Chromatin modifications are covalent modifications of nuclear histone proteins that can result in activation or repression of transcription of DNA. Some chromatin modifications have been linked to fertility and specification of reproductive cells called germ cells. We found that trimethylation of Lysine 9 in Histone H3 becomes prominent in late embryo germ cells of C. elegans, which has not been previously reported. Our research has been focused on identifying the methyltransferase that generates H3K9me3 in germ cells to help determine if H3K9me3 is required for germ cell development and fertility.Previous reports suggested that SET-25 is a major H3K9-trimethylating enzyme in C. elegans (Towbin et al., 2012). We found
set-25 mutant embryos lose H3K9me3 in all somatic cells, but maintain H3K9me3 enrichment in the germ cells of later-stage embryos. We employed two strategies to find the H3K9 methyltransferase responsible for the residual H3K9me3 in the germ cells of
set-25 mutant. In one approach, we used a double
set-25;
met-2 mutant, which was reported to completely prevent H3K9 methylation in the embryos (Towbin et al., 2012). We find that the
set-25;
met-2 double mutant embryos have almost no H3K9me3 in any cells and a fraction of resulting adults manifests temperature dependent sterility. This suggests that trimethylation of H3K9 may be important for germ cell development and fertility.Our second approach was RNAi screen of predicted H3K9 methyltransferases in
set-25 mutant background to identify conditions that would disrupt the residual H3K9me3 germ cell enrichment. Through this approach, we identified two other possible regulators of H3K9me3,
set-9 and
set-26. Both
set-9 and
set-26 RNAi increased sterility in
set-25 worms. Ongoing research includes determining if mutants of
set-9 and
set-26 affect the levels of H3K9me3 in germ cells to further examine the role of H3K9me3 in fertility. Since H3K9me3 modification has been shown to play a significant role in germ cell development in Drosophila and mouse, we hope our research in C. elegans will identify conserved targets of this regulatory mechanism.