Developmental mRNA clearance by PIWI-bound endo-siRNAs in Paramecium

The clearance of untranslated mRNAs by Argonaute proteins is essential for embryonic development in metazoans. However, it is currently unknown whether a similar process exists in unicellular eukaryotes. The ciliate Paramecium tetraurelia harbors a vast array of Argonaute proteins of the Piwi-clade involved in various small RNA pathways, many of which have not yet been investigated. In this work, we investigated the function of a Piwi protein, Ptiwi08, whose expression is limited to a narrow time window during development, concomitant with the start of zygotic transcription. We show that Ptiwi08 acts in an endo-siRNA pathway involved in the clearance of a set of mRNAs at the post-transcriptional level. Based on their features, we hypothesized that these mRNAs may be untranslated. In this dataset, we used mass spectrometry to determine whether any protein products of these mRNAs can be found.