formerly thought to be static in adult life contain…
stem cell popoulations - examples include heart and CNS
_____ are born constatntly throghuout life in specific brain region
Neurons
Where deoes adult neurogenesis occur?
subventricular zone and hippocampus - new neurons from SVZ wind up in the olfactory epithelium
Hippocampal neurogenesis may have a role in…
learning and memory
The four types of differentiated cell in the adult gut are formed constantly from ..
stem cells in the crypts - deep inside the tissue
very characteristic structure
Wnt signalling and notch signalling can….
modulate the stem cells in crypts
Extrinsic signaling from surrounding cells reguatles..
stem cell proliferation
In continuously renewing cells, The long term repopulating cells in a tissue are often ______
What do they give rise to?
Quiescent - ticking over very slowly
They then give rise to active stem/progenitor cells which move out from that region (i.e hair cell can move to to epidermis or down to the shaft)
Conditionally renewing cells
Liver can regenerate by ..
proliferation of hepatoctyes, or from bipotential stem cells found in the biliary tree
hepatocytes, just re-enter the cell cycle
What happens in biliary atresia?
blockage of bile duct, accumulation of bile in the liver and cirrhosis
Bipotential biliary cells proliferate in an attempt to repair the damage
What are the 3 sources of pluripotent stem cells?
directly from embryos (ICM)
Can make from adult stem cells with reprogramming
somatic cell nuclear transfer (SCNT)
What is the process of SCNT?
take an egg, remove genetic material, put an adult cell nucleus back in and the egg can then reprogramming the adult cell nucleus back to its develpomental state, such that it can recapitulate all the process of animal development
stop at a point (don’t want to make a cloned human), and take the cell
What are the properties of pluripotent stem cells
grow indefinitely in vitro
maintain normal genetic makeup - not getting cancer-line changes
cloned lines capable of differentiation into a wide range of somatic and extra embryonic tissue in vivo and in vitro-at high frequency and under and range of conditions
capable of colonising all tissues including germ line after blastocyst injection to give chimeric offspring
What are the key ethical points about the blastocyst stage of development?
body plan not yet apparent
many cells will not form new human, but will give rise to tissue such as placenta which support pregnancy
Embryo does not necessarily represent a unique individual (twins can still form)
No precursors of nervous system yet
Not possible to predict whether embryo will be able to develop to term
Teratomas are a way of showing..
pluripotency
A teratoma is a tumor with tissue or organ components resembling normal derivatives of more than one germ layer.
can inject into a mouse with no immune system to test whether the cells cells that were isolated are indeed pluripotent
What are seven signalling system s that control animals develpoment:
WNT
HEDGE HOG
NOTCH
TGF BETA
TYR KIN
JAK-STAT
NUCLEAR REC
ES cell differntiation goes though germ layer _______
intermediates - knowing the signalling pathways to these intermediates can hep get what we want in a research context
many species of mammal have now been cloned
Can cloning technology be use to surmount immunological barrier to stem cell transplantation?
yes, pluripotent cells can be grown from iPSC
SCNT is very difficult to get right to make dolly, there were ___ separate attempts
200
What are the key applications for pluripotent stem cells in biomedical research?
basic studies of early human development and it’s disorders-birth defecs, childhood cancers
Functional genomics in human cells
Discovery of novel factors controlling tissue regeneration and repair
In vitro models for dug discovery and toxicology
Schizophrenia, autism and epilepsy are disorder of brain develpoment - what can be used to study them?
ES and iPS cell can model human cortical development
iPSC from patients with these diseaase can be used to recapitulate key events in pathogenesis
