The function of non-muscle myosin-2C in the intestinal epithelium
Chinowsky, Colbie Rose
The surface of the intestinal tract exhibits morphological adaptations at multiple levels of scale, which collectively serve to increase surface area available for nutrient absorption. Large folds of tissue called villi are covered with transporting epithelial cells, known as enterocytes. These cells in turn extend an array of microvilli from their apical surface, which further expands the surface of interaction with the luminal contents. Although cytoskeletal mechanisms have been invoked to explain how these adaptations arise during development and differentiation, the molecular details remain unclear. Here, we identify the actin-based motor non-muscle myosin-2C (NM2C) as a force-generating component of the enterocyte sub-apical terminal web, a highly crosslinked filamentous meshwork at the base of microvilli, where it works to control the length of microvilli via contractility-dependent actin turnover. NM2C is also found in the circumferential actin belt that surrounds the cell at the level of the terminal web, which had been previously demonstrated to be under tension. Based on this localization and data, we proposed that NM2C may play a role in generating and/or propagating mechanical forces that are needed to control cell and tissue morphology of the small intestine and potentially, collective epithelial migration up the crypt-villus axis. To investigate the role of NM2C in vivo, we characterized the phenotype of NM2C knockout (KO) mice. NM2C KO mice display abnormal villus architecture; with enterocytes, that exhibit elongated and, in some cases, compressed profiles when viewed laterally. Additionally, NM2C KO tissues exhibit “ruffled” junctions, which are less linear compared to WT junctions and suggest reduced levels of mechanical tension in these structures. Furthermore, using organoids generated from KO mice, we found that epithelial cells lacking NM2C display ruffled ZO-1 signal, which indicates weakened cell-cell junctions. Consistent with a decrease in barrier function due to weakened junctions, NM2C KO mice and organoids present with tuft cell hypertrophy within the epithelium. Collectively, these findings demonstrate that NM2C forms a contractile network, which spans the enterocyte at level of the terminal web and generates tension needed for maintaining normal cell and tissue-scale morphology of the small intestinal epithelium.