Symmetry breaking and axis formation in Hydra*

During animal development, a near-uniform collection of genetically identical cells self-organizes to form an organism with a well-defined anterior-posterior body axis. Axial patterning is the earliest and most fundamental event that gives rise to the complexities of a full animal. The freshwater polyp Hydra is an excellent model system to study axial patterning due to its simple anatomy and incredible regenerative abilities. Hydra can regenerate from small tissue pieces or from cell aggregates. The physicists Alfred Gierer and Hans Meinhardt recognized Hydra’s self-organizing properties > 40 years ago. However, the physical mechanisms underlying cell sorting, symmetry breaking, and axis specification in Hydra remained elusive as existing studies failed to distinguish between different driving mechanisms. In my talk, I will present our recent work that answers some of these questions. Our results challenge key assumptions in existing mathematical models of Hydra regeneration and require that we re-examine the mechanisms driving axis specification and pattern formation.