Geometry, packing, and synchronization in three-dimensional (3D) multicellular development and diseases

Abstract

Three-dimensional (3D) multicellular systems, along with their developmental and pathological processes, present unique features compare to 2D flat systems. Both the spatial organization and temporal cell dynamics can be influenced by fundamental difference in cell-microenvironment interactions, cell mechanics, as well as cell physical properties. However, the effort to understanding the fundamental physics and mechanics is limited due to the constraint in 3D techniques. Moreover, the evolving multicellular properties during biological processes are unclear. In this thesis, we systematically study the geometry, packing, and synchronization in three-dimensional multicellular development and diseases.

First, we give a perspective on the emerging evidence of 3D tissue geometry in guiding morphogenesis and abnormal growth during diseases. We review the effort in fabricating various tissue-mimicking structures to study collective cell behaviors, and emphasize how tissue geometry influences physical, mechanical, and biological properties. At the end, we propose future directions, challenges, and potential applications in geometry-induced stem cell therapeutics.

Second, we report a surprising result that cells can feel the substrate curvature that they live on. We find that epithelial cells tend to form hexagonal packs to minimize the free energy; cells in these hexagonal packs are more solid-like compared to the cells out of packs. As a result, when the substrate curvature increases, the size of these hexagonal cell packs decreases to release bending energy. Therefore, on more curved surface, we observe a more fluid-like cell monolayer with more active cell dynamics and less collectiveness. Such behavior is observed not only on fabricated geometries, but also on a spontaneously growing human lung alveolosphere system in 3D derived from human induced pluripotent stem cells.

Third, as building blocks of life, cells actively coordinate their positions to form various structures and perform functions. A central question is how do cells in three-dimensional organisms accurately arrange their positions and morphology on curved structures during development? We observe an emergence of topological order, specifically a topological gas-to-liquid transition, during the growth of human lung alveolospheres, regulated by the increasing nucleus-to-cell size ratio. Our finding reveals the critical role of cell nuclear size in regulating cell packing during tissue development, and suggests the importance of topological phase changes in establishing tissue stability.

Last, from a temporal perspective, we report an experimental observation of large-scale synchronized oscillations generated by sustained contraction and expansion, revealing un- expected phase dynamics in epithelia. We then apply this temporal analysis to studying proliferating epithelia undergoing jamming transition and cancer invasion across various degrees of malignancy. Remarkably, this method provides an original perspective to assess the stage of tissue development, estimate cancer malignancy level, as well as distinguish healthy tissues from the diseased ones.