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Tissues are integrated groups of specialized cells that perform specific functions.
Stem cells are relatively unspecialized cells that can divide and differentiate into different cell types.
Adult stem cells, also known as somatic stem cells, are found in mature tissues; embryonic stem cells make up early embryos.
Stem cells can be used therapeutically to engineer or regenerate tissues and organs.
Making new tissues requires both cell division and cell differentiation. Cell differentiation is the process by which an unspecialized cell becomes a specialized cell with a unique function.
All cells in the body have the same genome but express different genes. Such differential gene expression causes each cell type to produce different proteins and to have different functions.
Adult stem cells are multipotent, capable of differentiating into a limited number of different cell types.
Embryonic stem cells are pluripotent, capable of differentiating into nearly any cell type in the body.
Embryonic stem cells can be obtained from human embryos or from cloned embryos. They may also be created by inducing adult cells to “de-differentiate.”
In somatic cell nuclear transfer (SCNT), also known as cloning, the nucleus of an unfertilized egg is replaced by the nucleus of a donor cell to produce an embryo with the same genes as the donor cell.
Both adult and embryonic stem cells are being investigated as possible therapies to restore damaged tissue in humans.
MORE TO EXPLORE
Catalyst, ABC television (Oct, 2012): Organ Bioprinting http://www.abc.net.au/catalyst/stories/3618385.htm
Atala, A. (2011) TED Talk: Printing a human kidney http://www.ted.com/talks/anthony_atala_printing_a_human_kidney.html
Atala, A., et al. (2006) Tissue-engineered autologous bladders for patients needing cystoplasty. The Lancet 367:1241–46.
Raya-Rivera, A., et al. (2011) Tissue-engineered autologous urethras for patients who need reconstruction: an observational study. The Lancet 377:1175–82.
Junying, Y., et al. (2007) Induced pluripotent stem cell lines derived from human somatic cells. Science 318:1917–1920.