Identification of novel, functional, long noncoding RNAs involved in programmed, large-scale genome rearrangements

Abstract

Non-coding RNAs (ncRNAs) make up to ~98% percent of the transcriptome of a given organism. In recent years one relatively new class of ncRNAs, long non-coding RNAs (lncRNAs), were shown to be more than mere by-products of gene expression and regulation. The unicellular eukaryote Paramecium tetraurelia is a member of the ciliate phylum, an extremely heterogeneous group of organisms found in most bodies of water across the globe. A hallmark of ciliate genetics is nuclear dimorphism and programmed elimination of transposons and transposon-derived DNA elements, the latter of which is essential for the maintenance of the somatic genome. Paramecium and ciliates in general harbour a plethora of different ncRNA species, some of which drive the process of large scale genome rearrangements, including DNA elimination, during sexual development. Here, we identify and validate the first known functional lncRNAs in ciliates to date. Using deep-sequencing and subsequent bioinformatic processing and experimental validation, we show that Paramecium expresses at least 15 lncRNAs. These candidates were predicted by a highly conservative pipeline and informatic analyses hint at differential expression during development. Depletion of two lncRNAs, lnc1 and lnc15, resulted in clear phenotypes, decreased survival, morphological impairment and a global effect on DNA elimination.