MadSci Network: Cell Biology

Re: What is an exact definiton of a stem cell?

Date: Tue Apr 1 10:25:17 2003
Posted By: Pamela Norton, faculty, Dept. of Medicine, Thomas Jefferson Univ.
Area of science: Cell Biology
ID: 1045949000.Cb

Your understanding is partly correct, with the added feature that stem 
cells can continue to proliferate and generate more stem cells as well as 
to differentiate into more specialized cells. Stem cells are more or less 
operationally defined as a population of cells that continuously renews 
itself and gives rise to one or more specialized cell types.

A little more information, which may be more than you wanted. Stem cells 
can generally be divided into embryonic stem cells and adult stem cells. 
Embryonic stem cells (ES cells) are derived from early embryos and can give 
rise to all embryonic cell types. Mouse ES cells are widely used to 
introduce defined genetic changes into mice; subsequent breeding leads to 
animals with the defined change in all cells. These have been used to model 
aspects of human genetic diseases. Adult stem cells have more limited 
potential, with distinct cells that repopulate the blood, or intestine, or 
skin, all tissues where cell turnover occurs normally. The stem cells 
provide replacements for the cells that die off.

A highly detailed dsicussion of stem cells is available at the NIH web 

Although these are fairly recent source, this is a fast moving field. 
Serious ethical issues exist concerning the isolation and use of human stem 
cells. The use of adult stem cell populations avoids this problem, although 
these cells are thought to have a more restricted range of cell types that 
can be generated. Some reports suggest that these cells may have a wider 
potential than thought, but other workers have contradictory results. The 
following news release, although potentially baised, outlines some of this 
controversy; more information is likely to follow.

Good luck with your project.

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