Effects of Symbionts on Structure and Function of A. Pallida Gastrodermal Cells

Nooreen Rubin, Vassar College ’09 and Prof. Jodi Schwarz

A fundamental element of the tropical sea anemone Aiptasia pallida is an endosymbiosis characterized by a complex relationship between the animal host and unicellular dinoflagellate symbionts (Symbiodinium spp.). While it is well established that symbiotic hosts house these endosymbionts within membrane-bound vacuoles in their gastrodermal cells and that the symbionts are taken up through phagocytosis, the cellular mechanisms of this uptake and its effects on the arrangement of the cytoskeleton are poorly understood. As a result of symbiont uptake, several sub-cellular features such as the arrangement of the actin and tubulin cytoskeletons, the position of vital organelles such as the nucleus and mitochondria, the host cell membrane and the symbiont-bearing vacuole must undergo substantial restructuring. In order to explore the effect that the presence of symbionts has on host cells, we utilized several staining and microscopy techniques to visualize the arrangement of tubulin and actin in the cell as well as the structure and location of the host nuclei during the process of infection. We observed that gastrodermal cells in aposymbiotic anemones are smaller than those in symbiotic anemones. Microinjection of symbionts directly to the gastric cavity resulted in a noticeable infection of gastrodermal cells in the tentacle within two days. We found that the introduction of symbionts to the gastrodermal cells severely displaces host nuclei and disrupts host cell structure.