Robert, Valerie et al. (2017) International Worm Meeting "The SET-2/SET1 histone H3K4 methyltransferase maintains cell fate in the Caenorhabditis elegans germline."

Strome, Susan, Palladino, Francesca, Yvert, Gael, Robert, Valerie, Knutson, Andrew Kekupa'a, Rechtsteiner, Andreas

[International Worm Meeting, 2017]

Maintenance of germ cell fate is of critical importance for species survival. In C. elegans, translational repression, P granules, chromatin factors and histone tail modifications have been shown to be essential to maintain germ cell identity. We previously showed that the conserved SET-2/SET1 histone H3K4 methyltransferase plays a crucial role in maintaining germline immortality and totipotency, two defining features of germline identity. set-2 mutant animals grown at 25 deg C become sterile over several generations, which is reminiscent of what happens in mortal germline (mrt) mutants. This sterility, which is reversible when animals are switched back to 20 deg C, is associated with a loss of germline-specific markers, transcriptional derepression of somatic genes, and transdifferentiation of the germline into soma. To look at how the transcriptional landscape changes in the absence of SET-2 across generations and to identify pathways involved in germline maintenance, we performed transcriptome analysis of germlines dissected from fertile animals grown for 2 generations at 25 deg C and on both fertile and sterile animals grown for 4 generations at 25 deg C. We are currently analyzing these transcriptome data and performing RNAi to identify triggering events of transdifferentiation and transcriptional networks deregulated in transdifferentiated germlines. I will present preliminary results of this analysis.

Herbette, Marion et al. (2017) International Worm Meeting "Transgenerational requirement for C. elegans SET-2/SET1 in genome stability and DNA repair."

Burny, Claire, Michal, Fanny, Herbette, Marion, Yvert, Gael, Robert, Valerie, Palladino, Francesca, Cluet, David, Mercier, Marine, Bedet, Cecile

[International Worm Meeting, 2017]

Maintaining the integrity of genetic information across generations is essential for both cell survival and reproduction, and requires the timely repair of DNA damage. Specific post-translational modifications of histone tails play a central role in the DNA repair process through the recruitment of proteins and complexes with specific enzymatic activities, or by altering the chromatin state at the site of DNA lesions. I will present data showing that SET-2, the C. elegans homologue of the conserved Set1 histone methyltransferase (HMT), is required for genome stability in the germline. SET1 family HMTs are responsible for methylation of histone H3 on Lysine 4 (H3K4), a modification universally found at transcriptional start sites and associated with gene transcription. The absence of SET-2 results is a strong reduction of H3K4 di- and tri-methylation in the distal part of the germline and correlates with a mutator phenotype and a sensitivity to DNA damage inducing agents which increases transgenerationally. Following exposure to ionizing radiation, set-2 mutant germlines show a delay in the repair of mitotic DNA double strand breaks (DSBs), and increased fragmentation in oocytes.. These observations stongly suggest that SET-2 and H3K4 methylation play an essential role in genome stability in the germline of C. elegans. Experiments performed to better understand the requirement of SET-2 and H3K4 methylation in genome stability show that the DNA damage response (DDR) pathway is still functional in the absence of SET-2 suggesting that SET-2 acts downstream or in parallel of the DDR to control genome stability in the C. elegans germline. Experiments designed to detect DSB repair defects at CRISPR- induced targets, or de novo mutations by whole-genome resequencing, will also be presented.