Over the past decade, scientists have discovered a number of cell-surface markers that might identify prostate stem cells. But all these markers are also expressed in other stem cell types. Now, researchers have found a new marker for a rare adult mouse prostate stem cell population, and showed that a single cell from this population can generate a new prostate after transplantation in vivo. The ability to recreate this organ should help researchers better understand how prostate cancer starts and possibly even help them to grow replacement prostate tissue in the laboratory.

To pinpoint definitive prostate stem (PS) cells, Wei-Qiang Gao of Genentech in South San Francisco, California, and his colleagues noticed that many of the previously described PS cell markers were preferentially expressed in the region of the prostate nearest to the urethra. They then discovered that another marker, the cytokine receptor CD117, or c-Kit, had a similar expression profile. Treating prostates from young mice with anti-CD117 antibodies in culture for several days prevented the formation of prostate internal structure, indicating that CD117 is required for normal prostate development1.

Gao's team then identified a multipotent, self-renewing PS cell population defined by CD117 expression in combination with three other surface markers — Sca-1, CD133 and CD44 — which constituted 0.12% of a population of possible PS cells. The researchers transplanted single mouse PS cells together with rat urogenital mesenchymal stromal cells into 97 immunocompromised mice, successfully generating 14 functional, secretion-producing prostates.

The prostate now joins the mammary gland, blood and skin as organs that can be successfully regenerated from single murine stem cells. “It generalizes to another organ with a complex structure that a single cell can do this from scratch,” says Connie Eaves at the British Columbia Cancer Research Centre in Vancouver, Canada, whose team was one of the first to reconstitute an entire mammary gland from single stem cells2. Eaves also notes that the purity of the PS cells isolated by Gao's team was much greater than in most other studies — around 10% as judged by the fraction of cells following serial dilutions that gave rise to prostates on transplantation in vivo. “That's impressive,” she says. “That means that you can start to do something with these populations and draw inferences from them.”

“It's a great technical breakthrough,” says David Hudson, of the University of York, UK,who recently characterized a population of putative human PS cells expressing CD133 (ref. 3). In Gao's mouse PS cells, CD133 was expressed alongside CD117, so Hudson thinks he and others were on the right track to finding human PS cells; they just hadn't found the most definitive marker. “Given the conservation of other markers, including CD44 and CD133, between species,” he says, “there's not really any reason for us to think that there's going to be a huge difference” between mice and humans. In addition to the mouse experiments, Gao's team showed that CD117 is expressed in human prostate tissue. It now remains to be seen whether CD117-marked human cells are true PS cells, and if single human cells can generate new prostates, Hudson notes.