Stem Cell

Cellula praecursoria

STEM CELL

What Is Stem Cell ?

The human body is made up of about 200 different kinds of specialized cells such as muscle cells, nerve cells, fat cells and skin cells. All specialized cells originate from stem cells. A stem cell is a cell that is not yet specialized.

Different types of stem cells have different levels of potential. A stem cell that can become every type of cell in the body is called pluripotent and a stem cell that can become only some types of cells is called multipotent.

In the growing body, stem cells are responsible for generating new tissues, and once growth is complete, stem cells are responsible for repair and regeneration of damaged and ageing tissues.

Why Are Stem Cells So Important ?

Identification of Stem CellsAlthough there is not complete agreement among scientists of how to identify stem cells, most tests are based on making sure that stem cells are undifferentiated and capable of self-renewal.

One way to identify stem cells in a lab, and the standard procedure for testing bone marrow or hematopoietic stem cell (HSC), is by transplanting one cell to save an individual without HSCs. If the stem cell produces new blood and immune cells, it demonstrates its potency.

A laboratory procedure can also be employed in vitro to test whether single cells can differentiate and self-renew. Researchers may also inspect cells under a microscope to see if they are healthy and undifferentiated or they may examine chromosomes.

Properties of Stem Cells

SELF-RENEWAL1.Obligatory asymmetric replication: a stem cell divides into one mother cell that is identical to the original stem cell, and another daughter cell that is differentiated.

2.Stochastic differentiation: when one stem cell develops into two differentiated daughter cells, another stem cell undergoes mitosis and produces two stem cells identical to the original.

POTENCY DEFINITION

Pluripotent, embryonic stem cells originate as inner cell mass (ICM) cells within a blastocyst. These stem cells can become any tissue in the body, excluding a placenta. Only cells from an earlier stage of the embryo, known as the morula, are totipotent, able to become all tissues in the body and the extraembryonic placenta.

POTENCYTotipotent - the ability to differentiate into all possible cell types. Examples are the zygote formed at egg fertilization and the first few cells that result from the division of the zygote.

Pluripotent - the ability to differentiate into almost all cell types. Examples include embryonic stem cells and cells that are derived from the mesoderm, endoderm, and ectoderm germ layers that are formed in the beginning stages of embryonic stem cell differentiation.

Multipotent - the ability to differentiate into a closely related family of cells. Examples include adult stem cells that can become red and white blood cells

Oligopotent - the ability to differentiate into a few cells. Examples include (adult) lymphoid or myeloid stem cells.

Unipotent - the ability to only produce cells of their own type, but have the property of self-renewal required to be labeled a stem cell. Examples include (adult) muscle stem cells.

Tissue Specific Stem CellsTissue specific stem cells are undifferentiated cells found in the tissues and organs of the body. They are capable of self-renewal. The chief role of tissue specific stem cells is to maintain and repair the tissue in which they are found.

It now appears that all tissues probably contain adult stem cells. Most tissues contain only tiny numbers of stem cells. In each tissue, adult stem cells are used to produce new mature cells as old ones die in the natural processes of ageing.

Mesenchymal stem cells are the stem cells that form our fat, muscle, bone and cartilage and they can also differentiate into nerve cells. Mesenchymal stem cells can be found in the bone marrow but are also found in several other sites in the body such as the placenta. This means that mesenchymal stem cells could be useful as therapies for diseases caused by immune attack on specific tissues.

Haematopoietic stem cells are the stem cells from which all blood cells and many of the cells of our adult immune system are derived.

Umbilical cord blood stem cells are a type of tissue specific stem cell. Cord blood stem cells may be used to treat a range of blood disorders and immune system conditions such as leukaemia, anaemia and autoimmune diseases.

Pluripotent Stem Cell

EMBRIYONIC STEM CELLS

Human embryonic stem cells are derived from human blastocysts (early stage embryos) that are 5 to 7 days old.

9-week Human Embryo

Adult Stem Cells

Stem cell division and differentiation. A: stem cell B: progenitor cell C: differentiated cell 1: symmetric stem cell division 2: asymmetric stem cell division 3: progenitor division 4: terminal differentiation

These stem cells have been found in tissues such as the brain, bone marrow, blood, blood vessels, skeletal muscles, skin, and the liver. They remain in a quiescent or non-dividing state for years until activated by disease or tissue injury.

Adult stem cells are limited in their ability to differentiate based on their tissue of origin, but there is some evidence to suggest that they can differentiate to become other cell types.

Adult stem cells, also called somatic stem cells, are stem cells which maintain and repair the tissue in which they are found. They can be found in children, as well as adults.

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.

a. FETALThe primitive stem cells located in the organs of fetuses are referred to as fetal stem cells. There are two types of fetal stem cells:

1.Fetal proper stem cells: Come from the tissue of the fetus proper, and are generally obtained after an abortion. These stem cells are not immortal but have a high level of division and are multipotent.

2.Extraembryonic fetal stem cells: Come from extraembryonic membranes, and are generally not distinguished from adult stem cells

b. AMNIOTIC

Multipotent stem cells are also found in amniotic fluid. These stem cells are very active.Amniotic stem cells are multipotent and can differentiate in cells of adipogenic, osteogenic, myogenic, endothelial, hepatic and also neuronal lines. Amniotic stem cells are a topic of active research.Use of stem cells from amniotic fluid overcomes the ethical objections to using human embryos as a source of cells

Stem Cell’s Disadvantages

• Pluripotency in certain stem cells could also make it difficult to obtain a specific cell type. It is also difficult to obtain the exact cell type needed, because not all cells in a population differentiate uniformly. Undifferentiated cells can create tissues other than desired types.

• Some stem cells form tumors after transplantation; pluripotency is linked to tumor formation especially in embryonic stem cells, fetal proper stem cells, induced pluripotent stem cells. Fetal proper stem cells form tumors despite multipotency.

KEY RESEARCH EVENTS1908: The term "stem cell" was proposed for scientific use by the Russian histologist Alexander Maksimov (1874–1928) at congress of hematologic society in Berlin.

1978: Haematopoietic stem cells are discovered in human cord blood.

1997: Dr. B.G. Matapurkar's surgical technique on regeneration of tissues and organs is published. Regeneration of fallopian tube and uterus is published.

1997: Leukemia is shown to originate from a haematopoietic stem cell, the first direct evidence for cancer stem cells.

1998: James Thomson and coworkers derive the first human embryonic stem cell line at the University of Wisconsin–Madison.

2000: Several reports of adult stem cell plasticity are published.

2001: Scientists at Advanced Cell Technology clone first early human embryos for the purpose of generating embryonic stem cells.

2004–2005: Korean researcher Hwang Woo-Suk claims to have created several human embryonic stem cell lines from unfertilised human oocytes.

April 2006: Scientists at the University of Illinois at Chicago identified novel stem cells from the umbilical cord blood with embryonic and hematopoietic characteristics.

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 led by Dr. Anthony Atala and Harvard University report discovery of a new type of stem cell in amniotic fluid. This may potentially provide an alternative to embryonic stem cells for use in research and therapy.

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 with adult fibroblasts

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

30 October 2008: Embryonic-like stem cells from a single human hair.

January 2009: Yong Zhao and colleagues confirmed the reversal of autoimmune-caused type 1 diabetes by Cord Blood-Derived Multipotent Stem Cells (CB-SCs) in an animal experiment.

11 October 2010: First trial of embryonic stem cells in humans.

2012: Katsuhiko Hayashi used mouse skin cells to create stem cells and then used these stem cells to create mouse eggs. These eggs were then fertilized and produced healthy baby offspring. These latter mice were able to have their own babies.

2013: Scientists at Scotland's Heriot-Watt University developed a 3D printer that can produce clusters of living human embryonic stem cells, potentially allowing complete organs to be printed on demand in the future.

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MEHMET EROĞLU