H4K20me1 plays a dual role in transcriptional regulation during regeneration and axispatterning of Hydra
The evolution of the first body axis in the animal kingdom and an extensive ability to regenerate makes Hydra, a Cnidarian, an excellent model system for understanding the underlying epigenetic mechanisms. We identify that SETD8 is critical for regeneration due to its interaction with {beta}-catenin to fine-tune the underlying gene regulatory network. Its target histone mark, H4K20me1, colocalizes with transcriptional activation machinery locally at the {beta}-catenin bound TCF/LEF binding sites on the promoters of head-associated genes, marking an epigenetic activation node. Contrastingly, genome-wide analysis of the H4K20me1 occupancy revealed a negative correlation with transcriptional activation. We propose H4K20me1 as a general repressive histone mark in Cnidaria and describe its dichotomous role in transcriptional regulation in Hydra.