Vie de l'IBPC

The H3K9 demethylase JHDM2 hampers piRNA

 production from specific genomic regions

Karine Casier

Institut de Biologie Paris-Seine (IBPS)

Laboratoire de Biologie du Développement (UMR7622)

invitée par Teresa Teixeira

le mardi 28 janvier à 11h  - Salle de conférence

In animals, genome integrity of the germ line is protected from the activity of the transposable elements (TEs) by small non-coding RNA called PIWI-interacting RNAs (piRNAs). The production of piRNAs is initiated from heterochromatic loci enriched in histone H3 trimethylated on lysine 9 (H3K9me3) and made of repetition of remnant called piRNA clusters. However, several genomic regions have characteristics similar to piRNA clusters but do not produce piRNAs asking the question of what defines an active piRNA cluster. Here we show that the loss of function of the H3K9 demethylase JHDM2 converts a transgenic construct made of repeated sequences into a new piRNA cluster in Drosophila. Using a genetic screen, we first identified the splicing factor half pint (hfp) as being able to prevent the production of piRNAs from repeated sequences. Among the tested genes whose germinal expression is affected by the loss of hfp function, only JHDM2 also prevents piRNA production from inactive transgenic sequences. We show that hfp is needed to splice JHDM2 transcripts. At the genomic level, we identified several other regions that produce de novo piRNAs in a JHDM2 mutant context. Interestingly, most of the genes included in these regions encoded somatic transcriptional factors and presented, in the JHDM2 mutant context, an abnormal germinal expression. Our results demonstrate that specific genomic regions may be actively prevented for piRNA production in the germline and open interesting perspectives to understand epigenetic determination of somatic versus germline cell lineages.