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Stem cells are cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
 cell division
Cell division

Cell division is a process by which a cell , called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle....
 and differentiating
Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of Tissue and cell types....
 into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian
Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
 scientists Ernest A. McCulloch
Ernest McCulloch

Dr. Ernest Armstrong McCulloch Order of Canada, Order of Ontario, Royal Society of Canada is a Canada cellular biology, best known for demonstrating – with James Till – the existence of stem cells....
 and James E. Till
James Till

Dr. James Edgar Till Order of Canada, Order of Ontario, Royal Society of Canada is a Canada biophysics, best known for demonstrating – with Ernest McCulloch – the existence of stem cells....
 in the 1960s. The two broad types of mammalian stem cells are: embryonic stem cell
Embryonic stem cell

Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
s that are isolated from the inner cell mass
Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
 of blastocyst
Blastocyst

The blastocyst is the structure formed in early embryogenesis, after the formation of the blastocoel, but before implantation.It possesses an inner cell mass, or inner cell mass which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast which later forms the placenta....
s, and adult stem cell
Adult stem cell

Adult stem cells are cell differentiation cell , found throughout the body after embryonic development, that multiply by cell division to replenish dying cells and regenerate damaged biological tissue....
s that are found in adult tissues.






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Encyclopedia


Mouse Embryonic Stem Cells
Stem cells are cells
Cell (biology)

The cell is the structural and functional unit of all known Life organisms. It is the smallest unit of an organism that is classified as living, and is often called the building bricks of life....
 found in most, if not all, multi-cellular organisms. They are characterized by the ability to renew themselves through mitotic
Mitosis

Mitosis is the process in which a eukaryotic cell separates the chromosomes in its cell nucleus, into two identical sets in two daughter nuclei....
 cell division
Cell division

Cell division is a process by which a cell , called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle....
 and differentiating
Cellular differentiation

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of Tissue and cell types....
 into a diverse range of specialized cell types. Research in the stem cell field grew out of findings by Canadian
Canada

Canada is a country occupying most of northern North America, extending from the Atlantic Ocean in the east to the Pacific Ocean in the west and northward into the Arctic Ocean....
 scientists Ernest A. McCulloch
Ernest McCulloch

Dr. Ernest Armstrong McCulloch Order of Canada, Order of Ontario, Royal Society of Canada is a Canada cellular biology, best known for demonstrating – with James Till – the existence of stem cells....
 and James E. Till
James Till

Dr. James Edgar Till Order of Canada, Order of Ontario, Royal Society of Canada is a Canada biophysics, best known for demonstrating – with Ernest McCulloch – the existence of stem cells....
 in the 1960s. The two broad types of mammalian stem cells are: embryonic stem cell
Embryonic stem cell

Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
s that are isolated from the inner cell mass
Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
 of blastocyst
Blastocyst

The blastocyst is the structure formed in early embryogenesis, after the formation of the blastocoel, but before implantation.It possesses an inner cell mass, or inner cell mass which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast which later forms the placenta....
s, and adult stem cell
Adult stem cell

Adult stem cells are cell differentiation cell , found throughout the body after embryonic development, that multiply by cell division to replenish dying cells and regenerate damaged biological tissue....
s that are found in adult tissues. In a developing embryo
Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
, stem cells can differentiate into all of the specialized embryonic tissues. In adult
Adult

The term adult has at least three distinct meanings. It can indicate a biologically grown or mature person. It may also mean a plant, animal, or person who has reached full growth or alternatively is capable of reproduction, or a person who has attained the legally fixed age of majority; as opposed to a minor....
 organisms, stem cells and progenitor cell
Progenitor cell

Like stem cells, progenitor cells have a capacity to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific: they are pushed to differentiate into their "target" cell....
s act as a repair system for the body, replenishing specialized cells, but also maintain the normal turnover of regenerative organs, such as blood, skin or intestinal tissues.

Stem cells can now be grown and transformed into specialized cells with characteristics consistent with cells of various tissues such as muscles or nerves through cell culture
Cell culture

Cell culture is the process by which prokaryote or eukaryote cells are grown under controlled conditions. In practice the term "cell culture" has come to refer to the culturing of cells derived from multicellular eukaryotes, especially animal cells....
. Highly plastic adult stem cells from a variety of sources, including umbilical cord blood and bone marrow
Bone marrow

Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
, are routinely used in medical therapies. Embryonic cell lines and autologous
Autologous

In biology, autologous refers to cell , tissues or even proteins that are reimplanted in the same individual as they come from. Bone marrow, skin biopsy, cartilage, and bone can be used as autografts....
 embryonic stem cells generated through therapeutic cloning have also been proposed as promising candidates for future therapies.

Properties

The classical definition of a stem cell requires that it possess two properties:
  • Self-renewal - the ability to go through numerous cycles
    Cell cycle

    The cell cycle, or cell-division cycle, is the series of events that take place in a cell leading to its division and duplication . In cells without a nucleus , the cell cycle occurs via a process termed binary fission....
     of cell division
    Cell division

    Cell division is a process by which a cell , called the parent cell, divides into two or more cells, called daughter cells. Cell division is usually a small segment of a larger cell cycle....
     while maintaining the undifferentiated state.
  • Potency - the capacity to differentiate into specialized cell types. In the strictest sense, this requires stem cells to be either totipotent
    Totipotency

    Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism, including extraembryonic tissues....
     or pluripotent
    Pluripotency

    Pluripotency in the broad sense refers to "having more than one potential outcome." In biological systems, this can refer either to cell or to biological compounds....
     - to be able to give rise to any mature cell type, although multipotent or unipotent
    Unipotent cell

    In cell biology, a unipotent cell is one that has the capacity to develop/differentiate into only one type of tissue/cell type. The most common of these in humans are skin cells....
     progenitor cell
    Progenitor cell

    Like stem cells, progenitor cells have a capacity to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific: they are pushed to differentiate into their "target" cell....
    s are sometimes referred to as stem cells.


Potency definitions

Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell.

  • Totipotent
    Totipotency

    Totipotency is the ability of a single cell to divide and produce all the differentiated cells in an organism, including extraembryonic tissues....
     (a.k.a omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable, organism. These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent.
  • Pluripotent
    Pluripotency

    Pluripotency in the broad sense refers to "having more than one potential outcome." In biological systems, this can refer either to cell or to biological compounds....
     stem cells are the descendants of totipotent cells and can differentiate into nearly all cells, i.e. cells derived from any of the three germ layer
    Germ layer

    A germ layer is a group of cell s, formed during animal embryogenesis. Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sea sponge produce two or three primary tissue layers ....
    s.
  • Multipotent
    Multipotency

    Multipotent progenitor cells have the potential to give rise to cells from multiple, but a limited number of lineages. An example of a multipotent stem cell is a hematopoietic cell ? a blood stem cell that can develop into several types of blood cells, but cannot develop into brain cells or other types of cells....
     stem cells can differentiate into a number of cells, but only those of a closely related family of cells.
  • Oligopotent
    Oligopotency

    In biology, oligopotency is the ability of progenitor cells to differentiate into a few cell types. It is a degree of stem cell#Potency definitions....
     stem cells can differentiate into only a few cells, such as lymphoid or myeloid stem cells.
  • Unipotent cells can produce only one cell type, their own, but have the property of self-renewal which distinguishes them from non-stem cells (e.g. muscle stem cells).


Identification

The practical definition of a stem cell is the functional definition - a cell that has the potential to regenerate tissue over a lifetime. For example, the gold standard test for a bone marrow or hematopoietic stem cell (HSC) is the ability to transplant one cell and save an individual without HSCs. In this case, a stem cell must be able to produce new blood cells and immune cells over a long term, demonstrating potency. It should also be possible to isolate stem cells from the transplanted individual, which can themselves be transplanted into another individual without HSCs, demonstrating that the stem cell was able to self-renew.

Properties of stem cells can be illustrated in vitro
In vitro

In vitro refers to the technique of performing a given procedure in a controlled environment outside of a living organism. Some may argue that in vitro refers to a process that is created in a "test tube"; however, Robert Kail and John Cavanaugh on page 58 in the 4th edition of Human Development: A Life-Span View cite that in fact th...
, using methods such as clonogenic assay
Mesenchymal stem cell

Mesenchymal stem cells, or MSCs, are multipotent stem cells that can Cellular differentiation into a variety of cell types. Cell types that MSCs have been shown to differentiate into in vitro or in vivo include osteoblasts, chondrocytes, myocytes, adipocytes, and, as described lately, Beta cell....
s, where single cells are characterized by their ability to differentiate and self-renew. As well, stem cells can be isolated based on a distinctive set of cell surface markers. However, in vitro culture conditions can alter the behavior of cells, making it unclear whether the cells will behave in a similar manner in vivo
In vivo

In vivo means that which takes place inside an organism. In science, in vivo refers to experimentation done in or on the living tissue of a whole, living organism as opposed to a partial or dead one or a in vitro....
. Considerable debate exists whether some proposed adult cell populations are truly stem cells.

Embryonic


Embryonic stem cell lines (ES cell lines) are cultures of cells derived from the epiblast
Epiblast

In embryology, the epiblast is a tissue type derived from the inner cell mass. It lies above the hypoblast.In mammalian embryogenesis, the columnar cells of the epiblast are adjacent to the trophoblast, while the cuboidal cells of the hypoblast are closer to the Blastocoele....
 tissue of the inner cell mass
Inner cell mass

In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
 (ICM) of a blastocyst
Blastocyst

The blastocyst is the structure formed in early embryogenesis, after the formation of the blastocoel, but before implantation.It possesses an inner cell mass, or inner cell mass which subsequently forms the embryo proper, and an outer layer of cells, or trophoblast which later forms the placenta....
 or earlier morula
Morula

A morula is an embryo at an early stage of embryonic development, consisting of Cell in a solid ball contained within the zona pellucida....
 stage embryos. A blastocyst is an early stage embryo
Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
—approximately four to five days old in humans and consisting of 50–150 cells. ES cells are pluripotent and give rise during development to all derivatives of the three primary germ layer
Germ layer

A germ layer is a group of cell s, formed during animal embryogenesis. Germ layers are particularly pronounced in the vertebrates; however, all animals more complex than sea sponge produce two or three primary tissue layers ....
s: ectoderm, endoderm and mesoderm. In other words, they can develop into each of the more than 200 cell types of the adult body
Human body

The human body is the entire physical and mental structure of a human organism, and consists of a head, neck, torso, two arms and two legs.By the time the human reaches adulthood, the body consists of close to 10 trillion Cell , the basic unit of life....
 when given sufficient and necessary stimulation for a specific cell type. They do not contribute to the extra-embryonic membranes or the placenta
Placenta

The placenta or afterbirth is a highly vascularized ephemeral organ present in Placentalia vertebrates that connects the developing fetal tissues to the uterine wall....
.

Nearly all research to date has taken place using mouse embryonic stem cells (mES) or human embryonic stem cells (hES). Both have the essential stem cell characteristics, yet they require very different environments in order to maintain an undifferentiated state. Mouse ES cells are grown on a layer of gelatin and require the presence of Leukemia Inhibitory Factor (LIF). Human ES cells are grown on a feeder layer of mouse embryonic fibroblasts (MEFs) and require the presence of basic Fibroblast Growth Factor (bFGF or FGF-2). Without optimal culture conditions or genetic manipulation, embryonic stem cells will rapidly differentiate.

A human embryonic stem cell is also defined by the presence of several transcription factors and cell surface proteins. The transcription factors Oct-4
Oct-4

Oct-4 is an abbreviation of Octamer-4. It is a homeobox of the POU family. This protein is critically involved in the self-renewal of undifferentiated embryonic stem cells....
, Nanog
NANOG

NANOG is the North American Network Operators' Group, which runs meetings, talks, surveys and an influential mailing list for Internet service providers....
, and SOX2
SOX2

SRY -box 2, also known as SOX2, is a transcription factor that is essential to maintain self-renewal of undifferentiated embryonic stem cells....
 form the core regulatory network that ensures the suppression of genes that lead to differentiation and the maintenance of pluripotency. The cell surface antigens most commonly used to identify hES cells are the glycolipids SSEA3 and SSEA4 and the keratan sulfate antigens Tra-1-60 and Tra-1-81. The molecular definition of a stem cell includes many more proteins and continues to be a topic of research.

After nearly ten years of research, there are no approved treatments or human trials using embryonic stem cells. ES cells, being pluripotent cells, require specific signals for correct differentiation - if injected directly into another body, ES cells will differentiate into many different types of cells, causing a teratoma
Teratoma

A teratoma is a kind of tumor . Definitive diagnosis of a teratoma is based on its histology: a teratoma is a tumor with biological tissue or organ components resembling normal derivatives of all three germ layers....
. Differentiating ES cells into usable cells while avoiding transplant rejection are just a few of the hurdles that embryonic stem cell researchers still face. Many nations currently have moratoria
Moratorium (law)

A moratorium mn:????? is a temporary ban or suspension of an activity.For instance, many animal rights activists and conservation authorities often request "Fishing Moratoriums" or "Hunting Moratoriums" on endangered animal species....
 on either ES cell research or the production of new ES cell lines. Because of their combined abilities of unlimited expansion and pluripotency, embryonic stem cells remain a theoretically potential source for regenerative medicine and tissue replacement after injury or disease.

Fetal

Fetal stem cells are primitive cell types found in the organs of fetuses . The classification of fetal stem cells remains unclear and this type of stem cell is currently often grouped into an adult stem cell. However, a more clear distinction between the two cell types appears necessary.

Adult


The term adult stem cell refers to any cell which is found in a developed organism that has two properties: the ability to divide and create another cell like itself and also divide and create a cell more differentiated than itself. Also known as somatic
Somatic

The term somatic refers to cells of the body, rather than gametes . In humans, somatic cells contain two copies of each chromosome , whereas eggs and sperm only contain one copy of each chromosome ....
 (from Greek S?µat??ó?, "of the body") stem cells and germline (giving rise to gametes) stem cells, they can be found in children, as well as adults.

Pluripotent adult stem cells are rare and generally small in number but can be found in a number of tissues including umbilical cord blood. A great deal of adult stem cell research has focused on clarifying their capacity to divide or self-renew indefinitely and their differentiation potential. In mice, pluripotent stem cells are directly generated from adult fibroblast cultures. Unfortunately, many mice don't live long with stem cell organs.

Most adult stem cells are lineage-restricted (multipotent) and are generally referred to by their tissue origin (mesenchymal stem cell
Mesenchymal stem cell

Mesenchymal stem cells, or MSCs, are multipotent stem cells that can Cellular differentiation into a variety of cell types. Cell types that MSCs have been shown to differentiate into in vitro or in vivo include osteoblasts, chondrocytes, myocytes, adipocytes, and, as described lately, Beta cell....
, adipose-derived stem cell, endothelial stem cell, etc.).

Adult stem cell treatments have been successfully used for many years to treat leukemia and related bone/blood cancers through bone marrow transplants. Adult stem cells are also used in veterinary medicine to treat tendon and ligament injuries in horses. The use of adult stem cells in research and therapy is not as controversial
Stem cell controversy

Stem cell controversy is the ethical debate centered on research involving the creation, usage and destruction of human embryonic stem cells. Not all stem cell research involves the creation, usage and destruction of human embryos....
 as embryonic stem cell
Embryonic stem cell

Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
s, because the production of adult stem cells does not require the destruction of an embryo
Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
. Additionally, because in some instances adult stem cells can be obtained from the intended recipient, (an autograft) the risk of rejection is essentially non-existent in these situations. Consequently, more US government funding is being provided for adult stem cell research.

Lineage

To ensure self-renewal, stem cells undergo two types of cell division (see Stem cell division and differentiation diagram). Symmetric division gives rise to two identical daughter cells both endowed with stem cell properties. Asymmetric division, on the other hand, produces only one stem cell and a progenitor cell
Progenitor cell

Like stem cells, progenitor cells have a capacity to differentiate into a specific type of cell. In contrast to stem cells, however, they are already far more specific: they are pushed to differentiate into their "target" cell....
 with limited self-renewal potential. Progenitors can go through several rounds of cell division before terminally differentiating into a mature cell. It is possible that the molecular distinction between symmetric and asymmetric divisions lies in differential segregation of cell membrane proteins (such as receptors
Receptor (biochemistry)

In biochemistry, a receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling molecule may attach....
) between the daughter cells.

An alternative theory is that stem cells remain undifferentiated due to environmental cues in their particular niche. Stem cells differentiate when they leave that niche or no longer receive those signals. Studies in Drosophila germarium have identified the signals dpp and adherens junctions that prevent germarium stem cells from differentiating.

The signals that lead to reprogramming of cells to an embryonic-like state are also being investigated. These signal pathways include several transcription factor
Transcription factor

In the field of molecular biology, a transcription factor is a protein that binds to specific DNA sequence and thereby controls the transfer of genetic information from DNA to RNA....
s including the oncogene
Oncogene

An oncogene is a gene that, when mutated or expressed at high levels, helps turn a normal cell into a cancer cell.Many cells normally undergo a programmed form of death ....
 c-Myc
Myc

Myc codes for a protein that binds to the DNA of other genes. When Myc is mutated, or overexpressed, the protein doesn't bind correctly, and often causes cancer....
. Initial studies indicate that transformation of mice cells with a combination of these anti-differentiation signals can reverse differentiation and may allow adult cells to become pluripotent. However, the need to transform these cells with an oncogene may prevent the use of this approach in therapy.

Treatments

Medical researchers believe that stem cell therapy has the potential to dramatically change the treatment of human disease. A number of adult stem cell therapies already exist, particularly bone marrow transplant
Bone marrow transplant

Hematopoietic stem cell transplantation is the transplantation of Pluripotential hemopoietic stem cell derived from the bone marrow or blood. Stem cell transplantation is a medical procedure in the fields of hematology and oncology, most often performed for people with diseases of the blood, bone marrow, or certain types of cancer....
s that are used to treat leukemia
Leukemia

Leukemia is a cancer of the blood or bone marrow and is characterized by an abnormal proliferation of blood Cell , usually white blood cells ....
. In the future, medical researchers anticipate being able to use technologies derived from stem cell research to treat a wider variety of diseases including cancer
Cancer

Cancer is a class of diseases in which a group of cell display uncontrolled growth , invasion , and sometimes metastasis . These three malignant properties of cancers differentiate them from benign tumors, which are self-limited, do not invade or metastasize....
, Parkinson's disease
Parkinson's disease

Parkinson's disease is a degenerative disorder of the central nervous system that often impairs the sufferer's motor skills and speech, as well as other functions....
, spinal cord injuries, Amyotrophic lateral sclerosis
Amyotrophic lateral sclerosis

Amyotrophic Lateral Sclerosis is a progressive, usually fatal, neurodegenerative disease caused by the degeneration of motor neurons, the nerve cells in the central nervous system that control voluntary muscle movement....
, multiple sclerosis
Multiple sclerosis

Multiple sclerosis is an autoimmune disease in which the immune system attacks the central nervous system, leading to demyelinating disease. Disease onset usually occurs in young adults, and it is more common in females....
, and muscle
MUSCLE

MUSCLE is public domain, multiple sequence alignment software for protein and nucleotide sequences.MUSCLE is integrated into UGENE bioinformatics tool as a plugin....
 damage, amongst a number of other impairments and conditions. However, there still exists a great deal of social and scientific uncertainty surrounding stem cell research, which could possibly be overcome through public debate and future research, and further education of the public.

Stem cells, however, are already used extensively in research, and some scientists do not see cell therapy as the first goal of the research, but see the investigation of stem cells as a goal worthy in itself.

Controversy surrounding research

There exists a widespread controversy over human embryonic stem cell research that emanates from the techniques used in the creation and usage of stem cells. Human embryonic stem cell
Embryonic stem cell

Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
 research is controversial because, with the present state of technology, starting a stem cell line
Stem cell line

A stem cell line is a family of constantly-dividing cell s, the product of a single parent group of stem cells. They are obtained from human or animal Biological_tissue and can replicate for long periods of time in vitro ....
 requires the destruction of a human embryo
Embryo

An embryo is a multicellular organism ploidy eukaryote in its earliest stage of development, from the time of first cell division until birth, Egg , or germination....
 and/or therapeutic cloning. However, recently, it has been shown in principle that adult stem cell lines can be manipulated to generate embryonic-like stem cell lines using a single-cell biopsy similar to that used in preimplantation genetic diagnosis
Preimplantation genetic diagnosis

In medicine and genetics preimplantation genetic diagnosis refers to procedures that are performed on embryos prior to implantation, sometimes even on oocytes prior to fertilization....
 that may allow stem cell creation without embryonic destruction. It is not the entire field of stem cell research, but the specific field of human embryonic stem cell research that is at the centre of an ethical debate.

Opponents of the research argue that embryonic stem cell technologies are a slippery slope
Slippery slope

In debate or rhetoric, a slippery slope is a classical informal fallacy. A slippery slope argument states that a relatively small first step inevitably leads to a chain of related events culminating in some significant impact, much like an object given a small push over the edge of a slope sliding all the way to the bottom....
 to reproductive cloning and can fundamentally devalue human life. Those in the pro-life
Pro-life

Pro-life is a term representing a variety of perspectives and activist movements in medical ethics. It is most commonly used, especially in the media and popular discourse, to refer to opposition to abortion....
 movement argue that a human embryo is a human life and is therefore entitled to protection.

Contrarily, supporters of embryonic stem cell research argue that such research should be pursued because the resultant treatments could have significant medical potential. It is also noted that excess embryos created for in vitro fertilization could be donated with consent and used for the research.

The ensuing debate has prompted authorities around the world to seek regulatory frameworks and highlighted the fact that stem cell research represents a social
Social

Social refers to a characteristic of living organisms . It always refers to the interaction of organisms with other organisms and to their collective co-existence, irrespective of whether they are aware of it or not, and irrespective of whether the interaction is voluntary or involuntary....
 and ethical challenge.

Key research events

  • 1908 - The term "stem cell" was proposed for scientific use by the Russia
    Russia

    Russia , or the Russian Federation , is a list of countries spanning more than one continent country extending over much of northern Eurasia....
    n histologist Alexander Maksimov
    Alexander Maksimov

    Alexander A. Maximov was a Russians academic.He was a polyglot, fluent in English, German, French, and Russian. He was a lecturer, who in his spare time enjoyed mountain climbing....
     (1874–1928) at congress of hematologic society in Berlin
    Berlin

    Berlin is the Capital of Germany city and one of sixteen States of Germany of Germany. With a population of 3.4 million within its city limits, Berlin is the country's largest city....
    . It postulated existence of haematopoietic stem cells.
  • 1960s - Joseph Altman
    Joseph Altman

    Joseph Altman discovered adult neurogenesis, the creation of new neurons in the adult brain, in the 1960s. An independent investigator at MIT, his results were largely ignored....
     and Gopal Das present scientific evidence of adult neurogenesis
    Neurogenesis

    Neurogenesis is the process by which neurons are created. Most active during pre-natal development, neurogenesis is responsible for populating the growing brain....
    , ongoing stem cell activity in the brain; their reports contradict Cajal
    Santiago Ramón y Cajal

    Santiago Ram?n y Cajal was a Spanish people histology, physician, pathologist and Nobel laureate. His pioneering investigations of the microscopic structure of the brain were so original and influential that he is considered by many to be the greatest neuroscientist of all time....
    's "no new neurons" dogma and are largely ignored.
  • 1963 - McCulloch
    Ernest McCulloch

    Dr. Ernest Armstrong McCulloch Order of Canada, Order of Ontario, Royal Society of Canada is a Canada cellular biology, best known for demonstrating – with James Till – the existence of stem cells....
     and Till
    James Till

    Dr. James Edgar Till Order of Canada, Order of Ontario, Royal Society of Canada is a Canada biophysics, best known for demonstrating – with Ernest McCulloch – the existence of stem cells....
     illustrate the presence of self-renewing cells in mouse bone marrow.
  • 1968 - Bone marrow
    Bone marrow

    Bone marrow is the flexible biological tissue found in the hollow interior of bones. In adults, marrow in large bones produces new blood cells....
     transplant
    Organ transplant

    Organ transplant is the moving of an organ from one body to another , for the purpose of replacing the recipient's damaged or failing organ with a working one from the donor site....
     between two siblings successfully treats SCID
    Severe combined immunodeficiency

    Severe combined immunodeficiency , or Boy in the Bubble Syndrome, is a genetic disorder in which both "arms" of the adaptive immune system are crippled, due to a defect in one of several possible genes....
    .
  • 1978 - Haematopoietic stem cells are discovered in human cord blood
    Cord blood

    Umbilical cord blood is up to 180mL of blood from a Infant that is returned to the neonatal circulation if the umbilical cord is not prematurely clamped....
    .
  • 1981 - Mouse embryonic stem cell
    Embryonic stem cell

    Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
    s are derived from the inner cell mass
    Inner cell mass

    In early embryogenesis of most eutherian mammals, the inner cell mass is the mass of cells inside the primordial embryo that will eventually give rise to the definitive structures of the fetus....
     by scientists Martin Evans
    Martin Evans

    Sir Martin John Evans Royal Society is a United Kingdom scientist, credited with discovering how to cell culture embryonic stem cells in 1981, and for his work in the development of the knockout mouse and the related technology of gene targeting....
    , Matthew Kaufman
    Matthew Kaufman

    In 1981 Matthew H. Kaufman and Martin Evans at the University of Cambridge in England and Gail R. Martin in America were the first to derive embryonic stem cells from mouse embryos....
    , and Gail R. Martin
    Gail R. Martin

    Professor Gail R. Martin, is in charge of the developmental biology program at the University of California, San Francisco. She is a member of the American Academy of Arts & Sciences, a member of the List of members of the National Academy of Sciences , and is the President of the Society for Developmental Biology....
    . Gail Martin is attributed for coining the term "Embryonic Stem Cell".
  • 1992 - Neural stem cells are cultured in vitro
    In vitro

    In vitro refers to the technique of performing a given procedure in a controlled environment outside of a living organism. Some may argue that in vitro refers to a process that is created in a "test tube"; however, Robert Kail and John Cavanaugh on page 58 in the 4th edition of Human Development: A Life-Span View cite that in fact th...
     as neurospheres.
  • 1997 - Leukemia is shown to originate from a haematopoietic stem cell, the first direct evidence for cancer stem cell
    Cancer stem cell

    Cancer stem cells are cancer cells that possess characteristics associated with normal stem cell, specifically the ability to give rise to all cell types found in a particular cancer sample....
    s.
  • 1998 - James Thomson
    James Thomson (cell biologist)

    James Alexander Thomson is an United States Developmental biology who is best known for deriving the first human embryonic stem cell line. He serves as director of regenerative biology at the Morgridge Institute for Research in Madison, Wisconsin, and is a professor at the University of Wisconsin School of Medicine and Public Health....
     and coworkers derive the first human embryonic stem cell line
    Stem cell line

    A stem cell line is a family of constantly-dividing cell s, the product of a single parent group of stem cells. They are obtained from human or animal Biological_tissue and can replicate for long periods of time in vitro ....
     at the University of Wisconsin-Madison.
  • 2000s - Several reports of adult stem cell
    Adult stem cell

    Adult stem cells are cell differentiation cell , found throughout the body after embryonic development, that multiply by cell division to replenish dying cells and regenerate damaged biological tissue....
     plasticity are published.
  • 2001 - Scientists at Advanced Cell Technology
    Advanced Cell Technology

    Advanced Cell Technology , a biotechnology company formed in 1994, is involved with therapeutic cloning and the cloning of animals. Among the animals it has cloned are transgenic cows....
     clone first early (four- to six-cell stage) human embryos for the purpose of generating embryonic stem cells.
  • 2003 - Dr. Songtao Shi of NIH discovers new source of adult stem cells in children's primary teeth.
  • 2004–2005 - Korean researcher Hwang Woo-Suk
    Hwang Woo-Suk

    Hwang Woo-Suk is a South Korean researcher and confidence man. He was a professor of theriogenology and biotechnology at Seoul National University who claimed a series of breakthroughs in the field of stem cell research....
     claims to have created several human embryonic stem cell
    Embryonic stem cell

    Embryonic stem cells are stem cells derived from the inner cell mass of an early stage embryo known as a blastocyst. Human embryos reach the blastocyst stage 4?5 days post Human fertilization, at which time they consist of 50?150 cells....
     lines from unfertilised human oocyte
    Oocyte

    An oocyte, ovocyte, or rarely ocyte, is a female gametocyte or germ cell involved in biological reproduction. In other words, it is an immature ovum, or ovum cell....
    s. The lines were later shown to be fabricated.
  • 2005 - Researchers at Kingston University
    Kingston University

    Kingston University is a university in the Royal Borough of Kingston upon Thames, south-west London.Formerly a polytechnic, it was granted university status in 1992 under the Further and Higher Education Act 1992....
     in England
    England

    native_name =|conventional_long_name = England|common_name = England|image_flag = Flag of England.svg|image_coat = England COA.svg|symbol_type = Royal Coat of Arms...
     claim to have discovered a third category of stem cell, dubbed cord-blood-derived embryonic-like stem cells (CBEs), derived from umbilical cord blood. The group claims these cells are able to differentiate into more types of tissue than adult stem cells.
  • August 2006 - Rat Induced pluripotent stem cell
    Induced pluripotent stem cell

    Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a "forced" expression of certain genes....
    s    : the journal Cell
    Cell (journal)

    Cell is a peer review scientific journal which publishes novel research in any area of experimental biology that is significant outside its field....
     publishes Kazutoshi Takahashi and Shinya Yamanaka
    Shinya Yamanaka

    is a Japanese physician and stem cell researcher. He serves as a professor at the Institute for Frontier Medical Sciences at Kyoto University and at the J....
    .
  • October 2006 - Scientists at Newcastle University in England create the first ever artificial liver cells using umbilical cord blood stem cells.
  • January 2007 - Scientists at Wake Forest University
    Wake Forest University

    Wake Forest University is a Private university, coeducational university in the U.S. state of North Carolina, founded in 1834. The university received its name from its original location in Wake Forest, North Carolina, near the state capital Raleigh, North Carolina....
     led by Dr. Anthony Atala
    Anthony Atala

    Anthony Atala, M.D., is the Director of the Wake Forest Institute for Regenerative Medicine, and Chair of the Department of Urology at the Wake Forest University School of Medicine in the state of North Carolina in the United States....
     and Harvard University
    Harvard University

    Harvard University is a private university in Cambridge, Massachusetts, Massachusetts, United States, and a member of the Ivy League. Founded in 1636 by the colonial Massachusetts legislature, Harvard is the Colonial Colleges institution of higher learning in the United States....
     report discovery of a new type of stem cell in amniotic fluid
    Amniotic fluid

    Amniotic fluid or liquor amnii is the nourishing and protecting liquid contained by the amnion of a pregnant woman.Amnion grows and begins to fill, mainly with water, around two weeks after fertilization....
    . This may potentially provide an alternative to embryonic stem cells for use in research and therapy.
  • June 2007 - Research reported by three different groups shows that normal skin cells can be reprogrammed to an embryonic state in mice. In the same month, scientist Shoukhrat Mitalipov reports the first successful creation of a primate stem cell line through somatic cell nuclear transfer
    Somatic cell nuclear transfer

    In genetics and developmental biology, somatic cell nuclear transfer is a laboratory technique for creating a clonal embryo, using an ovum with a donor nucleus ....
  • October 2007 - Mario Capecchi
    Mario Capecchi

    Mario Renato Capecchi is an Italy-born United States molecular geneticist and a co-winner of the 2007 Nobel Prize in Physiology or Medicine. He is currently Distinguished Professor of Human Genetics and Biology at the University of Utah School of Medicine, which he joined in 1973....
    , Martin Evans
    Martin Evans

    Sir Martin John Evans Royal Society is a United Kingdom scientist, credited with discovering how to cell culture embryonic stem cells in 1981, and for his work in the development of the knockout mouse and the related technology of gene targeting....
    , and Oliver Smithies
    Oliver Smithies

    Oliver Smithies is a United Kingdom United States geneticist and Nobel Prize in Physiology or Medicine Nobel laureate, credited with the invention of gel electrophoresis in 1955, and the simultaneous discovery, with Mario Capecchi, of the technique of homologous recombination of transgenic DNA with genomic DNA, a much more reliable method of...
     win the 2007 Nobel Prize for Physiology or Medicine for their work on embryonic stem cells from mice using gene targeting strategies producing genetically engineered mice (known as knockout mice) for gene research.
  • November 2007 - Human Induced pluripotent stem cell
    Induced pluripotent stem cell

    Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a "forced" expression of certain genes....
    s    : Two similar papers released by their respective journals prior to formal publication: in Cell
    Cell (journal)

    Cell is a peer review scientific journal which publishes novel research in any area of experimental biology that is significant outside its field....
     by Kazutoshi Takahashi and Shinya Yamanaka
    Shinya Yamanaka

    is a Japanese physician and stem cell researcher. He serves as a professor at the Institute for Frontier Medical Sciences at Kyoto University and at the J....
    , "Induction of Pluripotent Stem Cells from Adult Human Fibroblasts by Defined Factors", and in Science by Junying Yu, et al., from the research group of James Thomson
    James Thomson (cell biologist)

    James Alexander Thomson is an United States Developmental biology who is best known for deriving the first human embryonic stem cell line. He serves as director of regenerative biology at the Morgridge Institute for Research in Madison, Wisconsin, and is a professor at the University of Wisconsin School of Medicine and Public Health....
    , "Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells": pluripotent stem cells generated from mature human fibroblasts. It is possible now to produce a stem cell from almost any other human cell instead of using embryos as needed previously, albeit the risk of tumorigenesis due to c-myc and retroviral gene transfer
    Gene therapy

    Gene therapy is the insertion of genes into an individual's cell and Biological tissues to treat a disease, such as a hereditary disease in which a deleterious mutant allele is replaced with a functional one....
     remains to be determined.
  • January 2008 - Robert Lanza and colleagues at Advanced Cell Technology and UCSF create the first human embryonic stem cells without destruction of the embryo
  • January 2008 - Development of human cloned blastocysts following somatic cell nuclear transfer
    Somatic cell nuclear transfer

    In genetics and developmental biology, somatic cell nuclear transfer is a laboratory technique for creating a clonal embryo, using an ovum with a donor nucleus ....
     with adult fibroblasts
  • February 2008 - Generation of Pluripotent Stem Cells from Adult Mouse Liver and Stomach: these iPS cells seem to be more similar to embryonic stem cells than the previous developed iPS cells and not tumorigenic, moreover genes that are required for iPS cells do not need to be inserted into specific sites, which encourages the development of non-viral reprogramming techniques.
  • March 2008-The first published study of successful cartilage regeneration in the human knee using autologous adult mesenchymal stem cells is published by Clinicians from Regenerative Sciences
  • October 2008 - Sabine Conrad and colleagues at Tübingen, Germany generate pluripotent stem cells from spermatogonial cells of adult human testis by culturing the cells in vitro under leukemia inhibitory factor
    Leukemia inhibitory factor

    Leukemia inhibitory factor, or LIF, an interleukin 6 class cytokine, is a chemical in cell s that affects their growth and development....
     (LIF) supplementation.
  • 30 October 2008 - Embryonic-like stem cells from a single human hair.
  • 1 March 2009 - Andras Nagy, Keisuke Kaji, et al. discover a way to produce embryonic-like stem cells from normal adult cells by using a novel "wrapping" procedure to deliver specific genes to adult cells to reprogram them into stem cells without the risks of using a virus to make the change. The use of electroporation
    Electroporation

    Electroporation, or electropermeabilization, is a significant increase in the electrical conductivity and permeability of the cell membrane caused by an externally applied electrical field....
     is said to allow for the temporary insertion of genes into the cell.
  • 05 March 2009 Australian scientists find a way to improve chemotherapy of mouse muscle stem cells.


Funding & policy debate in the US

  • 1993 - As per the National Institutes of Health Revitalization Act, Congress and President Bill Clinton
    Bill Clinton

    William Jefferson "Bill" Clinton served as the List of Presidents of the United States President of the United States from 1993 to 2001. He was the fifteenth Democrat elected to that office....
     give the NIH direct authority to fund human embryo research for the first time.
  • 1995 - The U.S. Congress passes an appropriations bill attached to which is a rider, the Dickey Amendment
    Dickey Amendment

    The Dickey Amendment is the name of an appropriation's bill Rider_ attached to a bill passed by United States Congress in 1995, and signed by former President Bill Clinton which prohibits the United States Department of Health and Human Services from using appropriated funds for the creation of human embryos for research purposes or for rese...
     which prohibited federally appropriated funds to be used for research where human embryos would be either created or destroyed. President Clinton signs the bill into law. This predates the creation of the first human embryonic stem cell lines.
  • 1999 - After the creation of the first human embryonic stem cell lines in 1998 by James Thomson of the University of Wisconsin, Harriet Rabb, the top lawyer at the Department of Health and Human Services, releases a legal opinion that would set the course for Clinton Administration policy. Federal funds, obviously, could not be used to derive stem cell lines (because derivation involves embryo destruction). However, she concludes that because human embryonic stem cells "are not a human embryo within the statutory definition," the Dickey-Wicker Amendment does not apply to them. The NIH was therefore free to give federal funding to experiments involving the cells themselves. President Clinton strongly endorses the new guidelines, noting that human embryonic stem cell research promised "potentially staggering benefits." And with the guidelines in place, the NIH begins accepting grant proposals from scientists.
  • 2001–2006 - U.S. President
    President

    President is a title held by many leaders of organizations, company, trade unions, university, and country. Etymology, a "president" is one who Wiktionary:Preside, who sits in leadership ....
     George W. Bush
    George W. Bush

    George Walker Bush served as the List of Presidents of the United States President of the United States from 2001 to 2009. He was the 46th List of Governors of Texas from 1995 to 2000 before being United States presidential inauguration as President on January 20, 2001....
     signs an executive order which restricts federally-funded stem cell research on embryonic stem cells to the already derived cell lines. He supports federal funding for embryonic stem cell research on the already existing lines of approximately $100 million and $250 million for research on adult and animal stem cells.
  • 02 November 2004 - California
    California

    California is a U.S. state on the West Coast of the United States of the United States, along the Pacific Ocean. It is bordered by Oregon to the north, Nevada to the east, Arizona to the southeast, and to the south the Mexico state of Baja California....
     voters approve Proposition 71, which provides $3 billion in state funds over ten years to human embryonic stem cell research.
  • 5 May 2006 - Senator Rick Santorum
    Rick Santorum

    Richard John Santorum, Sovereign Military Order of Malta is a former United States Senate from the Commonwealth of Pennsylvania....
     introduces bill number S. 2754, or the Alternative Pluripotent Stem Cell Therapies Enhancement Act, into the U.S. Senate
    United States Senate

    The United States Senate is the upper house of the Bicameralism United States Congress, the lower house being the United States House of Representatives....
    .
  • 18 July 2006 - The U.S. Senate passes the Stem Cell Research Enhancement Act H.R. 810 and votes down Senator Santorum's S. 2754.
  • 19 July 2006 - President
    President

    President is a title held by many leaders of organizations, company, trade unions, university, and country. Etymology, a "president" is one who Wiktionary:Preside, who sits in leadership ....
     George W. Bush
    George W. Bush

    George Walker Bush served as the List of Presidents of the United States President of the United States from 2001 to 2009. He was the 46th List of Governors of Texas from 1995 to 2000 before being United States presidential inauguration as President on January 20, 2001....
     vetoes House Resolution 810 Stem Cell Research Enhancement Act
    Stem Cell Research Enhancement Act

    Stem Cell Research Enhancement Act was the name of two similar bills that both passed through the United States United States House of Representatives and United States Senate, but were both vetoed by President George W....
    , a bill that would have reversed the Dickey Amendment which made it illegal for federal money to be used for research where stem cells are derived from the destruction of an embryo.
  • 07 November 2006 - The people of the U.S. state of Missouri
    Missouri

    Missouri is a U.S. state in the Midwestern United States of the United States bordered by Iowa, Illinois, Kentucky, Tennessee, Arkansas, Oklahoma, Kansas and Nebraska....
     passed Amendment 2
    Missouri Constitutional Amendment 2 (2006)

    Missouri Constitutional Amendment 2 is a state constitutional amendment initiative that concerns stem cell research and human cloning in Missouri....
    , which allows usage of any stem cell research and therapy allowed under federal law, but prohibits human reproductive cloning.
  • 16 February 2007 – The California Institute for Regenerative Medicine became the biggest financial backer of human embryonic stem cell research in the United States when they awarded nearly $45 million in research grants.
  • 04 November 2008 - The people of the U.S. state of Michigan
    Michigan

    Michigan is a Midwestern United States U.S. state of the United States of America. It was named after Lake Michigan, whose name is a French adaptation of the Anishinaabe language term mishigama, meaning "large water" or "large lake"....
     passed Proposal 08-2
    Michigan State Proposal - 08-2 (2008)

    Michigan State Proposal - 08-2 of 2008 proposes to amend the state Constitution to remove restrictions on stem cell research in Michigan while maintaining the ban on human cloning....
    , allowing Michigan researchers to make embryonic stem cell cultures from excess embryos donated from fertility treatments.
  • 23 January 2009 - The FDA approves clinical trials for human embryonic stem cell therapy.
  • 9 March 2009 - President
    President

    President is a title held by many leaders of organizations, company, trade unions, university, and country. Etymology, a "president" is one who Wiktionary:Preside, who sits in leadership ....
     Barack Obama
    Barack Obama

    Barack Hussein Obama II is the List of Presidents of the United States and current President of the United States. He is the first African American to hold the office....
     reverses federal opposition to Stem Cell research.


See also

  • The American Society for Cell Biology
    The American Society for Cell Biology

    The American Society for Cell Biology is a non-profit organization whose purpose is to promote and develop the field of cell biology. Founded in 1960, the society currently has grown to serve more than 11,000 members....
  • California Institute for Regenerative Medicine
    California Institute for Regenerative Medicine

    The California Institute for Regenerative Medicine was created by California's Proposition 71 , which authorized it to issue $3 billion in grants, funded by bonds, over ten years for embryonic stem cell and other biomedical research....
  • Genetics Policy Institute
    Genetics Policy Institute

    The Genetics Policy Institute is a 501 nonprofit organization that educates the public and promotes supportive public policy for stem cell research and other forms of cutting-edge medicine....
  • Cancer stem cells
  • Induced Pluripotent Stem Cell
    Induced pluripotent stem cell

    Induced pluripotent stem cells, commonly abbreviated as iPS cells or iPSCs, are a type of pluripotent stem cell artificially derived from a non-pluripotent cell, typically an adult somatic cell, by inducing a "forced" expression of certain genes....
     (iPS Cell)
  • Meristem
    Meristem

    A meristem is the biological tissue in all plants consisting of undifferentiated cells and found in zones of the plant where growth can take place....
  • Stem cell marker
    Stem cell marker

    Stem cell markers are cell surface receptors used by scientists to isolate and identify stem cells. A receptor is a specialized protein included in the surface of any cell in the body that is capable to selectively bind to other "signaling" molecules....


External links

General
  • *


Peer-reviewed journals