The role of H3K36 methylation and associated methyltransferases in chromosome-specific gene regulation
In Drosophila, two chromosomes require special mechanisms to balance their transcriptional output to the rest of the genome. These are the male-specific lethal complex targeting the male X-chromosome, and Painting of fourth targeting chromosome 4. The two systems are evolutionarily linked to dosage compensation of the X-chromosome and the chromosomes involved display specific chromatin structures. Here we explore the role of histone H3 tri-methylated at lysine 36 (H3K36me3) and the associated methyltransferases in these two chromosome-specific systems. We show that the loss of Set2 impairs the MSL complex mediated dosage compensation; however, the effect is not recapitulated by H3K36 replacement and indicates an alternative target of Set2. Unexpectedly, balanced transcriptional output from the 4th chromosome requires intact H3K36 and depends on the additive functions of NSD and the Trithorax group protein Ash1. We conclude that H3K36 methylation and the associated methyltransferases are important factors to balance transcriptional output of the male X-chromosome and the 4th chromosome. Furthermore, our study highlights the pleiotropic effects of these enzymes.