UCLA scientists prove endothelial cells give rise to blood ...( Stem cell researchers at UCLA have p...),Health

Stem cell researchers at UCLA have proven definitively that blood stem cells are made during mid-gestational embryonic development by endothelial cells, the cells that line the inside of blood vessels.

While the anatomic location in the embryo where blood stem cells originate has been well documented, the cell type from which they spring was less understood. The UCLA finding, published in the Dec. 4, 2008 issue of the journal Cell Stem Cell, puts to rest a long-standing controversy over whether blood stem cells were created, or born, in the endothelium or originated from another cell type in a nearby location.

Researchers from the Eli and Edythe Broad Center of Regenerative Medicine and Stem Cell Research at UCLA used a cell fate tracing technique to identify the source of blood stem cells. They genetically marked endothelial cells to discover what other cells they gave rise to and where those cells migrated to in the body.

"We genetically traced the endothelial cells to find out what they became over time," said Luisa Iruela-Arispe, senior author of the paper, a professor of molecular, cell and developmental biology and director of the Cancer Cell Biology Program Area at UCLA's Jonsson Comprehensive Cancer Center. "In that way, we were able to understand that, within the embryo, endothelial cells were responsible for the generation of blood stem cells. They make blood, they aren't just the pipes that carry it."

The finding ultimately could lead to new therapies for certain blood disorders and cancers, said Ann Zovein, the first author of the study and a California Institute for Regenerative Medicine-Broad Stem Cell Research Center Training Grant postdoctoral fellow in Iruela-Arispe's lab.

Blood stem cells currently cannot be grown outside of the body without losing their "stemness," meaning they then differentiate into the different cells that make up blood, including red blood cells, white blood cells
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