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In humans and other mammals, the stem cells that give rise to all blood cells are located in the bone. But in fish, blood stem cells are found in the kidney. Since the late 1970s, when biologists first realized that blood develops in a specific location in the body—the 'blood stem cell niche'—they have wondered why different creatures have evolved to carry out this function in different locations.
Forty years later, scientists have found a valuable clue: the niche evolved to protect blood stem cells from the harmful ultraviolet (UV) rays in sunlight.
Findings - Nature - Researchers - Harvard - Department
The findings are published in Nature by researchers at the Harvard Department of Stem Cell and Regenerative Biology, Boston Children's Hospital's Stem Cell Program, and the Harvard Stem Cell Institute. This new piece of the 'blood stem cell niche' puzzle will help the team improve the safety of blood stem cell transplants.
The inspiration for this study came from an incidental observation in the zebrafish, an animal model used in many laboratories.
Blood - Stem - Cells - Microscope - Layer
"I was trying to look at blood stem cells under the microscope, but a layer of melanocytes above the kidney blocked my view," said Friedrich Kapp, M.D., now at the Center for Pediatrics, University of Freiburg Medical Center in Germany. Melanocytes are cells that produce melanin, the pigment responsible for the color of human skin.
"The shape of the melanocytes above the kidney reminded me of a parasol, so I thought, do they provide UV protection to blood stem cells?" said Kapp.
Kapp - Zebrafish - Zebrafish - Melanocytes - UV
So Kapp exposed normal zebrafish and mutant zebrafish lacking melanocytes to UV radiation. Sure enough, the number of blood stem cells decreased in the mutants.
Moreover, the normal zebrafish lost blood stem cells when they were turned upside down and irradiated. This confirmed...
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