The Top 10 Everything of 2009

The birth of yet another laboratory mouse is hardly worth noting — unless the furry creature is the first to be developed from stem cells that do not involve embryonic cells. That deserves to be called a breakthrough. The new pups, whose creation in two separate labs in China was announced in July, were the first to be bred from induced pluripotent stem (iPS) cells. These are adult cells (usually skin cells) that scientists reprogram back to their embryonic state by introducing four genes. The reprogrammed stem cells are then programmed again to develop into mice, a feat that has been accomplished before only using embryonic stem cells. Breeding an entire mouse that is itself capable of reproducing — as the mice did in one of the Chinese labs — is a strong sign that iPS cells may be as useful as embryonic stem cells for a potential source of treatments for disease, scientists said.