Download Unit 5: Stem cells and Cloning Stem Cells 1. Degenerative diseases

Unit 5: Stem cells and Cloning
Stem Cells
1. Degenerative diseases are diseases where tissues and organs (in full or parts) slowly
break down or die over time
a. Usually continue to weaken until the organs fail
b. Major cause of death in industrialized nations
c. The hope is that stem cells may be able to replace the damaged tissue and
restore it to normal functioning
2. What are stem cells?
a. Stem cells were first isolated from humans in 1998 by Dr. James Thomson at
UW-Madison
b. Stem cells have two basic characteristics
i. Stem cells continue to grow and divide indefinitely
ii. Stem cells can differentiate into a variety of cell types
1. This requires signals, usually hormones or growth factors
3. What is potency?
a. Potency refers to the different possibilities of what stem cells can become
b. Unipotent – can differentiate into one single cell type
c. Multipotent – can differentiate into multiple different cell types
d. Pluripotent – can differentiate into most or all adult cell types (210)
e. Totipotent – can differentiate into all adult cell types as well as specific
developmental cell types (ie. placenta)
4. Where do stem cells come from?
a. There are many sources for stem cells
i. Embryonic stem cells (ES cells)
1. One of the first cells formed during embryonic development
2. Go on to differentiate into all the cells in the adult body
3. Can be cultured and differentiated in a laboratory setting
4. Appear to be pluripotent
ii. Embryonic germ cells (EG cells)
1. Derived from progenitor cells tat will become germ (sperm
and egg) cells
2. From early fetal tissue (5-9 weeks)
iii. Adult stem cells (AS cells)
1. Not only found in adults but also in infants, the placenta and
umbilical cord blood
2. Also called tissue stem cells and non-embryonic stem cells
3. Found in almost all tissues because as ES cells start to
differentiate, the develop slowly and some remain as stem
cells or progenitor cells
Embryonic Stem Cells (ES Cells)
1. Embryonic stem cells form 5-7 days after conception
a. At this point the mass of cells is called a blastocyst (it looks like a hollow
ball)
Unit 5: Stem cells and Cloning
2.
3.
4.
5.
6.
i. The inner layer is called the inner cell mass and these cells are the ES
cells
ii. The outer layer is called the trophoblast and becomes the placenta
Embryonic stem cells can potentially be grown indefinitely in laboratory cultures and
current research supports this
In order to isolate ES cells, and embryo must be destroyed
a. This is one reason for controversy
i. Is a life being destroyed or not?
ii. Even if it is a life, is it worth sacrificing one life to potentially save
others?
How can we tell what ES stem cells can do?
a. There are three primary growth layers in an embryo which are semi
specialized
i. Ectoderm
1. skin, brain and nerves
ii. Mesoderm
1. blood, heart, bone, kidney, muscle, and caritlage
iii. Endoderm
1. lungs, liver, and digestive system
b. In an embryo, we know that stem cells can form into any type of tissue from
any of the three layers
c. If cultured stem cells are injected into an organism and form tissues from
each layer, they are likely to be pluripotent
What is the hope for ES cells?
a. Cells can be grown and then triggered by hormones to become a desired
tissue
i. Could potentially cure or aid in treatment of many degenerative
diseases
1. New nerve cells could be produced for Parkinson’s or
Alzheimer’s patients
2. New pancreas cells could be produced for diabetics
3. New spinal cord neurons could be produced to treat spinal
injury (paralysis)
b. Many years of research are still needed
i. Hormone signals
ii. Transplantation and rejection
iii. Specificity
What are some potential problems with ES cells?
a. Inefficiency of starting and maintaining growth
i. Only 1 in 10 embryos produce stem cells in laboratory culture
b. Inefficiency of forming specific cells outside the embryo
i. Usually, a mixture of cells is produced
ii. Often continue to grow and can form tumors
c. There are no current treatment uses for degenerative diseases
i. In animals, results are modest at best
d. Transplant rejection
Unit 5: Stem cells and Cloning
i. The immune system responds and destroys foreign tissues
ii. Requires anti-rejection drugs
iii. Genetic engineering and cloning are potential solutions
e. Unstable control of gene expression
i. There is quite a bit of variability in how genes are turned on and off
ii. It is difficult to get specific results
Unit 5: Stem cells and Cloning
Adult Stem Cells
1. Adult stem cells are a potential alternative to using embryonic stem cells
2. There have been many challenges and questions (some are valid and others are not)
a. They aren’t in every type of tissue
b. They can’t make all body tissues
c. The are difficult to isolate
d. They are only present in small numbers
e. They cannot keep growing indefinitely they are difficult to use to treat
diseases
3. Recent studies have shown some interesting results that are making scientists
rethink these challenges and questions
a. It appears that adult stem cells have the same key characteristics as ES cells
b. Maybe, adult stem cells are a better answer than embryonic stem cells for
curing degenerative diseases
i. Adult stem cells can also form all body tissues
1. New studies show that stem cells from bone marrow and the
brain can form most tissues
a. Researchers have found what appears to be the
“ultimate stem cell” from bone marrow
i. Can grow indefinitely in lab cultures
ii. Can make all body tissues
ii. Stem cells can be found in most adult tissues
1. Bone marrow has been researched the most
2. Have recently been found in the brain
a. Can be “awakened” to for new brain and nerve cells
(formerly thought to be impossible)
b. Not limited to making nerve tissue
3. Even found in some fat
4. Even though they are found in most tissues, they are difficult
to isolate from some tissue types
a. Brain and spinal cord
5. They can be easily isolated from others
a. Blood, bone marrow, skin
iii. Adult stem cells multiply almost indefinitely
1. Relatively low numbers of adult stem cells can be isolated, but
they can multiply up to one billion fold within weeks in a
laboratory culture
a. Researches originally thought adult stem cells would
get “old” and stop dividing
i. This does not appear to be true
ii. Can still differentiate into all body tissues
iv. Adult stem cells are effective in treating animal disease models
1. Adult stem cells have had very good success treating diseases
in animals
a. Examples include repairing damage from
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Unit 5: Stem cells and Cloning
i. Heart attacks
ii. Stroke
iii. Liver damage
iv. Diabetes
v. Spinal cord injuries
v. Adult stem cells are successfully treating human patients NOW
1. Bone marrow transplants have been done and researched for a
long time
a. Currently, bone marrow transplants are being used to
treat
i. Many cancers
ii. Anemia
iii. Immune deficiencies
iv. Some blood disorders
2. In new, experimental therapy, bone marrow cells are removed
and chemotherapy is used to destroy cancer cells or
malfunctioning immune cells
a. This also kills the remaining bone marrow tissue, but
the stem cells are replaced after therapy, and
regenerates new, healthy bone marrow
3. There are more hopeful treatments in the future
a. These include but are not limited to:
i. Forming new bone
ii. Forming new cartilage
iii. Repairing corneas to treat blindness
iv. Replacing neural tissue to treat strokes
v. Repairing heart muscle tissue to treat heart
attacks
vi. Repairing or replacing damaged skin
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Unit 5: Stem cells and Cloning
Cloning
1. Cloning simply means making an identical copy of something
a. DNA, Cells, Organisms
b. Cloned organisms start as a single celled embryo then grow and develop
c. The first cloned animals were frogs in the 1960’s
d. The first cloned mammal was Dolly the sheep in 1996
2. How does cloning work?
a. Cloning is asexual reproduction rather than sexual reproduction
b. Both sexual and asexual reproduction produce a one-celled embryo, the
difference is how they are produced
c. Sexual reproduction (fertilization)
i. An egg and a sperm cell join
ii. Each cell brings ½ of the genetic variation
iii. A genetically unique embryo is formed
d. Asexual reproduction (cloning)
i. Nuclear material from an egg is removed
1. This process is called enucleation
ii. The nuclear material from a somatic (body) cell of the organism being
cloned is put into the enucleated nucleus
1. This process is called nuclear transplantation or somatic cell
nuclear transfer
iii. The cloned cell is then stimulated to begin development and then
implanted into a woman’s womb at or close to the blastocyst stage
iv. This produces an embryo with no genetic diversity (or VERY little)
3. Why clone?
a. Agricultural uses
i. Identify the “best” animal or plants and then clone them to have ideal
organisms for meat, milk, feed, food, etc
ii. Produce animals that can produce organs for human transplants
b. Humans
i. Reproductive human cloning
1. Allow infertile couples or homosexual couples to have a
genetically related child
2. Replace a child who died in infancy or during the pregnancy
ii. Therapeutic human cloning
1. To harvest embryonic stem cells
4. Reproductive cloning
a. Dolly was the first mammal cloned (1996) and since then mice, goats, pigs,
cattle rabbits, and cats have been cloned as well
i. Most clones don’t survive
1. Very little or no success with dogs, cattle monkeys, and
endangered/extinct animals
b. Reproductive cloning is usually a very inefficient process
i. 277 tries for Dolly (29/277 made it to the blastocyst stage)
ii. 613 tries resulted in 5 mice being born
Cloning
Unit 5: Stem cells and Cloning
iii. 1000 tries resulted in 2 mice being born
iv. 1852 tries resulted in 6 rabbits being born
v. 72 tries resulted in 5 pigs being born
vi. 85 tries resulted in 3 goats being born
vii. 496 tries resulted in 24 cattle being born
viii. 188 tries resulted in 1 kitten being born
c. Problems with reproductive cloning
i. Dolly had early onset arthritis
ii. Most cloned mice die at a young age
iii. Many clones have fertility problems (Dolly did reproduce normally,
however)
iv. Clones typically develop larger and faster and can cause problems for
the surrogate mother
v. Gene reprogramming may be the cause of many of the problems
1. Genes of the egg and the sperm are imprinted (set) to act
differently than those in the adult cell
2. The cytoplasm of the host egg cell must “reset” or
“reprogram” the genes in the new nucleus
3. The failure of this process to occur is likely the reason so
many clones do not survive
vi. There has been almost no success in cloning primates
1. Recent studies have shown that a protein needed for lining up
the chromosomes for proper cell division in mammals is
located next to the nucleus
2. This protein is likely removed during removal of the egg cell
nucleus
d. Human reproductive cloning
i. In April of 2003, the largest documented cloned human embryo and
first intended for reproductive purposes was announced
1. Panos Zavros, from the University of Kentucky, announced
he had created an 8 cell cloned human embryo
2. He plans to do genetic tests for abnormalities and then
implant the embryo into a surrogate mother
5. Therapeutic cloning
a. Theoretically, the embryonic stem cells that could be created would be nearly
identical matches to the patient in need of the treatment
i. The only difference would come from mitochondrial DNA in the host
egg cell
1. This can be up to 1% of the total DNA
2. Up to 13 genes including some surface proteins
b. Problems with therapeutic cloning
i. Because of the inefficiency of cloning, many egg cells would be
required (100’s) for each attempt
1. Women only produce one active egg cell per month
a. Would require hormone therapy and then surgery
which is potentially dangerous
Cloning
Unit 5: Stem cells and Cloning
2. The proposal is to use cow and rabbit eggs instead
a. Do we really want to start mixing species?
c. Alternatives to therapeutic cloning
i. Research is being done on parthenogenesis
1. Causing an egg cell to keep 100% of the DNA and then
reprogramming it to start development
a. Would only benefit women of child bearing age
ii. Research is also being done on androgenesis
1. Placing nuclear material from two sperm cells into one
enucleated egg
a. So far does not produce normal embryos
Cloning