In a series of recent experiments, scientists have transformed cells from mouse embryos into skin, heart muscle, and even eggs. In addition to providing insight into how such tissues develop, these feats have renewed the political and ethical debate over whether similar experiments should be conducted with cells derived from human embryos.
Known as embryonic stem cells, the lab-grown mouse cells are unspecialized and can grow in lab dishes seemingly forever. Scientists at the University of Pennsylvania created apparently normal mouse eggs from such stem cells, according to a report in the May 23 Science. While observing batches of stem cells, the biologists detected a small number of cells that began to display a genetic marker of egg cells.
The stems cells that appear to have become eggs cells also ended up surrounded by structures similar to the so-called follicles that envelop typical eggs. These appear to be the first mammalian eggs formed completely in a l