Hydra is a freshwater cousin of the jellyfish.

Body-axis formation in Hydra

Hydra can regenerate from tissue spheres formed from tissue pieces excised from the body column of an adult and, from aggregates of cells. These tissue spheres undergo osmotically driven shape oscillations which are characterized by a sawtooth like timecourse of the radius of the sphere over time. Initially the tissue spheres expand isotropically, characterized by high amplitude long period oscillations. But, over time, the tissue sphere becomes more elliposidal and is characterized by low amplitude short period oscillations. This change in shape and oscillation pattern involves symmetry breaking - at some point, the tissue sphere breaks spherical symmetry and a head-tail axis emerges. This symmetry breaking arises from coupling between the Wnt signalling pathway and mechanical properties of the epithelial tissue for the formation of a chemical gradient that defines the head and tail, as well as the formation of an ellipsoidal body from the initially spherical tissue. We used gain-of-function and loss-of-function experiments to show how a transition in the period and amplitude of osmotically driven shape oscillations in regenerating tissue spheres is caused by the formation of an actively regulated mouth structure. This finding challenged the current understanding of the temporal markers of stages during regeneration in Hydra and necessitates a re-examination of the mechanisms driving axis formation in Hydra.

Mechanical control of mouth opening in Hydra

Linalool as a fast and reversible anaesthetic for Hydra research

During the various Hydra related projects I worked on, we constantly came up against trying to immobilize the animals for 'surgeries' and imaging without significantly affecting the long-term health of the animals. While various anesthetics had been used in Hydra studies in the past, they tended to be toxic over the course of a few hours or their long-term effects on animal health are unknown. We found that the monoterpenoid alcohol linalool is a useful anesthetic for Hydra. Linalool is easy to use, non-toxic, fast acting, and reversible. It has no detectable long-term effects on cell viability or cell proliferation. We demonstrated that the same animal could be immobilized in linalool multiple times at intervals of several hours for repeated imaging over 2–3 days. This uniquely allows for in vivo imaging of dynamic processes such as head regeneration. We directly compared linalool to currently used anesthetics and show its superior performance. Linalool can be a useful tool for tissue manipulation and imaging in Hydra research in both research and teaching contexts.