The Ciliary Protein IFT57 in the Macronucleus of Paramecium

The intraflagellar transport IFT57 protein is essential for ciliary growth and maintenance. Also known as HIPPI, human IFT57 can be translocated to the nucleus via a molecular partner of the Huntingtin, Hip1, inducing gene expression changes. In Paramecium tetraurelia, we identified four IFT57 genes forming two subfamilies IFT57A/B and IFT57C/D arising from whole genome duplications. The depletion of proteins of the two subfamilies induced ciliary defects and IFT57A and IFT57C localized in basal bodies and cilia. We observed that IFT57A, but not IFT57C, is also present in the macronucleus and able to traffic toward the developing anlage during autogamy. Analysis of chimeric IFT57A-IFT57C-GFP-tagged proteins allowed us to identify a region of IFT57A necessary for nuclear localization. We studied the localization of the unique IFT57 protein of Paramecium caudatum, a species, which diverged from P. tetraurelia before the whole genome duplications. The P. caudatumIFT57C protein was excluded from the nucleus. We also analyzed whether the overexpression of IFT57A in Paramecium could affect gene transcription as the human protein does in HeLa cells. The expression of some genes was indeed affected by overexpression of IFT57A, but the set of affected genes poorly overlaps the set of genes affected in human cells.