A menagerie of stem-cell models

Abstract

I n 2007, Wei Li had identified what he thought was the perfect model to study colour vision: the thirteen-lined ground squirrel (Ictidomys tridecemlineatus). Common prairie-dwellers, these squirrels stand on their rear legs, meerkat-like, to survey their surroundings. Approximately 86% of the light-detecting cells in their retinas are cone cells, which respond to various wavelengths to detect colour. In humans and mice, the proportion is less than 10%. But squirrel biology put Li's idea on ice-literally. Ground squirrels hibernate, so for six months each year, Li's study subjects snooze in a refrigerator. And Li, a vision researcher at the National Eye Institute in Bethesda, Maryland, and his then-postdoctoral researcher Jingxing Ou knew that cells from conventional models, such as rats, mice, fruit flies and even humans would not give them the information they Endangered species such as the northern white rhinoceros (Ceratotherium simum cottoni) could benefit from work to recreate their stem cells.