Thanks to a little mouse named Tiny, researchers have now shown that full, living mammals can be grown from so-called induced pluripotent stem cells—cells from an adult that act in many ways like embryonic stem cells

Xiao Xiao, as the rodent is called in its native Chinese, was one of dozens created from induced pluripotent stem cells (iPS cells) and born to a surrogate mother. The process is described in a study published yesterday in Nature (Scientific American is part of Nature Publishing Group).

Researchers used a virus to deliver four genes into fibroblast cells taken from adult mice, triggering the change to iPS cells. These cells were then implanted into an embryo that didn’t have the requisite genetic information for it to develop beyond a placenta. That these implanted embryos developed into full baby mice proved that these cells could indeed do all the work of natural embryonic stem cells.

“This gives us hope for future therapeutic interventions using patients’ own reprogrammed cells,” study author Fanyi Zeng of Jiao Tong University said in a statement, The Washington Post reported.

The team had a birth rate of just 3.5 percent of the 624 embryos they injected. Even the mice that were born alive frequently died after just a couple days. But of those that did live, a dozen were mated and produced reportedly healthy offspring—offspring that have now mated, producing even third-generation mice.

Another team, based out of the National Institute of Biological Sciences in Beijing, has been working on a parallel project and also produced a live mouse from iPS cells. They published their results in Cell's Stem Cell yesterday.

The results have generated renewed concern about human cloning, but the lead author of the Nature paper, Qi Zhou of Beijing’s Institute of Zoology, told Nature News that it is “an important model for understanding reprogramming. … It is not intended to be a first step towards using iPS cells to create a human being.”

Photo of the first iPS mouse, “Tiny,” courtesy of Qi Zhou