Protein that keeps stem cells poised for action identified

Scientists from Stanford University School of Medicine have identified a protein that appears to play a critical role in keeping stem cells poised to quickly become more specialised cell types.

The protein called Jarid2 maintains a delicate balancing act - one that both recruits other regulatory proteins to genes important in differentiation and also modulates their activity to keep them in a state of ongoing readiness.

"Understanding how only the relevant genes are targeted and remain poised for action is a hot topic in embryonic stem cell research," said Dr Joanna Wysocka, assistant professor of developmental biology and of chemical and systems biology.

"Our results shed light on both these questions," Wysocka added.

Jarid2 works through a protein complex called PRC2, for Polycomb Repressive Complex 2, which is necessary to regulate the expression of developmentally important genes in many types of cells.

According to the researchers, PRC2 activity allows the cell to carefully manage its degree of readiness for the subsequent unwrapping and expression of genes involved in differentiation of the embryonic stem cells into more specialised cells.

"It was just as we would have predicted," said Wysocka. "Without Jarid2, which keeps the genes silent yet poised for activation, the embryos stop developing."

The researchers now plan to further investigate the mechanism by which Jarid2 summons PRC2 to differentiation-specific genes in the stem cells, and how it affects gene expression.

The interaction may be important in human cancers as well.

The study appears in journal Cell.