Stem cells Flashcards
What is a stem cell?
- cells able to divide to give rise to new cells required to make and maintain the cells, tissues and organs of multicellular organisms.
- undifferentiated, not engaged in a specific physiological function
- have “potential”
- “self-renewal”
Describe “potential”
- aka potency
- a population of stem cells can be the source of some, many or even all cell types in an organism
Describe “self-renewal”
maintained through rounds of cell division
Describe asymmetric cell division
gives rise to one “stem cell” and one “committed cell”
Describe symmetric division with asymmetric population behaviour
gives rise either to two “stem cells”, OR two “committed cells”
Cells acquire … during development
more restricted fates
Describe development from the zygote
- blastula
- gastrula
- germ cells (male, female) and derm layers (endo, meso, ecto)
Describe the endoderm
- stomach cells make digestive tube
- thyroid cells in pharynx
- alveolar cells in respiratory tubes
- intestinal epithelium cells
Describe the mesoderm
- dorsal notochord
- paraxial bone tissue
- intermediate kidney tubule cells
- lateral erythrocytes, lymphocytes and monocytes
- facial muscles in the head
Describe the ectoderm
- epidermal fibroblast on outer surface
- neurones of CNS
- melanocytes of neural crest
Describe fate-mapping
identifies early cells
Describe totipotency
- makes everything, including extraembryonic tissue (placenta)
- zygote and morula
Describe pluripotency
- can make all cells in the embryo and adult
- germ layer specified
- blastocyst
Describe multipotency
- all cell types of a tissue or organ
- germ layer specified
- blastocoel and grastula
Describe oligopotency
can make several, related cell types
Describe unipotentcy
can make only one cell type
What happens at the grastula boundary?
- differentiation
- proliferation
- migration
- signalling
- morphogenesis
- organogenesis
- growth
- homeostasis
- regeneration
Describe the lineage process
- stem cells become progressively more ‘determined’ during development
- potency deceases as lineage progresses
Describe adult stem cells
continue to maintain our tissues and organs in response to ”wear and tear”, ”infection/disease” and
“other environmental factors/toxins”
Describe developmental stem cells
maintained as adult stem cells
Which stem cells makes intestinal epithelial cells?
intestinal stem cells
Which stem cell makes lymphocytes, monocytes and erythrocytes?
haemtopoetic stem cells
Which stem cells makes skin fibroblast?
epidermal stem cell
Describe transit amplifying cells
- derived from stem cells later in development and adult stem cells
- lineage committed
- neither differentiated nor “self- renewing”
- divide several times to expand to a population of cells that eventually differentiates
- reduces the number of divisions a stem cell makes
Describe gene regulation inside stem cells
- TFs
- epigenetic/chromatin modifications
- microRNAs
- external signals can drive differentiation to the required fates
- for control and manipulation of stem cells
Describe TFs in stem cells
- maintain a stable undifferentiated state
- supress genes that drive differentiation
Describe epigenetic/chromatin modification in stem cells
- histone modifications
- DNA methylation
- transcriptionally silence regions that would lead to differentiation
- allow expression of genes for the present state
Describe microRNAs in stem cells
alternate splicing of transcripts
ICM
inner cell mass
Describe the production of mammalian pluripotent embryonic stem cells
- taken from the ICM of embryos
- highly defined mix of media and growth/signalling factors
- maintained in an undifferentiated state
- different levels of readiness to differentiate
Describe the different levels of readiness to differentiate
naive > formative > primed
Describe mammalian pluripotent ESCs
- pluripotent
- able to form teratomas
- distinct gene expression profile, associated with
animal germlines
Describe an embryo
- trophectoderm
- inner cell mass
- primitive endoderm
Human embryonic stem cells can
self-organise and pattern in culture
Describe the in vivo evidence of ESC pluripotency
- take blastocyst from mouse with white fur
- inject ESC from mouse with black fur to create a chimera
- second generation you can get a mouse with black fur
Summarise the in vivo evidence of ESC pluripotency
generation of donor genotype in the F2 confirms contribution to the chimeric germline
Describe gene targeting for transgenic mice
target gene undergoes homologous recombination
Describe random integration for transgenic mice
integration and insertion within a random gene
Describe assaying pluripotency
- in vitro experiments study cell competence and regulation over time
- in vivo reimplantation of ESCs back into embryos allows observation of their contribution
- genetic manipulation of cells for transgenic mice
Describe iPSCs
- 4 TFs responsible for reprogramming activity
- form teratomas
- can contribute to all 3 germ layers, and the germline
Describe Gurdon’s expts
- nuclear transfer in frogs
- prove the genome is not diminished as a method of gene regulation during differentiation
- challenged prevailing theory that cells fates were stable
- frog egg cytoplasm could reprogram the transplanted nucleus of a differentiated cell
Which are the 4 TFs necessary for reprogramming?
- Oct3/4
- Sox2
- Klf4
- c-Myc
c-Myc
oncogene
Describe transcriptional control in “primed” pluripotent cells
- levels of TFs vary stochastically
- addition of BMP4 pushes cells with low Oct4 to extraembryonic fates
Describe epigenetic/chromatin based regulation of primed human pluripotent stem cells
- genes required for pluripotency are ON
- genes required for later differentiation are OFF
- genes that might need to switch on soon are in a BIVALENT state
Describe gene bivalence
ready to switch on or to be
silenced depending on the initial differentiation decision made
Describe haematopoietic stem cells (HSCs)
- relatively rare (40k-200K)
- produce >200 billion RBCs alone
- > 2.3 million cells produced per second
- different progenitors in the lineage with different potencies
Where did the stem cell concept arise?
study of the bone marrow transplants into irradiated mice
How are different HSCs identified
- creating antibodies to distinct combinations of cell surface markers
- FACS allows them to be isolated from the rest of the population
FACS
Fluorescence Activated Cells Sorting
Which diseases and conditions are treated with HSCs?
- sickle cell anaemia
- autoimmune diseases
Describe adult intestinal stem cells
- Paneth cells at the base of the intestinal crypts
What is one underlying cause of ageing?
the capacity of stem cells to replicate and maintain tissues is limited
