When Eri Nishihara started at the Graduate School of Life Science, University of Hyogo, she was interested in protozoa. Protozoa possess all of the functions to survive in a single cell, performing predation, reproduction (mating and/or division) and excretion. Eri observed, using microscopy, that the contractile vacuole (CV) of Amoeba proteus showed interesting movement. This raised several questions: what was CV? What was the function of CV? It was on this basis that she began her studies.

Eri first studied the physiological function using an isolated CV. She speculated water channel proteins were present in the CV, since rapid water movement was observed. Accordingly, she tried to identify the molecule responsible for this rapid water movement in CV and succeeded in cloning an aquaporin gene in A. proteus (ApAQP). An antibody generated against ApAQP clearly demonstrated the localization of ApAQP to CV membranes. In addition, Eri also found that a H⁺ pump was abundantly present in CV membranes. These results suggested that osmotic pressure generated by H⁺ pump and high water permeability via ApAQP are involved in water uptake into CV.

Furthermore, Eri succeed in visualization of the dynamics of the CV in living cell using FM dye. Just after contraction, the CV membrane was flattened. Then, a few vesicles formed from the fattened membrane began to fuse each other, and became a single CV again. This dynamic event takes only 3-5 min.

Eri believes that these results are an important step in the understanding of all mechanisms that occur in Amoeba CV.

This spring, Eri finished her work for her PhD thesis at the University of Hyogo. Now, she is continuing to study the CV under the direction of Dr Sei Sasaki, MD, PhD, at Tokyo Medical and Dental University as a Medical Fellow.