Are There Changes in Human Embryonic Stem Cells after Long Periods in Culture?
One unique characteristic of human embryonic stem cells (hESCs) is their ability to remain unchanged even after long periods in culture. Scientists know that cells grown in laboratory culture for a long time have the tendency to develop changes in their DNA and that even hESCs will eventually develop such changes. They are using sensitive techniques to monitor hESC DNA. Two groups of scientists have recently reported their results using different techniques to analyze the DNA of hESCs on the NIH Human Embryonic Stem Cell Registry. One group examined the expression of specific genes regulated by a process known as imprinting. In imprinting, one of the two copies of a gene inherited from the parents is normally turned off, or inactivated, by the addition of a chemical group known as a methyl (CH3). When a gene is inactivated by adding CH3, the process is known as methylation. Although the group identified some disruptions in normal methylation after a long period in cell culture, they co
