Mechanical boundaries in 3D models for confluent tissue

A stratified epithelium, such as human skin, consists of many different layers of tissue that each express unique combinations of signaling and adhesion proteins, with strong and sharp boundaries between each layer. To create this tissue structure during development, and maintain it over time in mature organisms, carefully regulated cell divisions and cell migration are required. Specifically, cell divisions occur only in the lowest layer, and new cells must differentiate and delaminate from the basement membrane and move to the upper layers without disrupting the boundaries. We investigate possible mechanisms for the creation and stabilization of these boundaries using an extended 3D Vertex model with features specific to stratified epithelia, such as additional heterotypic tension at interfaces between cells of different types. We then make predictions about how these features affect the geometric and dynamic behavioral signatures of cells in each layer. We explore how changes to individual cell mechanical properties might drive migration across a layer boundary, as well as how the surrounding heterogeneous tissue mechanically responds to a migrating cell.