To better mimic the crosstalk between epithelial and stromal cells in the native tissue, we have recently established an in vitro colonic assembloid model derived from adult murine primary epithelial and stromal cells1. These assembloids encompass most stromal cell subpopulations, including different fibroblast subpopulations (trophocytes and telocytes) and myofibroblasts as well as small numbers of endothelial cells, neurons, and glial cells. Crucially, we found that combining epithelial and stromal cells in this way enables self-organization of both compartments to take place. The model allowed us to determine that epithelium and stroma directly shape each other through reciprocal signaling loops involving predominantly BMP agonists and antagonists. The resulting signaling gradients establish a spatial organization of the stroma along the axis of the emerging epithelial crypts, consisting of different subpopulations with different functions. These different stromal subpopulations are in turn able to drive the establishment of a fully mature crypt structure: Once self-organization has taken place, the system is able to maintain itself, with stromal cells producing appropriate growth factors for neighboring epithelial cells. Crucially, the resulting independence from external growth factors supplied via the culture medium allows these localized signals to control cell fate and establish a native crypt structure with stem cells at the base and fully mature cells at the surface. This is in stark contrast to existing colonic organoid technology, where cell fate is controlled by medium supplementation, effectively preventing mature and proliferating cell types from being maintained simultaneously.
Several other gastrointestinal co-culture systems have recently been developed, based on adult primary cells, cell lines, or pluripotent stem cells cultured in different systems, e.g. conventional static co-culture in basement membrane matrix, air-liquid interface, organ-on-a-chip, and pluripotent stem cell-derived organoids. While these approaches allow important insights into cell communication, they fail to fully recapitulate the self-organization of the adult gastrointestinal mucosa with a mature crypt structure and compartmentalized multicomponent stromal niche. Our assembloid system also offers important advantages to facilitate broad application within the scientific community: It is low-tech and comparatively low-cost, requiring only basic equipment without the need for engineered scaffolds, microfluidic devices, or bioreactors.
The data were published in Lin et al., Nature Communications 2023.
