Stem Cells & Differentiation Flashcards
Differentiation (unspecialized to specialized)
Occurs in
- Embryo - embryonic development
- After birth- growth
- Adulthood - maintenance
Differentiation
Distinct ID differential gene expression (morphology & phenotype) also involved in differential gene expression
Differentiation can be triggered by __________
Extracellular signals (inducer to responder)
Fully differentiated
- Terminally differentiated, stop dividing & stable state (have major structural change)
- Blood stem cells - red blood cells lose nucleus & become hemoglobin, white blood cells have multibody nucleus & are granules
Genes for differentiation
RTFs master regulators that are necessary & sufficient for differentiation
MyoD
- RTF muscle differentiation
- Mutate- no muscle (necessary)
- Ectopic expression-muscle (sufficient)
Muscle differentiation
- somites → myoblasts → muscle (Pax3+ + Pax7+ committed, but not differentiated)
- myoblasts divide & stop dividing
- Differentiation make muscle proteins & structural changes (fuse → myotubes → muscle fibers)
Muscle stem cells
Satellite cells (injury → activation → regeneration)
Blood differentiation
Hematopoietic stem cells (HSCs) where its niche is bone marrow, stem cell hallmarks have self-renewal & multipotent
Stem cells
Self-renewal asymmetric division
Skin differentiation
epidermis outer, harsh environ. regenerate (stem cells niche)
Gut differentiation
Gut lining, harsh environ.
regenerate every 4 days (stem cell niche)
Adult stem cells (ASCs) (need niche)
- multipotent (limited)
- HSCs (blood)
- satellite cells (muscle)
- gut stem cells (gut)
Embryonic stem cells (ESCs)(don’t need niche)
- pluripotent (not limited)
- Make all 3 germ layer
- Inner Cell Mass of blastocyst (ICM)
Mouse ESCs
- Self-renewal in vitro
- Indefinity (no niche)
- Pluripotent- inject into blastocyst make all 3 germ layers
ESCs can lead to ________
Disease cells
Maintaining mouse ESCs
- LIF + BMP
- Increase Oct 3/4, Sox2, Esrrb, Kfl4 (RTFs)
- Decrease differentiation
Mouse epiSCs (5 days old)
- Epiblast stem cells (not ESCs)
- Pluripotent in vitro like ESCs
- Can’t form chimera in new animals in vivo unlike ESCs
Human ESCs (not ethical)
- Same RTFs as mouse ESCs
- Maintain stemness in culture
- FGF + Nodal (unlike mouse ESCs)
- BMP → differentiation (unlike mouse ESCs)
Human ESCs is similar to ________
Mouse epiSCs
Plasticity of differentiated cells
- Can dedifferentiate
- Lose differentiated characteristics become “stem cell”
go backwards (divide) - can transdifferentiate no dedifferentiation to diff. cell type
- Test by cloning if a mature nucleus can support embryonic development
Cloning (frogs)
- Somatic cell nuclear transfer (SCNT), somatic nucleus can support embryonic development
- Adult nucleus are old & decrease efficiency & tadpole nucleus is young increase efficiency
Cloning experiment (frogs)
- Adult nucleus ↓ efficiency
- Tadpole nucleus ↑ efficiency
- Blastocyst nucleus ↑↑ efficiency
Genomic equivalence (Frogs)
- Adult nucleus similar to embryonic nucleus
2. No permanent changes to DNA
Cloning in mammals (mouse or sheep like dolly)
- Most die before birth, if survive they became sick
- Low efficiency, where it had incomplete reprogramming of nucleus, reverse epigenetic changes, DNA methylation, & histone modification
- Improper expression (5% of total genes & 50% of imprinted genes)
Cloning in humans
- Therapeutic cloning to blastocyst stage (not implanted)
2. Isolate ESCs for research
Cloning in human have a ________
14-day rule (individualization)- starts gastrulation & stops twinning or fusion
Reproductive cloning
Cloned embryo which led to a cloned uterus which led to a cloned baby (banned)
Therapeutic cloning
Cloning by SCNT, cloned embryo matches the patient, human beings can still give twins (no gastrulation) but it also destroys blastocyst
Is IVF ethical?
Extra embryos (frozen, donated, discarded)
Reprogramming by cell fusion
- Fuse 2 cells (common in cytoplasm, tetraploid)
Chick blood cell
- No transcription
- Fuse with human cell, chick blood cell starts transcription
- Human cell reprogramed chick cell
(shows conservation)
Human liver cells
1. Fuse with mouse muscle human cell (expresses muscle genes)
_________ factors can reprogram
Cytoplasmic
Transdifferentiation
- Reversible stability, change gene expression
- C. elegans- epithelium → neuron
- Common in regeneration
Regenerative medicine
- Organ donation- shortage for 3-5 years & rejection from immunosuppressive drugs
Pros & Cons of ESCs
- Pro: pluripotent
2. Con: Too potent tumor risk & may face rejection if not your own cells
Pro & Cons of ASCs
- Pro: no rejection if from self
2. Con: not pluripotent
iPSCs (induced pluripotent stem cells)
Skin cells + 4 genes → iPSCs, where the 4 genes are the different RTF (Oct 4, Sox2, Kfla4, c- Myc) & also iPSCs is equivalent to ESCs where they are self-renewal & pluripotent (chimera)
Clinical trials with iPSCs
- Macular degeneration
- Skin cells → iPSCs → eye cells
(Injected into patients found not an immune match, had safe slight improvements & the injected cells led to mutations)
Clinical trials with iPSCs (recently)
Patient → iPSCs → eye cells → inject immune match (They started with the eyes because easy access
not vital, easy readout, & 2 eye)
Skin cells → iPSCs → heart cells
Spontaneously assemble beating in a dish
Organoids
Could make things like mini brains or mini kidneys
Blastoids
Artificial “embryo”( Implanted, no live embryo, but has placental cells)