Characterization of Apoptotic Mechanisms Involved in R Body Induced Death in Paramecia tetraurelia

Abstract

t. Paramecium tetraurelia is a unicellular eukaryotic ciliate. Certain strains of paramecia have been shown to contain endosymbiotic bacteria. Furthermore, some of these endosymbiotic bac- teria confer a killing ability on the host paramecia, known as killer paramecia, because the endosym- biont can be lethal to other paramecia, known as sensitive paramecia, if it is released into the environ- ment. This death has been connected to a protein found within the P. tetraurelia known as an R body. Interestingly, the R body-related-death resembles apoptosis in that it causes membrane blebbing, a characteristic of apoptosis. Furthermore, paramecia contain another marker of apoptosis, a mecha- nism to degrade DNA which is used in normal paramecia conjugation. Therefore, exposure to the R body and toxin may be activating some existing pathways in the paramecia, leading to apoptosis. To determine whether the mode of cell death induced by the R bodies is apoptotic, a flow cytometer was used to examine DNA fragmentation, a characteristic of apoptosis, using a Terminal Deoxynucleoti- dyl Transferase Biotin-dUTP Nick End Labeling (TUNEL) assay. Three groups of paramecia were examined with TUNEL: sensitive-alone, killer-alone, and killer mixed with sensitive. The results of the TUNEL assay were inconclusive because the only cell group showing positive TUNEL staining was the sensitive paramecia group. This could possibly be due to the DNA degradation that occurs during normal cell conjugation. Therefore, this study was the first to use flow cytometry in order to examine R body induced cell death and provides a clear basis for further researc