Intestinal epithelial organoids fuse to form self-organizing tubes in floating collagen gels.

Multiple recent examples highlight how stem cells can self-organize to establish organoids that closely resemble their counterparts. Single Lgr5 mouse intestinal stem cells can be cultured under defined conditions forming ever-expanding epithelial organoids that retain cell polarization, cell type diversity and anatomical organization of the epithelium. Although exhibiting a remarkable level of self-organization, the so called 'mini-guts' have a closed cystic structure of microscopic size. Here, we describe a simple protocol to generate macroscopic intestinal tubes from small cystic organoids. Embedding proliferating organoids within a contracting floating collagen gel allows them to align and fuse to generate macroscopic hollow structures ('tubes') that are lined with a simple epithelium containing all major cell types (including functional stem cells) of the small intestine. Cells lining the central contiguous lumen closely resemble the epithelial cells on luminal villi , whereas buds that protrude from the main tube into the surrounding matrix closely resemble crypts. Thus, the remarkable self-organizing properties of Lgr5 stem cells extend beyond the level of the microscopic cystic organoid to the next, macroscopic, level of tube formation.