What’s the story?
Earlier this month the National Institutes of Health (NIH) announced it is planning to lift its ban on federal funding of some research that creates chimeras by injecting human stem cells into animal embryos.
According to The New York Times, there are two types of experiments being considered for funding: (1) adding human stem cells to the embryos of animals before the embryos reach a stage when organs are starting to develop, and (2) adding stem cells into embryos of animals (other than rodents) where the cells could get into and modify the animals’ brains.
Because nonhuman primates like monkeys and chimpanzees are so genetically close to people, the Times notes, researchers working with such primates who want NIH funding would have to wait until an embryo was further developed before adding human stem cells.
What are chimeras?
Chimeras are animals composed of cells that originate from two or more different species. To create a chimera, scientists introduce cells from one species into the developing embryo or fetus of another. (The name chimera comes from Greek mythology and describes a creature with the head of a lion, the body of a goat, and the tail of a serpent).
What are stem cells?
In the human body there are around 200 different cells. Most cells are a particular type (such as the ceruminous gland cell) and have a specific function (in the case of the ceruminous gland cell, producing earwax). Stem cells differ, though, in that they are relatively undifferentiated and unspecialized — they have not yet obtained a special structure and function. These cells are either multipotent, meaning they can give rise to several other differentiated and specialized cells of the body (for example, liver cells, kidney cells, brain cells) or pluripotent, can give rise to all of the cell types that make up the body. All specialized cells arise originally from stem cells, and ultimately form a small number of embryonic cells that appear during the first few days of development.