Epigenetic control of programmed DNA elimination in Paramecium

Orateur : Sandra DUHARCOURT (Institut Jacques Monod, Paris)

The eukaryote Paramecium tetraurelia provides an extraordinary model for studying the mechanisms involved in programmed DNA elimination. At each sexual cycle, differentiation of the somatic nucleus from the zygotic nucleus is characterized by massive and reproducible deletion of transposable elements and of 45,000 short, dispersed, single-copy sequences. A specific class of small RNAs produced by the germline during meiosis, the scnRNAs, are involved in the epigenetic regulation of DNA deletion but the underlying mechanisms are poorly understood. I will present our recent data showing that the underlying genetic properties of the germline DNA segments, such as their length, might act in concert with H3 post-translational modifications to define germline sequences to delete. Intriguingly, our data further showed that scnRNAs are only required for the elimination of transposable elements and longer (more recent) single copy elements, while the vast majority of single copy elements are efficiently excised in the absence of scnRNAs. These data suggest that other mechanisms are involved in clearing the genome of parasitic DNA, particularly for the oldest and smallest elements.

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