Although mammals have a limited capacity to regenerate teeth, mouse incisors contain stem cells and grow continuously throughout life. Using a combination of mouse mutant analyses, organ culture experiments, and gene expression studies, Xiu-Ping Wang and colleagues identify the key signaling molecules that regulate epithelial stem cell proliferation in the stem cell niche. Their work is published online this week in the open-access journal PLoS Biology.

The researchers show that signals from the adjacent mesenchymal tissue regulate epithelial stem cells and form a complex regulatory network with epithelial signals. They also show that spatial differences in the expression levels of two key genes, Activin and Follistatin, contribute to the characteristic asymmetry of rodent incisors, which are covered by enamel only on their labial (front) side. Subtle variations in this or related regulatory networks may explain the different regenerative capacities and asymmetric development of various organs and animal species.