Curious about "stem cells", I googled and found this stuff. It may (or may not!) be accurate.
A fertilized human egg divides, one becomes two, two becomes four, etc. etc. ... but they are identical cells: stem cells.
These initial "stem cells" can renew themselves through cell division, but they are unspecialized.
In an adult human being, there are a variety of cells with very different characteristics -- such as muscles cells or brain cells or red blood cells.
At some point in the process of cell division, these stem cells must "differentiate", becoming one of the many varieties.
Normally, these muscle cells, brain cells, red blood cells etc. etc. can no longer divide.
>So an adult has no stem cells, right?
Wrong. Scientists have found adult stem cells in many more tissues than they thought possible.
There are stem cells in bone marrow which can divide to repair damaged cells.
Normally, however, stem cells in adults only divide under special circumstances.
That's the remarkable thing about stem cells: they can develop into many different types as the body matures.
With every division, the new stem cells have the potential to become another type of specialized cell.
red blood cells
Nevertheless, it has recently been discovered that, in certain cases, adult bone stem cells may be able to differentiate into completely different cell types.
>May? Can they or can't they?
The jury is still out on that one.
The interesting thing is that, whereas embryonic stem cells can proliferate in the laboratory, most adult stem cells do not.
That's one of the mysteries surrounding stem cell research.
>Buy why do adult stem cells divide when they're in a living being?
What is it about being in a living organism that enables cell division?
That's another mystery.
>So there are two kinds of stem cells?
It seemed that way: embryonic stem cells and adult stem cells.
Embryonic stem cells were first discovered in 1981, from mouse embryos.
Within a few years it was possible to grow human embryonic stem cells.
These could be fertilized in vitro as an infertility treatment.
The stem cells that were not used for the treatment were given to researchers
(with the consent of the donor).
Then, in 2006, it was discovered that some specialized adult cells could be "reprogrammed" to assume a kind of stem cell state.
They're induced stem cells.
>And can stem cells be programmed to change into a differentiated cell?
Apparently it took years to learn how to grow stem cells that remained stem cells. They tended to spontaneously differentiate into specific cell types.
If the stem cells are allowed to clump together, they may start to differentiate.
>So how does a stem cell know when to differentiate and what to differentiate into?
That's another of the mysteries in stem cell research.
It clearly depends (in mysterious ways) upon the genetic structure of the cells, the characteristics of the neighbouring cells, the molecular
environment it's in, its chemical surrounding, the phases of the moon, certain astrological charts ...
>You have no idea, do you?
Me? Of course not. Do I look like a cellular biologist? I just regurgitate what I find.
Remember, there are some 300 types of cells in the human body.
Just imagine a stem cell being able to transmute to any one of these.
Mind boggling, eh?
Also, the stem cells can replicate a finite number of times
... then they either stop dividing or become one of those specialized cell.
On the other hand, germ cells, such as the unfertilized egg or sperm, can subdivide forever.
>So there are two kinds of cells in the body?
There are three basic types: germ cells (or gametes), stem cells and all the rest (somatic cells).
Altogether, a human has about 100,000,000,000,000 cells.
stem cell colony
- 1908 - The term "stem cell" was proposed for scientific use by the Russian histologist Alexander Maksimov (1874–1928) at congress of hematologic society in Berlin. It postulated existence of blood (haematopoietic) stem cells.
- 1960s - Joseph Altman and Gopal Das present scientific evidence of adult ongoing stem cell activity in the brain.
- 1963 - McCulloch and Till illustrate the presence of self-renewing cells in mouse bone marrow.
- 1968 - Bone marrow transplant between two siblings successfully treats SCID.
- 1978 - Haematopoietic stem cells are discovered in human cord blood.
- 1981 - Mouse embryonic stem cells are derived from the inner cell mass by scientists Martin Evans, Matthew Kaufman, and Gail R. Martin. Gail Martin is attributed for coining the term "Embryonic Stem Cell".
- 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.
- 2003 - Dr. Songtao Shi of NIH discovers new source of adult stem cells in children's primary teeth.
- 2005 - Researchers at Kingston University in England 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.
- 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.
- 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.
- October 2007 - Mario Capecchi, Martin Evans, and Oliver Smithies 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.
- 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.
- 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 (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.
- 05 March 2009 Australian scientists find a way to improve chemotherapy of mouse muscle stem cells.
- 09 March 2009 US President Obama lifted federal funding limits on human embryonic instituted by former President Bush.