Mechanisms of cell height changes that mediate epithelial invagination

Epithelial invagination is a morphogenetic process that converts flat cell sheets into tubular structures and contributes to the formation of three-dimensional organs during development. Because the cells in tubular structures have smaller apical than basal surfaces, apical constriction is thought to be critical for the process of epithelial invagination. In addition, the invagination process is also accompanied by cell elongation, followed by cell shortening and basal expansion. While the mechanisms involved in apical constriction have been well-characterized, recent technical advances are just beginning to unravel the mechanisms involved in cell height control, which include cytoskeletal changes, cortical tension generation, cell adhesion, and cytoplasmic flow. Furthermore, cell height changes associated with mitosis and apoptosis have recently been shown to contribute to epithelial invagination. To develop a comprehensive understanding of epithelial invagination, it is important to elucidate the mechanisms that mediate cell shape changes and facilitate their coordination. In this review, we summarize the recent advances in this field, focusing on the mechanisms that control cell height.