Genome-wide mapping of H3K9me2 in DOT1L-deficient worms.

Histone modification marks such as H3K4me1 and H3K27ac have been used to map putative enhancers, but these marks represent only a fraction of the full repertoire of histone modifications decorating these regulatory regions. In mammals, methylation of histone H3 on lysine 79 (H3K79me), deposited by the methyltransferase DOT1L, is present at enhancers. In C. elegans, putative enhancers have been predicted based on chromatin modifications and regions of chromatin accessibility. Our own overlap analysis has revealed that both DOT-1.1, the C. elegans DOT1L homologue, and its major interacting partner, the chromatin-binding factor ZFP-1 (AF10 in mammals), are enriched at both distal and intragenic enhancers. Previous work has shown that Dot1 proteins prevent encroachment of heterochromatin to actively transcribed regions in yeast and in MLL-rearranged leukemias. Here we find that, in C. elegans, loss of DOT-1.1 is accompanied by ectopic H3K9me2, a hallmark of heterochromatin, at distal and intragenic enhancers. This observation suggests a new role for DOT1L in the control of heterochromatin formation at enhancers, which may partake on the control of developmentally regulated genes. Overall design: Profiling of H3K9me2 in ced-3 and dot-1.1; ced-3 mutant third larval (L3) stage Caenorhabditis elegans.