The inner-most surface of the gastrointestinal tract is covered by single-layered, well-polarized epithelial cells. My research group has recently developed a three-dimensional culture method for colonic epithelial cells of mice and humans, in which colonic cells form a cystic structure preserving their epithelial nature. Taking advantages of this newly developed in vitro culture system, I will investigate the mechanisms regulating the formation and maintenance of epithelial polarity in colonic cells,.

First I will assess how colonic cells build up a cystic structure that invariably allocates the apical membrane to its inner surface and the basal membrane to the outer side. In particular, I will look into the initial process by which such cellular polarity is introduced, analyzing the spatiotemporal behavior of membrane proteins during the early phase of cyst formation from single cells (Fig.1). Secondly, the role of extracellular milieu in regulating colonic epithelial polarity will be investigated. The colonic cysts grown in our culture have a luminal space inside where the cells create a unique environment by secreting or transporting many substances. By analyzing the composition of the luminal fluid, we will assess how the composition gradient across the cultured cells would influence the form, function or the polarity of colonic cells in vitro.

The approach I will make in this project would allow us to elucidate the mechanisms of how normal colonic epithelial cells form and maintain the epithelial polarity. The loss of polarity and disruption of epithelial integrity are common features of colorectal cancers or inflammatory bowel diseases, and, thus, the achievement of this project would build a basis for understanding the pathophysiological mechanisms involved in these diseases.