Different levels of canonical Wnt signaling exert distinct roles in the colonic epithelium

There is a gradient of -catenin expression along the colonic crypt axis with the highest levels at the crypt bottom. However, it remains unclear whether different levels of canonical Wnt signaling exert distinct roles in the colonic epithelium. In the present study, we first showed that the canonical Wnt signaling is active in the proliferative compartment of normal colonic crypts by separating actively proliferating progenitor cells from non-proliferating cells in the colon using transgenic mice expressing a histone H2B-green fluorescent protein (GFP) fusion protein under the control of a tetracycline responsive regulatory element. Subsequently, we investigated the dose-dependent effect of canonical Wnt activation on colonic epithelial differentiation by controlling the expression levels of stabilized -catenin using a doxycycline-inducible transgenic system in mice. We show that elevated levels of Wnt signaling induce the amplification of Lgr5+ cells, which is accompanied by crypt fission and a reduction in cell proliferation among progenitor cells. In contrast, lower levels of -catenin induction enhanced cell proliferation rates of epithelial progenitors without affecting crypt fission rates. Notably, slow-cycling cells produced by -catenin activation exhibit activation of Notch signaling and the treatment of -catenin expressing mice with a Notch inhibitor turned such slow-cycling cells into actively proliferating cells. Our results indicate that the activation of the canonical Wnt signaling pathway is sufficient for de novo crypt formation, and suggest that different levels of canonical Wnt activations, in cooperation with Notch signaling, establish a hierarchy of slower-cycling stem cells and faster-cycling progenitor cells characteristic for the colonic epithelium.

4

Hirata A, Utikal J, Yamashita S, Aoki H, Watanabe A, Yamamoto T, Okano H, Bardeesy N, Kunisada T, Ushijima T, Hara A, Jaenisch R, Hochedlinger K, Yamada Y