Figure 1.

WNT/β-catenin signaling, metabolic zonation, proliferation, and tissue stem cell potential in the pericentral hepatocyte zone and the intestinal crypt–villus unit. While proliferation is low and similar in all three liver zones, the intestinal crypt shows high levels of proliferation that are required to compensate for constant loss of cells at the villus tip. Lineage tracing studies* collectively indicate that AXIN2/LGR5⁺ crypt base columnar (CBC) cells and AXIN2⁺ transit-amplifying (TA) cells repopulate the villus and give rise to more differentiated cells. In contrast, the majority of lineage tracing studies suggest that AXIN2/LGR5⁺ pericentral hepatocytes neither repopulate the liver during homeostasis nor do their descendants stream into the periportal zone. *We only mention lineage tracing mice in this figure that have been discussed in this review. Lineage tracing of crypt cells has been pioneered with different LGR5 lineage tracing mice51, and many more mouse lines successfully recapitulated and extended this finding.