Stem cell

Stem cell
MSC high magnification.jpg
Transmission electron micrograph of an adult stem cell displaying typical ultrastructural characteristics.
Details
Identifiers
LatinCellula praecursoria
D013234
H1.00.01.0.00028, H2.00.01.0.00001
63368
Anatomical terminology

Stem cells are biological cells that can differentiate into other types of cells and can divide to produce more of the same type of stem cells. They are found in multicellular organisms.

In mammals, there are two broad types of stem cells: embryonic stem cells, which are isolated from the inner cell mass of blastocysts, and adult stem cells, which are found in various tissues. In adult organisms, stem cells and progenitor cells act as a repair system for the body, replenishing adult tissues. In a developing embryo, stem cells can differentiate into all the specialized cells—ectoderm, endoderm and mesoderm (see induced pluripotent stem cells)—but also maintain the normal turnover of regenerative organs, such as blood, skin, or intestinal tissues.

There are three known accessible sources of autologous adult stem cells in humans:

  1. Bone marrow, which requires extraction by harvesting, that is, drilling into bone (typically the femur or iliac crest).
  2. Adipose tissue (fat cells), which requires extraction by liposuction.[1]
  3. Blood, which requires extraction through apheresis, wherein blood is drawn from the donor (similar to a blood donation), and passed through a machine that extracts the stem cells and returns other portions of the blood to the donor.

Stem cells can also be taken from umbilical cord blood just after birth. Of all stem cell types, autologous harvesting involves the least risk. By definition, autologous cells are obtained from one's own body, just as one may bank his or her own blood for elective surgical procedures.

Adult stem cells are frequently used in various medical therapies (e.g., bone marrow transplantation). Stem cells can now be artificially grown and transformed (differentiated) into specialized cell types with characteristics consistent with cells of various tissues such as muscles or nerves. Embryonic cell lines and autologous embryonic stem cells generated through somatic cell nuclear transfer or dedifferentiation have also been proposed as promising candidates for future therapies.[2] Research into stem cells grew out of findings by Ernest A. McCulloch and James E. Till at the University of Toronto in the 1960s.[3][4]

Properties

The classical definition of a stem cell requires that it possesses two properties:

  • Self-renewal: the ability to go through numerous cycles of cell division 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 or pluripotent—to be able to give rise to any mature cell type, although multipotent or unipotent progenitor cells are sometimes referred to as stem cells. Apart from this it is said that stem cell function is regulated in a feed back mechanism.

Self-renewal

Two mechanisms exist to ensure that a stem cell population is maintained:

1. 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.

When a stem cell self-renews it divides and does not disrupt the undifferentiated state. This self-renewal demands control of cell cycle as well as upkeep of multipotency or pluripotency, which all depends on the stem cell.[5]

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 meaning

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.
Human embryonic stem cells
A: Stem cell colonies that are not yet differentiated.
B: Nerve cells, an example of a cell type after differentiation.

Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell.[6]

  • Totipotent (a.k.a. omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism.[6] 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.[7]
  • Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells,[6] i.e. cells derived from any of the three germ layers.[8]
  • Multipotent stem cells can differentiate into a number of cell types, but only those of a closely related family of cells.[6]
  • Oligopotent stem cells can differentiate into only a few cell types, such as lymphoid or myeloid stem cells.[6]
  • Unipotent cells can produce only one cell type, their own,[6] but have the property of self-renewal, which distinguishes them from non-stem cells (e.g. progenitor cells, which cannot self-renew).

Identification

In practice, stem cells are identified by whether they can regenerate tissue. For example, the defining test for bone marrow or hematopoietic stem cells (HSCs) is the ability to transplant the cells and save an individual without HSCs. This demonstrates that the cells can produce new blood cells over a long term. 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, using methods such as clonogenic assays, in which single cells are assessed for their ability to differentiate and self-renew.[9][10] Stem cells can also be isolated by their possession of a distinctive set of cell surface markers. However, in vitro culture conditions can alter the behavior of cells, making it unclear whether the cells shall behave in a similar manner in vivo. There is considerable debate as to whether some proposed adult cell populations are truly stem cells.[11]

Other Languages
Afrikaans: Stamsel
العربية: خلية جذعية
বাংলা: মাতৃকোষ
беларуская: Стваловыя клеткі
български: Стволова клетка
čeština: Kmenová buňka
dansk: Stamcelle
Deutsch: Stammzelle
eesti: Tüvirakud
Ελληνικά: Βλαστοκύτταρο
español: Célula madre
Esperanto: Praĉelo
euskara: Zelula ama
français: Cellule souche
Gaeilge: Gaschill
galego: Célula nai
客家語/Hak-kâ-ngî: Kon-se-pâu
한국어: 줄기세포
Bahasa Indonesia: Sel punca
interlingua: Cellula originator
íslenska: Stofnfruma
עברית: תא גזע
Basa Jawa: Sel Punca
ಕನ್ನಡ: ಆಕರ ಕೋಶ
latviešu: Cilmes šūna
magyar: Őssejt
македонски: Матична клетка
मराठी: मूलपेशी
Bahasa Melayu: Sel tunjang
монгол: Үүдэл эс
မြန်မာဘာသာ: ပင်မဆဲလ်
Nederlands: Stamcel
日本語: 幹細胞
norsk: Stamcelle
ਪੰਜਾਬੀ: ਸਟੈੱਮ ਸੈੱਲ
Plattdüütsch: Stammzell
português: Célula-tronco
română: Celule stem
Scots: Stem cell
Simple English: Stem cell
slovenčina: Kmeňová bunka
slovenščina: Matična celica
српски / srpski: Изворна ћелија
srpskohrvatski / српскохрватски: Matična ćelija
Basa Sunda: Sél punca
suomi: Kantasolu
svenska: Stamcell
తెలుగు: మూల కణం
Türkçe: Kök hücre
Tiếng Việt: Tế bào gốc
ייִדיש: סטעם צעל
粵語: 幹細胞
中文: 幹細胞