| ery little is known about the nature of stem cells in living organisms. Stem cells, in any tissue, produce all the cell lineages in a given tissue. It is, therefore, probable that they are the origin of cancerous mutations. Since stem cells comprise only 0.1% or less of the population of all cells in most tissues, it has been very difficult to identify stem cells as well as measure stem cell proliferation. Studies in the past have involved treating animals with high doses of tritiated-thymidine for short intervals of time, which may have caused cell death, resulting in the underestimation of a stem cell's cell cycle time. This study has used new methods employing 10 to 100 times lower levels of radioisotope than used in the past, thus maintaining the steady state of each tissue. DNA labelling with... |
