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What are stem cells?
Stem cells are generally very early stage cells that have the ability to turn into
other specialised types of cells.
For example a stem cell can turn into liver cells, skin cells , nerve cells etc.
These early stage cells can have differing abilities to turn into more specialised
cells.
There are generally 3 types of stem cells that are important:
embryonic stem cells
adult stem cells
umbilical cord stem cells
Stem cells are called stem cells because of the way the word 'stem' is used.
A dictionary will tell you that 'stem' means the main ascending (going up) stalk
of a plant. Similarly there are main cells that grow through time, a main stem from
which other stems can branch out from.
If you follow the origin of a particular cell backwards through its' life there are
particular you will get to a point at which all the cells are essentially the same
biochemically.
The diagram below gives you an analogy of a tree stem and the the types of cells
that are derived from the main 'stem' or mother of all cells.
The word 'stem' is thought to be from the old english but the word also can sometimes
mean 'to stop or to slow down' (from old Norse) so it could be that stem cells tend
to stop at a particular point and doesn't continue in the same direction for ever.
As tem slows down and changes direction. For stem cells they tend to stop and slow
down and turn into other types of cells.
Why are stem cells important?
Stem cells are significant for a number of reasons. These include things like:
Potential therapeutic uses such as:
cures for diabetes, brain diseases like Parkinson. Treatments for cancer
or Multiple sclerosis (MS)
Ethical concerns
Issues of when is a human human, misuse.
Scientific curiosity- simply knowing how cells can change from one function to another.
On a very basic level stem cells are interesting in trying to understand how such
cells store information and then turn into other cells with very different properties
is quite a fascinating topic.
How a cell goes from type A to type B is part of discovering something about ourselves
and the world we live in.
Stem cell research may also be useful for improvement of livestock or other animals
How are stem cells classified?
Generally there are 2 types of stem cells, embryonic and adult stem cells.
Embryonic - technically called totipotent
and produce all types of tissue. This is the very early stage of a recently fertilised
egg and has only about 8 cells( morula)
Inner cells-pluripotent
can become almost all types of cells and are taken from an early embryo stage.
Adult stem cells are typically called multipotent
cells like bone marrow cells that can produce a wide range of different blood cells.
There are also some cell types in the body that have be
But there is continuing research into if it is possible to make multipotent cells
into pluripotent types.
How are these types of cells developed?
Embryonic stem
cells are 'harvested' or collected from the very early stages of a fertilised egg
called a blastocyst.
Adult stem cells
are collected from a limited number of cell types in the body. Typically these are
bone marrow cells or from very early stages of tissue development.
Umbilical cord stem cells
are collected from the cells of the umbical cord of a recently born baby. Some of
these cells are slightly undeveloped and so can turn into other types of cells (multipotent)
There are wide range of chemical signals from nearby cells that direct what the cells
should become. There are even signals from the uterus where the embryos are normally
held.
What is the history of stem cells?
Stem cells themselves have actually been around for almost as long as life has been
on earth. In essence all life evolved from stem cells of some kind.
Many of the earliest forms of life on earth were not much more complex than stem
cells.
Stem cell research has been around for almost as long as microscopes. Though it is
only within the 1980s that more sophisticated genetechnology developments have allowed
for the culturing (growing of cells) in laboratories.
Fetal nerve cells were one of the first 'stem cells" not real stem cells though were
used to treat Parkinson.
source:
Lasker Foundation
Later in 1998 a team from
University of Wisconsin
managed to grow human stem cells in culture.
The future of stem cells?
Stem cell research is about the future, it is cutting edge technology that brings
a headline each day. So stem cell research is likely to continue in various forms.
The main controversy is the use of human embryonic stem cells.
The future of stem cells is a consideration of the benefits and dangers of the technology.
It is similar to many other kinds of technology.
EurekaAlert provides a portal to some of the most recent scientific discoveries about
stem cells
that points to the future uses of stem cells.
About the Author
Richard, has worked explaining science for the past 10 years, including at Questacon,
Mount Stromlo, CSIRO, the Maritime Museum in Greenwich, and various schools in South
East London. He studied immunology and biochemistry at ANU.
If there is something important missing please let me know
THANK YOU FOR VISITING
stem cells.
ClearlyExplained.Com
http://clearlyexplained.com/nature/life/cells/stemcells.html
>
This document covers basic information about stem cells. For a more detailed discussion,
see our
Research on stem cells is advancing knowledge about how an organism develops from
a single cell and how healthy cells replace damaged cells in adult organisms. This
promising area of science is also leading scientists to investigate the possibility
of cell-based therapies to treat disease, which is often referred to as
regenerative or reparative medicine
.
Stem cells are one of the most fascinating areas of biology today. But like many
expanding fields of scientific inquiry, research on stem cells raises scientific
questions as rapidly as it generates new discoveries.
The NIH developed this primer to help readers understand the answers to questions
such as: What are stem cells? What different types of stem cells are there and where
do they come from? What is the potential for new medical treatments using stem cells?
What research is needed to make such treatments a reality?
A. What are stem cells and why are they important?
Stem Cells for the Future Treatment
of Parkinson's Disease
Parkinson's disease (PD) is a very common neurodegenerative disorder that affects
more than 2% of the population over 65 years of age. PD is caused by a progressive
degeneration and loss of dopamine (DA)-producing
neurons
, which leads to tremor, rigidity, and hypokinesia (abnormally decreased mobility).
It is thought that PD may be the first disease to be amenable to treatment using
stem cell transplantation. Factors that support this notion include the knowledge
of the specific cell type (DA neurons) needed to relieve the symptoms of the disease.
In addition, several laboratories have been successful in developing methods to induce
embryonic stem cells to differentiate into cells with many of the functions of DA
neurons.
In a recent study, scientists directed mouse embryonic stem cells to differentiate
into DA neurons by introducing the
gene
Nurr1. When transplanted into the brains of a rat model of PD, these stem cell-derived
DA neurons reinnervated the brains of the rat Parkinson model, released dopamine
and improved motor function.
Regarding human stem cell therapy, scientists are developing a number of strategies
for producing dopamine neurons from human stem cells in the laboratory for transplantation
into humans with Parkinson's disease. The successful generation of an unlimited supply
of dopamine neurons could make neurotransplantation widely available for Parkinson's
patients at some point in the future.
Stem cells have two important characteristics that distinguish them from other types
of cells. First, they are unspecialized cells that renew themselves for long periods
through cell division. The second is that under certain physiologic or experimental
conditions, they can be induced to become cells with special functions such as the
beating cells of the heart muscle or the insulin-producing cells of the pancreas.
Scientists primarily work with two kinds of stem cells from animals and humans:
embryonic stem cells
and
adult stem cells
, which have different functions and characteristics that will be explained in this
document. Scientists discovered ways to obtain or derive stem cells from early
mouse
embryos more than 20 years ago. Many years of detailed study of the biology of mouse
stem cells led to the discovery, in 1998, of how to isolate stem cells from
human
embryos and grow the cells in the laboratory. These are called
human embryonic stem cells
. The embryos used in these studies were created for infertility purposes through
in vitro fertilization
procedures and when they were no longer needed for that purpose, they were donated
for research with the informed consent of the donor.
Stem cells are important for living organisms for many reasons. In the 3- to 5-day-old
embryo, called a
blastocyst
, stem cells in developing tissues give rise to the multiple specialized cell types
that make up the heart, lung, skin, and other tissues. In some adult tissues, such
as bone marrow, muscle, and brain, discrete populations of adult stem cells generate
replacements for cells that are lost through normal wear and tear, injury, or disease.
It has been hypothesized by scientists that stem cells may, at some point in the
future, become the basis for treating diseases such as Parkinson's disease, diabetes,
and heart disease.
Scientists want to study stem cells in the laboratory so they can learn about their
essential properties and what makes them different from specialized cell types. As
scientists learn more about stem cells, it may become possible to use the cells not
just in
cell-based therapies
, but also for screening new drugs and toxins and understanding birth defects. However,
as mentioned above, human embryonic stem cells have only been studied since 1998.
Therefore, in order to develop such treatments scientists are intensively studying
the fundamental properties of stem cells, which include:
1. determining precisely how stem cells remain unspecialized and self renewing for many
years; and
2. identifying the
signals
that cause stem cells to become specialized cells.
B. Scope of this document
This primer on stem cells is intended for anyone who wishes to learn more about the
biological properties of stem cells, the important questions about stem cells that
are the focus of scientific research, and the potential use of stem cells in research
and in treating disease. The primer includes information about stem cells derived
from the embryo and adult. Much of the information included here is about stem cells
derived from human tissues, but some studies of animal-derived stem cells are also
described.
II. What are the unique properties of all stem cells?
Stem cells differ from other kinds of cells in the body. All stem cells—regardless
of their source—have three general properties: they are capable of dividing and renewing
themselves for long periods; they are unspecialized; and they can give rise to specialized
cell types.
Scientists are trying to understand two fundamental properties of stem cells that
relate to their
long-term self-renewal
:
1. why can
embryonic stem cells
proliferate for a year or more in the laboratory without differentiating, but most
adult stem cells
cannot; and
2. what are the factors in living organisms that normally regulate stem cell
proliferation
and self-renewal?
Discovering the answers to these questions may make it possible to understand how
cell proliferation is regulated during normal embryonic development or during the
abnormal
cell division
that leads to cancer. Importantly, such information would enable scientists to grow
embryonic and adult stem cells more efficiently in the laboratory.
Stem cells are unspecialized.
One of the fundamental properties of a stem cell is that it does not have any tissue-specific
structures that allow it to perform specialized functions. A stem cell cannot work
with its neighbors to pump blood through the body (like a heart muscle cell); it
cannot carry molecules of oxygen through the bloodstream (like a red blood cell);
and it cannot fire electrochemical
signals
to other cells that allow the body to move or speak (like a nerve cell). However,
unspecialized stem cells can give rise to specialized cells, including heart muscle
cells, blood cells, or nerve cells.
Stem cells are capable of dividing and renewing themselves for long periods
. Unlike muscle cells, blood cells, or nerve cells—which do not normally replicate
themselves—stem cells may replicate many times. When cells replicate themselves many
times over it is called proliferation. A starting population of stem cells that proliferates
for many months in the laboratory can yield millions of cells. If the resulting cells
continue to be unspecialized, like the parent stem cells, the cells are said to be
capable of long-term self-renewal.
The specific factors and conditions that allow stem cells to remain unspecialized
are of great interest to scientists. It has taken scientists many years of trial
and error to learn to grow stem cells in the laboratory without them spontaneously
differentiating into specific cell types. For example, it took 20 years to learn
how to grow
human embryonic stem cells
in the laboratory following the development of conditions for growing mouse stem
cells. Therefore, an important area of research is understanding the signals in a
mature organism that cause a stem cell population to proliferate and remain unspecialized
until the cells are needed for repair of a specific tissue. Such information is critical
for scientists to be able to grow large numbers of unspecialized stem cells in the
laboratory for further experimentation.
Stem cells can give rise to specialized cells. When unspecialized stem cells give
rise to specialized cells, the process is called
differentiation
. Scientists are just beginning to understand the signals inside and outside cells
that trigger stem cell differentiation. The internal signals are controlled by a
cell's
genes
, which are interspersed across long strands of DNA, and carry coded instructions
for all the structures and functions of a cell. The external signals for cell differentiation
include chemicals secreted by other cells, physical contact with neighboring cells,
and certain molecules in the
microenvironment
.
Therefore, many questions about stem cell differentiation remain. For example, are
the internal and external signals for cell differentiation similar for all kinds
of stem cells? Can specific sets of signals be identified that promote differentiation
into specific cell types? Addressing these questions is critical because the answers
may lead scientists to find new ways of controlling stem cell differentiation in
the laboratory, thereby growing cells or tissues that can be used for specific purposes
including
cell-based therapies
.
Adult stem cells typically generate the cell types of the tissue in which they reside.
A blood-forming adult stem cell in the bone marrow, for example, normally gives rise
to the many types of blood cells such as red blood cells, white blood cells and platelets.
Until recently, it had been thought that a blood-forming cell in the bone marrow—which
is called a
hematopoietic stem cell
—could not give rise to the cells of a very different tissue, such as nerve cells
in the brain. However, a number of experiments over the last several years have raised
the possibility that stem cells from one tissue may be able to give rise to cell
types of a completely different tissue, a phenomenon known as
plasticity
. Examples of such plasticity include blood cells becoming
neurons
, liver cells that can be made to produce insulin, and hematopoietic stem cells that
can develop into heart muscle. Therefore, exploring the possibility of using adult
stem cells for cell-based therapies has become a very active area of investigation
by researchers.
III. What are embryonic stem cells?
A. What stages of early embryonic development are important for generating embryonic
stem cells?
Embryonic stem cells
, as their name suggests, are derived from embryos. Specifically, embryonic stem
cells are derived from embryos that develop from eggs that have been fertilized
in vitro
—in an
in vitro fertilization
clinic—and then donated for research purposes with informed consent of the donors.
They are
not derived from eggs fertilized in a woman's body. The
embryos
from which
human embryonic stem cells
are derived are typically four or five days old and are a hollow microscopic ball
of cells called the
blastocyst
. The blastocyst includes three structures: the
trophoblast
, which is the layer of cells that surrounds the blastocyst; the
blastocoel
, which is the hollow cavity inside the blastocyst; and the
inner cell mass
, which is a group of approximately 30 cells at one end of the blastocoel.
B. How are embryonic stem cells grown in the laboratory?
Growing cells in the laboratory is known as
cell culture
. Human embryonic stem cells are isolated by transferring the
inner cell mass
into a plastic laboratory culture dish that contains a nutrient broth known as
culture medium
. The cells divide and spread over the surface of the dish. The inner surface of
the culture dish is typically coated with mouse embryonic skin cells that have been
treated so they will not divide. This coating layer of cells is called a
feeder layer
. The reason for having the mouse cells in the bottom of the culture dish is to give
the inner cell mass cells a sticky surface to which they can attach. Also, the feeder
cells release nutrients into the culture medium. Recently, scientists have begun
to devise ways of growing embryonic stem cells without the mouse feeder cells. This
is a significant scientific advancement because of the risk that viruses or other
macromolecules in the mouse cells may be transmitted to the human cells.
Over the course of several days, the cells of the inner cell mass proliferate and
begin to crowd the culture dish. When this occurs, they are removed gently and plated
into several fresh culture dishes. The process of replating the cells is repeated
many times and for many months, and is called
subculturing
. Each cycle of subculturing the cells is referred to as a
passage
. After six months or more, the original 30 cells of the inner cell mass yield millions
of embryonic stem cells. Embryonic stem cells that have proliferated in cell culture
for six or more months without differentiating, are
pluripotent
, and appear genetically normal are referred to as an
embryonic stem cell line
.
Once cell lines are established, or even before that stage, batches of them can be
frozen and shipped to other laboratories for further culture and experimentation.
C. What laboratory tests are used to identify embryonic stem cells?
At various points during the process of generating embryonic stem cell lines, scientists
test the cells to see whether they exhibit the fundamental properties that make them
embryonic stem cells. This process is called characterization.
As yet, scientists who study human embryonic stem cells have not agreed on a standard
battery of tests that measure the cells' fundamental properties. Also, scientists
acknowledge that many of the tests they do use may not be good indicators of the
cells' most important biological properties and functions. Nevertheless, laboratories
that grow human embryonic stem cell lines use several kinds of tests. These tests
include:
growing and subculturing the stem cells for many months. This ensures that the cells
are capable of long-term self-renewal. Scientists inspect the cultures through a
microscope to see that the cells look healthy and remain
undifferentiated
.
using specific techniques to determine the presence of
surface markers
that are found only on undifferentiated cells. Another important test is for the
presence of a protein called Oct-4, which undifferentiated cells typically make.
Oct-4 is a transcription factor, meaning that it helps turn
genes
on and off at the right time, which is an important part of the processes of cell
differentiation
and embryonic development.
examining the chromosomes under a microscope. This is a method to assess whether
the chromosomes are damaged or if the number of chromosomes has changed. It does
not detect genetic mutations in the cells.
determining whether the cells can be subcultured after freezing, thawing, and replating.
testing whether the human embryonic stem cells are pluripotent by 1) allowing the
cells to differentiate spontaneously in cell culture; 2) manipulating the cells so
they will differentiate to form specific cell types; or 3) injecting the cells into
an immunosuppressed mouse to test for the formation of a benign tumor called a
teratoma
. Teratomas typically contain a mixture of many differentiated or partly differentiated
cell types—an indication that the embryonic stem cells are capable of differentiating
into multiple cell types.
D. How are embryonic stem cells stimulated to differentiate?
Graphic depicting steps in directed differentiation of mouse embryonic stem cells
Figure 1. Directed differentiation of mouse embryonic stem cells.
Click here
for larger image.
As long as the embryonic stem cells in culture are grown under certain conditions,
they can remain undifferentiated (unspecialized). But if cells are allowed to clump
together to form
embryoid bodies
, they begin to differentiate spontaneously. They can form muscle cells, nerve cells,
and many other cell types. Although spontaneous differentiation is a good indication
that a culture of embryonic stem cells is healthy, it is not an efficient way to
produce cultures of specific cell types.
So, to generate cultures of specific types of differentiated cells—heart muscle cells,
blood cells, or nerve cells, for example—scientists try to control the differentiation
of embryonic stem cells. They change the chemical composition of the culture medium,
alter the surface of the culture dish, or modify the cells by inserting specific
genes. Through years of experimentation scientists have established some basic protocols
or "recipes" for the
directed differentiation
of embryonic stem cells into some specific cell types (
Figure 1
). (For more examples of directed differentiation of embryonic stem cells, see Chapters
5–9 and Appendices B and C of the NIH report
Stem Cells: Scientific Progress and Future Research Directions
.)
If scientists can reliably direct the differentiation of embryonic stem cells into
specific cell types, they may be able to use the resulting, differentiated cells
to treat certain diseases at some point in the future. Diseases that might be treated
by transplanting cells generated from human embryonic stem cells include Parkinson's
disease, diabetes, traumatic spinal cord injury, Purkinje cell degeneration, Duchenne's
muscular dystrophy, heart disease, and vision and hearing loss.
IV. What are adult stem cells?
An adult stem cell is an
undifferentiated
cell found among differentiated cells in a tissue or organ, can renew itself, and
can differentiate to yield the major specialized cell types of the tissue or organ.
The primary roles of
adult stem cells
in a living organism are to maintain and repair the tissue in which they are found.
Some scientists now use the term
somatic stem cell
instead of adult stem cell. Unlike
embryonic stem cells
, which are defined by their origin (the
inner cell mass
of the
blastocyst
), the origin of adult stem cells in mature tissues is unknown.
Research on adult stem cells has recently generated a great deal of excitement. Scientists
have found adult stem cells in many more tissues than they once thought possible.
This finding has led scientists to ask whether adult stem cells could be used for
transplants. In fact, adult blood forming stem cells from bone marrow have been used
in transplants for 30 years. Certain kinds of adult stem cells seem to have the ability
to differentiate into a number of different cell types, given the right conditions.
If this differentiation of adult stem cells can be controlled in the laboratory,
these cells may become the basis of therapies for many serious common diseases.
The history of research on adult stem cells began about 40 years ago. In the 1960s,
researchers discovered that the bone marrow contains at least two kinds of stem cells.
One population, called
hematopoietic stem cells
, forms all the types of blood cells in the body. A second population, called
bone marrow stromal cells
, was discovered a few years later.
Stromal cells
are a mixed cell population that generates bone, cartilage, fat, and fibrous connective
tissue.
Also in the 1960s, scientists who were studying rats discovered two regions of the
brain that contained dividing cells, which become nerve cells. Despite these reports,
most scientists believed that new nerve cells could not be generated in the adult
brain. It was not until the 1990s that scientists agreed that the adult brain does
contain stem cells that are able to generate the brain's three major cell types—
astrocytes
and
oligodendrocytes
, which are non-neuronal cells, and
neurons
, or nerve cells.
A. Where are adult stem cells found and what do they normally do?
adult stem cells have been identified in many organs and tissues. One important point
to understand about adult stem cells is that there are a very small number of stem
cells in each tissue. Stem cells are thought to reside in a specific area of each
tissue where they may remain quiescent (non-dividing) for many years until they are
activated by disease or tissue injury. The adult tissues reported to contain stem
cells include brain, bone marrow, peripheral blood, blood vessels, skeletal muscle,
skin and liver.
Scientists in many laboratories are trying to find ways to grow adult stem cells
in
cell culture
and manipulate them to generate specific cell types so they can be used to treat
injury or disease. Some examples of potential treatments include replacing the dopamine-producing
cells in the brains of Parkinson's patients, developing insulin-producing cells for
type I diabetes and repairing damaged heart muscle following a heart attack with
cardiac muscle cells.
B. What tests are used for identifying adult stem cells?
Scientists do not agree on the criteria that should be used to identify and test
adult stem cells. However, they often use one or more of the following three methods:
(1) labeling the cells in a living tissue with molecular markers and then determining
the specialized cell types they generate; (2) removing the cells from a living animal,
labeling them in cell culture, and transplanting them back into another animal to
determine whether the cells repopulate their tissue of origin; and (3) isolating
the cells, growing them in cell culture, and manipulating them, often by adding growth
factors or introducing new
genes
, to determine what differentiated cells types they can become.
Also, a single adult stem cell should be able to generate a line of genetically identical
cells—known as a
clone
—which then gives rise to all the appropriate differentiated cell types of the tissue.
Scientists tend to show either that a stem cell can give rise to a clone of cells
in cell culture, or that a purified population of candidate stem cells can repopulate
the tissue after transplant into an animal. Recently, by infecting adult stem cells
with a virus that gives a unique identifier to each individual cell, scientists have
been able to demonstrate that individual adult stem cell clones have the ability
to repopulate injured tissues in a living animal.
C. What is known about adult stem cell differentiation?
Graphic depicting steps in hematopoietic and stromal stem cell differentiation
Figure 2. Hematopoietic and stromal stem cell differentiation.
Click here
for larger image.
As indicated above, scientists have reported that adult stem cells occur in many
tissues and that they enter normal
differentiation
pathways to form the specialized cell types of the tissue in which they reside.
Adult stem cells may also exhibit the ability to form specialized cell types of other
tissues, which is known as
transdifferentiation
or
plasticity
.
Normal differentiation pathways of adult stem cells.
In a living animal, adult stem cells can divide for a long period and can give rise
to mature cell types that have characteristic shapes and specialized structures and
functions of a particular tissue. The following are examples of differentiation pathways
of adult stem cells (
Figure 2
).
Hematopoietic stem cells give rise to all the types of blood cells: red blood cells,
B lymphocytes, T lymphocytes, natural killer cells, neutrophils, basophils, eosinophils,
monocytes, macrophages, and platelets.
Bone marrow stromal cells (
mesenchymal stem cells
) give rise to a variety of cell types: bone cells (osteocytes), cartilage cells
(chondrocytes), fat cells (adipocytes), and other kinds of connective tissue cells
such as those in tendons.
neural stem cells
in the brain give rise to its three major cell types: nerve cells (neurons) and
two categories of non-neuronal cells—astrocytes and oligodendrocytes.
Epithelial stem cells in the lining of the digestive tract occur in deep crypts and
give rise to several cell types: absorptive cells, goblet cells, Paneth cells, and
enteroendocrine cells.
Skin stem cells occur in the basal layer of the epidermis and at the base of hair
follicles. The epidermal stem cells give rise to keratinocytes, which migrate to
the surface of the skin and form a protective layer. The follicular stem cells can
give rise to both the hair follicle and to the epidermis.
Adult stem cell plasticity and transdifferentiation. A number of experiments have
suggested that certain adult stem cell types are
pluripotent
. This ability to differentiate into multiple cell types is called plasticity or
transdifferentiation. The following list offers examples of adult stem cell plasticity
that have been reported during the past few years.
Hematopoietic stem cells may differentiate into: three major types of brain cells
(neurons, oligodendrocytes, and astrocytes); skeletal muscle cells; cardiac muscle
cells; and liver cells.
Bone marrow stromal cells may differentiate into: cardiac muscle cells and skeletal
muscle cells.
Brain stem cells may differentiate into: blood cells and skeletal muscle cells.
Current research is aimed at determining the mechanisms that underlie adult stem
cell plasticity. If such mechanisms can be identified and controlled, existing stem
cells from a healthy tissue might be induced to repopulate and repair a diseased
tissue (
Figure 3
).
D. What are the key questions about adult stem cells?
Many important questions about adult stem cells remain to be answered. They include:
How many kinds of adult stem cells exist, and in which tissues do they exist?
What are the sources of adult stem cells in the body? Are they "leftover" embryonic
stem cells, or do they arise in some other way? Why do they remain in an undifferentiated
state when all the cells around them have differentiated?
Do adult stem cells normally exhibit plasticity, or do they only transdifferentiate
when scientists manipulate them experimentally? What are the
signals
that regulate the
proliferation
and differentiation of stem cells that demonstrate plasticity?
Is it possible to manipulate adult stem cells to enhance their proliferation so that
sufficient tissue for transplants can be produced?
Does a single type of stem cell exist—possibly in the bone marrow or circulating
in the blood—that can generate the cells of any organ or tissue?
What are the factors that stimulate stem cells to relocate to sites of injury or
damage?
Graphic depicting plasticity of adult stem cells
Figure 3. Plasticity of adult stem cells.V. What are the similarities and differences between embryonic and adult stem cells?
Human embryonic
and
adult stem cells
each have advantages and disadvantages regarding potential use for
cell-based regenerative therapies
. Of course, adult and embryonic stem cells differ in the number and type of differentiated
cells types they can become.
Embryonic stem cells
can become all cell types of the body because they are
pluripotent
. Adult stem cells are generally limited to differentiating into different cell types
of their tissue of origin. However, some evidence suggests that adult stem cell
plasticity
may exist, increasing the number of cell types a given adult stem cell can become.
Large numbers of embryonic stem cells can be relatively easily grown in culture,
while adult stem cells are rare in mature tissues and methods for expanding their
numbers in
cell culture
have not yet been worked out. This is an important distinction, as large numbers
of cells are needed for stem cell replacement therapies.
A potential advantage of using stem cells from an adult is that the patient's own
cells could be expanded in culture and then reintroduced into the patient. The use
of the patient's own adult stem cells would mean that the cells would not be rejected
by the immune system. This represents a significant advantage as immune rejection
is a difficult problem that can only be circumvented with immunosuppressive drugs.
Embryonic stem cells from a donor introduced into a patient could cause transplant
rejection. However, whether the recipient would reject donor embryonic stem cells
has not been determined in human experiments.
VI. What are the potential uses of human stem cells and the obstacles that must be
overcome before these potential uses will be realized?
There are many ways in which human stem cells can be used in basic research and in
clinical research. However, there are many technical hurdles between the promise
of stem cells and the realization of these uses, which will only be overcome by continued
intensive stem cell research.
Studies of
human embryonic stem cells
may yield information about the complex events that occur during human development.
A primary goal of this work is to identify how
undifferentiated
stem cells become differentiated. Scientists know that turning
genes
on and off is central to this process. Some of the most serious medical conditions,
such as cancer and birth defects, are due to abnormal
cell division
and
differentiation
. A better understanding of the genetic and molecular controls of these processes
may yield information about how such diseases arise and suggest new strategies for
therapy. A significant hurdle to this use and most uses of stem cells is that scientists
do not yet fully understand the
signals
that turn specific genes on and off to influence the differentiation of the stem
cell.
Human stem cells could also be used to test new drugs. For example, new medications
could be tested for safety on differentiated cells generated from human
pluripotent
cell lines. Other kinds of cell lines are already used in this way. Cancer cell
lines, for example, are used to screen potential anti-tumor drugs. But, the availability
of pluripotent stem cells would allow drug testing in a wider range of cell types.
However, to screen drugs effectively, the conditions must be identical when comparing
different drugs. Therefore, scientists will have to be able to precisely control
the differentiation of stem cells into the specific cell type on which drugs will
be tested. Current knowledge of the signals controlling differentiation fall well
short of being able to mimic these conditions precisely to consistently have identical
differentiated cells for each drug being tested.
Perhaps the most important potential application of human stem cells is the generation
of cells and tissues that could be used for
cell-based therapies
. Today, donated organs and tissues are often used to replace ailing or destroyed
tissue, but the need for transplantable tissues and organs far outweighs the available
supply. Stem cells, directed to differentiate into specific cell types, offer the
possibility of a renewable source of replacement cells and tissues to treat diseases
including Parkinson's and Alzheimer's diseases, spinal cord injury, stroke, burns,
heart disease, diabetes, osteoarthritis, and rheumatoid arthritis.
Graphic depicting heart muscle repair with adult stem cells
For example, it may become possible to generate healthy heart muscle cells in the
laboratory and then transplant those cells into patients with chronic heart disease.
Preliminary research in mice and other animals indicates that bone marrow stem cells,
transplanted into a damaged heart, can generate heart muscle cells and successfully
repopulate the heart tissue. Other recent studies in
cell culture
systems indicate that it may be possible to direct the
differentiation
of embryonic stem cells or adult bone marrow cells into heart muscle cells (
In people who suffer from type I diabetes, the cells of the pancreas that normally
produce insulin are destroyed by the patient's own immune system. New studies indicate
that it may be possible to direct the differentiation of human embryonic stem cells
in cell culture to form insulin-producing cells that eventually could be used in
transplantation therapy for diabetics.
To realize the promise of novel cell-based therapies for such pervasive and debilitating
diseases, scientists must be able to easily and reproducibly manipulate stem cells
so that they possess the necessary characteristics for successful differentiation,
transplantation and engraftment. The following is a list of steps in successful cell-based
treatments that scientists will have to learn to precisely control to bring such
treatments to the clinic. To be useful for transplant purposes, stem cells must be
reproducibly made to:
Proliferate extensively and generate sufficient quantities of tissue.
Differentiate into the desired cell type(s).
Survive in the recipient after transplant.
Integrate into the surrounding tissue after transplant.
Function appropriately for the duration of the recipient's life.
Avoid harming the recipient in any way.
Also, to avoid the problem of immune rejection, scientists are experimenting with
different research strategies to generate tissues that will not be rejected.
To summarize, the promise of stem cell therapies is an exciting one, but significant
technical hurdles remain that will only be overcome through years of intensive research.
The NIH has a wide array of new scientific programs designed to support research
that uses
embryonic stem cell lineshttp://stemcells.nih.gov/info/basics/basics7.asp
A Tyle dotychczas wydrukowałam:
Co to są komórki macierzyste?
Komórki macierzyste są ogólnie bardzo wczesnym stadium komórek, które mają zdolność, by przekształcić się w
inne typy wyspecjalizowanych komórek.
Na przykład komórka macierzysta może zamienić się w komórkę wątroby, komórki skóry , komórki nerwowe etc.
Te wczesne stadia komórek mogą mieć różne zdolności, by zamienić się w bardziej wyspecjalizowane komórki. .
Są generalnie 3 typy komórek macierzystych, które są ważne:
embrionalne komórki macierzyste, czyli macierzyste komórki zarodkowe.
dorosłe komórki macierzyste,
komórki macierzyste krwi pępowinowej
Komórki macierzyste są nazywane komórkami macierzystymi ponieważ wywodzą się od słowa "steem"- łodyga, której tłumaczenie słownikowe może powiedzieć Ci, iż steem oznacza główną pnącą się ku górze łodygę rośliny.
Podobnie do niej główne komórki, tóre rosną, stanowią główną łodygę od której mogą rozwijać się inne łodygi.
Jeśli prześledzisz genezę konkretnej komórki cofając się wstecz przez jej życie, otrzymasz konkretne wskazówki (...)
Dlatego, iż zależy mi na czasie, będę ogromnie wdzięczna za pomoc.
e-mail:
[email]