Stem cells are different from all other cells in our body because they retain the remarkable genetic plasticity to self-renew indefinitely, as well as develop into cell types with more specialized functions. However, this remarkable self-renewal capacity comes with a price, as stem cells can become seeds of cancer. Identifying genetic programs that maintain self-renewing capabilities therefore is a vital step in understanding the errors that derail a normal stem cell, sending it on a path to become a cancer stem cell. Isolating cells from various other cell types is very much like fishing -- you need a good "hook" that can recognize a specific protein marker on the surface of a cell, in order to pull that cell out. Until now, isolating pure mammary gland stem cells (MaSCs), which are important in mammary gland development, as well as breast cancer formation, has posed a challenge. MaSCs are scarce and share common cell-surface markers with other cells. In a paper published online on April 11, 2013 in PNAS, scientists in the laboratory of Professor Gregory Hannon at Cold Spring Harbor Laboratory (CSHL) in New York used a mouse model to identify a novel cell surface marker on MaSCs. Using that marker, the team was able to assemble a sample of MaSCs of unprecedented purity. "We are describing a marker called Cd1d (see image)," says CSHL research investigator Camila Dos Santos, Ph.D., the paper's first author. The marker, also present at the surface of specialized immune cells, is expressed on the surface of a defined population of mammary cells in both mice and humans. The team took advantage of the fact that MaSCs divide much mpre slowly than other cells.
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