Fish “Umbrella” Protects Stem Cells from Sun
This is a zebrafish larva, swimming in the sunlight. These fish use a clever trick to keep certain stem cells safe. Vulnerable stem cells inside fish kidneys produce blood cells. HHMI Invesetigator Leonard Zon’s team found cells called melanocytes on top of the kidney. These darkly pigmented cells shade the stem cells from the sun’s harmful rays. In mutant fish lacking malanocytes, sunlight killed the stem cells. The melanocytes form an umbrella that protects the stem cells from damaging UV light, Zon’s team discovered. In humans and other mammals, these stem cells reside in the bones. What’s the evolutionary explanation? Overexposure to sunlight may have driven these cells from the kidneys to the interior of UV-blocking bones.