Practice question

A functional niche must provide structural support, adhesive contacts, and signaling milieu that maintains stemness. The intestinal crypt exemplifies this model: Paneth cells intercalated with Lgr5-positive stem cells at crypt base secrete Wnt3, EGF, and Notch ligands DLL1 and DLL4, creating high Wnt environment. Stromal telocytes and basement membrane contribute R-spondin and BMP inhibitors. This arrangement promotes proliferation and suppresses differentiation upward along villus. Mature red blood cells, trophoblast, and apoptotic cells lack stem-supporting signaling capacity, thus not considered niches. Crypt architecture demonstrates niche control of division mode and lineage output.