Evidence of subfunctionalization in the calcineurin gene family in Paramecium tetraurelia

Jordan Welker, The College of Wooster

Abstract

A typical eukaryotic organism has between two and four genes that code for the calcium dependant serine/threonine protein phosphatase, calcineurin. Paramecium tetraurelia, however, has 14 copies of this gene grouped into 7 isoform pairs or ohnologs. This multiplicity of the gene for calcineurin is suspected to be the result of several whole genome duplication events during the course of evolution of Paramecium. We hypothesized that each isoform plays a different role in Paramecium rather than being redundant copies, as previously proposed. To test this hypothesis we utilized RNAi to systematically silence the 7 isoforms of the calcineurin catalytic subunit. The silenced cells were tested for abnormalities in various cilia mediated swimming behaviors. We found that silencing CaNA-2, CaNA-4, CaNA-5, or CaNA-6 decreased the time spent swimming backwards in a 30 mM potassium chloride solution. Previous work has shown that silencing of CaNA-3 and CANA-7 causes Paramecium to swim backwards for extended amounts of time, and that silencing of CaNA-1 shows no phenotype in wild type swimming behavior. Forward swimming speed was also measured and found to show variations from wild type. We present our hypotheses that these duplicated genes have been maintained due to subfunctionalization processes and are not being retained strictly for redundancy.