Ciliates are a highly divergent group of unicellular eukaryotes with separate somatic and germline genomes found in distinct dimorphic nuclei. This characteristic feature is tightly linked to extremely laborious developmentally regulated genome rearrangements in the development of a new somatic genome/nuclei following sex. The transformation from germline to soma genome involves massive DNA elimination mediated by non-coding RNAs, chromosome fragmentation, as well as DNA amplification. In this review, we discuss the similarities and differences in the genome reorganization processes of the model ciliates Paramecium and Tetrahymena (class Oligohymenophorea), and the distantly related Euplotes, Stylonychia, and Oxytricha (class Spirotrichea).

In the ciliated protozoan Paramecium tetraurelia, Piwi-associated small RNAs are generated upon the elimination of tens of thousands of short transposon-derived DNA segments as part of development. These RNAs then target complementary DNA for elimination in a positive feedback process, contributing to germline defense and genome stability. In this work, we investigate the formation of these RNAs, which we show to be transcribed directly from the short (length mode 27 bp) excised DNA segments. Our data support a mechanism whereby the concatenation and circularization of excised DNA segments provides a template for RNA production. This process allows the generation of a double-stranded RNA for Dicer-like protein cleavage to give rise to a population of small regulatory RNAs that precisely match the excised DNA sequences. VIDEO

DNA strand breaks induced by nuclear hijacking of neuronal NOS as an anti-cancer effect of 2-methoxyestradiol DNA strand breaks induced by nuclear hijacking of neuronal NOS as an anti-cancer effect of 2-methoxyestradiol