Download STEM CELLS

Bi 1
“Drugs and the Brain”
Lecture 24
Tuesday, May 23, 2006
Cell cycle, Stem Cells, and Stem Cell Therapy
(Thanks to Prof David Anderson for some of the slides)
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Bi 1 in the next 2 weeks (for undergraduates)
Tuesday, May 23. Lecture 26. Cycle Cycle / Stem Cells
Problem Set 8 posted. Parkinson’s disease, stem cells, cell cycle
Thursday, May 25. Lecture 27. Evolution 1: Molecular Biology.
Thursday-Friday, May 25/26. Section meetings as usual. 5:30 Fri Undergrad BBQ
Monday, 5/28. Memorial day, no lecture.
Tuesday, 5/29. Lecture 28. Evolution 2. The eye.
Problem Set 8 due, 11 AM (seniors too)
Thursday 6/1. Lecture 29. Last lecture.
Evolution 3. Voyages to the Galapagos; the Physiology of Diving.
Final exam review Session: 4 PM here, 119 Kerckhoff
Thursday 6/1: Final Exam posted
Thursday-Friday 6/1-2 Section meetings as usual
Friday 6/9. Final exam due 4:30 PM, Bi 1 closet.
for the “official word”, see http://www.its.caltech.edu/~bi1/schedule.html
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Overview of the cell cycle
mitosis
gap2
(growth2)
mammals
24 h
gap1
(growth1)
yeast
90 min
DNA
synthesis
based on
Little Alberts 19-2
© Garland publishing
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”Checkpoints” in the cell cycle
based on
Little Alberts 18-4
4
© Garland publishing
Cdk-cyclin complexes govern progression through the checkpoints
(simplified view)
These proteins are regulated by
1. Kinase-mediated protein phosphorylation (lecture 14);
2. Ubiquitin-mediated proteolysis (lecture 18).
a cyclin-dependent
kinase (Cdk):
phosphorylates
many proteins
a cyclin:
required
for kinase
activity
P
Cdk is
itself activated by
phosphorylation
based on Little Alberts 18-7
© Garland publishing
Cdk is deactivated
by
dephosphorylation
when the cyclin is
destroyed
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Cdk-cyclin complex is a “mitosis promoting factor” (MPF)
also assayed by injecting into frog eggs
based on
Little Alberts 18-6
© Garland publishing
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Yeast uses the same Cdk at
both checkpoints;
mammals use different Cdks
at each checkpoint.
A yeast whose own Cdk is
mutated, and therefore
fails to divide, can be
rescued by expressing
human Cdk.
 the cell cycle machinery
arose > 109 y ago !
Lectures 27, 28, 29 will
concern evolution.
Little Alberts 18-13
© Garland publishing
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Some growth factors instruct cells to continue in the cell cycle
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9
onco-, cancer
But many molecules in this pathway can mutate to form oncogenes
inactive growth
factor receptor
activated growth
factor receptor
abnormally active
growth factor receptor
abnormally
active GPCR
based on
Little Alberts 1st edition 18-23
© Garland publishing
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A final stage, cell death, is also regulated by multiple mechanisms
dying nerve cells
Some autistic people have abnormally large brains.
There is speculation about insufficient cell death.
Little Alberts 18-27
© Garland publishing
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After Several Cell Cycle Divisions, most Cells Eventually Differentiate . . .
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. . . But Undifferentiated Cells Called “Stem Cells” Persist in some Adult Tissues
Embryo
Persistent
Undifferentiated
Cell
Adult
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Stem Cells can Both
Differentiate
and
Continue Cycling (Self-Renewal)
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Stem Cells can Generate Several Types of Differentiated Cells
D1
D2
........
Dn
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As noted in slide 13, Stem Cells Exist in both Embryos and Adults
Embryonic Stem Cells
Adult Stem Cells
Newly formed tissues and
organs
Natural turnover
Regeneration
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Isolating Stem Cells
Piece of Tissue
Multipotency
Self-renewal
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Stem Cells are Sometimes Purified Using Specific Cell Surface Markers
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Early example: a “Tissue-Specific” Stem Cell for the Blood and Immune System . . .
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. . . now we can work with Neural Stem Cells
Neural
Tube
Peripheral
neurons and
related cells,
some muscles
CNS
Neurons
Some types of glia
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“Regenerative Medicine”:
Stem Cells for Repair of Diseased or Injured Tissue?
•Blood
•Skin
•Pancreas
•Heart
•Liver
•Muscle
•Brain
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Cell Replacement Therapy for Neurodegenerative Disease?
Parkinson’s
Huntington’s
Alzheimer’s
Amyotrophic lateral sclerosis (ALS)
Spinal cord injury
Multiple sclerosis (MS)
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Theoretical example:
Cell Transplant Therapy for Parkinson’s Disease
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Approaches to Stem Cell Therapies For Neurological Disease
1.
Transplantation of neural stem cells
Donor: fetal brain
Advantages
Disadvantages
What Organism Should Supply the Stem Cells?
People
Lawyers
Animals
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True Embryonic Stem Cells Can Generate All Cell Types in the Body
Tissue-specific stem cells:
Germ-line
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1998: Human ES Cells
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Contribution of ES Cells to Internal Tissues in Chimeras
(Carrying a GFP reporter gene)
Chimeric embryo reveals
ES-derived
GFP-expressing cells
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Approaches to Stem Cell Therapies For Neurological Disease
2.
Transplantation of ES cell-derived neural stem cells
3.
Advantages
Donor: blastocyst
Disadvantages
Material comes from IVF clinics;
access to aborted fetal tissue not
required
• Risk of graft vs. host disease;
Immunosuppression needed
Cloning: 1960’s
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1997: Dolly, a Cloned Mammal
Success rate: 1/277. Dolly is now dead
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Step 1: The Egg’s Nucleus is Removed
(= the Egg is Enucleated)
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Step 2: A Somatic Nucleus is Injected into the Enucleated Egg
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Step 3:
The Injected Egg is Chemically Activated to Induce Nuclear Division
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Step 5: The Embryoid is Cultured Until a Blastocyst Develops
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Step 6:
The Inner Cell Mass (A) is Removed from the Blastocyst and Cultured
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Step 7: Individual Human ES Colonies are Isolated
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Approaches to Stem Cell Therapies For Neurological Disease
3.
Transplantation of ES cell-derived neural stem cells
Donor: nuclear transfer
“somatic cell nuclear transfer” aka
“therapeutic cloning”
Advantages
Disadvantages
-economics
Pending legislation to criminalize procedure
Some Unsolved Questions in Cloning and Stem Cell Research
• Why is producing ES cells by nuclear transplantation so inefficient?
• What events are involved in reprogramming a somatic cell nucleus to
regain pluripotency?
• How do we differentiate ES cells along particular lineages?
• How do we move from cell differentiation, to organogenesis?
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2004: California Takes the Lead with Prop 71
• Establishes the California Institute of Regenerative Medicine (CIRM)
• Allocates $3 billion over a 10-year period for stem cell research
• Provides funding for research with hES lines not fundable with federal
funds
– ie, all hES lines generated after 8/9/01
• Funding can be used for somatic cell nuclear transplantation
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Neurogenesis: new neurons are born in the adult rat and mouse brain
. . . but we don’t know whether it happens in primate brain.
Hippocampus
Gage, F.H. (2000) Science 287:1433-1438
Olfactory Bulb
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Approaches to Stem Cell Therapies For Neurological Disease
4.
Transplantation of adult brain cells
Donor: adult brain
Advantages
Disadvantages
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Adult Stem Cell Plasticity:
Bone Marrow-Derived Stem Cells for Brain
Would Provide
Stem Cell Therapy without Transplantation
?
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Approaches to Stem Cell Therapies For Neurological Disease
5.
In vivo mobilization of endogenous brain stem cells with growth factors
Advantages
Disadvantages
• Not all brain regions may respond to
the factors
Bi 1
“Drugs and the Brain”
Lecture 24
Tuesday, May 23, 2006
Cell cycle, Stem Cells, and Stem Cell Therapy
45
Adult Stem Cell Therapies for Neurological Disease?
• Adult neural stem cells
• Adult bone-marrow-derived stem cells
• In vivo mobilization
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Mouse ES Cells Differentiated into Motor Neurons
Wichterle et al. (2002) Cell 110:385
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Does Any of This Have a Prayer of Working?
I SEE CELLS IN
YOUR BRAIN!
HOW LONG DO
I HAVE TO
WAIT?!
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We Need More Basic Research on Stem Cells
?
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