LAUSR

uch of our understanding of molecular mechaMnisms of diseases has relied historically on work performed in cancer cell lines. Although cancer-derived cell lines offer many advantages such as being easy to grow, relatively inexpensive, and amenable to experimental manipulation, the degree to which cell lines faithfully recapitulate biological processes that occur in vivo is unclear. The development of intestinal organoids or enteroids from primary adult epithelium by Sato et al in 2009 provided an innovative and valuable in vitro tool for scientists. Intestinal organoids mimic in vivo tissue more closely than traditional cell lines. The presence and maintenance of all intestinal cell types including enterocytes, tuft cells, goblet cells, enteroendocrine cells, stem cells, Paneth cells, and so forth in intestinal organoid culture offers a distinct advantage over cell lines that lack cell type diversity. Moreover, intestinal organoids can be derived from limited amounts of tissue, such as biopsy specimens, and expanded exponentially, making them a useful tool for studying disease mechanisms. Importantly, intestinal organoids recapitulate in vivo physiology with limited genetic alterations after long-term culturing. For the past decade, scientists have been tailoring intestinal organoid culture systems and techniques to fit specific experimental needs. Intestinal organoids originally were grown and manipulated in Matrigel (Corning, Bedford, MA) in a 3-dimensional format. However, 2-dimensional monolayers of intestinal organoids recently were generated to address questions that require access to the lumen or the apical membrane. In addition to these formats of organoid cultures, other techniques have begun to be implemented to better mimic in vivo conditions. One new piece of technology is the organ-on-a-chip system, which features a multichannel 3-dimensional microfluidic cell culture chip. The organ-on-a-chip platform simulates the mechanics and physiological conditions present in vivo. An important step in achieving more physiologically relevant in vivo–like conditions in the colon is the generation of a mucus bilayer in vitro. In vivo, the colonic epithelium is lined by a thick mucus bilayer produced by goblet cells that protect epithelial cells from bacterial contact and potential pathogens. The importance of the colonic mucus layer is shown by the fact that disruption of the layer results in colitis. Previously, the generation of a physiologically functional mucus bilayer in vitro had not been realized. SontheimerPhelps et al have reported successful in vitro generation of a mucus bilayer using human organoid-derived colonic epithelial cells cultured using an organ-on-a-chip microfluidic device. They show that dynamic flow conditions result in a polarized, confluent colonic epithelial layer that maintained barrier function in vitro. In addition, organoid-derived