Scientists would ultimately like to create a complete wiring diagram of the stem cell's regulatory circuit. To date, scientists from different labs have identified several of the top level control systems in the network. In a paper published in September, Rick Young, a biologist at Whitehead, and colleagues describe the use of microarray technology to identify a set of genes that are kept inactive in undifferentiated stem cells. Researchers theorize that when these genes are turned on, they produce transcription factors that spur the cell along different developmental paths. Young's collaborator, David Gifford, a computer scientist at MIT, is studying the packaging of DNA in an effort to determine whether some of these genes have been activated in specific cell types. The research was presented at a conference at MIT last week titled "Systems Biology of the Stem Cell."

Lemischka and colleagues at Princeton University have identified another set of genes that are kept inactive in undifferentiated stem cells. They are now examining how turning these genes on and off impacts different parts of the cell, such as its proteins, cDNAs, RNAs, and histone modifiers, the proteins that determine how DNA is packaged.

Scientists can also use array technologies to examine other characteristics of stem cells. Jaenisch and colleagues published a paper in the Proceedings of the National Academy of Sciences on January 16 showing that stem cells derived from cloned embryos are functionally identical to stem cells derived from fertilized embryos -- the two cell types show no difference in gene expression patterns. Previous research has shown that a high percentage of animals created from cloned embryos develop abnormally, so scientists had been concerned that stem cells derived from cloned embryos carry genetic abnormalities that make them unsuitable for therapeutic purposes. However, according to the latest finding, this does not seem to be the case.