The idea of reprogrammed adult stem cells as an alternative to embryonic stem cells in research has taken a number of hits this past year. So, a pioneer in induced pluripotent stem (iPS) cell research, Shinya Yamanaka of Kyoto University, is fighting back. iPS cells are seen by some as an ethically acceptable alternative to use of stem cells derived from embryos. Lately, though, there have been a number of puzzling genetic mutations in iPS cells that some scientists say call into question just how reliable non-embryonic stem cells are. The answer, says Yamanaka, is simple. Lab conditions differ around the world, resulting in heterogeneity between iPS cells and between iPS and embryo-derived stem cells. "Maybe the water in Kyoto" is to blame, he speculated, according to a report in Nature's Newsblog. Another iPS researcher, Rudolf Jaenisch of the Whitehead Institute in Cambridge, MA, discovered that slightly different vectors were used to shuttle genes in adult stem cells, resulting in slightly different results between labs. More here