Tracking the Elusive Stem Cell

Douglas Engel Photo: Lin Jones

An international team of scientists led by Douglas Engel, Ph.D., the Medical School’s G. Carl Huber Professor of Developmental Biology and chair of the Department of Cell and Developmental Biology, has found a way to see rare blood-forming adult stem cells, called hematopoietic stem cells, living in their natural environment.

Until now, scientists didn’t know exactly where to find these elusive stem cells — the only ones capable of forming all the different types of blood and immune cells found in mammals. Most scientists believed they clustered together somewhere in bone marrow, but no one knew for sure.

“We took time-lapse movies of sections from mouse leg bone as seen under a fluorescent microscope,” says Engel. “They clearly showed individual, isolated hematopoietic stem cells at the edge of the bone marrow.”

According to Engel, the discovery will make it possible to study these stem cells undisturbed and in their natural environment. That’s important, he says, because when stem cells are removed from bone marrow, they either die or start differentiating — changing into different types of specialized blood cells.

A single glowing blood-forming stem cell is visible among living mouse bone marrow cells. Photo: Douglas Engel, U-M Medical School

Scientists currently identify a hematopoietic stem cell by looking for a unique pattern of protein markers on the cell’s surface. The process is complicated and the flow cytometry equipment used to sort the cells is expensive. Plus the sorting process removes stem cells from bone marrow, which changes their properties in fundamental ways.

“There’s something about the physical location and cellular environment surrounding stem cells in their bone marrow niche that is at least partly responsible for their ability to remain in a primitive state,” Engel says. “Now that we can visualize them, we are in a better position to find out how they do it.”

—Sally Pobojewski

For an expanded version of the story:
www.med.umich.edu/opm/newspage/2006/stemcells.htm