Stem cell line
Encyclopedia
A stem cell line is a family of constantly dividing cell
Cell (biology)
The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. The Alberts text discusses how the "cellular building blocks" move to shape developing embryos....

s, the product of a single group of stem cells. They are obtained from human or animal tissues
Biological tissue
Tissue is a cellular organizational level intermediate between cells and a complete organism. A tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function. These are called tissues because of their identical functioning...

 and can replicate for long periods of time in vitro
In vitro
In vitro refers to studies in experimental biology that are conducted using components of an organism that have been isolated from their usual biological context in order to permit a more detailed or more convenient analysis than can be done with whole organisms. Colloquially, these experiments...

 ("within glass"; or, commonly, "in the lab", in an artificial environment). They are frequently used for research relating to embryonic stem cells or cloning entire orgasims.

Alternative sources

Adult stem cell
Adult stem cell
Adult stem cells are undifferentiated cells, found throughout the body after embryonic development, that multiply by cell division to replenish dying cells and regenerate damaged tissues...

 lines isolated from mature tissues are commonly used in stem cell research, as are cells isolated from umbilical cord blood
Cord blood
Umbilical cord blood is blood that remains in the placenta and in the attached umbilical cord after childbirth. Cord blood is collected because it contains stem cells which can be used to treat hematopoietic and genetic disorders.-Collection:...

. However, these cells have a genetic imprint of the host they were taken from, thus limiting their therapeutic use in genetic disorders. Also, adult stem cells are not totipotent or pluripotent like embryonic stem cells, but rather more specialized cells that are multipotent.

Another source of stem cells is the iPS (induced pluripotent stem) cell. This process involves reversing the differentiating cell signals that cause a stem cell to specialize. In this way, a somatic cell
Somatic cell
A somatic cell is any biological cell forming the body of an organism; that is, in a multicellular organism, any cell other than a gamete, germ cell, gametocyte or undifferentiated stem cell...

 can be worked backwards into a stem cell. One added advantage of this type of stem cell is that the pluripotent cell has the same DNA as the donor and can be used therapeutically towards that end without painful bone marrow and spinal cord extraction techiques. It also contributes to pain relief.

New techniques

Typically, stem cells have been maintained using tissue culture methods that essentially date from the 1950s. In particular, they are often "fed" using mouse embryonic fibroblasts ("feeder cells") while being simultaneously suspended in a nutrient solution ("media"). However, many scientists are recognizing the importance of using media that is completely free of animal ingredients. This not only liberates cell lines from animal feeder cells, but also brings the in vivo
In vivo
In vivo is experimentation using a whole, living organism as opposed to a partial or dead organism, or an in vitro controlled environment. Animal testing and clinical trials are two forms of in vivo research...

therapeutic use of stem cells one step closer to reality.

Nonmammalian Study model

One interesting study model that yields research results that can be subsequently tested on mammalian systems, is the fruit fly Drosophila (1)

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