Mechanisms of unusual collective cell movement lacking a free front edge in Drosophila

The shape and structure of tissues are generated by the dynamic behavior of various cell collectives during morphogenesis. These behaviors include collective cell movement, in which cells move coordinately in a given direction while maintaining cell-cell attachments throughout the collective. For a cell collective to acquire mobility, the cell collective generates forces, and the cells in the front sense extrinsic cues to decide the direction of the movement. However, some collectives that fill a confined space move even though they lack such front cells. These dynamic cell behaviors have been studied in detail in egg chamber rotation and male genitalia rotation in Drosophila; however, similar phenomena are found in mammals. Here we review how the movements of such front-edgeless cell collectives are generated.