Scientists have identified the stem cells behind the liver’s legendary ability to replenish its tissue.
Stem cells not only bolster their own numbers but also become other kinds of cells through a process called differentiation, thereby keeping an organ populated as mature cells die off. The stem cells underpinning this process in the liver had never been identified.
To trace the lineage of liver cells, scientists used a telltale marker — the cells’ response to signals delivered by a known stem-cell regulator called Wnt. In mice, a gene called Axin2 became more active when Wnt was present. Using a fluorescent tag to track cells with these Wnt-responsive genes, the scientists were drawn to a cluster of cells around the central vein in the liver. A population of cells there behaved like stem cells. Specifically, the Axin2-producing cells self-renewed, a cardinal characteristic of a stem cell. They also looked like stem cells, with two copies of each chromosome rather than a multiple chromosome arrangement that mature liver cells often have, the scientists report August 5 in Nature.