טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentShani-Zerbib Lital
SubjectActin Organization in Hydra Regeneration
DepartmentDepartment of Physics
Supervisors Professor Erez Braun
Professor Kinneret Keren
Full Thesis textFull thesis text - English Version


Abstract

Morphogenesis, the development of an organism's structure, is a complex process carried by multiple biochemical and physical processes. A developing tissue undergoes extensive deformations, including folding, swelling and shrinking which require mechanical forces. Understanding the role of mechanics during morphogenesis is an outstanding challenge. In our work we utilize the small fresh water animal, Hydra, and its remarkable regeneration capabilities, to study the role of the actomyosin cytoskeleton in morphogenesis. Hydra's has a cylindrical body made of bilayer of epithelial sheets (endoderm and ectoderm). The actomyosin cytoskeleton forms supracellular networks of contractile fibers near the basal side of each sheet, which span the whole organism. An adult Hydra can regenerate from a small fragment and even from a completely dissociated cell aggregate. The regeneration begins by folding of the tissue into a hollow spheroid, and proceeds with the emergence of tentacles and foot. In our work we find that the orientation of the supra-cellular actomyosin fibers in excised tissue segments is inherited from the donor Hydra, and determines the new body axis in the regenerating animal. This novel form of structural inheritance is non-trivial due to the tissue folding and dynamic actin reorganization involved. We further show that regenerating tissues with multiple fiber orientations in the initial folded spheroid develop into Hydra with multiple body axes (more than one head and/or foot). Using a stiff thin wire to anchor a regenerating tissue, we show that mechanical constraints induced by the wire promote order in the actomyosin organization, and suppress the emergence of multiple body axes. Together, these results consist an important step toward the development of an integrated understanding of morphogenesis which incorporates mechanics.