Cloning and Stem Cells
A wood panel painting
depicting the limb
transplantation miracle by
Saints Cosmas and
Damian. According to legend
Cosmos and Damian were
physicians who successfully
transplanted the limb of a
dead Ethiopian onto a
Turkish patient whose leg
required amputation (~C.A.
284).
Can we regenerate parts of the body?
• Red Deer replace their antlers every year. It takes
~3 months.
• We replace our blood cells. ~100 million /hour
• If part of the human liver is removed, it will re-grow
• Salamanders and Newts can re-grow their limbs
•Video – newt limb regeneration
In general:
regeneration in vertebrates doesn’t
work very well
Limbs and most organs aren’t replaced
How do cells know what to do,
and what not to do?
• Cells contain DNA
• DNA makes up discrete recipes or programs
called genes
• Every cell of the body has exactly the same set
of genes
• Depending on the type of cell, some genes are
“turned on” and many are “turned off”.
•Differentiated Cells are those cells with a
specialization, and have a very specific set
of genes activated. i.e. neurons, liver cells,
skin cells, etc.
What is a Stem cell?
An undifferentiated cell of an embryo that
can either
• Reproduce itself
OR
• Enter a differentiation pathway whereby
one of its daughters is differentiated and
the other stays an undifferentiated stem
cell (totipotent)
What are we trying to do with Stem Cells?
The goal is to replace cells damaged or destroyed by disease
with healthy functioning ones. Some of the diseases they can
help include:
• Cancer
• Parkinson's disease
• Diabetes
• Various injuries (e.g. spinal cord)
• Eye diseases
Types of Stem Cell Therapy
• Adult stem cell transplants using bone marrow stem cells
• Adult stem cell transplants using peripheral stem cells
• Stem cell transplants using umbilical cord blood
• Therapeutic cloning
Can cells be reprogrammed?
Experimental Example: Amphibian tadpole:
Preprogrammed Muscle cells were transplanted
into gut region of cells in the embryo but they
stayed as muscle cells.
Cells are programmed and “know’ what they
will become if the cells stay intact. How?
Totipotent: Having the ability to differentiate into
ALL cell types.
For example, the zygote (newly fertilized egg)
and early embryonic cells are totipotent since
they can differentiate into any cell type during
development.
Pluripotent: Having the ability to differentiate into
many cell types.
In Mammals, embryonic stem cells are pluripotent,
and came from totipotent cells. They can
differentiate into various fetal or adult cells.
Where do we get stem cells?
Stem cells can be found naturally in
1) A Fertilized Egg
(embryonic stem cells (ES)):
150 cells called (blastocyst) contains two types
of cells:
1) trophoblast
2) inner cell mass
Embryonic stem cells are obtained from the
inner cell mass.
Video: (human emb. development)
A reliable stem cell reference: http://www.isscr.org/science/faq.htm
Other ways to get stem cells:
2. Cancers can form a variety of cell
types
(connective tissue, cartilage, blood cells)
can be transplanted into host
Ovarian cancer stem cells
animals and in some cases turn into
non-cancerous normal cells
3. (Since 1981)
Start w/ an embryo.
Blastocyst cells can be put in culture and
grow indefinitely.
When put into a host they will differentiate
into a variety of cells.
Stem cells are found in small numbers in
various tissues in the fetal and adult body
Examples:
• blood stem cells are found in bone
marrow → give rise to all specialized
blood cell types.
• newborn baby: umbilical cord,
possibly baby teeth and amniotic fluid
These adult stem cells are multipotent – able to
differentiate into a limited number of cell types.
Stem cells tend to make a
heterogeneous collection
of differentiated cells
Video: creating lines
We haven’t figured out how
to make stems cells
differentiate into every
single type of tissue.
…..Yet.
Advantages of Embryonic Stem cells
• Capacity for indefinite proliferation in
culture
• Can be differentiated into a variety of
cells including germ cells
• Can be maintained as frozen stocks
•Problems:
–Undergo spontaneous genetic changes
–Hard to make into certain cell types (e.g. pancreas) (nerve
tissue is fairly easy to make, however)
–Immuno-rejection unless patient is immuno-suppressed. (not
ideal).
Nuclear reprogramming and
Therapeutic cloning
• Can we make
rejuvenated
embryonic cells from
adult
differentiated
cells (of the same
individual)?
• This would avoid the
problem of immunorejection
Somatic Cell Nuclear transfer
1. Start with egg (frog, mouse, human)
2. Use UV to kill pronucleus (egg chromosome)-left
w/ cytoplasm
3. Pick up another cell in a way such that the cell
wall is broken but intact nucleus (using a special
micropipette)
4. Inject the intact nucleus into the cytoplasm-only
egg cell. The cell thinks It’s been fertilized. It
starts to grow into an embryo and then an adult.
•This cloning is inappropriate in humans (called
reproductive cloning) video: SCNT
http://www.dnalc.org/cloning.html
Problems w/ SCNT
(somatic cell nuclear transfer)
• Some transplanted nuclei show a longterm memory of their original gene state
so they won’t allow reprogramming.
• only about 1/3 of nuclear transplants work
However, we’re making progress!
Legal Issues
In the United States, as of July 2011:
• it is illegal to use federal funding for
research on human embryos derived from
SCNT.
• It is legal to use federal funding for
research on embryos derived from IVF, if
those embryos are not going to be used
for anything else (like making a baby).
Long-term Goal
Reprogram cells without having them go
through a nuclear transfer to an egg
In the news:
Sept. 2007 “Researchers
Isolate Adult Stem
Cells for First Time in
Tendon tissue” (adult
fibroblasts)
Maybe a cure for Alzheimer's disease,
Parkinson's disease, and spinal cord injury,
Lots of stories out there….
Induced Plueripotent Stem cells (iPS)
also called Adult Stem cells
iPS cells from adult human cells
Developed by two independent research teams:
James Thomson and colleagues at University of
Wisconsin-Madison
Shinya Yamanaka and colleagues at Kyoto
University, Japan
Common Ethical Objections
• Slippery slope – where do you draw the line
between frogs & mice, and humans
• Cloning is unnatural. (Antibiotics are unnatural
also)
• Killing of a potential life. “An embryo = a human
being” Actually, an embryo would never
progress until it is put into a womb.
• It’s good for us to see how others tolerate
suffering.