Abstract

Paramecium tetraurelia are ciliated protozoa that contain membrane‐docked vesicles called trichocysts. Trichocysts fuse with the membrane in a calcium‐dependent manner and release proteins that form long crystalline spines, which help Paramecium escape predators. A bacteria‐mediated RNA interference (RNAi) protocol was used to determine if members of the calcium/calmodulin‐dependent protein phosphatase family (PP2B) present in Paramecium were involved in trichocyst discharge as suggested by previous work. After treatment, Paramecium cells were selected and exocytosis triggered by the addition of a saturated picric acid solution. After normalization, the extent of exocytosis was compared and indicated that RNAi treatment with one of the isoforms of Paramecium PP2B resulted in a reduced efficiency of exocytosis. The number of cells exhibiting full exocytosis was reduced from 76% in control cells (n=129) to 25% in PP2B treated cells (n=190). Cells exhibiting dramatically reduced exocytosis (<50% full discharge) increased from 2% (control treatment) to 41% (PP2B treatment). Based upon these results, we conclude that PP2B has a role in the regulation of calcium‐dependent exocytosis in Paramecium tetraurelia. Funding for this project was provided by the Wilson Research Awards and the Howard Hughes Medical Institute.

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