'Master Switches' Found for Adult Blood-Forming Stem Cells

Scientists have found a set of "master switches" that keep adult blood-forming stem cells in their primitive state. Unlocking the switches' code may one day enable scientists to grow new blood cells for transplant into patients with cancer and other bone marrow disorders. The scientists located the control switches not at the gene level but farther down the protein production line in more recently discovered forms of ribonucleic acid, or RNA. MicroRNA molecules, once thought to be cellular junk, are now known to switch off activity of the larger RNA strands that allow assembly of the proteins that let cells grow and function. "Stem cells are poised to make proteins essential for maturing into blood cells, but microRNAs keep them locked in their place."