Reg4 ⁺ deep crypt secretory cells function as epithelial niche for Lgr5 ⁺ stem cells in colon

Significance Stem cells crucially depend on their complex microenvironment, also called niche. The niche is defined as an anatomic site, consisting of specialized niche cells. These niche cells anchor stem cells and provide the stem cells with physical protection and essential growth and maintenance signals. In the murine small intestinal crypts, Paneth cells constitute an important part of cellular niche for Lgr5 + stem cells with which they are intermingled. Paneth cells provide molecules such as Wnt3, EGF, and Notch ligands to maintain intestinal stem cell. There exists no typical Paneth cell in the colon. Here, we show that Reg4-expressing deep crypt secretory cells function as the colon equivalent of Paneth cells.