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Why Do Stem Cells Rest? Study Reveals It’s a Matter of Choice



Prior to the study, which is published in the current edition of PLoS ONE, hematopoietic stem cells were thought to have no other option when they went into quiescence and that it was brought on by a lack of nutrients or stimulation.

However, Dr. Lacorazza said, "Our findings show that hematopoietic stem cells make the choice to stay in quiescence. This process is regulated by the protein G0S2. This type of stem cell is important because there are only a limited number that produce all our blood cells. So in a way the stem cells are balancing between proliferation and quiescence so they don't get exhausted."

The BCM team made its discovery after analyzing the gene expression in proliferating (multiplying) and non-proliferating cells. It noted that the G0S2 protein increased while in quiescence. When the researchers specifically examined hematopoietic stem cells they noted there were high levels of G0S2, but when proliferation began the levels reduced.

By forcing the expression of G0S2 they found they could increase the state of quiescence, "so it is a positive regulator," Dr. Lacorazza said. "Our next question was, 'How does it regulate this process; what are the mechanisms?' "

The BCM team then used mass spectrometry to search for proteins that interacted with G0S2 and came up with nucleolin, a protein that promotes cell growth and proliferation. When G0S2 binds with nucleolin, it retains it in the cytosol (the liquid inside a cell), preventing it from entering the nucleus and performing its proper function.

"In a sense G0S2 sequesters the nucleolin outside the nucleus of the cell extending quiescence," Dr. Lacorazza explained.

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