טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentLivshits Anton
SubjectInfluence of External Physical Fields on Symmetry-Breaking
in Regenerating Hydra
DepartmentDepartment of Physics
Supervisors Professor Erez Braun
Professor Kinneret Keren
Full Thesis textFull thesis text - English Version


Abstract

Development of a multicellular organism is a complex self organization process that leads to the formation of a well-defined pattern. This process of pattern formation is far from being understood. Hydra is a millimeter- sized multicellular freshwater organism with uniaxial symmetry, which exhibits remarkable regeneration capabilities. Starting from a small fragment of hydra tissue or a cell aggregate, the entire animal regenerates within a couple of days. We focus on the initial stages of this regeneration process, namely, the onset of symmetry breaking and the formation of the body axis. During the regeneration process hydra develop a foot, a head and tentacles in specific positions and size relative to one another. The underlying mechanisms are not well-understood. To explore pattern formation in hydra, we perturb hydra tissue segments during the regeneration process by applying external physical fields and mechanical constraints. We impose mechanical constraints by introducing stiff metal wires into the regenerating hydra and forcing regeneration on the wires. The wire defines an axis in this setup and introduces a new length scale- the wire diameter. The regeneration of hydra rings along wires of different diameters, aligned parallel or perpendicular to the original hydra axis is compared to the regeneration of free hydra tissue fragments and rings. We find difference in the morphologies of regenerated hydra, the orientation of the regeneration axis and the regeneration time between the different samples. We use both hydrodynamic flow and electric fields as external physical fields and study their influence on axis formation and regeneration. I describe the main experimental results and discuss their implications on our understanding of axis determination and pattern formation in regenerating hydra.