Master Regulator Keeps Embryonic Stem Cells in Check

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Directed by subtle chemical cues, embryonic stem cells have the ability to become virtually any cell type in the body. But in order to retain their unique properties, embryonic stem cells must quiet the signals that cause them to change, yet remain ready to switch them on quickly when needed.

Molecular biologist Richard A. Young, Ph.D., of the Whitehead Institute in Cambridge, Massachusetts, has been studying the molecular events that help keep embryonic stem cells hanging in this delicate balance. In a recent investigation, his team analyzed Polycomb proteins, known to be key players in establishing the body plans of organisms ranging from fruit flies to humans.

To examine the role of Polycomb proteins in the embryonic development of humans and mice, the scientists devised a way to monitor the proteins’ effects on gene activity. Young and his team discovered that Polycomb proteins shut down the activity of more than 500 genes in the embryonic stem cells of mice and humans. When the proteins were taken away, the stem cells nearly immediately "grew up" into various specialized cell types.

Knowing how Polycomb proteins regulate gene activity will yield new insights into human development. The findings also suggest potential means to develop therapies to treat diseases such as Parkinson’s, diabetes, and many other conditions in which certain cell types are lost or damaged.