Attempted Identification of the Calcium-Dependent Sodium Channel Gene in Paramecium tetraurelia using RNAi

Ion channels play an important role in the swimming behavior of Paramecium tetraurelia. Electrophysiological experiments indicate that a calcium-dependent sodium channel exists in Paramecium, but a gene has not been identified for this channel. It is hypothesized that this channel evolved from a voltage-dependent sodium channel after a whole genome duplication event. In this paper, 13 candidate genes were identified from the Paramecium genome based on their similarity to a reference human voltage-dependent sodium channel. Bioinformatics analysis of the selectivity filter of these putative ion channel genes suggested that at least 8 of the candidate genes were sodium channels and 4 were likely calcium channels. Functional analysis of 2 of the candidate genes thought to be sodium channel genes, via RNAi knockdowns and behavioral testing, led to the identification of a calcium channel.