The word “niche” implies a specialized environment. But to Fiona Doetsch, the stem cell niche is anything but. For brain stem cells, “the whole organism is the niche,” Doetsch told the audience at the third plenary session of the International Society for Stem Cell Research (ISSCR) annual meeting in Hamburg this week. It’s a surprising idea at first, given the brain’s protection from many circulating substances via a series of barriers, including the blood-brain barrier and the blood-cerebrospinal fluid barrier.