Defect mediated morphogenesis

It has been a long-standing mystery how complex biological structures emerge during embryonic development from such seemingly uncoordinated building blocks as cells and tissues without guidance. Recent experiments suggested that misalignment in the collective structure –so called topological defects– could play a fundamental guiding role in morphogenesis. Here, we provide a theoretical study explaining how active defects interact with geometry and how this could play a crucial role in morphogenetic processes. Using a combination of computational fluid dynamics and analytics we study the instabilities of a cell monolayer in the framework of the active gel theory. We consider an active polar liquid crystals coupled to an elastic deformable surface. We find that the cooperative interaction of active disclinations and geometry drives the buckling instability of the active membrane. This eventually results in the formation of long protrusions with a tentacle shape or even the nucleation of a vescicle. This work clarifies the interaction of active defects and geometry and provides potentially new insight into the physics beyond processes such as the metastatic cascade in cancer development or embryogenesis.